I've had one for a few years and used it for ssb, js8 and cw. I have never had a problem and no one has ever complained about my signal. I think there are just some hams that believe if you didn't have to take out a second mortgage to buy equipment then it junk. 73 and keep up the good vids de KF7VUT
No, that's exactly it. Many people lack the expertise to actually evaluate their equipment so the only thing they have to go on is price. Their only thought is "if it's expensive, it must be good!" There's a huge, unfilled market out there for inexpensive ham equipment if only someone would take notice.
Hey Kevin, I absolutely enjoy your workbench videos - building projects and testing gadgets. You're fun to watch work on the bench, I always learn something. Keep up the great work! 73s, KJ6ER / Silicon Valley
Thanks Kevin... I've had one for several years too and use it daily for FT4 with my FT-817 and an OCF dipole... It gives me great pleasure to receive great signal reports from all over the world from hams who are using towers, beams and high end HF transceivers.
Wow, haven't done that kind of measuring since Air Force days. Had to shake out the cobwebs to follow along. Thanks for reinforcing how old I really am.
I think l seen a video from (rate my radio) he checked checked the RF output of these’s amps, it looked alright. I always check my signal output with an SDRPlay don’t want anything funky spattering out there.... The only things to be wary about with these amps is the build quality. l took mine apart and found the PCB was excessively bending at the binding posts, and the main transistor was not flush with a gap at the heat sink. It’s worth checking.
Hmmm yea if the transistor is poorly mounted it's die could be getting a lot hotter than acceptable even with brief durations of key down which will mean goodbye amplifier pretty fast
I have one that I bought a year or two ago, I am happy with it but when I raise the power input the output start saturating above 25 watts output on all bands. In SSB or CW I don't have any heat problems but on ft8 it gets hot. However I installed a fan on top of the heat-sink and after that it remains just warm in ft8. Even with those limitations it is certainly worth the money. Like usual great video Kevin.
Follow up. I just did the gain compression calcs in decibels, both for power and voltage and the value came out the same for 80 meters: 3.08 dB. That's not horrible in my book. Well done.
You mean I can't get a lab quality amp for just under $200 shipped? Shocking! Good video Kevin! I would not use this for anything over the 2.5 watt input anyway as you want to save the 817 finals.
Kevin, Really enjoyed your video. I have one of these amps and run it in CW mode almost exclusively and I don't run it full out. For the price thats being asked its a good deal. Its easy to make definitive statements without the testing to back it up. I'm sure the amp does have a non linear part of the curve as every amp does. You made mention of current off the shelf amps not being able to be run at full duty cycle for an extended amount of time. Back in the mid 80s Alpha had a contest where the person who came closest to the dollar cost of the electricity that the amp used for the test would win the amp. They took a commercial exciter and loaded their amp up to 1500w out and put a brick on the key for 18 days. Back then that amp cost as much as some new cars. Great performance with a price tag to match. Amps built today are not designed for full duty cycle at full power for very long... .
The data sheet I found for this amp shows that the specs were measured at 15V input. You were likely operating it on 13.4V from the previous video. The linearity and power output will improve somewhat at 15V. (Getting 15V from a 12V system is a bit difficult.) I'm considering an amp for an IC-705 so thanks for the measurements! --N2GX
Hi Kevin I found your video on the Amp very interesting. I purchased on of these about six months ago. Like yours the driver transistor is un-marked. I did some similar tests to check linearity and found the sweet spot to be around 3W input. After that I also found that the output started to compress. One area that does bother me is that the PTT relay seems to be directly driven by the transceiver switch. There is no switching transistor. The bigger concern is the relay coil does not appear to have a diode across it. The back EMF as the relay releases is directly applied to the transceiver. I have checked the data sheet for the relay and it does not appear to have a diode built in.
The PTT switching is crude, and something to be wary of as it could place a lot more load on some solid state PTT circuits than they are designed for, in the case of the ft817 it's probably ok.
It's Chinese circuitry...if you want linearity your going to pay more than $150.00. Honestly I love not paying hundreds of dollars on my ham gear when I can. This Amp allowes me to operate my 818 at lower power settings and not over heat my transceiver finals during heavy duty cycles. Id rather burn out this little Amp than my FT818. Great break down!
Not "terrible" I would agree! If your scope can do FFT (like most modern digital ones can), a 2 tone test at full power may possibly be the most revealing measurement. With enough attenuation, the 7300's receive band display could also be used to clearly confirm the close-in results.
It doesn't look bad to me but one has to bare in mind that there is a element of Chinese quality in them so it's possible that he's on the money with the amp he ordered but got the short end of the stick
I was wondering about this as well. I think the IC-7300 vertical scale was 10dB. It looked as though the LSB was perhaps only 10-20dB down? I will hazard a guess that the relativeIy high level of LSB is related to the test configuration. The Yaesu FT-817 specification for opposing sideband suppression is greater than 50dB.
Perhaps you could do the same test with the 7300 and tune it to each multiple of the tx frequency. I tend to use an RTLSDR with the preamp gain right down when making measurements like this. I use the same trick at locations which suffer from high noise due to nearby commercial towers to find which frequencies the commercial stuff is on so I can try and filter it out enough to stop it overloading my front end. I have one of these amps I briefly used with my kx3 but I only ever ran it to about 30-40w. I have the matching elecraft amp now and I'm curious how they compare since they're both solid state amps for QRP rigs and one costs more than 5x the price of the other
Now THAT was an informative video. You answered my apprehensions with facts (even if your setup was not professional "lab" quality, as you say) to the point where I am fairly confident that the amp won't get me into trouble. I am going to use the amp with a HERMES Lite 2 SDR XCVR and PowerSDR HPSDR with its "Pure Signal" output. Even if the MX P50M does not put out 50 watts on all bands, its power output will be within what my PreciseRF EXPRESS Mag Loop antenna can handle, which is around 45 watts max. Great stuff. I like your "no nonsense" attitude. VE2DPE
hi Kevin, I measured my amp using an output power meter only and got similar results to you. I don't have anything accurate enough to measure 0 to 5 watts, so I took the 817's power levels as correct. It was realigned for each power level when I upgraded the output stage to the 817ND final amp only a few years ago. My power in/out results were 0.5/10, 1.0/20, 2.5/40, 5/45. So it starts at low power levels with a gain of 20, but reduces a bit as the drive level increases, compressing slightly before the 2.5/40 level, (a gain of 16) and by 5/45 it is definitely saturating as the gain is down at 9. A truly linear amplifier would have a consistent gain across its rated power range. But this is typical for solid state amplifiers, nothing new here. So I run my 817 at 2.5w, that produces 40w and that is 9 db greater than 5watts. That's good enough for me and I know I'm not using the amplifier as a speech processor! The problem is of course that while it may indicate a bit more output power, some of that power is in adjacent channels. It's not a smart way to operate, so I operate it below that level and know it's not only legal, but also not wiping out the users on the adjacent frequencies. I think the amplifier will have a longer life when operated at that level too. 73 Andrew vk1da
Great job testing this amp, I just ordered mx-p50 to take the output from Hermes lite 2 up to 25 watts max to drive my mercury 3s, so this is perfect for my use, with the mercury 3s 5w in is about 500w out on 80 n 40m, 10 to 15w in is about 1000w out , on 20m 20w in about 1000w out, perfect for my use, thanks for doing this test, just 1 last thing ,I noticed there using a MOSFET transistor, when buying other similar amps there using it appears to be same MOSFET, but running either 13.8v or 24v maybe check into this and see if raising voltage fixes linearity, if it possible, find out if MOSFET there using can run safely at higher voltage. Thank again great review, it works for me
The 10 MOhm impedance is relevant for DC - you have to consider the probe's parallel capacity (I'd guess 30-15pF?) and frequency you're measuring, too. While most scopes allow this at DC, don't try to measure 300V RMS at 1 Ghz. Edit: Saw you didn't use a probe at all at first - scopes usually have 1 MOhm input (and it's parallel capacitance) - you get 10 MOhm with a 10x probe.
A lot of these amps are using ~28V Cell base station transistors (yeah, I know, 800MHz devices but they work at HF too), it's a shame yours has no markings on the device but if it's not the MRF186 (which is also a 28V 800MHz device) they're usually something like the MRF9120 which is a 120W device, www.nxp.com/docs/en/data-sheet/MRF9120.pdf The MiniPA kits are a fine example www.ebay.co.uk/itm/new-MINIPA-DIY-KITS-100W-SSB-linear-HF-Power-Amplifier-For-YAESU-FT-817-KX3-h I *think* these would behave a lot better if run on 25-30V
agreed , but simply just adding voltage without re-tuning the internal circuitry is a crap shoot.... it will usually always change other characteristics in the circuit somewhat... which could mean anything from re-adjusting the voltage on the bias settings to capacitance/and/or inductance across the output transformer and the input of the chebychev (or whatever other filter it might be using).... I've seen it to where you have to change values in the filter slightly to get the right Q needed to suppress harmonics .... So simply upping the voltage to match the efficiency of the devise could make a nasty amp out of it.
You need more data points to see the flattening on the graph. It's much easier to see if you calculate gain for the last 2 data points; 2.4W drive and 27W output = 10.5dB gain, 4.6W drive for 31.5W output = 8.4dB gain, therefore the amplifier is well into compression (which starts when gain drops by more than 1dB). It would be useful to use dedicated equipment for measuring power, as oscilloscope Vpp calculation only really works with perfect sine waves and perfect matching, which is not always the case. Also, injecting a two-tone signal in the mic input (from the computer, using free software) is much better at identifying splatter (IMD products) than saying "hello" in the microphone. By the way, I've built a similar amp, they're OK for what they are, I think the PA section can safely run at 24V for about 100W output, with a decent fan and low duty cycle. The power device is a 120W 28V transistor pair in one package.
Kevin, Glad you did this follow up. It shows that there can be a big difference between amps, probably depending on what device is used. The one I tested was 20W out with 1W drive, 35W out with 2W drive, 40W out with 3W drive and 40W out with 4W drive, so it saturated at that level. Returned for refund. Yours is better but not good at advertised output, and probably OK at around 2.5W drive. I used Bird 43 with correct slugs for input and output measurements. Also monitored results on my old HP spectrum analyzer. There is some comments that it might be good with some compression if you don't have a speech compressor. This idea is WRONG since speech compressor result is filtered to about 2.4KHz BEFORE leaving the radio. Adding compression after the radio is not good, but 1dB compression is acceptable and many ,or most amps advertise output at 1dB compression. I am hereby retracting the TERRIBLE statement. Hope you get a decent amp and use wisely. Stay safe.
The scope input impedance is not 10Mohm, it's (10Mohm || k pF), for some k (should be written on the scope). Be careful because that capacitance becomes the dominating factor pretty soon with high frequencies.
Very informative video Kevin, thanks for sharing! I have to tell you, I enjoy all your videos and I pretty much learn something from every video you make! Stay cool! KL7CA
I think the guy was actually complaining about the spectral purity of this amp, not how much power it can put out. Would love to see it on a spectrum analyzer !
I thought I'd talked about that in one of these vids. It's been awhile. Anyway. drive it with more than 3 watts and the amplification factor compresses and it starts to clip, throwing out garbage out to 5 to 6 khz in both sidebands. I thought I'd mentioned that it was best not to drive it with more than 2.5 to 3 watts in the vid. But, it has been awhile.
If your amplifier is NOT linear (ie. the gain varies), it WILL generate harmonics. That's precisely why linearity is important! The quality of the filters may play a role in the results. In any case, this was good testing considering the ressources at hand 👍
I can not see any compliance to do not measure the power output signal with a scope. I don't know where they are comming from. But, in my case I always use a scope probe connected to the dummy load instead of a coax link to the PA output since then there is no reflection influence and you can also use a 1:10 or 1:100 probe for much higher power levels. By using a scope You can see also the real power envelop from the PA and it's real power level. I realy do not know where the scope complience come and there arguments to do not use a scope for this purpose.
If you want to see splatter , Just tune around the HF bands when there's a contest on .... No one seems to care at all about splatter when running in contests ... 3KW amps Running flat out etc , So this little amp , Ide not worry at all about using it on the air .
Hey Kevin!: I think the test says more about you as a person, the fact that you took a viewers comments sincerely and responded to them with the test says a lot in my opinion. Great video! de seeker/Jeff WA7LFP
Nice work, but please stop apologizing for your equipment and methods. If someone can do better, they should, post a video, and leave you a link in the comments so we can see the difference. Three requests: - Can you please run the same tests with the 7300 (at appropriately low powers, of course). It's a much more modern rig than an 817, and, IIRC, has more granularity in power output. It -might- yield more discreet and meaningful results. - Please jigger your spreadsheet graphs to display the input and output, in different colors, on the same graph. That way, like the example graph you showed, the compression will be more obvious. Posting a link to the actual spreadsheet would also be nice. - In your copious free time, and if this particular amp supports it, can you explore your radio(s) automatically shifting the frequency of the amp via the control cable? Please don't take any of this as criticism, or at least other than of the constructive variety, and thanks for all the work you put into what you do and post.
I copied the first 2 tests Pin and Pout data, and drew some, I hope it was 80m then 40m in the spreadsheet. i.imgur.com/sqReeDS.png Edit: To explain what's wrong with the charts in the video,. They appear to be comparing output power on the Y axix to test number on the X axis, then a second chart that has input power vs test number. This doesn't show linearity. One needs to compare output power to input power to see the linearity of a system. This requires a scatter chart(or XY chart) rather than a line chart.
@@TheRakerr I was just about to do the same as you - thanks for saving me the work! Not very "terrible" above 25W out, but personally I wouldn't use it above that output power.
Scope 10Meg impedance makes no difference. If the frequency was higher, something like a 50 ohm coax that connects the scope can screw things up though. At 1/4 length the open coax should look like a short and so on. Connecting the scope probe to an adapter directly would be then helpful because scope leads are made from high impedance coax (like 100kohm) that is somewhat terminated with the scope. Edit: what a surprise, I wrote the comment just before you told you run into problems due to the scope coax! :)
Good video. I hope I'm wrong, but it seems like your FT-817 has poor opposite sideband rejection. Maybe I wasn't interpreting the IC-7300's spectrum scope correctly. Two-tone tests are good for determining splatter as well. Thanks.
I don't think hams understand linearity. An amplifier would be perfectly linear if the output WAVEFORM would be an identical copy of the input waveform. Linearity also must be measured during instantaneous changes, dv/dt. Hams like to make up stuff as they get knowledge by thinking their way to it instead of learning from Engineering known principles.
Hi Kevin. I enjoy watching your videos a lot. Perhaps you could dig into how good the band filter in the amp is behaving for the different bands. Perhaps even replacing the main mosfet for a quality one. Vy 73 DO6WJ
If you haven't seen it yet, I talk about the filter quality in the latest video and provide a link in the description to a blog post where extensive testing was done on it. It's good.
Mine came defective: on 40m band the output power is _twice_ as high as on other bands. I.e. for 2.5w of input it is not 45w, but close to 90. This was measured when running on 12v LiFePo battery. When running on 13.8v power supply the output was even higher - ~110W. I replaced the unlabeled MOSFET with the original motorola 186 one but that did not fix the issue. Does anybody have any idea about some other possible reason of the issue?
In your previous video you mentioned that the main transistor varied wildly and could be a knock-off of a Motorola part. I wonder if some people might have a really bad transistor that runs hotter?
Your amplifier response curves are normal, as you explained yourself, although when testing the amp with the Yaesu ft817 I am wary of your observations, you could perhaps perform the same test without the amplifier to verify that the ft817 isn't itself the source of the observed 'splatter', as I have observed this with the ft817 myself when I was testing the microphones on the ft817 and producing a time averaged response curve via an SDR receiver.
You may have missed it, but the last bit there I said lets turn off the amp and here's the 817 at 5 watts. To show that it's output was clean and not over modulated.
So which input , output power chart was the 20 meter band. That would be helpful, just ordered one the I plan to use on my xiegu g106, it only puts out around 2 watts to 2.5 watts max on ssb. Thanks.
The real test to me is how you sound at the distant end I got lucky 40 meters was very short on SSB portion just happened to be a guy about 50 or 60 miles away and he said I sounded good now CW is different as long as you get 5nn or whatever when you expect it I wouldn't worry
I use the IC705 with this amp. I noticed yesterday with my 1/4 wave ground plane antenna for 20meters that my IC705 states that the SWR is below 1.5 for 40 meters! I don't believe it. So I tried it and I was talking to someone 30 miles away. Have you noticed that on the IC705, you will read a low SWR on bands that the antenna doesn't support?
If the amp is in-line and active, the meter reading on the radio won't be accurate. The filters in the amp are changing things on the radio side. You really need an SWR meter in-line between the amp and your antenna or antenna tuner.
@@loughkb Thank you Kevin. I thought that would be the case. I do have a SWR meter and the antenna doesn't resonate at 40 meters, just thought that was strange it did. Although, the SWR was about 7. Not good for the radio. :/
well, that completely depends on what radio you have and what type of a connector your radio has for the keying input. I would suggest you look at your radios manual, and once you know the connector type then you can know where to look for it. if it is a Yazoo ft817, it's a PS2 style connector that you can probably find on an old mouse or keyboard.
Yes, it has four low pass filters on the output of the PA, switch selectable from the front panel knob. The schematic has a placeholder text referencing them.
Just don't drive it into compression. This is literally a characteristic of amplifiers. Even audio amps do this. Low pass or band pass and you'll be fine.
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I've had one for a few years and used it for ssb, js8 and cw. I have never had a problem and no one has ever complained about my signal. I think there are just some hams that believe if you didn't have to take out a second mortgage to buy equipment then it junk. 73 and keep up the good vids de KF7VUT
No, that's exactly it. Many people lack the expertise to actually evaluate their equipment so the only thing they have to go on is price. Their only thought is "if it's expensive, it must be good!" There's a huge, unfilled market out there for inexpensive ham equipment if only someone would take notice.
Nicely done!
You can't make everyone happy. As long as you are satisfied, that is all that counts.
Thanks for having a look at that. Its interesting to find out a little more about them.
Hey Kevin, I absolutely enjoy your workbench videos - building projects and testing gadgets. You're fun to watch work on the bench, I always learn something. Keep up the great work! 73s, KJ6ER / Silicon Valley
Very helpful . You proved what I hoped that it used less power at 35 ish watts. For my future back pack set up. I learned a lot. Thank you
Thanks Kevin... I've had one for several years too and use it daily for FT4 with my FT-817 and an OCF dipole... It gives me great pleasure to receive great signal reports from all over the world from hams who are using towers, beams and high end HF transceivers.
Wow, haven't done that kind of measuring since Air Force days. Had to shake out the cobwebs to follow along. Thanks for reinforcing how old I really am.
I think l seen a video from (rate my radio) he checked checked the RF output of these’s amps, it looked alright. I always check my signal output with an SDRPlay don’t want anything funky spattering out there.... The only things to be wary about with these amps is the build quality. l took mine apart and found the PCB was excessively bending at the binding posts, and the main transistor was not flush with a gap at the heat sink. It’s worth checking.
Hmmm yea if the transistor is poorly mounted it's die could be getting a lot hotter than acceptable even with brief durations of key down which will mean goodbye amplifier pretty fast
Good for you using Open Source software! I love your channel.
I have one that I bought a year or two ago, I am happy with it but when I raise the power input the output start saturating above 25 watts output on all bands. In SSB or CW I don't have any heat problems but on ft8 it gets hot. However I installed a fan on top of the heat-sink and after that it remains just warm in ft8. Even with those limitations it is certainly worth the money. Like usual great video Kevin.
Thanks for highlighting these issues, I don't own an amplifier but I do have an 817 so if I were to buy one I now know what to check.
Follow up. I just did the gain compression calcs in decibels, both for power and voltage and the value came out the same for 80 meters: 3.08 dB. That's not horrible in my book. Well done.
Wow, some people expect ALOT for under $200....
Like demanding your Big Mac be made from Kobe beef....
Excellent. Thanks for posting
You mean I can't get a lab quality amp for just under $200 shipped? Shocking! Good video Kevin! I would not use this for anything over the 2.5 watt input anyway as you want to save the 817 finals.
Kevin, Really enjoyed your video. I have one of these amps and run it in CW mode almost exclusively and I don't run it full out. For the price thats being asked its a good deal. Its easy to make definitive statements without the testing to back it up. I'm sure the amp does have a non linear part of the curve as every amp does. You made mention of current off the shelf amps not being able to be run at full duty cycle for an extended amount of time. Back in the mid 80s Alpha had a contest where the person who came closest to the dollar cost of the electricity that the amp used for the test would win the amp. They took a commercial exciter and loaded their amp up to 1500w out and put a brick on the key for 18 days. Back then that amp cost as much as some new cars. Great performance with a price tag to match. Amps built today are not designed for full duty cycle at full power for very long... .
The data sheet I found for this amp shows that the specs were measured at 15V input. You were likely operating it on 13.4V from the previous video. The linearity and power output will improve somewhat at 15V. (Getting 15V from a 12V system is a bit difficult.) I'm considering an amp for an IC-705 so thanks for the measurements! --N2GX
I think the original complaint is about the spectral purity of the signal coming out of the amp, not the amount of power it will do !
Hi Kevin
I found your video on the Amp very interesting. I purchased on of these about six months ago. Like yours the driver transistor is un-marked. I did some similar tests to check linearity and found the sweet spot to be around 3W input. After that I also found that the output started to compress. One area that does bother me is that the PTT relay seems to be directly driven by the transceiver switch. There is no switching transistor. The bigger concern is the relay coil does not appear to have a diode across it. The back EMF as the relay releases is directly applied to the transceiver. I have checked the data sheet for the relay and it does not appear to have a diode built in.
The PTT switching is crude, and something to be wary of as it could place a lot more load on some solid state PTT circuits than they are designed for, in the case of the ft817 it's probably ok.
I address that in the next video. I put a single transistor relay driver in the amp.
Thanks for video Kevin and taking time to do the test. Really interesting 👍.
Keep Up the Great Work!
Thanks Kevin! You’ve taught me a lot about amp usage!
Thank you for sharing your conclusions on this little Amp Kevin. Good stuff! 73, dave/W6TUX
It's Chinese circuitry...if you want linearity your going to pay more than $150.00. Honestly I love not paying hundreds of dollars on my ham gear when I can. This Amp allowes me to operate my 818 at lower power settings and not over heat my transceiver finals during heavy duty cycles. Id rather burn out this little Amp than my FT818. Great break down!
Not "terrible" I would agree! If your scope can do FFT (like most modern digital ones can), a 2 tone test at full power may possibly be the most revealing measurement. With enough attenuation, the 7300's receive band display could also be used to clearly confirm the close-in results.
Thanks Kevin
For a fine video very instructive. I own a Ft817 so might take a look at this map. 73 G0STE
It doesn't look bad to me but one has to bare in mind that there is a element of Chinese quality in them so it's possible that he's on the money with the amp he ordered but got the short end of the stick
I am surprised at the amount of lower sideband present at the output of the FT817 on 20 meters. Ron W4BIN
I was wondering about this as well. I think the IC-7300 vertical scale was 10dB. It looked as though the LSB was perhaps only 10-20dB down? I will hazard a guess that the relativeIy high level of LSB is related to the test configuration. The Yaesu FT-817 specification for opposing sideband suppression is greater than 50dB.
Hi Kevin,
I think your measurements have merit. Does your o'scope have an FFT function to use it as a spectrum analyzer? Stay safe. 73 WB3BJU
Perhaps you could do the same test with the 7300 and tune it to each multiple of the tx frequency. I tend to use an RTLSDR with the preamp gain right down when making measurements like this. I use the same trick at locations which suffer from high noise due to nearby commercial towers to find which frequencies the commercial stuff is on so I can try and filter it out enough to stop it overloading my front end. I have one of these amps I briefly used with my kx3 but I only ever ran it to about 30-40w. I have the matching elecraft amp now and I'm curious how they compare since they're both solid state amps for QRP rigs and one costs more than 5x the price of the other
Now THAT was an informative video. You answered my apprehensions with facts (even if your setup was not professional "lab" quality, as you say) to the point where I am fairly confident that the amp won't get me into trouble. I am going to use the amp with a HERMES Lite 2 SDR XCVR and PowerSDR HPSDR with its "Pure Signal" output. Even if the MX P50M does not put out 50 watts on all bands, its power output will be within what my PreciseRF EXPRESS Mag Loop antenna can handle, which is around 45 watts max. Great stuff. I like your "no nonsense" attitude. VE2DPE
hi Kevin, I measured my amp using an output power meter only and got similar results to you. I don't have anything accurate enough to measure 0 to 5 watts, so I took the 817's power levels as correct. It was realigned for each power level when I upgraded the output stage to the 817ND final amp only a few years ago. My power in/out results were 0.5/10, 1.0/20, 2.5/40, 5/45. So it starts at low power levels with a gain of 20, but reduces a bit as the drive level increases, compressing slightly before the 2.5/40 level, (a gain of 16) and by 5/45 it is definitely saturating as the gain is down at 9. A truly linear amplifier would have a consistent gain across its rated power range. But this is typical for solid state amplifiers, nothing new here. So I run my 817 at 2.5w, that produces 40w and that is 9 db greater than 5watts. That's good enough for me and I know I'm not using the amplifier as a speech processor! The problem is of course that while it may indicate a bit more output power, some of that power is in adjacent channels. It's not a smart way to operate, so I operate it below that level and know it's not only legal, but also not wiping out the users on the adjacent frequencies. I think the amplifier will have a longer life when operated at that level too. 73 Andrew vk1da
Great job testing this amp, I just ordered mx-p50 to take the output from Hermes lite 2 up to 25 watts max to drive my mercury 3s, so this is perfect for my use, with the mercury 3s 5w in is about 500w out on 80 n 40m, 10 to 15w in is about 1000w out , on 20m 20w in about 1000w out, perfect for my use, thanks for doing this test, just 1 last thing ,I noticed there using a MOSFET transistor, when buying other similar amps there using it appears to be same MOSFET, but running either 13.8v or 24v maybe check into this and see if raising voltage fixes linearity, if it possible, find out if MOSFET there using can run safely at higher voltage. Thank again great review, it works for me
The 10 MOhm impedance is relevant for DC - you have to consider the probe's parallel capacity (I'd guess 30-15pF?) and frequency you're measuring, too. While most scopes allow this at DC, don't try to measure 300V RMS at 1 Ghz. Edit: Saw you didn't use a probe at all at first - scopes usually have 1 MOhm input (and it's parallel capacitance) - you get 10 MOhm with a 10x probe.
Nice job. Excellent for the equipment you have. N6OA
A lot of these amps are using ~28V Cell base station transistors (yeah, I know, 800MHz devices but they work at HF too), it's a shame yours has no markings on the device but if it's not the MRF186 (which is also a 28V 800MHz device) they're usually something like the MRF9120 which is a 120W device,
www.nxp.com/docs/en/data-sheet/MRF9120.pdf
The MiniPA kits are a fine example
www.ebay.co.uk/itm/new-MINIPA-DIY-KITS-100W-SSB-linear-HF-Power-Amplifier-For-YAESU-FT-817-KX3-h
I *think* these would behave a lot better if run on 25-30V
agreed , but simply just adding voltage without re-tuning the internal circuitry is a crap shoot.... it will usually always change other characteristics in the circuit somewhat... which could mean anything from re-adjusting the voltage on the bias settings to capacitance/and/or inductance across the output transformer and the input of the chebychev (or whatever other filter it might be using).... I've seen it to where you have to change values in the filter slightly to get the right Q needed to suppress harmonics .... So simply upping the voltage to match the efficiency of the devise could make a nasty amp out of it.
You need more data points to see the flattening on the graph. It's much easier to see if you calculate gain for the last 2 data points; 2.4W drive and 27W output = 10.5dB gain, 4.6W drive for 31.5W output = 8.4dB gain, therefore the amplifier is well into compression (which starts when gain drops by more than 1dB). It would be useful to use dedicated equipment for measuring power, as oscilloscope Vpp calculation only really works with perfect sine waves and perfect matching, which is not always the case. Also, injecting a two-tone signal in the mic input (from the computer, using free software) is much better at identifying splatter (IMD products) than saying "hello" in the microphone.
By the way, I've built a similar amp, they're OK for what they are, I think the PA section can safely run at 24V for about 100W output, with a decent fan and low duty cycle. The power device is a 120W 28V transistor pair in one package.
just one thing: input of the scope is 1M, and check max input Vpp. on mine is 50Vp-p
Kevin,
Glad you did this follow up. It shows that there can be a big difference between amps, probably depending on what device is used.
The one I tested was 20W out with 1W drive, 35W out with 2W drive, 40W out with 3W drive and 40W out with 4W drive, so it saturated at that level. Returned for refund.
Yours is better but not good at advertised output, and probably OK at around 2.5W drive.
I used Bird 43 with correct slugs for input and output measurements. Also monitored results on my old HP spectrum analyzer.
There is some comments that it might be good with some compression if you don't have a speech compressor.
This idea is WRONG since speech compressor result is filtered to about 2.4KHz BEFORE leaving the radio. Adding compression after the radio is not good, but 1dB compression is acceptable and many ,or most amps advertise output at 1dB compression.
I am hereby retracting the TERRIBLE statement. Hope you get a decent amp and use wisely.
Stay safe.
The scope input impedance is not 10Mohm, it's (10Mohm || k pF), for some k (should be written on the scope). Be careful because that capacitance becomes the dominating factor pretty soon with high frequencies.
Very informative video Kevin, thanks for sharing! I have to tell you, I enjoy all your videos and I pretty much learn something from every video you make! Stay cool! KL7CA
I think the guy was actually complaining about the spectral purity of this amp, not how much power it can put out. Would love to see it on a spectrum analyzer !
I thought I'd talked about that in one of these vids. It's been awhile. Anyway. drive it with more than 3 watts and the amplification factor compresses and it starts to clip, throwing out garbage out to 5 to 6 khz in both sidebands.
I thought I'd mentioned that it was best not to drive it with more than 2.5 to 3 watts in the vid. But, it has been awhile.
If your amplifier is NOT linear (ie. the gain varies), it WILL generate harmonics. That's precisely why linearity is important! The quality of the filters may play a role in the results. In any case, this was good testing considering the ressources at hand 👍
It's still a nice amp.
I can not see any compliance to do not measure the power output signal with a scope. I don't know where they are comming from. But, in my case I always use a scope probe connected to the dummy load instead of a coax link to the PA output since then there is no reflection influence and you can also use a 1:10 or 1:100 probe for much higher power levels. By using a scope You can see also the real power envelop from the PA and it's real power level. I realy do not know where the scope complience come and there arguments to do not use a scope for this purpose.
If you want to see splatter , Just tune around the HF bands when there's a contest on .... No one seems to care at all about splatter when running in contests ... 3KW amps Running flat out etc , So this little amp , Ide not worry at all about using it on the air .
Hey Kevin!:
I think the test says more about you as a person, the fact that you took a viewers comments sincerely and responded to them with the test says a lot in my opinion. Great video!
de seeker/Jeff WA7LFP
Nice work, but please stop apologizing for your equipment and methods. If someone can do better, they should, post a video, and leave you a link in the comments so we can see the difference.
Three requests:
- Can you please run the same tests with the 7300 (at appropriately low powers, of course). It's a much more modern rig than an 817, and, IIRC, has more granularity in power output. It -might- yield more discreet and meaningful results.
- Please jigger your spreadsheet graphs to display the input and output, in different colors, on the same graph. That way, like the example graph you showed, the compression will be more obvious. Posting a link to the actual spreadsheet would also be nice.
- In your copious free time, and if this particular amp supports it, can you explore your radio(s) automatically shifting the frequency of the amp via the control cable?
Please don't take any of this as criticism, or at least other than of the constructive variety, and thanks for all the work you put into what you do and post.
I'd be more concerned by the "other" sideband leak from your 817.
Interesting stuff. Did you try tuning your 7300 at a higher frequency (say +10khz up from the 817's transmit) and see if it was splattering higher up.
You should create a graph of power out vs power in. I think that will show a significant amount of compression.
I copied the first 2 tests Pin and Pout data, and drew some, I hope it was 80m then 40m in the spreadsheet.
i.imgur.com/sqReeDS.png
Edit: To explain what's wrong with the charts in the video,. They appear to be comparing output power on the Y axix to test number on the X axis, then a second chart that has input power vs test number. This doesn't show linearity. One needs to compare output power to input power to see the linearity of a system. This requires a scatter chart(or XY chart) rather than a line chart.
@@TheRakerr I was just about to do the same as you - thanks for saving me the work! Not very "terrible" above 25W out, but personally I wouldn't use it above that output power.
Scope 10Meg impedance makes no difference. If the frequency was higher, something like a 50 ohm coax that connects the scope can screw things up though. At 1/4 length the open coax should look like a short and so on. Connecting the scope probe to an adapter directly would be then helpful because scope leads are made from high impedance coax (like 100kohm) that is somewhat terminated with the scope.
Edit: what a surprise, I wrote the comment just before you told you run into problems due to the scope coax! :)
Good video. I hope I'm wrong, but it seems like your FT-817 has poor opposite sideband rejection. Maybe I wasn't interpreting the IC-7300's spectrum scope correctly. Two-tone tests are good for determining splatter as well. Thanks.
I don't think hams understand linearity. An amplifier would be perfectly linear if the output WAVEFORM would be an identical copy of the input waveform. Linearity also must be measured during instantaneous changes, dv/dt. Hams like to make up stuff as they get knowledge by thinking their way to it instead of learning from Engineering known principles.
Hi Kevin. I enjoy watching your videos a lot. Perhaps you could dig into how good the band filter in the amp is behaving for the different bands. Perhaps even replacing the main mosfet for a quality one. Vy 73 DO6WJ
If you haven't seen it yet, I talk about the filter quality in the latest video and provide a link in the description to a blog post where extensive testing was done on it. It's good.
Mine came defective: on 40m band the output power is _twice_ as high as on other bands. I.e. for 2.5w of input it is not 45w, but close to 90.
This was measured when running on 12v LiFePo battery. When running on 13.8v power supply the output was even higher - ~110W.
I replaced the unlabeled MOSFET with the original motorola 186 one but that did not fix the issue.
Does anybody have any idea about some other possible reason of the issue?
In your previous video you mentioned that the main transistor varied wildly and could be a knock-off of a Motorola part. I wonder if some people might have a really bad transistor that runs hotter?
Your amplifier response curves are normal, as you explained yourself, although when testing the amp with the Yaesu ft817 I am wary of your observations, you could perhaps perform the same test without the amplifier to verify that the ft817 isn't itself the source of the observed 'splatter', as I have observed this with the ft817 myself when I was testing the microphones on the ft817 and producing a time averaged response curve via an SDR receiver.
You may have missed it, but the last bit there I said lets turn off the amp and here's the 817 at 5 watts. To show that it's output was clean and not over modulated.
@@loughkb Yes, I missed the end of the video! Thank you for responding.
Interesting video Kevin. Thank you. de Gene, WB0RSZ
So which input , output power chart was the 20 meter band. That would be helpful, just ordered one the I plan to use on my xiegu g106, it only puts out around 2 watts to 2.5 watts max on ssb. Thanks.
That's actually fine. You don't want to drive it with more than 2.5 w or it'll clip the output and you'll splatter .
The real test to me is how you sound at the distant end I got lucky 40 meters was very short on SSB portion just happened to be a guy about 50 or 60 miles away and he said I sounded good now CW is different as long as you get 5nn or whatever when you expect it I wouldn't worry
Thanks
I use the IC705 with this amp. I noticed yesterday with my 1/4 wave ground plane antenna for 20meters that my IC705 states that the SWR is below 1.5 for 40 meters! I don't believe it. So I tried it and I was talking to someone 30 miles away. Have you noticed that on the IC705, you will read a low SWR on bands that the antenna doesn't support?
If the amp is in-line and active, the meter reading on the radio won't be accurate. The filters in the amp are changing things on the radio side. You really need an SWR meter in-line between the amp and your antenna or antenna tuner.
@@loughkb Thank you Kevin. I thought that would be the case. I do have a SWR meter and the antenna doesn't resonate at 40 meters, just thought that was strange it did. Although, the SWR was about 7. Not good for the radio. :/
Also not good for the amp. :-)
Nice video. Did you have the alc set on the transmitting radio?
As I recall, I was using CW mode for a constant carrier.
Sir, jut a new stupid question, i am missing the end of the ptt cable that connects to the radio, tell ian can buy one and where thank you
well, that completely depends on what radio you have and what type of a connector your radio has for the keying input. I would suggest you look at your radios manual, and once you know the connector type then you can know where to look for it. if it is a Yazoo ft817, it's a PS2 style connector that you can probably find on an old mouse or keyboard.
@@loughkb thanks so it would be a build ? the radio is a 817
Yes.
My observations are too many HAM's are gear snobs.
Great review (but megohms, please). 👍
output spread harmonic is the issue there...,!! no band pass filter in the PA ....!!
Yes, it has four low pass filters on the output of the PA, switch selectable from the front panel knob. The schematic has a placeholder text referencing them.
Just don't drive it into compression. This is literally a characteristic of amplifiers. Even audio amps do this. Low pass or band pass and you'll be fine.
👋 👍
🐱👋
All Amps need to have a tuned output. The Chinese only want to make money, they don't care if you splatter or not.
omg that Hantek scope makes my eyes hurt. Ugh. Please god don't make me look at that.