Many thanks to ON7OFF for translating and hosting this video. This video was released in September 2022, at the same time I released harmonic testing and IMD3 testing. Maybe ON7OFF can pick them up at a later time.
I had also made some IMD3 (2-tone 700Hz/1900Hz) testing. In fact, if I use the amp at 80m with input 1W, the IMD3 was only around -15dbc, which was *not* acceptable. Another problem was, the SSB audio was not clean, it was a little bit distorted, escpecially at 80m. I increase the BIAS up to 3.72V for both IRFs, after that it looks much better. IMD3 came up to -35dbc (not perfect, but acceptable) and distortion was gone, SSB signal at 80m was now usable (before it wasn't) up to 10m. Other people they build amps with the IRF530N came to the same results like me, BIAS voltage need around 3.7V for an usable SSB signal. Yes, the temp of the IRFs will be higher, but that is the compromise. But they are low cost transistors and can be changed if blowing.😉 The issue with the SWR I had too, start from 17m and higher. Measurements with a dummy load don't show this (!), but with resonant dipole antennas, SWR 1,2..1,4 the amp show a wrong SWR >2. I change R36 with a potientiometer and made measurements with an external SWR meter. As result I need change the R36 from 10k down to 2.1k. After this the SWR from amp was equal to SWR of my external SWR meter. You need to check this out, why there is a difference between dummy load and real nearly resonant antennas. But all in all it is a good amp for increase the power of QRP transceiver in a cost-effective way. 73 Heiko, DL1BZ
During the video I noticed the SWR meter connected between the radio and PA50 showing values up to around 1.6:1 and the translation mentions that this value is “very important”. What causes the “input” SWR value between the radio and PA50 to be greater than around 1:1? Thank you for creating such a great amplifier !
If you have looked at other external power amplifiers, you will find that the input standing wave is relatively large. This is caused by various reasons such as MOS gate impedance and section capacitance. It presents different impedances at different frequencies. The input standing wave problem was considered in the early design of MicroPA50. We need to reduce the input standing wave to less than 2.0:1 to ensure that your radio will not be damaged.
I would like to know if the output can be turned down to around 20 watts PEP or can the input power just be lowered to get this output level on SSB ? Also will it work on CB ?
The power cannot be controlled. The output power is controlled by controlling the input power into the amplifier. And yes, you can use it on the CB band.
Hi, my new MicroPA50+ has firmware of 2.8.5 and on 15m, when I press PTT, it shows BYP in place of TX. Unable to remove that. If I change band, it works just fine. Only in 15m. SWR is good on the band at 1.2. Do you know why BYP is coming up ? Thanks.
I had the same issue. 15m and 30m don't work and just show BYP. There is a multi-click option that is missing from every manual I can find, that is for "30/15m Open/Close". This comes up after 8 clicks. Do the 8 clicks until it says "open". Then power the amp off and back on. This seems to enable/disable 30m and 15m operation. Same as for the 7 click menu option for "17m/15m SWR On/Off". No mention in the manuals, but turns the SWR meter on and off for 17 and 15m (no power cycle needed).
Many thanks to ON7OFF for translating and hosting this video. This video was released in September 2022, at the same time I released harmonic testing and IMD3 testing. Maybe ON7OFF can pick them up at a later time.
I had also made some IMD3 (2-tone 700Hz/1900Hz) testing. In fact, if I use the amp at 80m with input 1W, the IMD3 was only around -15dbc, which was *not* acceptable. Another problem was, the SSB audio was not clean, it was a little bit distorted, escpecially at 80m. I increase the BIAS up to 3.72V for both IRFs, after that it looks much better. IMD3 came up to -35dbc (not perfect, but acceptable) and distortion was gone, SSB signal at 80m was now usable (before it wasn't) up to 10m. Other people they build amps with the IRF530N came to the same results like me, BIAS voltage need around 3.7V for an usable SSB signal. Yes, the temp of the IRFs will be higher, but that is the compromise. But they are low cost transistors and can be changed if blowing.😉
The issue with the SWR I had too, start from 17m and higher. Measurements with a dummy load don't show this (!), but with resonant dipole antennas, SWR 1,2..1,4 the amp show a wrong SWR >2. I change R36 with a potientiometer and made measurements with an external SWR meter. As result I need change the R36 from 10k down to 2.1k. After this the SWR from amp was equal to SWR of my external SWR meter. You need to check this out, why there is a difference between dummy load and real nearly resonant antennas.
But all in all it is a good amp for increase the power of QRP transceiver in a cost-effective way.
73 Heiko, DL1BZ
one of the best qrp amp around for the price. hope you can build a 100w of this version. thank you and 73.
During the video I noticed the SWR meter connected between the radio and PA50 showing values up to around 1.6:1 and the translation mentions that this value is “very important”. What causes the “input” SWR value between the radio and PA50 to be greater than around 1:1?
Thank you for creating such a great amplifier !
If you have looked at other external power amplifiers, you will find that the input standing wave is relatively large. This is caused by various reasons such as MOS gate impedance and section capacitance. It presents different impedances at different frequencies.
The input standing wave problem was considered in the early design of MicroPA50. We need to reduce the input standing wave to less than 2.0:1 to ensure that your radio will not be damaged.
I would like to know if the output can be turned down to around 20 watts PEP or can the input power just be lowered to get this output level on SSB ? Also will it work on CB ?
The power cannot be controlled. The output power is controlled by controlling the input power into the amplifier. And yes, you can use it on the CB band.
Nice info, what are the harmonic levels and spurs?
Hi, my new MicroPA50+ has firmware of 2.8.5 and on 15m, when I press PTT, it shows BYP in place of TX. Unable to remove that. If I change band, it works just fine. Only in 15m. SWR is good on the band at 1.2. Do you know why BYP is coming up ? Thanks.
I had the same issue. 15m and 30m don't work and just show BYP.
There is a multi-click option that is missing from every manual I can find, that is for "30/15m Open/Close". This comes up after 8 clicks. Do the 8 clicks until it says "open". Then power the amp off and back on. This seems to enable/disable 30m and 15m operation.
Same as for the 7 click menu option for "17m/15m SWR On/Off". No mention in the manuals, but turns the SWR meter on and off for 17 and 15m (no power cycle needed).