Decibels, S-Meters, Amplifiers, and Gain
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- เผยแพร่เมื่อ 19 พ.ย. 2024
- #hamradio #decibels #s-units #linearamplifier
My friend Joel, KC4WZB, suggested a video to discuss gain, signal meters, and Decibels (dB). This video covers S-meter variations, the origin of the Decibel, and the results one might expect from using a linear amplifier.
S-meter readings are relative. If someone is judging their station by the S-meter reading I give them, I like to qualify the reading by telling them the type of antenna I’m using, and my transceiver model. If I have them at S9+10dB with a dipole, that’s one thing. If I have them at S9+10dB with a 4-element Yagi beam aimed at them, I’m doing some heavy lifting. So it’s all relative. I listen for the amount of background noise between words. I can do the same with SSB and CW. I generally consider full-quieting (no background noise between words) as S9. My QRP CW rig doesn’t even have an S-meter, so have to give signal reports completely by ear. My “by-ear” scale is as follows:
S1 = Barely readable
S3 = Readable but noisy
S5 = Easily readable but still noisy
S7 = Perfectly readable with only a slight hiss
S9 = Perfectly readable with no noise (aka full quieting)
There was a study in 2004 by M.C. Killion that measured the ability to detect changes in SNR. In the case of the Killion study, SNR stands for Speech to Noise Ratio. The subjects were hearing-aid users but I think we can extrapolate some useful insight from the study as it relates to the ability to detect changes in sound relative to a noise floor. Sixteen hearing-aid wearers made paired comparisons between different SNRs, using values of between −6 dB and +6 dB above the noise, in 2 dB increments. The results showed that the test participants only randomly detected a difference of 2dB between speech and noise. However, they were able to detect a 4dB difference about 90% of the time. With a 6dB difference between speech and noise the participants were able to detect the change with 100% accuracy. The 2004 Killion study concluded that while a 2dB change in SNR could bring benefit, such benefit was unlikely to be noticed in a real-world setting. With my by-ear S-meter reading estimate, I am loosely applying the insights gained from the Killion study.
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73, de N4HNH
Great video Doug. Learned a lot about decibels, S meters and amplifiers. Just got my licenses and had no idea that going from S1 to S2 was anything but 6dB. That's why I love your videos! Always walk away knowing something new.
I’m glad you found the video helpful, James. 73, Doug
Great video. I learned a lot. I still use the s-meter because it is more for my reference although relative, I can tell what the received signal is doing. I can compare how diffent signals compare to each other. Once you learn how a decibel works it easy. Thank you!
Indeed Larry! The S-meter is a great tool for relative measurements. Each of us learn what to expect our meter to read for certain people we talk to regularly. You have the right idea.
Thanks for checking in!
73, Doug
Such great information. Loved this video
Glad it was helpful, Kayden.
73, Doug
It was a pleasure to have a great QSO with you on 40; NY:GA. 73 de K2LED
Thank you Bob! It was definitely a pleasure to meet you. We had a nice roundtable discussion going on; you, Bill, and me. Bill seems like such a nice guy too.
Hopefully we can do that again in the near future.
73, de N4HNH
I agree, I don’t use s meters anymore. All I need it my ears. With radios like the 101/5k and 891 .
Close your eyes and try to tell the difference between a 5/5 and 5/9 , I bet you can’t
Soooo true my friend!
73, de N4HNH
An S unit is supposed to be the change in sound volume that is readily perceptible by the human ear and that is 6 dB. A 3 dB change in power from 1000W to 2000W may or may not be perceptible depending on how good the hearing is. However the human ear can hear a change in loudness from 500W to 2000W - 6 dB. But you can't run 2000W (beyond the legal limit). Those first 600 watts is the lion's share - 100X the power from QRP. or 3 S units. Going to legal limit is only another S unit. Great video Doug.
Thank you Ariel! Your comment puts the icing on the cake. 73, Doug
Excellent
Thanks Joel!
I have the KPA-500 and we ran ARRL Field Day at 150 watts - which is the max power allowed for "low power" and we drove it with only 10 watts or so of drive. We placed 4th in the country for 2A (two transmitters). I am not sure we could have done much better at 500 watts or even 1500 watts in terms of QSO's and we would definitely be handicapped in terms of points allowed per QSO had we run more power. Like you explained - the first 500-600 watts is the lions share of the gain from QRP.
On 7.209 right now with a couple of guys interested in SOTA. Jump in.
73, de N4HNH
I wished you could have joined us. It was a good group. Yes, that first 500-600W packs the punch and doesn’t break the bank. If propagation isn’t cooperating 1500W isn’t going to help.
73 my friend! Doug
Sorry Doug - I was otherwise occupied
@@n4hnhradio The only time those extra watts seem to help is during very marginal conditions - especially 80m and 160m when both the DX and I are trying to dig out each other out of the noise floor. Beverages help improve the S/N ratio.
Indeed, a beverage is great! I want to eventually put one up. I had one but it wasn’t long enough.
Isn’t the opposite true, as it applies to QRP?
That is, 5w is two S units less than 100w and 20w is 1 S unit less than 100w. It’s the reason QRP works.
I see a lot of new Hams who think they need more power to make contacts. While there are many reasons that go into why radio works at all, I hate seeing newbies feel their 100w rig isn’t enough. “Isn’t 100w twenty times better than 5w?”. Then you’ve got “experts” telling them QRP is pointless. Great video!! Tnx de WB3CFN…dit dit
3dB gain for 5W is 10W. That represents 0.5 S-units on a perfect S-meter. Another 3dB and you have 20W, plus another 0.5 S-units. So, if you were S1 at 5W, you are now S2 at 20W. Another 3dB, from 20W to 40W, and you will be S2.5. Increase the 40W by 3dB, to 80W, and your original 5W QRP signal has increased from S1 to S3. You will need another 3dB, or 160W, to achieve S3.5.
So it is quite amazing when you compare 5W (QRP) to 100W. It’s a difference of 2 or 3 S-units. The bigger difference is in the audio, if operating SSB. For CW, the difference tends to be less noticeable.
The same thing happens again when you go from 100W to 400W. There is a significant increase in the audio, more noticeable than the difference in S-units.
People are too fixated on S-units. My QRP transceiver doesn’t even have a signal meter. I give signal reports by ear, which is the basis of S-units anyway. It takes a 6dB change in volume for our ears to detect the change. Hence the origin of 1 S-unit representing a 6dB change in signal strength.
2x (3dB) power for 0.5 s-unit. Not worth it. Get a good antenna!
Do both, if possible. Some people have space limitations. I get so many questions about what antenna to use if you have limited space, or antenna restrictions.
If you find yourself hearing stations who can’t hear you, they might be using an amplifier, and maybe even a directional antenna.
The point of this video is to show that you gain the most in the first 400W. Amplifiers that can reach 1500W cost exponentially more and require 230/240vAC. A great 500W amplifier is the best value.