EMRFD Message Archive 3473
Message Date From Subject 3473 2009-08-14 12:37:40 timshoppa Musings on S-Meter readings I have my homebrew receiver I've been tinkering with for a while. It's a very traditional bandpass + diode ring mixer + 2N5179 post mixer amp + homebrew crystal filter + Hycas IF amp + BFO + audio amp.
Only recently did I add an S-meter to the Hycas IF amp (following almost verbatim the one suggested in hycas-apps). I use the standard attack/decay timings. I went so far as to calibrate the S-meter with pen markings on the meter scale: S2 is 0.4uV, S8 is 25uV, set using my signal generator and attenuators.
My antenna is a 135-foot-long doublet (fed with ladder line and an antenna tuner) up 90 feet between trees at the corners of the property. (I'm real proud of that.)
It's summertime so of course 80M is horrendously noisy... probably more than usual last night when I was goofing around. Lightning crashes on 80M kept the S-meter above S9 most of the time, but sometimes there would be a lull where I could read a S6 or S7 background noise level. There were a few loud signals coming in above S9, some others in the S6 range which were obviously weaker than the lightning crashes that peaked the S-meter but still readable during the quiet times.
40M was somewhat noisy, lots of crashes above S6, but 20M was in comparison quite free of QRN. Except for some occasional crashes I could hear a fairly even white noise (what I've always called "band noise", probably a meaningless term but that's what I call it to distinguish it from lightning crashes.). This is pretty typical for summertime.
I know the S-meter "standard" is there to provide some actual relevance to compare signal strengths. But I'm a little dubious of the standard calibration in terms of actual usage. Signals that were officially S4 on 20M were, to my ears, very very loud and clear and way above the noise, and I would've subjectively given them S8 or S9. And signals that were officially S9 on 80M were competing with the lightning crashes and during the worst bursts uncopyable.
All that said and done, I almost wish I didn't put a S-meter on the panel. I can't imagine ever using offical S-units instead of subjective S units. But maybe it will come in handy for antenna comparisons or something else.
3474 2009-08-14 15:20:49 Rick Re: Musings on S-Meter readings Hi Tim,
Your receiver is an excellent choice for measuring noise levels on various bands, since it has nearly constant gain from band to band. If I understand correctly, the first gain in your receiver is after the mixer, and that will be the same no matter what band you are listening to. I expect your front-end filters are probably similar within a few dB.
Rather than dismissing the S-meter readings, I'd encourage you to log them and continue to make band-to-band comparisons. When I first started designing serious HF receivers, I lived in the Upper Peninsula of Michigan, and had an antenna very similar to yours. I sent some of my receivers out to Wes, who commented that they didn't have enough gain. Since moving out here to the Northwest, i've observed that when 40m is quiet, I need better noise figure than I ever felt was necessary in the UP.
I like your term "band noise." I also use it to distinguish between local QRN, the sound of the band, and internal receiver noise. I like a receiver that has internal noise about 10 dB below the band noise, so I can really hear what the band is doing even at 3:00 a.m. with no signals. I optimized the new microR2 for 40m with a dipole in the Northwest. One reason that 40m is quiet out here is that thunderstorms within one ionospheric hop are less comm
3475 2009-08-14 15:32:59 Lasse Re: Musings on S-Meter readings Tim
may I suggest you redesign the faceplate to show dBm rather than S-units...
This way you can still let your ears tell you the s-strength and not be
fooled by the meter, and have an accurate measure of the received level too!
> I have my homebrew receiver I've been tinkering with for a while. It's a very traditional bandpass + diode ring mixer + 2N5179 post mixer amp + homebrew crystal filter + Hycas IF amp + BFO + audio amp.
3476 2009-08-14 16:35:00 w4zcb Re: Musings on S-Meter readings I like your term "band noise." I also use it to distinguish between
local QRN, the sound of the band, and internal receiver noise. I like
a receiver that has internal noise about 10 dB below the band noise,
so I can really hear what the band is doing even at 3:00 a.m. with no
signals. I optimized the new microR2 for 40m with a dipole in the
Northwest. One reason that 40m is quiet out here is that thunderstorms
within one ionospheric hop are less common than in the Eastern and
For which you can thank the cold waters of the Japanese current
Rick.Your three to 5 thunderstorm days a year out there has a hard
time comparing to the 90-100 plus of the gulf coast of FL.
I too like an "S" meter. Although mine is a row of LEDS, each one
below "S"-9 is 6 dB and the next one over 9 is -63 dBm, I can hook the
computer to the rig and measure accurately in 1 dB steps.Makes a near
lab quality piece of test equipment and the results of various
meassurements gets logged on the backside of my paper logbook.
Excellent reference data, makes quite interesting reading on occasion.
3483 2009-08-17 08:37:11 timshoppa Re: Musings on S-Meter readings