RF meter sensitivity

[Lkaskel]

Hey Gang,
I mainly work on older (late 70's) radios and I occasionally have and issue with the RF meter readings. I did a 1st edition Washington a few months back and I just finished a GE Superbase with this issue. That includes a recap and alignment as well as what ever else they need. Both radios receive awesome but the S-meters are not as responsive as I would hope. Mos of the radios I refurb work as expected. I set them to S-9 with -73db and the RF gain is aligned fine but somewhere around S-7 to S-5 they both quit reading well. If I receive someone that should give me S-4 to S-5 for instance they barely move the needle. I can still hear folks that come in with the noise fine so the radio is receiving well its just not showing on the meter. I am concerned when I sell them that the new owner will not be satisfied with that issue.

Anyone have any experience with this or is there a way to troubleshoot/measure the output to the meter to know if its the meter or the circuit driving it?

Thanks as always!!! All the best!

 

[oldtymer]

-73db =50uv according to the service manual 100uv from the generator for s9

 

[Unit 75]

-67dB=100uV

 

[Lkaskel]

I understand the confusion....
Watch this and tell me your thoughts.

 

[sunbulls]

I never put too much stock into the accuracy of the cheap meters found in CB radios. After calibrating an S-meter according to specification, the only thing you can say is that your S9 reading is somewhat accurate, nothing more. That doesn’t mean an S3 or 20Db over 9 reading is also accurate. After making this adjustment, what bothers me is that you will often see meters that are either incapable of reading full scale or a meter that pins the needle while another nearby radio is transmitting. After observing this, out of frustration I sometimes calibrate the meter full scale (saturation point) instead using my HT keyed next to it. With that, at least I know that a full scale reading indicates some transmitter is close, a valuable indication while trying to track a signal on a fox hunt. I know it’s a cheap and dirty way to do it, but then again, most of these radios have cheap and dirty meters as well as circuitry driving them. They’re fun to look at, but not to be believed.

 

[2315 Robert]

Affirm Sunbulls. I can get three and they do work, just not exactly the same. Sure if they are way crazy you could a small resistor, not worth the time. I was just in San Angelo TX and the person I was working for thought that he had 3 bad radios. They all worked, just the meters were not functioning.

 

[M0GVZ]

IARU states 6dB per S point but a lot of radios, even amateur ones, have S meters calibrated as 3dB per S point up to S9. It could be that the meters you have are conforming to the 6dB per S point standard.

 

[Lkaskel]

Thanks everyone for your reply's. I do know that these meters are for reference only and that they will not be all that accurate. For me, it's more about selling a radio that someone may questions its competence because the meter does not reflect lower signals. We all do know that there is a world of folks out there that "watch" the meter and place value on its readings.

Thanks again!!!

 

[tramd]

Here's the scale for using 50uv = S9. This will allow you to see how linear your meter is.
S9 = 50
S8 = 25
S7 = 13
S6 = 6.3
S5 = 3.2
S4 = 1.6
S3 = .79
S2 = .40
S1 = .20
(If using 100uv = S9, the output would be doubled for each).
There's a lot of info like this on the web.

 

[M0GVZ]

For me, it's more about selling a radio that someone may questions its competence because the meter does not reflect lower signals. We all do know that there is a world of folks out there that "watch" the meter and place value on its readings.

That's the very reason that Icom, Yaesu and Kenwood deviate from the 6dB per S point and instead use 3dB per S point from S0 to S9.

I remember testing a Commtron CB, a radio in the UK which had a strong reputation for being deaf, on some test gear. It wasn't deaf at all, it produced the same SINAD readings down to -120dBm as everything else I tested. The problem with the radio is that a signal of S9 strength fed into it only showed S6/7 on the meter and there was no potentiometer to adjust the calibration of the S meter in the radio, it was done by a fixed value resistor and one with a low tolerance to boot.

 

[Slowmover]

In the truck I sure find it handy as a clue about distance. One is moving in a direction and so are others. Then, there are base stations. After awhile, what’s what and who’s who have some reference.

Eastbound on IH40 across OKC of an evening I can start to pick up the locals. Been great to ask questions about how my gear is coming across.

Strongest signals near downtown, but can start to pick them up west of the El Reno scales and still “see” the meter showing activity once past Tinker AFB even as noise has degraded audio past legibility.

What reading is irrelevant to this. Just that the meter moves some and I can extrapolate.

That meter movement told me noise was justification for trying a West Mountain Radio ClearSpeaker. Yup, expensive test WORKED!!

All due to a lowly meter.

.