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Author Topic: S-Meter accuracy...LED or needle types  (Read 13248 times)
KT0DD
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Posts: 283




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« on: August 21, 2012, 05:40:15 AM »

Looking at my LED type Yaesu FT-950 s-meter, I was reminded of a sales pitch by a stereo audiophile salesman I dealt with years ago.

I was looking at a high end Nakamichi casette deck with LED bar type V/U meters when they first came out in the 80's. The salesman said the new LED meters were much faster and accurate than the mechanical meters because they worked electronically at "The speed of light" where mechanical meters were subject to slower response due to their mechanical movements.

While it was quite a sales pitch, It seemed to be logical.

Is this necessarily true? I know alot of hams still like the needle type S-meters, probably out of nostalgia reasons.

Just wondering about this useless little memory running around in my head...Hi Hi.

73. Todd - KT0DD
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AD4U
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Posts: 2179




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« Reply #1 on: August 21, 2012, 05:47:40 AM »

LED meters probably move faster and follow a signal faster than mechanical meters.  As far as S meter "accuracy" is concerned, very few S meters of any kind are "accurate", especially if you compare them to the old standard of 50uV = S9.  A typical S meter is no more than a relative signal strength meter which is not calibrated to any specific standard.

Dick   AD4U
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AA4PB
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Posts: 12990




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« Reply #2 on: August 21, 2012, 05:57:47 AM »

While an LED meter may have the ability to move faster, they are still limited by the time constants in the receiver AGC which supplies the voltage that the S-meter reads.

With VU meters, the designers build in time delays that slow the LED meter down so that you can read them. There are specs regarding these time constants. If the LED meter were permitted to follow the audio waveform in real time it would appear as a blur. I think you were given some sales guy's marketing hype  Cheesy

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K0OD
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Posts: 2578




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« Reply #3 on: August 21, 2012, 07:20:48 AM »

Had a Radio Shack guy try to sell me those high end "gold" cables by telling me electricity moved faster in them.

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K8AXW
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Posts: 3963




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« Reply #4 on: August 21, 2012, 07:58:40 AM »

OD:  You mean it doesn't?
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AC4RD
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Posts: 1235




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« Reply #5 on: August 21, 2012, 09:12:29 AM »

Had a Radio Shack guy try to sell me those high end "gold" cables by telling me electricity moved faster in them.

 :->  :->  :->

Gosh, explain to me again, Mister Salesman, how if I spend enough money, the laws of physics no longer apply to my stereo.  :-)


"Radio Shack:  You've got questions, we've got blank stares, lies, and overpriced cellphone contracts."

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KA5N
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Posts: 4380




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« Reply #6 on: August 21, 2012, 10:29:30 AM »

Meters that measure with "globs" of light go against nature and the radio gods.
I like real electromecanical meters.  Suppose you gave a signal report that was a half a
dB low because the led resolution wasn't good enough to read exactly?   Why the affront
to the other ham would be unforgiveable!!
Real meters forever!

Allen KA5N
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AD4U
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Posts: 2179




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« Reply #7 on: August 21, 2012, 10:43:10 AM »

OM UR signal report on this end is 2 red LEDs over 5 green ones.  I just love technology.

Dick  AD4U
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G3RZP
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« Reply #8 on: August 21, 2012, 10:49:46 AM »

The 'S' stands for 'suspicious'.
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WB2WIK
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Posts: 20636




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« Reply #9 on: August 21, 2012, 11:03:13 AM »

I don't really care and hardly ever look at any of my "S" meters on anything.

Being able to copy the station = good.

Not being able to copy the station = bad.

My S-meter really only needs a red light (bad) and a green light (good).

But anyway, there are modern LCD meters that look so much like vane type meters it's almost scary.  The technology is certainly available and has been for a long time, you just need a TFT panel or similar to make it work.  Take a look at the "meters" on an IC-7800.  You can almost feel the breeze from the meter "needles" going up and down...until you realize there aren't any.
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AA4PB
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« Reply #10 on: August 21, 2012, 12:33:05 PM »

I think all S-Meters should have mirrored scales so that we can read it down to the nearest tenth of a dB  Cheesy
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N9RO
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Posts: 124


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« Reply #11 on: August 21, 2012, 02:10:08 PM »

I use the Smeter readings as a reference when analyzing signals.  I use a Smeter logger that writes the readings (from two different receivers and antennas) to a file and graphs them out over time, I can then go back and analyze the file with tools like R.  The correlation between the listener's qualitative impression of signal strength and the actual strength due to AGC holding the signal constant is poor so I find little use for it.

Interesting the things we do when we have time on our hands.

Tim  N9RO
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Real techies don't use knobs.
NO2A
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Posts: 825




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« Reply #12 on: August 21, 2012, 02:50:25 PM »

I like the multicolor led on my FT-857D. The zero beat function is very accurate for cw use. Even with weaker signals.
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W4OP
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Posts: 441


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« Reply #13 on: August 21, 2012, 03:08:17 PM »

The Elecraft K3 and its companion P3 can be accurately calibrated to read dBmV. I regularly depend on the P3 for spectrum analyzer measurements.
The only other  rig I know of (non SDR) that has a calibrated S meter is the ADT 200A out of Europe.
I am quite sure the HPSDR unit from TAPR also has the capability of absolute calibration.

Unfortunately, the rest of  the rigs are a guess and even worse, the preamp effects the S meter reading.

Dale W4OP
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K0OD
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Posts: 2578




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« Reply #14 on: August 21, 2012, 03:54:07 PM »

Quote
The only other  rig I know of (non SDR) that has a calibrated S meter is the ADT 200A

Flex S-meters are calibrated in dBm and several other selectable scales. Precise.

I don't understand why some still focus on the ADAT. Their group is moribund... has been for several years.
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