Tecsun, Grundig Digital Signal Strength Meter Question

[Schroedingers Cat]

I've asked this before, but I can't find the thread.

Which Tecsun model had the digital signal strength meter with the greatest dynamic range? It seems like one went from 20-99 dB or something like that. I known that the dB scale is not dBu, may not be linear, and may vary with frequency. I do figure that you could roughly calibrate it to 1 dB, or an accuracy of 10% in field intensity, with enough effort. I know Rich tried this, but I think it needed more fudge factors added. I am used to fudge factors, as they are used in scientific research all the time, and mostly legitimately, so I am not intimidated by it.

What about the Grundig Satellit 750? Does that have a digital signal meter in addition to the d'Arsonval type S meter?

 

[pianoplayer88key]

I think the newer Eton Traveler III has the widest range. I've seen from 00 to 99 on it. Also unlike the Tecsuns, it doesn't show high numbers on blank channels, like 34/00, 41/00, 50/00 (the highest it goes in that case) if you're near a transmitter. I had one briefly, but returned it cause the volume was much lower on weak signals (10s-20s dBu) than strong signals 70s-80s dBu, and other little things that added up. Also I think that calibration is very rough. It might be okay in a narrow range like 60-80 dB indicated (I find my PL-606 indicates about 21 or 22 or so dB lower than actual in that range - for example 1130 KSDO indicates 75 dBu and their field here is estimated at about 63 mV/m), but outside that range it falls apart. Above it it gets compressed, for example I'm almost at 80 dBu about 9 miles from KCBQ, but for it to stay above 90 I have to be within 1/4 mile of them. And in the lower range it's almost all over the place, and can greatly be affected by nearby strong stations.

 

[rfry]

Below are the results of my earlier observations (May 2010).

The fudge factor as determined for those conditions and assumptions is shown in the far right-hand column.

 

[Schroedingers Cat]

Thanks, pianoplayer and Rich for reposting that information. If you stay on one frequency on an older FI meter, and don't do a bandscan with it, you may not notice the considerable variation in gain across the dial. That may vary with both the standard oscillator and receiver in an unpredictable way, smoothed out by recalibration at each frequency. I imagine that the newer FI meters have less variation, but probably have some. From what I have heard, they are much easier to use. Those old FI meter tubes that used 1.5 V D batteries for the filaments, and 67.5 V plate voltages had considerable changes in performance also with time.

So it's probably not much more complicated to plot out the fudge factors for the digital S meter with frequency and dynamic range. Using the attenuator might place the signals in a more linear range also, like grid bias puts signals in the linear part of the amplification curve.

As you can see, there is about a 7 dB change in fudge factors across the mid to upper part of the dial, but more frequencies and field intensity levels would be required to establish gain variations and nonlinearity in the scale.

 

[Schroedingers Cat]

I looked up the manual for the Grundig Satellit 750 and it is a d'Arsonval style meter. Some receiver meters have reversed the movement so that maximum is to the Left instead of Right. I assume that this may be to neutralize deflection to minimize battery drain, since on most signals, the pin just stays in the resting position. But I would think that you could make an LCD and light display that would simulate the look of a d'Arsonval type meter without the coil in the meter draining the battery.

Has anyone compared the performance of this Grundig to the Panasonic RF-2200? The ferrite rod looks to be about the same size.