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Signal Strength Meters On The Different Tecsun Models

S

Schroedingers Cat

I know we had a thread that discussed the various Tecsun models and the signal strength meters, but I cannot find it on a google search. There was a particular discussion about the dB ranges of the meters on two or more particular models.

Can anyone direct me to that thread or tell me again the various ranges and the upside downside of each model? I think our San Diego member pianoplayer88keys discussed the two indicators and their ranges on different models, one for signal strength, the other for signal to noise ratio.

Also, is one or the other superior out of the box, as one link discussed a model that had to be modified but then it was great.

Discuss the sensitivity and selectivity of the various models on AM/FM/SW also. Do all of these have DSP, and what about the image and RITOIE rejection of various models? Or does DSP trump all that? It's hard for me to believe that a radio with a good RF and IF section AND DSP wouldn't be better still.
 
All of the Tecsun PL-3xx series radios use the same Si4734 DSP so the meters will all have the same ranges. In the larger radios like the PL-390 a larger ferrite rod AM antenna is used so reception may be better on them. I have only owned the PL-390 so I can't compare.

From the top of my head the signal strength meter ranges are around 0 to 70dbu on FM which is the same range used on other Silicon Labs DSP FM chips. On shortwave I've seen it in the 80dbu range before and it may peak around 90 if I recall. I don't pay enough attention to the SNR display to be able to tell you what its ranges are.

The sensitivity on these is just as good as the XDR-F1HD if not better when there are no strong locals near. With strong locals near the FM chip automatically adjusts the RF gain down to avoid overload. Its not user adjustable as far as I know, its just a property of the chip. The selectivity is not as good as the XDR-F1HD (part of the issue is the whole FM band RF gain being lowered in the presence of the strong adjacent), but still a lot better than most consumer grade radios.
 
The Grundig G8 is a Tecsun with a different name. On AM/SW/LW the meter maxes at 88, although I have ocasionally seen an 89 under very rare conditions for a second or so. In the AM modes it bottoms at 15 while FM will go down to 0.
 
From a post I made on this topic a few years ago...

The link below leads to a comparison of the display in "dBu" shown on a Tecsun PL-310 for the actual field intensity at the points of measurement. So if a PL-606 is comparable to the PL-310, and they both "meet spec," then this will give you three data points showing actual field intensity vs. the display shown for it on the Tecsun receiver.

Note that the dBu reading on the Tecsun receivers reports the conducted voltage across an internal resistance in the receiver. It is not a calibrated measure of the field intensity of the arriving radio wave

Others have measured the linearity of the Tecsun dBu display with varying r-f input voltages, and found it to be quite good. So as long as the radio is not over-driven, and the measured frequency is not much different from one shown in my comparison, then the approximate field intensity at the location of measurement can be calculated from the data given in the link.

For example, on 1440 kHz my PL-310 displayed 58 dBu when the arriving field intensity was about 28.9 mV/m. So in another case if the Tecsun displayed 38 dBu for a 1440 kHz signal, then the arriving field intensity = 1/10^(dBu difference/20) * reference field, or 1/10^(20/20) * 28.9 mV/m = 2.89 mV/m.

If the measured field is greater than the reference field then the equation is 10^(dBu difference/20) * reference field.

For medium wave signals the receiver should be positioned so that the long dimension of the case is in the horizontal plane, and the meter reading should be maximum when the case is perpendicular to the compass bearing to the transmit antenna. If both of these do not exist together then the reading can have significant error. (The whip on the Tecsun receiver is not used for MW reception, and should be collapsed and stowed on top of the receiver.)

http://i62.photobucket.com/albums/h85/rfry-100/Tecsun_PL-310_Signal_Readings.gif
 
Thanks, everyone. If pianoplayer88keys is out there, he is probably the expert on what the top dB level is, from his overload experiment trips to transmitter sites and putting the radio next to vertical conductors.

The Technics STG-5 and Technics STG-50 tuners signal meters went to 54 and 58 repectively, and they would only max out for a second and drop to the next dB level. Those are in 2 dB steps. From what I have read, AGC dependent signal meters are inaccurate at the top and bottom of the scale.

I do recommend those Technics Tuners as the best practical value in the age of IBOC. They have a 25 dB first adjacent rejection, an don't drift. The MR-78 (55 dB) and MR-80 (60 dB) drift, and still won't get IBOC limited first adjacents. I'm still waiting for someone to come up with a tuner that gets rid of IBOC sidebands. It would probably require DSP and/or noise cancelling technology.
 
I would think that tuned radio frequency stages would reduce the desensitizing by strong signals. I always found that with my experiments with AM BCB preamps, modifying Tom Kneitel's design in "103 Simple Transistor Projects". Present day digital tuned radios just seem to have a lot of blanketing interference in comparison to older analog radios, even tube radios. I told you about experiments I did in Park Ridge in WJJD's 500 mV/m contour. I had no problem with any of my Uncle's collection of 1940s tube radios with WJJD. Even a cheap phono had no problems, and neither did old school pulse dial phones.
 
It looks like the Tecsun 6XX series has a 5 segment liquid crystal display, not a digital dB display. But the 3XX series doesn't have SSB. I'd like to have better performance, SSB, and a digital display.

I guess I'm looking for a radio that performs like an RF-2200 on AM, a MR-78 or MR-80 on FM, one of those military receivers on SW, SSB, LSB, USB, CW, and NBFM, with selectable synchronous detection, PLL, DSP, and IBOC sideband cancellation. The signal meter would have both an old school d'Arsonval S Meter, calibrated field strength meter, and digital readout in both dB and mV/m. Also, large ferrite rods and detachable large loop, and a detachable cardioid direction finder antenna. Must also glow in the dark. All for under $100.00.
 
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