Another Comparison - BCDX36HP/SDS100 - Opinions?

[jonwienke]

Demodulation happens downstream of IF, so I'm not sure what you're arguing against. Regardless of the IF bandwidth fed into the ADC, everything downstream is digital. Given the fact that 455KHz filters aren't being made any more, it's highly unlikely that the IF frequency would be 455MHz, it would have to be more like 10-12MHz.

 

[maus92]

I raved about the SDS100 last month immediately after getting my hands on it simply because it passed my one test. I live within 7.5 miles of two towers that transmit the Louisville Metrosafe system. With my 436HP, it wasn't worth listening to. The SDS100 fixed that problem. Before diving deeper into my dilemma, let me preface it by saying that I spent very little time until now testing other systems (mistake) and 100% assumed that the 436 and SDS would be nearly equivalent except for improved simulcast reception. By other systems, I mean Indiana Safe-T and others on my side of the river. I live in Indiana, but I'm right on the river. I have the greatest interest in the Indiana systems, but it can be boring while Louisville is almost always entertaining. Unfortunately, at my house, I have discovered that the SDS is missing at least 30-50% (conservative guess) of the transmissions that the 436 is picking up on the Indiana Safe-T. I loaded the exact same profiles into each and also used the exact same antenna (RS 800 MHz). I even swapped the antennas to be sure that one of them wasn't faulty. All service types are on. Here's the interesting part; the talk groups that my 436 receives at home that the SDS does not, will come in crystal clear 8-10 miles down the road (closer to the more populated areas of New Albany, IN and Louisville, KY). The transmissions that the 436 picks up at my house that the SDS does not are almost always crystal clear and always have been. Literally, for the last 10 minutes the 436 has been constantly receiving transmissions on Clark County Safe-T talkgroups while my SDS is quite. With the SDS, I can now listen to Louisville, but if I want to listen to Indiana Safe-T, I have to use the 436. How can this be? I've had my 436 for years and the radios are so similar that I don't think it's incompetence, or a basic setting. I'm thrilled that I can finally listen to Louisville from my house, but not if I have to sacrifice a large percentage of Indiana Safe-T. It's too late to return it. I've read through almost all of the posts regarding "missing transmissions" and haven't found a fix. I guess I'll have to send it in and have it tested. If it tests ok, then I made a huge mistake. Any suggestions or ideas would be greatly appreciated. To be clear, I know the SDS will receive the talkgroups that I miss at my house because it will pick them up when I change locations, but I refuse to believe that Uniden put a radio on the market that is inferior to it's predecessor (except for simulcast). Not sure what to do at this point.

I hope you keep the radios widely separated when you do comparison testing. I have 3 scanners monitoring the same site in my great room, strategically placed in more or less opposite corners so as to not interfere with each other (I'm running a test on scratchy analog audio using a 536, PSR-800 / WS1080.)

 

[SteveSimpkin]

Demodulation happens downstream of IF, so I'm not sure what you're arguing against. Regardless of the IF bandwidth fed into the ADC, everything downstream is digital. Given the fact that 455KHz filters aren't being made any more, it's highly unlikely that the IF frequency would be 455MHz, it would have to be more like 10-12MHz.

According to page 15 of its datasheet, the IF output center frequency of the Rafael R836 tuner used on the SDS100 varies between 1.90 MHz and 5.60 MHz, depending on the settings used. The IF output bandwidth varies between 1.7 to 10 MHz, again depending on the settings used. I don't believe anything has been mentioned about the number of bits or sample rate of the A/D converter in the SDS100 that would typically be used to sample the tuner's IF output.

https://forums.radioreference.com/a...h_performance_dtv_silicon_tuner_datasheet.pdf

 

[KA1RBI]

I'm not sure what you're arguing against.

haha, you were "pretty sure" yesterday - what has changed?

Given the fact that 455KHz filters aren't being made any more, it's highly unlikely that the IF frequency would be 455MHz, [sic]

The Whistler TRX-2 manual that I just pulled shows the 3rd IF as 455 KHz. Same for the TRX-1. So according to this argument the TRX-1 and TRX-2 are no longer being made? And the https://www.mouser.com/ProductDetai...GAEpiMZZMv0IfuNuy2LUbZSv7VcJ%2b2PMVEzapjlI4g= page shows thousands of 455 KHz IF transformers in stock.

Accordingly, I conclude the above-quoted passages are just more misinfo and disinfo... There is also a nice little typo in your second quote, above...

Max

 

[mricketts]

I hope you keep the radios widely separated when you do comparison testing. I have 3 scanners monitoring the same site in my great room, strategically placed in more or less opposite corners so as to not interfere with each other (I'm running a test on scratchy analog audio using a 536, PSR-800 / WS1080.)

I've had them side by side, one on while the other off, feet apart, miles apart....etc. Unfortunately, a huge difference in reception seems to exist. In my original post I think I mentioned that I had to travel 8-10 miles from my house with my SDS to start picking up some of what the 436 was receiving. That was a bit overstated. It's closer to 4-6 miles.

 

[KA1RBI]

and of course it's also very possible to choose a final IF in the supersonic range, say 25-50 KHz, via a quadruple-conversion superheterodyne receiver design for example. In such a case the resource demands on the DSP (to do the so-called "I/Q" demodulation) would be considerably lower, not to mention the reduced A/D sampling rate that could be used.

As a result I'd expect the unit would not run anywhere near as hot (nor chew up batteries) as much as the SDS-100 is reputed to do...

Max