SDS200 On Aircraft Bands

[KA1RBI]

The receiver chip in SDS100 and RTL-SDR are more or less of the same performance.

If the pertinent specs for the specific A/D chip used in the SDS scanners have been published, I haven't seen it.

However a ham friend (with decades of two way radio experience professionally) has said that the SDS performance is a disaster on VHF in his area, a metro area.

I have heard that the SDS is designed to block-downconvert the desired frequency band into the low-HF range, say 5 MHz, and the entire resulting I.F. swath which is a few MHz wide, is digitized. If we assume Ubbe is correct and the SDS uses the same 8-bit ADC as the RTL-SDR, and we use the rule of thumb that each A/D bit is equivalent to approx. 6 dB of dynamic range, this would place the SDS in the 48 dB DR ballpark (quite a poor spec. value -- especially considering this ranges over a few MHz, not just immediately adjacent to the signal center frequency).

This would also be a good match with the variation in reports, i.e., good for some users and not-good for others. Reception on a given frequency can be affected by other signals that might be as much as a few MHz offset from the desired frequency.

That's ridiculous. The SDS has front end filters the SDR sticks do not.

Ah, but these SDS filters do absolutely nothing for in-band interference.

Max

 

[sfb88]

From searching the forum for Rafael

 

[SteveSimpkin]

From searching the forum for Rafael



View attachment 95503

Just to clarify. I was referring to RF AGC in the post shown above. W6KRU was asking about audio AGC in his post, not RF AGC.

 

[sfb88]

Just to clarify my post, I was responding to the post about chip specs by trying to identify the chip and was not referring to the AGC.

 

[bearcatrp]

Been reading this thread with interest as am considering the SDS200 for air band. Are you folks doing these tests on regular air band or mil air also? My R30 does great but want a desktop. Used to own a 436. Worked good on P25 in my area. So far from reading, some say the SDS 200 works good, some say it sucks.

 

[jonwienke]

Most UHF/VHF/800 antennas aren't tuned for milair, so that's most likely the issue.

 

[bearcatrp]

Been looking at the BCT15X too but like whatever I get do more than one particular thing.
jonwienke, does that include discone antennas?

 

[Ubbe]

...some say the SDS 200 works good, some say it sucks.

SDS scanners are a lot more dependent of the RF situation in a location than any other scanner. If you are unlucky you will have something that interfere with your reception. Mil air should be a pretty quiet frequency band without any high power transmitters that would give you a better chance of a problem free monitoring situation.

I have a SDS100 connectected to the same splitter as a 436 and a 536 and monitor weak signal satellites in the 250MHz band and the SDS really struggles with that. The signals are FM modulated on the brink of being overmodulated and the SDS scanner increase it's noise level with high modulated FM signals when they are weak in signal strenght. In my local area Mil-air uses FM in the 250-380MHz band and my BCD scanners have been superior to the SDS with those transmissions. Hopefully the SDS's AM reception will do better than FM in Mil-air.

/Ubbe

 

[jonwienke]

Been looking at the BCT15X too but like whatever I get do more than one particular thing.
jonwienke, does that include discone antennas?

A discone will work well through at least a 4:1 frequency ratio without any coverage gaps. Other designs have gaps.