SDS 100 - antenna and receiver sensitivity tests

[K9JLR]

So far I've been impressed with how well the SDS 100 handles simulcast systems as I've been doing some traveling.

Just for fun, N0SWP and I did some testing on the sensitivity of the receiver on VHF (150 MHz), UHF (450 MHz) and 850 MHz (each was in analog only), as well as a Wilton anritsu site master sweep of the stock antenna, at least to get an idea of what frequency it was most resonant at, with the idea being to see where it also might have more optimal receiving ability.

VHF - 0.316 uV, UHF - 0.158 uV, and 800 MHz - 0.200 uV where the corresponding levels were the receiver broke squelch at the level 3 setting on the SDS 100 (did not do a sinad test). I found that the sensitivity was just slightly better than the Home Patrol 1 on UHF and 800 MHz analog, with the same squelch setting at the same level, at least on those two individual, albeit mutually exclusive receivers.

Regarding the antenna, best resonance was at 157 MHz, 472 MHz, 745 MHz, and 900 MHz.

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[Ubbe]

But remember that a 50 ohm dummy load would measure a perfect swr but do not radiate at all. You will get some indication but you probably have to do a proper radiate test as UPMan did when he tested different portable antennas performance at different frequencies.

Also the sensitivity measurement at a lab enviroment without any exposure to interferencies and overload ghosting are not what a user would experiance using it live.

I did comparisons with an Icom scanner having less than 0,2uV sensitivity and a Pro2006 at 0,5uV and when connected to a roof antenna and exposed to RF the Icom measured worse than 5uV and the Pro2006 0,6uV. The result being that the Icom had 10 times worse reception in a real live situation.

/Ubbe

 

[SOFA_KING]

Nice testing! Thanks for that. I recognize that equipment right off the bat. I had both back in my old job around 2000 or so. Loved that 8935, and wish I could have bought one from my former employer, as 3 of them were just going to waste in the stock room for many years until I left that company.

Now back in two-way, I have access to some fancy stuff again...that also does P25, LSM and CQPSK. Doing an effective sensitivity test by injecting into a attenuated (-40 dB) coupler while connected to a decent outdoor antenna would yield "real world" sensitivity numbers. Of course the RF environment can change drastically when going from rural to city environments, but that's all part of the proper test.

I would also lower the squelch to the minimum setting that keeps it closed with no antenna (or no on-air signal). Squelch settings being higher than that can vary and cut usable signal out.

I too swept all the stock antennas with my Anritsu. Although that tells us nothing about radiation angles, it was interesting to see all those seemingly resonant points in good places. Lots of testing on real site signals led me to the Comet SMA-24. Better than the Diamond everyone keeps using...especially on 700/800 MHz. Although my brother in law demonstrated that Radio Shack 800 antenna against my Comet, and it did pretty well on VHF and UHF. Better than I expected.

Getting real verifiable test numbers with the proper test setup is "the real deal", and not speculation. I would also do some serious Image testing to see if there are problems with stronger signals. As I'm an avid searcher, that would be a test I would need before purchasing an SDS-100, especially being a new SDR design.

Phil

 

[UPMan]

I'll add that squelch is handled completely differently between SDR and "analog" receiver designs, so comparing at a particular squelch level may or may not provide a good comparison. There are so many new variables when functions are being handled by DSP vs. discrete components.

 

[K9JLR]

I'll add that squelch is handled completely differently between SDR and "analog" receiver designs, so comparing at a particular squelch level may or may not provide a good comparison. There are so many new variables when functions are being handled by DSP vs. discrete components.

Yeah, and even two different analog receivers can be mutually exclusive at the same setting. I really just wanted to have some fun getting some specs from a home lab environment and share some of those findings. All of the simulcast sites I've monitored in the Kansas City area are handling better than the 536HP thus far. I haven't noticed any issues with cell site interference on the receiver.