SDS100/SDS200: Sensitivity measurements

[wa8pyr]

Since the topic has come up in the past (and I'm naturally hoping for a distinct improvement with the SDS150), I decided to drag one of my service monitors out and get some rough sensitivity measurements on the SDS100.

I didn't get too carried away, dragging out the SINAD meter and other stuff in addition to the service monitor; I just put a signal into the radio and gradually increased the generator output level at each test frequency until it got to a point where the 1000 Hz tone was comfortable to listen to without a bunch of noise.

Semi-Scientific Results (Freq in MHz - Level in Microvolts):
25 - .98
40 - .98
55 - 1.2
136 - .99
150 - .75
174 - .75
220 - 1.7
300 - 1.2
350 - 1.2
400 - 1.0
450 - 1.0
512 - 1.1
760 - .9
775 - .9
800 - .65
850 - .65
900 - 1.2
950 - 1.2

Actual squelch break was a bit below the noted figures, but I was looking for the point where the signal was comfortable to listen to, not headache-inducing.

I didn't go above 950 MHz as the service monitor I was using (CT3000B) doesn't go above 999; I could have used my HP8920A, but it's a heavy beast and dragging it up to the shack is no fun, plus I figured the CT3000B would give decent enough readings for the particular area of interest (VHF/UHF).

The above readings aren't really bad as such, but they're not great, either. I was interested to note that the sensitivity figures for 700 MHz were worse than VHF, while 800 MHz was (as expected) rather better.

For my next project, I'll get the TRX-1 and the BC125AT out and do those for comparison. If I really get motivated, I'll break out the HP8920A and the SINAD meter and find the actual 12dB SINAD point.

Update: Just for giggles I got out my TRX-1 and used an already-programmed VHF frequency as a test subject. Squelch break is around .2 microvolts and comfortable listening around .6uV. Considerably better.

 

[K9KLC]

For my next project, I'll get the TRX-1 and the BC125AT out and do those for comparison. If I really get motivated, I'll break out the HP8920A and the SINAD meter and find the actual 12dB SINAD point.

Doesn't the HP8920 do the SINAD test just within itself or was that an option of some kind and it was just always on the ones I used to use on occasion.

 

[prcguy]

12dB SINAD will leave you with a moderately noisy signal and your levels may be higher than what the radio is actually doing.

 

[K9KLC]

12dB SINAD will leave you with a moderately noisy signal and your levels may be higher than what the radio is actually doing.

Agreed, the 12dB SINAD signals I always heard by ear had noise in them.

 

[wa8pyr]

Doesn't the HP8920 do the SINAD test just within itself or was that an option of some kind and it was just always on the ones I used to use on occasion.

It does, but I always preferred using a separate SINAD meter; besides, if I don't drag it out for stuff like this, the SINAD meter will just keep gathering dust being sad and lonely. Sad and lonely test equipment makes me sad. I paid big bucks for this stuff, I might as well use it; it's not been used much since I retired.

 

[wa8pyr]

12dB SINAD will leave you with a moderately noisy signal and your levels may be higher than what the radio is actually doing.

Agreed, the 12dB SINAD signals I always heard by ear had noise in them.

True, but I just want an accurate, consistent point of measurement. I suppose I could go with 20dB quieting.

 

[K9KLC]

True, but I just want an accurate, consistent point of measurement. I suppose I could go with 20dB quieting.

And we appreciate it. Just always like the reference point. Different people have different hearing. Hell my wife can hear stuff I seem to have problems with due to a ringing in my ears that's gotten pretty annoying these days and she's usually sitting across the room where as I'm right there! LOL.

73!

 

[K9KLC]

It does, but I always preferred using a separate SINAD meter; besides, if I don't drag it out for stuff like this, the SINAD meter will just keep gathering dust being sad and lonely. Sad and lonely test equipment makes me sad. I paid big bucks for this stuff, I might as well use it; it's not been used much since I retired.

Ok I was just trying to see if my memory had gone even further south than I thought it had. I understand the getting it out and using it stuff!
Thanks!

 

[prcguy]

True, but I just want an accurate, consistent point of measurement. I suppose I could go with 20dB quieting.

Yes, that's what we did before SINAD meters hit the market.

 

[wa8pyr]

Yes, that's what we did before SINAD meters hit the market.

20dB quieting is always fun with an analog meter. Using a DMM sucks; that jumping number is almost impossible to pin down.

 

[buddrousa]

What do you have a Simpson 360?
Your numbers look alot like the old numbers from Regency and Bearcat did 80's and 90's

 

[wa8pyr]

What do you have a Simpson 360?

Simpson 260-6P. It's the only way to fly. Also has the optional case with the roll-up door (which works and isn't broken). A truly manly meter.

Series 6 was, IIRC, the first one that used the D cell and 9v battery combo.

Amazingly enough, Simpson still sells the 260; they're up to the -8 and -8P.

 

[K9KLC]

20dB quieting is always fun with an analog meter. Using a DMM sucks; that jumping number is almost impossible to pin down.

I always used my Simpson 260 for that. Even when we had went to digital meters for a lot of things that Simpson still had its place.

 

[buddrousa]

Trying to remember the model number from 1977 school I just looked it was the Simpson 260.

 

[JASII]

This is great information to have.

Thank you for doing that and posting the results.

 

[scanner_nut]

Would changing the RF filter options affected these test results? I am trying to understand SDS100 and SDS200 filter options to optimize reception and searching for freq's in the Federal VHF, MILAIR bands. Thanks!

 

[Ubbe]

Would changing the RF filter options affected these test results? I am trying to understand SDS100 and SDS200 filter options to optimize reception and searching for freq's in the Federal VHF, MILAIR bands. Thanks!

Filter setting might improve reception slightly, 1-2dB, in its Off setting when connected directly to a signal generator.

Filter are setting a 10MHz wide IF filter to different offset settings and its Off setting are symmetrical in the middle to let the signal pass with a 5MHz gap to each side, like in most other Uniden scanners, and that filter often has less attenuation in the middle of its frequency range. The Normal and Inverse push the filter offset with 1MHz to one end and 9MHz to the other and Wide goes halfway with its offset something like 3MHz to one end and 7MHz to the other.

Filter settings are used to block interfering signals, if one are at 5MHz higher than what you are monitoring you then select a setting that use the filter at +1MHz and -9MHz to block that +5MHz interference. If you are using search and doing 150-170MHz then an interfering transmitter at 160MHz will be both below and above the frequency you are monitoring during search and the filter settings will be less useful.

The IFX setting can be done per frequency, so if the scanner stops from interference then do Function+7 and IFX will be shown on the display for that frequency and will continue to search if that helped. And first set the filter in the search option to be Off before trying other settings and filters are locations dependent, so that recommendations from other people may not be the best to use for your unique location.

/Ubbe

 

[scanner_nut]

Thanks @Ubbe! I found your postings on uniden filters in other forums very helpful to understand the different filter options as I went down the list located here - SDS100 and SDS200 FAQ Page - The RadioReference Wiki .