I see the posts on the uniden Facebook pages about the sds100 problems on vhf/uhf analog channels. There's a lot. So, I'm not the only one. I can put the SDS 100 on a dmr uhf control channel on 472.425 and it hardly decodes it. My 325p2 gets it just fine. Just using stock antennas by the way. Also there is a Pennsylvania state wide VHF P25 system here locally by me and my SDS100 won't pick it up but my 436 gets it just fine. There's something wrong with the vhf/uhf sensitivity. It's disappointing that a$600 radio would have these issues. It reminds me of when they rolled out the 436 the early production ones that had the UHF noise where you cover the battery door with copper tape then they fixed the issue by putting a capacitor on the board.
My SDS100 is wiped out on VHF from VHF paging transmitters nearby.
It appears to be a desense problem as the front end basically shuts down when a VHF paging transmitter comes on the air which is almost always on the air unfortunately.
I'm able to use a notch filter to notch the paging band from 152 to 153 MHz. The only problem, our statewide system also has about 50 or more VHF sites across the state that also have control or voice channels setup on reallocated frequencies in that same 152 to 153 MHz paging band! So a notch filter will cure the desense issues in the SDS100 but it also notches out the very system you are trying to receive. Not an easy problem to fix.
I can lower the main paging signal strength just enough to where the front end or AGC circuit in the SDS100 will work again. This allows me to track and monitor only one nearby P25 statewide site. The other sites I monitor cannot be heard because of the needed notch filter. They are more distant sites which do not have a strong signal.
I don't know what's in the SDS100 front end but rumor has it that it is just a basic cheap TV Tuner.
My x36HP and older x96T and XT models all receive the statewide VHF system very well as the VHF sites are not simulcast. The older models are also not bothered by the strong paging signals either. At least not the Uniden models. Any GRE designed models work about as well as the SDS100 due to their poor or no filtering in their front ends which allows the paging sites as well as FM Broadcast stations to desense their front ends.
The paging sites do not mess with my 7/800 MHz simulcast site reception. The SDS100 does a good job receiving simulcast systems and sites in the 7/800 MHz bands.
I've not bothered with 450 MHz reception as we don't have much there worth monitoring.
In the end, my older models that can suffer from LSM work way better than this new SDS100 does! It's a shame as I really like the display features of the SDS100.
I'm keeping it as I have plenty of stuff to monitor outside of the 152 MHz paging band where the notch filter will not bother.
When troubleshooting this issue, I did a test using analog weather and other VHF signals, both strong and weak signal strengths. To my surprise, those analog signals still make it through pretty well even when the paging sites are on the air. When monitoring VHF analog signals, one can hear a faint hiss from the paging data or signal but it does not shut the front end down. Analog still works. I'm sure the noise I do hear is enough to wipe out cc data though but I was expecting the front end to shut down like it appears to do with digital modes. The RSSI indicator on the SDS100 does not go crazy when monitoring analog VHF signals either which it does when monitoring VHF P25 sites and one or more of the nearby paging transmitters come on the air.
The two VHF statewide sites I'm monitoring produce a RSSI of -68 or -102 dBm, depending on the site, when paging xmitters are not on the air. When one or more VHF paging sites come on the air, the RSSI reading shoots up to -40 or -45 dBm which I think is the highest reading it can reach. That's about equal to standing right next to the SDS100s antenna and transmitting with a portable on the tuned frequency. This wipes out the SDS100.
I'd made another post about this problem, in that post I incorrectly stated the VHF paging sites were also wiping out 7/800 MHz P25 signals.
That was bad info but I could no longer edit my post when I discovered "operator error" was the cause of what seemed like desense in the 7/800 MHz band on the SDS100. My SDS100 works well on 7 or 800 MHz P25 sites when the VHF paging transmitter(s) is/are on the air.
I can replicate the paging signal overload or desense issue using nothing more than a signal generator set to a random VHF frequency (I tested between 150 and 160 MHz) and a small portables antenna on the SGs output jack. It does not take a lot to kill the front end in the SDS100 it seems. Maybe one day I'll run the SG through a range of frequencies and see if I can find a low and high frequency where the signals no longer wipe out the SDS front end.
This firmware update did nothing for my VHF reception problem nor has any firmware version (I tried every version I could find!). The problem exists and it is not firmware dependent. I don't know how much control the Uniden engineers have over the front end or whatever stage is being hammered by the paging signals but hopefully that stage can be altered via firmware. I'm not keeping my fingers crossed though as these problems are usually physical hardware issues that firmware can't fix.
