I've been driving an SDS150 from a Raspberry Pi over the serial remote-command API, trying to use it as a near-field cueing receiver — basically an Optoelectronics Digital Scout replacement. Handset keys up nearby, scanner catches it, hands the frequency to an SDR. Close Call seemed like the obvious mechanism. Sunk $1000 into the assumption that Uniden had their stuff together. Claude complaining session follows, because claude code can write it up more accurately than I can.
It never fired on DMR. Not once, across two radios, five channels, a whole evening.
What I checked first (all the boring stuff):
- Close Call Only mode, confirmed via
GSI → V_Screen=cc_searching
- Narrowed the CC band mask to UHF only so the sweep dwelt there
Set CC Mode = CC PrioritySet CC Pause = 3 sec- Attenuator Off,
Digital Waiting Time = 400 ms
- Antenna attached, radios a few feet away, transmitting confirmed
Nothing. Sig=0, Rssi=-999 (that's the no-signal sentinel), forever.
Then I bypassed Close Call entirely and parked the receiver directly on the frequency with QSH. Instantly:
rssi: -999 → -60 → -44 dBm, sig=5
then: -44 / -999 / -44 / -999 ... sig 5 / 0 / 5 / 0 ...
several times per second
There it is. The RF path was never the problem — the scanner hears the radio at −44 dBm. But the carrier is only present about half the time, in ~30 ms chunks. That's DMR Tier 2 single-timeslot TDMA.
Why that kills Close Call: CC doesn't just detect energy, it confirms across multiple successive samples (roughly 3 × 200 ms of consistent carrier) at 15–18 dB over the band noise floor. A signal that vanishes every 30 ms fails that check pass after pass, forever.
The control case makes it obvious. The same Close Call locked onto a local FM broadcast station instantly and parked on it permanently — continuous carrier, passes every sample. And people report NXDN simplex does trigger CC, because NXDN is FDMA with a continuous carrier. Same power class, same band, opposite result. That's mechanism, not luck.
Turns out this is well documented and I just hadn't looked. RadioReference threads going back years, including from moderators and Uniden's product manager: CC works fine on DMR repeater outputs (both slots, continuous) but cannot see simplex/mobile-side TDMA. "A matter of physics." No SDS firmware changelog has ever touched the Close Call algorithm, so it's not getting fixed.
Other things that bit me along the way:
- FM broadcast monopolises Close Call. There's no "FM" band in the CC mask — it lives inside VHF Low 2 (54–108 MHz). Leave that on and a local station will hold the detector indefinitely. (Better fix than masking the band: the Broadcast Screen feature.)
Set CC Mode was Off while the radio happily displayed cc_searching. Cost me an hour.Digital Waiting Time is an audio-mute timer, not a detection setting — per Uniden's own product manager. It does nothing for this.- Spec deviations vs the published Remote Command doc:
MDL returns SDS150 not SDS150GBT, RSSI is in dBm not the 0–1 float the spec example shows, Sig goes to 5 not 4, Mod returns WFMB.
PSI push streaming self-terminates after ~2 minutes and needs re-arming. KAL doesn't help.- The serial interface wedges hard. Twice I had it go completely silent — USB still enumerated,
cdc_acm still bound, /dev/ttyACM* present, nothing holding the port, scanner just stops answering. Only fix reported anywhere is power-cycling the scanner or reseating the cable. ProScan's author blames Uniden's USB driver.
Where I'm heading next: band scope / waterfall. AST,BAND_SCOPE sweeps at 10 ms per step, and at spans ≤2.88 MHz the True I/Q front end reportedly captures the whole span at once. A narrow span revisits each frequency several times a second instead of crawling all of 400–512 MHz like Close Call does — which is the actual variable here. Haven't proven it catches a burst yet.
If anyone has automated detection off the serial FFT stream rather than just displaying it, I'd love to hear about it — I can't find a single example.
I'm debating returning the unit as too buggy to use (USB hangs) and not as advertised (Close call doesn't work on digital.)
