SDS100/SDS200: Close Call

rbuxton · Jul 10, 2018

How is Close Call supposed to work? I have been sitting within 20 feet of people with Motorola HTs chatting away for a couple hours (entrance to UVA hospital) and have heard nothing on CC Only mode. Enabling and disabling bands periodically. The radios look to be in the 460 or 900 range.

Also, as I watch the activity bar above the band's they indicate something, bar jumps to the top of the meter, I hear zero. Thought I might test out my new SDS100's close call and figure out what freqs the UVA Hospital parking ops are using.

UPMan · Jul 10, 2018

If they are using DMR, then you won't get a hit on a HT. They are putting out a signal that is only 50% duty cycle of about 60mS each cycle (so when they transmit, the transmit for 30 mS, then have no carrier at all for 30 mS). The scanner will almost never see a stable frequency count (3 counts of identical value in a row) under this condition, as each sample will have a portion of no carrier mixed with some portion of carrier and each reading will have a different mix.

rbuxton · Jul 10, 2018

UPMan said:
If they are using DMR, then you won't get a hit on a HT. They are putting out a signal that is only 50% duty cycle of about 60mS each cycle (so when they transmit, the transmit for 30 mS, then have no carrier at all for 30 mS). The scanner will almost never see a stable frequency count (3 counts of identical value in a row) under this condition, as each sample will have a portion of no carrier mixed with some portion of carrier and each reading will have a different mix.

Hmmm, okay. And what of the activity bars?

UPMan · Jul 10, 2018

Might find them under one of these listings:

Charlottesville City, Virginia (VA) Scanner Frequencies and Radio Frequency Reference

Possibly: http://wireless2.fcc.gov/UlsApp/UlsSearch/license.jsp?licKey=1277679 (which is DMR).

UPMan · Jul 10, 2018

Activity bars are showing RF noise floor (or highest in-band signal level). They will be responsive to DMR simplex transmissions, as they just indicate the RF energy level.

devicelab · Jul 11, 2018

UPMan said:
If they are using DMR, then you won't get a hit on a HT.

Just to be clear about this point, if they're using a DMR base/mobile then it should be possible to get close call hits, correct?

When I first got my SDS100 I was in a high-volume shopping center area (outside at a Starbucks) and had several close call DMR hits. One was from a nearby hotel that was using DMR. The transmission was nearly flawless so I presumed it was likely from a dispatcher (or base station.)

Or can a long-transmission from a portable still get picked up too?

jonwienke · Jul 11, 2018

Close Call will work on DMR where both slots are broadcast. But if only one slot is broadcast, not so much.

UPMan · Jul 11, 2018

Base/mobile will not typically generate a hit. The hit you got was most likely from the output of a repeater, which transmits both slots.

n9mxq · Jul 11, 2018

jonwienke said:
Close Call will work on DMR where both slots are broadcast. But if only one slot is broadcast, not so much.

Baloney.. works fine single slot with my DMR hotspots.

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UPMan · Jul 11, 2018

The hotspot is likely transmitting continuously for both slots.

n9mxq · Jul 11, 2018

Slot 2 only.

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UPMan · Jul 11, 2018

Can you confirm that the carrier completely drops for 30mS every 30 mS? (Easy to hear if you tune the freq conventionally/analog.) I would suspect that during Slot 1 it is continuing to transmit idle bursts and is not dropping the carrier.

n9mxq · Jul 11, 2018

https://youtu.be/F4xSUNnzInE

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WoodburyMan · Jul 11, 2018

Most HotSpots like UPMan says utilitize both timeslots as they operate essentially in Simplex mode where both time slots are occupised.

DVMega and other MMDV boards I read even though TimeSlot 1 is supposedly disabled, and you must set TimeSlot 2 on your Radio, still use both timeslots or something. They aren't quiet standard. I cannot for the life of me find the reference though. But it would explain how you can pick it up.

The real test would be on a actual DMR Repeater. Close call would not operate as UPMan says there unless say both timeslots were being actively used at the same time which would be rare.

n9mxq · Jul 11, 2018

Well, I learned something.. turn the hotspot off, using just the HT on local 9 on slot 2 and the scanner ignores it..

Gladly admit I'm wrong here.. Sorry guys..

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devicelab · Jul 11, 2018

UPMan said:
Base/mobile will not typically generate a hit. The hit you got was most likely from the output of a repeater, which transmits both slots.

Roger that & call that confirmed.

ULS License - Industrial/Business Pool, Conventional License - WQWS711 - MARRIOTT INTERNATIONAL, INC DBA REDMOND MARRIOTT TOWN CENTER - Frequencies Summary

SDS100/SDS200: Close Call

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