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SDS100 Close Call in downtown high RF area


Sep 6, 2019
Hi folks,

I live in Seattle and have tried Close Call ("Only") while walking my SDS100 around downtown and near the University a bit. These are very high RF environments. I have never gotten a "close call" in the wild yet, and wanted to see if I should do something different.

For example, I walked right up to a cell tower site that also has public safety and various other antennas on it (45th Street Exit of I-5) and no close calls. This is a site bristling with not only cell/microwave antennas but several verticals that seem to be for VHF/UHF (e.g. vertical antennas from 1' to 4' long, guessing they are 1/4 up to 5/8 waves). No close calls (lots of "bars" in the Close Call monitoring screen though).

I also walked and drove downtown near the Columbia Tower, home of the main public safety simulcast plus lots of other antennas. Most of the buildings also have building maintenance and security radio operations on walkie-talkies. Plus lots of contractors, some of which I know to be using GMRS (I can sometimes pick them up on GMRS radios), all working downtown (we have one of the busiest construction booms in the country going on here).

Something tells me I may be doing something wrong or sub-optimal here given that I'm in probably one of the noisiest RF floor areas outside of Manhattan.

Any suggestions on things I should try? Close Call same spots with Attenuator on?


Super Moderator
Jan 7, 2001
Somewhere other than home :(
To receive a close call "hit", a signal needs to be about 18 dB stronger than ANY other signal in that same band. In a high RF environment that may be difficult.

In town I get considerably fewer CC hits than I do way out in the country. I can get hits from VHF repeaters 5 miles away when I'm way out of town where the band is quiet.


Jul 23, 2005
Just make sure squelch is at 2. I have used it in town and out of town with no issues.


Sep 8, 2006
Stockholm, Sweden
That 18dB figure are important. 20dB are 100 times lower than the signal that you want to catch with CC. I seldom get any CC hits from home but if I connect a FM trapfilter I get every transmission from airplanes even more than 10 miles away. Filtering in a narrower frequency band using bandpass filters or blocking out other powerfull transmitters with trap filters makes wonders for the success rate of closecall.