Monday, January 22, 2018

800 MHz digital trunking antenna

While my attic 1980 vintage Radio Shack scanner antenna works well for VHF/UHF it doesn't bring in reliable signals for the local 800 MHz multi site digital trunked system. I believe there are five different transmitting sites, so I needed a directional antenna to null out the simulcast distortion and improve the radio's decoding. I picked up this GSM yagi antenna for a few dollars on Amazon. It's meant to be used to boost cell phone signals but works great on trunked radio frequencies; it has 11 dB of gain and works in the 800-900 MHz range...


Here's the original link on Amazon:  https://www.amazon.com/gp/product/B00L3ZRF9A/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

It has an N-type connector so I got an N to BNC adapter and feed the signal to the Pro-197 with an RG6 GE UltraPro quad shield coax. I mounted the antenna to the underside of a bookshelf with a single screw so it could pivot in an arc, allowing me to aim it exactly at the closest transmitter. On most days my Pro-197 reports 99% decode quality.

If you suffer from simulcast distortion (as evidenced by poor audio) on your digital system there are lots of resources on the net with recommendations for reducing the problem; here are a few:

http://www.scannermasterblog.com/the-digital-blues-or-why-does-my-local-digital-system-sound-like/

https://wiki.radioreference.com/index.php/Simulcast_digital_distortion

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