Scanning in a High RF Enviroment

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pb_lonny

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Over the years I have been involved in the radio scanning hobby, I have found a couple of good locations around Launceston for undertaking portable scanning sessions. Freelands Lookout and the Talbot Lookout have been two of my go to locations. Recently I have found that Freelands Lookout causes my Uniden UBC126AT scanner some issues, especially when running in close call mode. The bottom half of the of UHF band also has some issues at this location.

Yesterday I was out driving when I decided to explore around the West Launceston communications site. This is an area I have driven past a few times over the years but have never stopped as I expected that being such a high RF environment that my scanners would not cope. Below are some details on the site, some photos and a video.

Here are links to the ACMA database entries for this location, as can be seen it has a real mix of frequencies, from around 79MHz up to 23GHz. This includes multiple mobile phone carriers, broadcast TV and radio plus multiple VHF / UHF / 800MHz two way radio users.

Photos and video here: https://launcestonanalyticalradioscanning.blogspot.com.au/2017/01/scanning-at-west-launceston.html
 

ScannerSK

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Some scanners do better than others near strong interference. I had read that Uniden and Bearcat scanners were better than most.

Some of the worst scanners in my opinion are the GRE (now Whistler) line of scanners. I own a GRE PSR-500 and a PSR-600 and both suffer terribly in the VHF band from digital TV stations in the Denver, CO area. Using a non-amplified roof-mounted scanner antenna on my truck, I will get a full 5 bars signal strength across the entire VHF band from about 160-173 within twenty miles or so of the television towers. The bars start increasing across the band at a distance of over 40 miles from the television towers! My present understanding is that one of the television stations is broadcasting on a frequency assigned to one of the I.F. mixing frequencies used by the scanner.

I was just out experimenting near strong radio interference and found it odd that even some professional receivers work better without the ground connected to the antenna terminal in this type of environment. It's definitely a learning experience.

Shawn
 

pb_lonny

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I just found it interesting that a site with only a few radio repeaters is worse than this site with heaps of different users.
 

n0nhp

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Most high use sites have requirements for circulators and RF bonding designed to cut down on the harmonic mixing. Smaller sites with just a few machines will not have the problem of interfering with their neighbors so will not go to the added expense of suppressing the extraneous RF. Unless someone complains the FCC and site managers are not going to go looking.
 

ko6jw_2

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I am involved with a 440 repeater located on a mountain top with hundreds of transmitters. We have had to instal pre-selectors on our Icom commercial repeater to prevent it from overloading. In such an environment the most common problem with scanners is that they are de-sensitized by the high RF level. Also, they may be subject to intermods from signals mixing in the radio. My avatar shows just two towers of many on this peak. Frequencies range from 42 Mhz into the microwave region. Scanners were never made to operate in such a situation. Even commercial radios may need protection. Yes, everyone uses circulators and common grounding etc, but with hundreds of signals you can't eliminate overloads.
 
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