My PSR-600 seems to have problems with intermod here in the Denver area. I primarily listen to aircraft and railroads, very little public safety. I ran across a FM Band Trap and put it into the antenna feed line and found the intermod was reduced...
Anyone else found this to be true? I'm just wondering if I stumbled on to something or am I just having a good day in the neighborhood. Thanks!
Yes, yes! The interference is being caused by one of the towers atop Lookout Mountain. At first, I thought it was one of the towers itself creating noise across the band however that was ruled out as it does not affect all receivers (only GRE PSR-600 type scanners). I tried one of the FM traps on my PSR-600 and it did not help at all or very, very little. Attenuation also does not help.
There is something different going on in Denver with the PSR-600 than simple overload as the interference begins to break the squelch South of Platteville, CO and gets steadily worse as I approach Lookout Mountain. As I am driving from Platteville to Denver, anything that gets in the way of the towers atop Lookout Mountain (a passing semi-truck, a tall hill, another mountain, tall buildings, etc.) drastically reduces or entirely eliminates the interference.
I experimented up in Golden with this exact problem. Heading West on Highway 58 into Golden approaching Highway 6 (with the Lookout Towers in clear sight), the interference across the VHF band (esp. 160-173 MHz) is S5 even with attenuation turned on and a FM trap installed making the band entirely useless. This was while using a 2-meter roof mounted antenna. However, if you continue driving just another 1/2 mile or so West past Highway 6 a mountain blocks the view of the Lookout towers and the interference vanishes completely!!
Now what is really fascinating about this issue is that the interference being caused by the Lookout towers begins to break the squelch on frequencies in the 170 MHz range just south of the city of Platteville, CO which is over 40 miles away!! How can that be explained?? The squelch has to be progressively turned up higher and higher (esp. on freq.'s in the 160-173 MHz range) as one drives further South from Platteville toward the Lookout towers.
Digital television stations these days just sound like white noise when tuned in on a scanner. I've pondered whether digital white noise from one of the television stations is entering the scanner and then not being filtered out properly prior to the mixing sections of the circuit. If the cause of the problem is a signal near the 1st IF mixer frequency of 380.8 MHz (television station frequency range) then the digital television white noise could affect every frequency across the band as it would get mixed into every frequency.
I do not experience any problems anywhere else (Loveland, Fort Collins, Greeley, Cheyenne, etc.) only from the Lookout towers West of Denver and it starts over 40 miles away from the towers!
I ordered one of the new Whistler TRX-2 units due to this very problem in the Denver area. The TRX-2 is touted not to have the same issues the PSR-500/600 scanners have with desense, open squelch, unwanted noise across bands, etc. The TRX-2 has some issues of its own (does not power on when vehicle turned on, long power on times {30 seconds to one minute}, have to press scan when finally turns on, missing STAT option in multi-site settings, etc.) however if it fixes the problem with all the noise across the upper part of the VHF band it may be worth it. If you are interested, I will report back on my findings of how the TRX-2 performs compared to the PSR-600 type scanners in the Denver area.
Shawn
73, n9zas
