Lookout Mountain-Wide-Band VHF White Noise 108-400MHz (S5 in Signal Strength) Filter?

[ScannerSK]

That could be it. KOSI (101.1), KQMT (99.5), KBPI (106.7), KRFX (103.5), KTCL (93.3) are all up on Lookout. All those are 70,000 or 100,000 watt commercial FM stations.

It did occur to me yesterday, though, that my Vertex VXD-720 was having trouble with intermod on the Denver Connected Repeater at 145.310. I don't normally run with RX PL tones and the radio doesn't have an external squelch knob. It was only that repeater and intermittent. It was along the length of I-25 between 144th and 104th, so I suspect it was related to the construction there or maybe a locally strong something.

Yes, I agree that it was likely related to something in the immediate area. I can always tell when Public Service is in my small town as every time they key up their radios I receive intermod from one of the weather channels on one of the frequencies I monitor.

Shawn

 

[jim202]

Thank you! "Full-scale overload across the entire band" as mentioned in this article is a good way to describe this issue especially the closer one approaches the Lookout towers.

I had previously read and was aware of this issue with the GRE branded scanners (at least the PSR-500/600 which I own) however it did not seem to fit the bill. My question was whether towers 40 miles distant could begin to exhibit this effect on some GRE branded scanners? That would seem to be very extreme to say the least! Is this really possible as the explanation? How much signal could be left after traveling 40 miles to overload a scanner? That just did not make sense in my mind as a possible explanation. However, I just looked up some of the television towers atop Lookout and they (KCNC, KWGN, KTVD) are calculated as having an ERP of 1,000,000 watts which is substantial! I suppose after 40 miles there could be enough signal left to cause problems on a GRE scanner??

Another puzzle, I am constantly driving around and have never noticed this type of problem in any other cities such as Fort Collins, Loveland, Greeley, Cheyenne, etc. Why only from the towers on Lookout?

In the Lookout scenario the signal strength of the noise increases toward the VHF television frequencies so this would appear to rule out the possibility of it originating from the 88-108 FM band.

Next time I am in Denver, I will have to take along my NooElec dongle which covers the entire VHF TV spectrum to ascertain whether it exhibits the same issue or can shed light on which frequency the noise is centered upon.

Shawn

Time to get or borrow a different type of radio. Maybe an ICOM, Vertex, Motorola or what ever. Get away from a scanner to see just what your issue is. Having been in this field for well over 45 years, I never trust a scanner to do any frequency looking or trouble shooting. They will lead you down the merry path way too often.

 

[joeuser]

I'll be heading to Lookout myself quite soon. I'll be glad to share my results.

 

[ScannerSK]

I'll be heading to Lookout myself quite soon. I'll be glad to share my results.

Yes, please. I wish you an enjoyable stay here in Colorado and splendid views from atop Lookout!

Shawn

 

[ScannerSK]

The greatest distance I have ever noticed the noise from the Lookout towers has been 50 miles away and this was while driving South on Weld County Road 49 (a rather elevated road) SW of Kersey, CO and then only while driving over the tallest hills. I was tuned once again to a frequency near 174 MHz. I'm just racking my brain on how this could possibly be desense or overload at that great of distance from the transmitter? I could understand desense and overload within possibly 5-10 miles at the most but 40 or 50 miles does not make sense.

Using my NooElec dongle at home revealed there is a very substantial increase in white noise from 174-180 MHz and 186-192 MHz which correspond respectively to TV stations 7 and 9. The reception of digital TV signals sounds identical to white noise. I could not audibly discern any type of distinguishable modulation or digital sounds to set digital television transmissions apart from white noise. Three examples of digital TV stations I receive North of Denver which are capable of being received on nearly any scanner are between 476-482 MHz, 494-500 MHz and 500-506 MHz (500-506 MHz corresponds to virtual TV channel 20.1 and is from atop Lookout).

Something I found interesting is that the GRE scanner behaves the same way when tuned to an actual known digital television transmission! Take for example 500-506 MHz which is RF TV channel 19 from atop Lookout Mountain (virtual TV channel 20.1). The GRE scanner shows a steady signal strength of S3 on my handheld PSR-500 on every frequency from 500.1 MHz up to 505.9 MHz (the assigned frequency range for this television channel is 500-506 MHz). Tuning to any frequency in this entire range requires a higher squelch setting to close the squelch than if the antenna is not attached and there is increased white noise noticeable when the antenna is reattached. However, on my baofeng radio, the squelch is not affected in the least by the presence of this real television station broadcasting in this range of frequencies and there is no noticeable change in noise levels when the antenna is removed and reattached.

Apparently, different radios react differently to digital television signals. You might try tuning your radio from 500-506 MHz (virtual TV channel 20.1 from atop Lookout Mountain) to see how your radio responds to digital TV transmissions. I bet most radios will simply act as if no signal is present in the above frequency range other than possibly the ATSC pilot signal at 500.31 MHz.

Could it be possible that only GRE scanners are capable of detecting the presence and signal strength of digital TV signals while most radios simply act as if nothing is present at all?

Could it be that either TV channel 7 or 9 is bleeding digital noise outside of the set frequency boundaries for that channel and only GRE scanners are capable of detecting this? This would appear to be a possibility from the above experiment.

Just a thought...

I guess the takeaway is how interesting that the GRE scanner detects the presence of actual digital TV signals while the baofeng acts as if nothing is present at all.

Shawn
KB0LSW

 

[NDRADIONUT]

Most of the people who have had the GRE 138-174 noise / desense issue have had the problem solved with a 88-108 filter or a 98 mhz coax stub T trap which worked wonders for me....

 

[ScannerSK]

Most of the people who have had the GRE 138-174 noise / desense issue have had the problem solved with a 88-108 filter or a 98 mhz coax stub T trap which worked wonders for me....

I ordered a RadioShack FM Trap off e-bay to give it a try and have also looked into the PAR television filters.

I'm not convinced this is the same issue others have experienced or that it will be helped by a trap/filter however these are definitely worth a try.

Shawn

 

[Gunnar_Guy]

Could it be that either TV channel 7 or 9 is bleeding digital noise outside of the set frequency boundaries for that channel and only GRE scanners are capable of detecting this? This would appear to be a possibility from the above experiment.

I highly doubt channel 7, which is allocated actual RF channel 7, is exceeding their bandwidth. But their allocation is 174-to-180MHz, so it would be within the spectrum of concern for your receiver. Also, they are not one of the super high power stations, but rather transmit with an ERP I think of 54kW. Channel 9 is allocated RF 9, 186-to-192MHz, transmits with 45kW, so also not a MW transmitter, either.

I guess the takeaway is how interesting that the GRE scanner detects the presence of actual digital TV signals while the baofeng acts as if nothing is present at all.

Not sure I would use a Baofeng as a baseline for received signal quality.

 

[ScannerSK]

I was near the Lookout towers today and this time took along my HTX-202 ham radio. This radio is known to have a tight front-end that was made to reject out of band interference. To make a long story short, the HTX-202 did not experience the problem exhibited by the GRE scanners.

Add to this that the squelch on the handheld HTX-202 is so sensitive that it will open when lightning flashes nearby even when using it with a whip antenna inside the house so if there was any interference on the 2-meter band from Lookout this radio would have detected it however nothing was detected using a whip antenna on the HTX-202. Only when I attached the roof-top antenna was there the least hint of any noise on the HTX-202 radio while on the GRE PSR-600 radio with roof-top mounted antenna there was full strength S5 overload across the entire VHF band and the lower half of the UHF band even with attenuation enabled. This experiment was conducted while parked in the Mount Vernon Canyon Road parking lot along I-70 which is in full view of the Lookout towers and is one of the worst locations for VHF reception with GRE scanners.

Now, how does one explain why this "noise" is capable of being received at such a great distance from the transmitter (40+ miles)? I do not have a good explanation for this. One possibility may center around the first local oscillator frequency of 380.8 MHz. The second harmonic of 190.4 MHz (a frequency used by TV channel 9 atop Lookout) would be the local oscillator frequency of 380.8 MHz used in the PSR-500/600 series of scanners. It may be possible shielding is insufficient around the 1st local oscillator stage in the PSR-500/600 scanners thereby allowing reception of the 2nd harmonic of TV channel 9 which when mixed could create the "appearance" of wide-band noise across the entire VHF spectrum and lower half of the UHF spectrum. This is the best guess I have as an explanation.

I'll try an FM trap. Other than this, I may look into investing in a newer Bearcat BCD436HP scanner which I would hope does not have this issue especially as it offers, "Intermediate Frequency Exchange – Changes the IF used for a selected channel or frequency to help avoid image and other mixer-product interference on a frequency."

Thank you everyone for all your suggestions and assistance.

Shawn

 

[ScannerSK]

I received the RadioShack 15-577C FM Trap in the mail today.

I drove to an area that had S3 noise across the VHF band even with attenuation enabled. I installed the FM trap and it made no difference at all. There was still S3 noise across the VHF spectrum. This confirms it must be digital noise from one of the TV stations atop Lookout and not from the FM band.

I don't plan to spend any $ on a PAR Television filter for channels 7 or 9 however they would likely reduce or eliminate the problem for those who may experience it on the PSR-500/600 in the Denver area.

Shawn

 

[joeuser]

I received the RadioShack 15-577C FM Trap in the mail today.

I drove to an area that had S3 noise across the VHF band even with attenuation enabled. I installed the FM trap and it made no difference at all. There was still S3 noise across the VHF spectrum. This confirms it must be digital noise from one of the TV stations atop Lookout and not from the FM band.

I don't plan to spend any $ on a PAR Television filter for channels 7 or 9 however they would likely reduce or eliminate the problem for those who may experience it on the PSR-500/600 in the Denver area.

Shawn

I'm interested to see how my GRE PSR-800 does with this RFI. I've decided to not take the HP1E so the only Uniden(s) I'm taking will be my BCD436HP's & I'm hoping they won't have any issues!

Sent from my Lenovo TAB 2 A10-70F using Tapatalk