Reception Mystery - Help!

[emsflyer84]

Hey all, I've posted several times on the forums looking for help or advice to extend the range of my home scanner setup. I have a Whistler TRX-2 and a folded dipole antenna tuned to my scanning range, high VHF. In between is about 75' of low loss RG6 coax. For the past few months I've played around with different antennas, even buying and installing a Larsen tri-band whip antenna installed on a ground plane kit which was highly recommended for my situation. I still felt like I wasn't getting the range I should be. The reason being is that I was getting almost the same reception with a handheld scanner and rubber duck antenna while driving around in my car. Finally today I did an experiment. I took my folded dipole off the roof and ran a 3' jumper cable directly to my handheld scanner. I stood in my driveway and the reception was dramatically better then when the antenna was on the roof. I did the same test with the Larsen tri-band. Again, super performance, and the antenna was laying on it's side in my trunk. Still better reception then either antenna on the roof. Perfect! My feed line in the problem. Maybe water intrusion, maybe it's because I have two sections pieced together to make up the 75' run. So back on the roof I went to put my dipole back up. Just for fun I took the handheld scanner and 3' section of cable on the roof with me. I was shocked to find the reception was garbage again! The same setup that works amazingly well 30' lower in my driveway, now had junk reception. It seemed only SLIGHLY better while I was holding the antenna in my hand vs. when it was mounted on the metal mast I have on my roof. To make a long story longer, there is something about the physical location on the roof that is killing the reception. My house sits on a bit of a hill, with great line of sight for miles in all directions. I should have phenomenal reception on the roof. There are no other antennas, the electrical feed line from the street is on the other side of the house... I even took my wifi weather station down and turned it off with no change in reception. This part of my roof is above the master bedroom, and there is no electronics in that room by a tv and cable box. I've been chasing this issue for months thinking it was my equipment so it's frustrating to find out it's the location (which I cannot easily change).

Any thoughts at all about this? It's a total mystery to me. I'm glad it's not the equipment that's the problem and at least I'm getting somewhere here, but frustrating at the same time. Thanks again.

 

[wowologist]

Your using the folded dipole in horizontal polarization I would presume? Commercial/PS transmissions are done in the vertical plane. Folded dipole is not the best for scanner reception, at that point you may as well use a slim jim/j-pole type antenna (which are horrible and Like I always say if one works for you, so would a coat hanger). Scanners don't have major ground planes/points built into them. A handheld like say the BCD325P2 has literally zero ground plane since it is entirely plastic inside instead of an aluminum chassis and that's over come in a simple way by adding what some call a "tiger tail" to the ground lug on the BNC, I myself just use copper snail tape down the back/side of the unit connected around the bottom of the BNC when I need to listen to something that I know the scanner itself is being defeated by it's own design.

An you may very well have say aluminum backed insulation in your attic that is acting like a huge faraday sheet blocking incoming signals.

And if you combined the rg-6, I hope you just didnt connect the shields / center connector with electrical tape, hopefully you used a proper BNC crimp or even screw on.

 

[emsflyer84]

Thanks. The dipole is actually vertical. The problem is that the dipole actually works really well when it’s not on my roof. Standing in the driveway? Great. Laying in my car? Great. Dipole and Larsen tri-band both perform the same (crappy) when on the roof. Both preform well when NOT on the roof.

 

[wowologist]

We'll you seem to be primarily interested in VHF/hi ~ so that's an easy one, lock the scanner on a WX channel and experiment. Walk around the roof to different spots ...if your dead set on using the dipole, set it up a tri-pod and check signal at different points/areas.

 

[byndhlptom]

It almost sounds like signal overload with the rooftop antennas.

Any of these can cause de-sense/noise floor aberrations:

Local FM radio transmitters
Local Am Radio transmitters
Cell Phones towers/Sites (especially for 700-800, but not limited to this band)
Pager Transmitters (especially a problem for VHF Hi band)
Commercial tower sites (Inter mod and spurs common)
and I'm sure there are others.....

I'd be curious what a spectrum analyzer would show on the roof.....

Some radios are very sensitive to signal overload..... don't know about the TRX-1....

$.02

 

[wowologist]

" I'd be curious what a spectrum analyzer would show on the roof..... "

Yeop, thers another option, what does an cheapo SDR spectrum waterfall show? Do you have an RTL-SDR or SDRPlay?

 

[emsflyer84]

This is why I like to have the conversation. You all bring up good points. Now that I'm thinking about it, when I'm on the roof, I can see an antenna only about 1/4 to 1/2 mile from my house. In doing a little digging, it seems it is the transmitter for the local AM radio station in my town.... I took my antenna and walked around my property and there were good and not so good spots for reception. But none as bad as on the roof. When I'm not on the roof, I can't see the AM tower. I did the same experiment about a mile away in a valley in the middle of my town and reception was even better there then it was on my property. And my property is probably 300' higher in elevation. Maybe my property is getting blown out by the AM transmitter.

 

[emsflyer84]

Here is a shot of the area. The AM transmitter is .39 miles from my house. My house is circled in red and the antenna site is yellow. The worst part is that, for some reason the tower was built down in a valley and my house is on a hill. So when I’m standing on my roof I’m looking at the top 1/3 of the tower.

 

[RFI-EMI-GUY]

Electrical noise inside the house, Cat5 wiring, routers, LCD monitors, "smart appliances" etc,,,.. Possible conducted up your 75 feet of feed-line that should be grounded. I am a proponent of transformer balanced 1/2 wave dipoles when operating in noisy environments. This to minimize conducted interference. Choke balun's , while they work turning energy to heat, can't provide as much electrical isolation as a transformer balun. Problem is, nobody makes an antenna for VHF/UHF like that in a price range for hobbyist.

 

[RFI-EMI-GUY]

That AM transmitter indeed could be lighting up all the wiring in your house an reradiating electrical and electronic noise. Further exacerbating your problem. Do you notice a difference between night time and daytime? Is your Whisltler TX-2 grounded to your utility ground? Can you power it temporarily from a battery to remove its switching AC power supply from the equation?

What is the model of your folded dipole antenna? If home made, provide details.

 

[emsflyer84]

That AM transmitter indeed could be lighting up all the wiring in your house an reradiating electrical and electronic noise. Further exacerbating your problem. Do you notice a difference between night time and daytime?

Not MUCH of a difference, but seems to be slightly better at night and early in the mornings. No scientific test on that...

The other thing is that is seems to be worse now then it was a few months ago.

 

[emsflyer84]

Electrical noise inside the house, Cat5 wiring, routers, LCD monitors, "smart appliances" etc,,,.. Possible conducted up your 75 feet of feed-line that should be grounded. I am a proponent of transformer balanced 1/2 wave dipoles when operating in noisy environments. This to minimize conducted interference. Choke balun's , while they work turning energy to heat, can't provide as much electrical isolation as a transformer balun. Problem is, nobody makes an antenna for VHF/UHF like that in a price range for hobbyist.

Thanks. The issue with reception is the same even when I run a 3' cable directly from the antenna to the scanner while standing on the roof. I think the interference is external....

 

[emsflyer84]

Well, the same station also transmits on an FM station as well.... I believe from the same tower.

 

[RFI-EMI-GUY]

Thanks. The issue with reception is the same even when I run a 3' cable directly from the antenna to the scanner while standing on the roof. I think the interference is external....

I suspect that your house wiring and your 75 ohm cable are reradiating all this. A spectrum analyzer might help, so might switching stuff off to see if the noise diminishes. . I have an AM transmitter around here somewhere, not even sure where that my telephone wiring was resonant to. I had to put big ferrite donuts on the wiring so that my answering machine would not record Latin music.

 

[RFI-EMI-GUY]

Well, the same station also transmits on an FM station as well.... I believe from the same tower.

Well I would start on that because most scanners have little rejection of the FM broadcast band. You will need a filter to block that. If you are using 75 ohm cable you can get a FM broadcast band filter from you local Radio Shack (LOL).

 

[emsflyer84]

Well I would start on that because most scanners have little rejection of the FM broadcast band. You will need a filter to block that. If you are using 75 ohm cable you can get a FM broadcast band filter from you local Radio Shack (LOL).

Believe it or not I have a local Radio Shack, haha. It’s literally in a guys house, I don’t know how he manages it but it’s awesome. He has all the weird cables and connectors I ever need.

So, my Whistler flashes FM on the screen constantly. Is that what that means? It’s picking up an FM signal? I was never sure what that meant.

Would a close FM transmitter cause such a drastic reduction in reception?

 

[krokus]

Would a close FM transmitter cause such a drastic reduction in reception?

Maybe... It could cause desense issues, which is where the automatic gain circuit thinks there is a really strong signal, and turns down the gain. However, the strong signal is not the one you want. (This happens a lot with aviation signals, when there is a nearby FM broadcast site, as well as 800 MHz when a cell site is nearby.)

Spend the money on a USB SDR dongle, or borrow one from someone, connect it to your antenna, and see what shows on the spectral display.

 

[vagrant]

FM is a mode type being used. It does not specifically mean an FM broadcast station. High power FM broadcast stations are probably the #1 problem for scanner and receiver enthusiasts, as long as their antennas and coax are working as they should.

Based on your various posts of late, these nearby AM & FM broadcast transmitters explain some of your issues. Purchase an AM & FM filter. It should help, but it may not solve it as those transmitters are in your back yard, so to speak. You may need better, or more filters. While you could put one on after the other and filter those signals more, you would be better served with a proper length of coax between the two filters to get the most out of the second one.

HPN-30118 Combined Notch Filter | Scanner Master

HPN-30118 Combined Notch Filter helps eliminate radio interference and scanner front-end overload.

www.scannermaster.com

You could also purchase these separate AM & FM filters for a little less, but the FM one is not friendly at the lower end of the civilian aircraft band. Depending on your interests, that may not be a problem for you. There are other FM broadcast filters as well.

VHF-FM Broadcast Filters | PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

PAR Electronics Inc. Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave

www.parelectronics.com

Connectorized Band Stop Filter, 88-105 MHz | ZBSF-95-N+ | Mini-Circuits

Mini-Circuits is a global leader in the design and manufacturing of RF, IF, and microwave components from DC to 86GHz.

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[RFI-EMI-GUY]

Believe it or not I have a local Radio Shack, haha. It’s literally in a guys house, I don’t know how he manages it but it’s awesome. He has all the weird cables and connectors I ever need.

So, my Whistler flashes FM on the screen constantly. Is that what that means? It’s picking up an FM signal? I was never sure what that meant.

Would a close FM transmitter cause such a drastic reduction in reception?

FM is the mode the scanner is receiving. Has nothing to do with the interference. Yes, a scanner will drastically degrade with strong FM or TV broadcasts nearby. Try a cheap FM broadcast notch filter from radio shack or even Lowes if they carry them. I have a cheapy and it was effective.

 

[emsflyer84]

Thanks. I guess I’m just not familiar with the effects of FM and AM transmissions on scanner antennas. So it is possible that these close transmitters are killing my reception, not just making it sound like there is interference?