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Author Topic: Pager interference  (Read 6745 times)
KE2KB
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Posts: 169




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« on: February 19, 2013, 04:24:22 PM »

Hi;
I am trying to determine the frequency or frequencies of the pager services that are interfering with my 2m and railroad reception on my VX-150.
yes, I do have the VX-150 connected to a Ringo Ranger ARX-2B on the roof, but I like to be able to hear those weak signals from the trains.
I am considering a notch or bandpass filter, but first, I need to determine what frequency the offending transmitter is using.
Without any test equipment, what is the best way to determine this?

Thanks

KE2KB
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WB2WIK
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Posts: 20633




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« Reply #1 on: February 20, 2013, 09:38:12 AM »

That's difficult.

Do you have a VHF scanner?  If so, you could let it free-scan throughout the whole VHF spectrum and note how strong signals are when it stops on an active channel. 

If you find one that's much stronger than the others, you may have your answer.
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KE2KB
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Posts: 169




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« Reply #2 on: February 20, 2013, 10:56:08 AM »

That's difficult.

Do you have a VHF scanner?  If so, you could let it free-scan throughout the whole VHF spectrum and note how strong signals are when it stops on an active channel. 

If you find one that's much stronger than the others, you may have your answer.
My VX-150 will scan from below 144Mhz to at least 174Mhz, and I did find that most of the pager activity is around 152Mhz. That said, I was thinking of installing a bandpass filter in the coax line; a filter tuned with a center frequency of 160Mhz, if it is sharp enough should attenuate the 152Mhz pagers sufficiently to put them below the level of the weak signals I am trying to capture.
There was one I looked at, but cannot recall the name at this time. It's a strip that is intended to be mounted inside a larger radio, but I could easily build an enclosure for it, and put it in-line at the radio.
Before I do anything like that though, I am working on improving my transmission system; such as grounding the surge arrestor immediately at the ground rod instead of 40ft away from it.
Every article I have read about transmission lines and grounding states that the antenna mast must be grounded to the ground rod (in as direct a run as possible, and with as heavy a wire as is practical), and that the surge protection device must be located as close as is possible to the ground rod and grounded directly to it. As it stood this morning before I disconnected the transmission line from the antenna, my surge arrestor was just below the antenna, and 40-50ft of #4 wire ran between the mast and the surge arrestor to the ground rod.
Not only is this a lousy ground system for my radio, it's not in conformance with the NEC.
So now I am going to re-do all of that, and run another length of LMR400 from the grounding point to my radio and see what I get. If I am still getting interference, I may look into the band-pass filter, or perhaps get a better radio suited for fixed use, rather than trying to make do with the HT.

I also ordered a better antenna for the HT, after realizing that the one I was using was not even 1/4 wave (only 12.5" long) on 2m, so I bought a Comet SMA24 for the HT. That, plus the counterpoise I already built should improve both the ERP and the receive on the radio. I may not even need the Ringo anymore <g>.
I am also looking for some good reference materials on RF antenna and transmission lines. I have the ARRL Antenna book from many years ago, but not much is mentioned about grounding. Perhaps someone here can suggest a better book for RF, transmission lines, shielding and grounding. I think it really pays (maybe literally) to become educated in the field of RF, as there is so much of it around, and I've seen lots of employment opportunities for RF engineers.

KE2KB
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WB2WIK
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« Reply #3 on: February 20, 2013, 02:37:26 PM »

The Ringo Ranger ARX-2B is a DC grounded antenna to begin with.  The whole antenna has direct connection to its mounting/supporting mast, so if you ground that, you've grounded "everything."

If you use an arrestor at all, it should be at the cable entry point to the house, and nowhere else.  Anywhere else doesn't even make sense. Wink

PAR sells a very effective 152 MHz pager notch filter with BNC connectors on it for external use.  It is extremely effective.  See here: http://www.parelectronics.com/amateur.php

It's not expensive and works a lot better than what most could homebrew.  I have about five of these, accumulated over the years. Tongue

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WB5ITT
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« Reply #4 on: February 20, 2013, 02:48:49 PM »

The notch filter is what you need...not a bandpass...a BP filter tuned to 160MHz will kill your 2m reception....I believe the PAR filter is rated for transmit as well so you can still use the radio on 2m while scanning the rail and other services (like marine, etc).

Chris
WB5ITT
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KE2KB
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Posts: 169




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« Reply #5 on: February 20, 2013, 04:10:43 PM »

The Ringo Ranger ARX-2B is a DC grounded antenna to begin with.  The whole antenna has direct connection to its mounting/supporting mast, so if you ground that, you've grounded "everything."

If you use an arrestor at all, it should be at the cable entry point to the house, and nowhere else.  Anywhere else doesn't even make sense. Wink

PAR sells a very effective 152 MHz pager notch filter with BNC connectors on it for external use.  It is extremely effective.  See here: http://www.parelectronics.com/amateur.php

It's not expensive and works a lot better than what most could homebrew.  I have about five of these, accumulated over the years. Tongue


Couldn't a nearby lightning hit cause an "RF" signal with a fast enough rise time to couple onto the center conductor?
In that case, the ICE arrestor should short it safely to ground. But the best lightning protection is to disconnect the radio; and that is what I normally do. It's just for those times when a storm comes up unexpectedly; especially at night.
The ICE arrestor is located on the mast, which is outside the attic window. The coax comes into the house (in the attic) only a few feet from where the ICE arrestor is located. So I suppose this is as good a place as any, except that the ground wire from it (and the mast) is about 40ft long. But that is #4 wire, so much better than if it were #10 or even #8.

I agree with WB5ITT on the filter. I was only considering the bandpass tuned to 160 for the railroad monitoring, but then I would have to remove it whenever I wanted to use the radio on 2m.
Interestingly, I get different "intermod" (although I'm not absolutely sure that it is all intermod) on different days. Today I was being bombarded by pager noise. Other days, I can hear someone talking and the NOAA weather broadcast on 162.55Mhz at the same time. I get more interference on the out of band freqs I monitor than I do on the 2m Ham band. That's good, of course, and it's what the radio was designed for, so its performance outside of the 2m Ham band is not going to be as good. I don't think Yaesu publishes specs for out of band receive on any of their Ham radios.

If I use the notch filter, I would prefer to locate it indoors, but perhaps being located outdoors and grounded to the rest of the system is what works best? In that case, I would need SO-239 connectors, not BNC.

KE2KB
I will check out the PAR filters.
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WB2WIK
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« Reply #6 on: February 21, 2013, 10:12:44 AM »


Quote
Couldn't a nearby lightning hit cause an "RF" signal with a fast enough rise time to couple onto the center conductor?

The center conductor is already DC grounded. 

Quote
In that case, the ICE arrestor should short it safely to ground. But the best lightning protection is to disconnect the radio; and that is what I normally do. It's just for those times when a storm comes up unexpectedly; especially at night.

I disagree the best protection is to disconnect anything.  The best protection is to have a good earth ground on the antenna mast, which in turn also completely grounds the entire antenna, and then install the arrestor at the cable entry point to the house via a grounded panel which is connected with a heavy gauge conductor to both the antenna ground rod and the AC mains service panel ground (unless those are already the same point, which is a great idea).  Then, there's no reason to disconnect anything.  Radio and television stations, cell sites, and all other commercial installations never disconnect anything and get hit by lightning all the time. Wink

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KE2KB
Member

Posts: 169




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« Reply #7 on: February 21, 2013, 02:16:37 PM »


Quote
Couldn't a nearby lightning hit cause an "RF" signal with a fast enough rise time to couple onto the center conductor?

The center conductor is already DC grounded. 

Quote
In that case, the ICE arrestor should short it safely to ground. But the best lightning protection is to disconnect the radio; and that is what I normally do. It's just for those times when a storm comes up unexpectedly; especially at night.

I disagree the best protection is to disconnect anything.  The best protection is to have a good earth ground on the antenna mast, which in turn also completely grounds the entire antenna, and then install the arrestor at the cable entry point to the house via a grounded panel which is connected with a heavy gauge conductor to both the antenna ground rod and the AC mains service panel ground (unless those are already the same point, which is a great idea).  Then, there's no reason to disconnect anything.  Radio and television stations, cell sites, and all other commercial installations never disconnect anything and get hit by lightning all the time. Wink


Do you agree that location of the arrestor should be as close to the grounding electrode (same as used for electric service) as possible, as well as immediately before the coax enters the building?
This is the info I have been reading over and over at every website I visit.

KE2KB
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WB2WIK
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Posts: 20633




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« Reply #8 on: February 22, 2013, 09:33:22 AM »



[/quote]
Do you agree that location of the arrestor should be as close to the grounding electrode (same as used for electric service) as possible, as well as immediately before the coax enters the building?
This is the info I have been reading over and over at every website I visit.

KE2KB
[/quote]

I think the only place an arrestor needs to be installed is right where the cable comes into the house; and even then, simply grounding the cable (without the arrestor) pretty much serves the same purpose.  A bulkhead feedthrough panel which is grounded, and tied back to the utility service ground, is usually all that's needed with respect to "transmission line" grounding.

This is a good treatise on the subject, I think: http://www.w8ji.com/station_ground.htm

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WB5ITT
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Posts: 100




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« Reply #9 on: February 22, 2013, 03:00:30 PM »

Your chance of listening to railroads will be going away soon....Most Class A railroads (BNSF, UP, etc) and a lot of smaller carriers are going digital...Kenwood NXDN/ICOM ICAS method. You will have to upgrade to a new radio...given that you are using a HT as the receiver, upgrading will be worth it and you MAY not need a filter! (food for thought)
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KE2KB
Member

Posts: 169




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« Reply #10 on: February 23, 2013, 04:55:31 AM »

Your chance of listening to railroads will be going away soon....Most Class A railroads (BNSF, UP, etc) and a lot of smaller carriers are going digital...Kenwood NXDN/ICOM ICAS method. You will have to upgrade to a new radio...given that you are using a HT as the receiver, upgrading will be worth it and you MAY not need a filter! (food for thought)
I've been hearing/reading about that change for at least 5yrs now. I think it's going to be another few years before they really go digital.
That said, with my current budget, I won't be buying a new scanner for a while. Perhaps by the time I can afford one, the prices will also be a lot lower.

One thing about digital I will miss is the pulling signals out of the mud. I enjoy doing that on 2m, even if I can't work the weak stations. I've been "DXing" on the RR band forever, and you would be surprised at what you can hear if you turn the squelch all the way down. With digital, that's gone. And the weak signals are going to be unreadable, as they are when cell coverage is weak.
Hopefully Ham radio won't go totally digital. I think I would give up on it if that happened.

KE2KB
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