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Author Topic: Best intermod rejecting mobile for base use.  (Read 825 times)
KD1RD
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Posts: 9




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« on: February 01, 2004, 12:12:37 AM »

Hello,

I am told that I live in one of the worst areas ever measured for intermod. I am interested in using a VHF or VHF/UHF mobile unit for use as a base station transceiver. I am wondering if anyone out there can recommend a radio they have used that has excellent intermod rejection.

I would like a dual band 2 m/70 cm unit, but I understand that I may need to get a mono band radio. Are there any recomendations?

I have read that the Icom IC-2100 and Yaesu FT-2800 are good at rejecting intermod. Are there any others to consider.

Thank you all for your time.

Paul

KD1RD

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KG4UDX
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« Reply #1 on: February 01, 2004, 01:05:38 AM »

For a fixed station, you may wish to consider an intermod filter.  PAR electronics makes several good one that notch out the 152 and/or 158 MHz pager frequencies.  MFJ also makes an intermod filter.

As for a radio that is intermod resistant, I've found that the Yaesu FT-8900 fares pretty well, but there are still a few areas I pass through that the intermod gets through.
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N3ZKP
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Posts: 2008




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« Reply #2 on: February 02, 2004, 12:45:52 AM »

PAR filters work very nicely on mobile rigs, too. Their use is not limited to fixed/base installations.

Lon
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WB2WIK
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Posts: 20611




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« Reply #3 on: February 02, 2004, 02:17:26 PM »

The PARs do work well (I have three of the little ones), but only notch one frequency, really: So, if you're in a true "intermod alley" location, which is usually created by multiple transmitters running lots of power very close by, a single-notch filter may not do much.  The PARs are most effective at reducing intermod due to VHF pagers (paging transmitters, that is).

My suggestion would be to contact a few repeater owners in your area and ask them what they use, or for suggestions in general.  You might also inquire if they know the specific source of all the "intermod" you've been warned about.  I see from your bio you're in southern NH; I didn't know that was so bad for VHF "intermod" problems, although I do remember from my old Boston days that there was a spot on I-95 in Needham Heights, MA where dozens of high-powered FM and TV transmitters were located that created severe problems hearing anything on VHF for a mile or two.

WB2WIK/6

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KD1RD
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Posts: 9




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« Reply #4 on: February 03, 2004, 09:46:28 AM »

Thanks for the input, guys.

While I will consider using a filter to help solve my intermod problems, I am hopeful that I can get a radio with a good front end that will reject most of the out of band inteference.

As far as the problem in my area goes, I live within sight of Mt. Uncanoonuc. By this I mean I can see the red lights flashing on the towers. There are several TV and radio stations up there as well as most of the local pager services. It's quite a mess just looking at all the antennas up there never mind the overload they cause.

Thanks again,

73 Paul
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WB2WIK
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Posts: 20611




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« Reply #5 on: February 03, 2004, 12:39:46 PM »

If you stick with a 2m rig that covers only 2m and has no out-of-band coverage, those in general tend to have much more selective "front ends," because they don't need to have any gain out of band.

But just because you can see an antenna farm on a local hilltop doesn't mean that stuff will cause you any particular problems.  I am line-of-sight to 3650' Oat Mountain, and I can not only see the red lights flashing on its hundreds of towers, I can see people walking in and out of the shacks up there, if I use simple binoculars.  I'm also line-of-sight to 5000'+ Mt. Lukens, same story.  If someone shined a reasonably good flashlight my way from up there, we could have a chat via Morse coded light pretty easily.  That hill has hundreds of high powered transmitters, including pagers, repeaters, FM stations, the local NOAA weather radio station, TV links, all sorts of stuff, and doesn't bother me in the slightest.  When I drive my car up there so I'm surrounded by towers, that's another story!

WB2WIK/6

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NA4IT
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« Reply #6 on: February 14, 2004, 09:55:03 AM »

I use the FT-8800R Yaesu and it seems to work good. We use a DCI DCI-146/440DB Intermod Filter in our club shack to help get rid of all kinds of stuff; primary law and fire, ambulance, a hospital pager about 4 blocks away, etc. It's big, ugly, a little expensive, but works!
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W9RAY
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Posts: 48


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« Reply #7 on: March 08, 2004, 08:38:23 PM »

  I would the get the 155 mhz pagers s9 down on 2 meters with my 746 with no coax hooked to the radio...

I have used A DCI Filter to getting rid of massive pager inteferance here... Worked Great... Also Run good quality double sheilded coax cable!!

  I got the 144-146 version because i mainly run down in the ssb portion anyway.

   My icom 2100 about died here...Intermod resistant.. yeah right...

Good luck
Ray J
W9RAY
EN44GT
www.w9ray.org


 
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