Fender L-bracket mounts

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MP 6.7
Posts: 109
Joined: Mon Aug 22, 2005 11:00 am
What radios do you own?: Spectra, Maxtracs, MT2k, GP300

Fender L-bracket mounts

Post by MP 6.7 »

I'm partway through putting a Spectra and an MCS2000 (both VHF) in my 05 F150. I'm using those NMO L-brackets that screw in where the hood meets the fender. I've tried using a 5/8 wave Larsen on the one going to the MCS (the spectra isn't in yet) and the performance is quite a bit down from mag mounting the same antenna on the roof. There's a bit of fender metal directly below the antenna but I'm not sure it's enough to make the 5/8 wave work right. Could a no ground plane antenna help things a bit, or do you really lose that much gain from going from the roof to the hood?

The antennas are mounted pretty far down the fender, I'd say probably 12-15 inches back from the front edge of the hood to lessen the RF in the cab. And I can't do a roof install; it's too tall even with a 1/4 wave up there...the stock FM antenna almost hits a parking structure this truck goes in.
Dale
KE7CEU
Current radios
Mobiles: 3x D43 A7 Spectras, T83 A9 Spectra, 2x KLM and 2x KLN MCS2000's, D43 Maxtrac 32ch, D35 Maxtrac 6ch modded for 896MHz receive, M33 M1225 4ch, Lowband Maratrac on 6 meters
Portables: 2x VHF GP300, VHF P110, UHF P110, VHF A7 MT2000
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Bill_G
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Fender L-bracket mounts

Post by Bill_G »

Short answer - yep.

Long answer - an end fed half wave vhf ground planeless antenna will recover some of your lost coverage, but it will be long. They exhibit gain with sufficient ground plane, and approach unity without. However, the longer rod will help your rcvr at the bottom of performance no matter what ground plane it has. In my experience, you need to make a coaxial cable balun at the base of the antenna to match them properly - two to three wraps of the RG58 feedline as close to the base as possible depending on the freq of operation. Wrap the cable around your fingers to make an approximate 3 inch circle. Use two tiewraps to hold it together. You'll have to experiment with the number of wraps needed by watching your wattmeter.
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Tom in D.C.
Posts: 3859
Joined: Tue Sep 04, 2001 4:00 pm
What radios do you own?: Progreso soup can with CRT

Re: Fender L-bracket mounts

Post by Tom in D.C. »

Dale,

What about trying a plain old quarter-wave vertical instead of the 5/8 wave? Of course it all depends on how much power you're able to run, how much distance you must cover, etc. etc. but it might be the easy way out of the problem.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
MP 6.7
Posts: 109
Joined: Mon Aug 22, 2005 11:00 am
What radios do you own?: Spectra, Maxtracs, MT2k, GP300

Re: Fender L-bracket mounts

Post by MP 6.7 »

Tom in D.C. wrote:Dale,

What about trying a plain old quarter-wave vertical instead of the 5/8 wave? Of course it all depends on how much power you're able to run, how much distance you must cover, etc. etc. but it might be the easy way out of the problem.
I'll give a 1/4 wave a try. I just got one for another project and I'll try driving around with that on for a while and see what happens.
Dale
KE7CEU
Current radios
Mobiles: 3x D43 A7 Spectras, T83 A9 Spectra, 2x KLM and 2x KLN MCS2000's, D43 Maxtrac 32ch, D35 Maxtrac 6ch modded for 896MHz receive, M33 M1225 4ch, Lowband Maratrac on 6 meters
Portables: 2x VHF GP300, VHF P110, UHF P110, VHF A7 MT2000
jhooten
Posts: 297
Joined: Sat Mar 06, 2004 12:58 pm

Re: Fender L-bracket mounts

Post by jhooten »

is there a ground strap from the hood to the fender? Don't depend on the hinge/prop for a good rf ground
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