[Mobile-Portable] Spot welds

[Jim Davis]

From: Jim Davis <aa7az at juno.com>
To: mobile-portable at mailman.qth.net
Cc: Mobile-portable at mailman.qth.net
Date: Sat, 11 Feb 2006 19:30:30 -0800
Subject: Re: [Mobile-Portable] Spot welds

Phil, 
Normally I just read the mail and don't make any comments, however,
seeing what you're going through to get a well functioning antenna
system, let me pass along my experience.
I have used the Don Johnson DK-3 screwdriver antenna and it has worked
well for me in two different installations. My first installation was on
a 94 Chev pickup. My installation included a ridged mount from the left
front frame of the PU which brought the antenna mount out just forward of
the left front fender and close to hood high. From there I ran 3/4 or 1
inch braid from 1/2 inch below the mounting pin for the antenna to a
fender bolt which I scraped clean of paint. My grounding strap or braid
was kept to 12 inches or less. Once the project was completed, I had no
difficulty resonating my antenna with an SWR of close to 1:1.. Even if it
were a bit higher, it's no big deal. I've been able to talk coast to
coast with this installation and it's not a super fancy installation. The
thing that you need to remember is "keep the ground lead short"... If you
still have noise to deal with, then address that after putting together a
good antenna system. You will find that your ground connections will need
to be brightened up periodically, but thats just part of keeping your
system in peak operating condition.
My second installation is on a 98 Dodge Caravan with the antenna mount
part of the trailer hitch on the left rear side of the car. Once again I
kept my ground strap short by using a self tapping screw inside the
taillight lens housing. I bet my ground strap is probably less than 8
inches long and it works great. In my opinion, the secret is keep your
ground strap to 12 inches or less and it should work fine.  Give that a
try and see what you come up with. 
Don Johnson has an excellent book out concerning mobile antennas and I've
learned alot from it it. I've also learned that SWR is not the bug a boo
that I thought it was, so if you end up with 2 or 2.5 to 1 in a mobile
installation, don't get worked up over it, it's not that big a deal. 
Jim/AA7AZ
On Sun, 12 Feb 2006 00:46:19 -0000 "Phil Atchley"
<beaconeer at sbcglobal.net> writes:
> 
> 
> 
> Hi All,
> 
> Please excuse all the "Stoopid" questions I've been asking, but 
> within the 
> constraints of my budget I want to do this install CORRECTLY.
> 
> Today I was crawling around under my '05 Ford F150 "SCREW" pickup, 
> trying to 
> see what is involved in "bonding and grounding" this critter, 
> preparatory to 
> putting HF in it (and skinned my elbow big time on the concrete 
> driveway 
> doing it 8^(
> 
> The (screwdriver) antenna will be mounted just over the driver side 
> wheel 
> well. Predictably the bed of this critter is comprised of several 
> different 
> pieces of sheetmetal. EACH sidewall AND the wheelwell is one piece, 
> the 
> floor is another piece, then of course there is the front of the  
> bed and 
> tailgate. I figured on having to bond the sidewalls to the floor 
> with braid 
> in several places, which would require sanding the paint etc and 
> leave it 
> open to rust and corrosion.
> 
> HOWEVER, crawling around under the truck I saw where BOTH the INSIDE 
> 
> sidewalls AND the floor have roughly a 3/4-1 inch lip bent down at 
> 90 
> degrees running the length of the bed, and where the two sections 
> meet they 
> are spot welded together at numerous places.
> 
> It SEEMS to me that these spot welds would be AT LEAST as good RF 
> wise as 
> bonding with a finite length of braid, possibly better?  They have 
> to be 
> strong as it is what holds the bed of the truck together!
> 
> Now, I realize that this won't NEGATE the need to bond the pickup 
> bed to the 
> cab (rubber bushing mounted), frame, hood to front fenders, firewall 
> etc. 
> But it DOES seem like the bed proper (except for tailgate) ahould be 
> 5x5.
> 
> Yes, I've given up on the Tuner/102" whip idea and will be going 
> with a 
> screwdriver, probably a DK3 as it meets my budget (and I won't be 
> oeprating 
> Mobile on a constant basis with constant tuning).
> 
> THOUGHTS on these grounding questions?
> 
> ******************************************************
> 73 de Phil,  KO6BB
> DX begins at the noise floor!
> 
> THE BEACONEER'S LAIR:  http://www.geocities.com/ko6bb/
> QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
> Merced, Central California,    37.3N  120.48W  CM97sh
> 
> ****************************************************** 
> 
> ----
> Your Moderator: Dick Flanagan K7VC, 
> mobile-portable-owner at mailman.qth.net
> 
> 


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