----- Original Message -----
From: "James Duffey" <JamesDuffey@comcast.net>
To: "VHF Contesting Reflector" <VHFContesting@contesting.com>; "Rover email
remailer" <rover@mailman.qth.net>
Cc: "James Duffey" <JamesDuffey@comcast.net>
Sent: Saturday, August 09, 2008 2:24 PM
Subject: [Rover] Rover antennas for use in motion
>I thought I would share my recent experiences with rover antennas to use
>while in motion.
>
> My first 6 roves, through the June 08 VHF contest, I did not operate
> while in motion. I went to good spot, stopped erected good antennas and
> operated. A point and shoot rover if you will. When the June contest was
> over, I realized that I needed to operate while in motion. I had spent as
> much time traveling from one site to another as I had operating. I had
> missed out on openings while traveling. I had to pull up stakes while the
> band was still open at one site to make it to another site. It almost
> made me cry. I figure that I could have made at least 50% more contacts
> if I had operated in motion.
>
> So I clearly needed to build antennas for use while in motion. I intended
> to operate the July CQ VHF WW contest on the way back from vacationing in
> the midwest, so that formed the impetus to finally build and design
> antennas for use in motion.
>
> For 6M I chose a half wave horizontal loop. Anything else is pretty large
> to travel with. I used this design from the web:
>
> < http://neasmn.org/squalo/squalo.htm >
>
> using 1/2 inch aluminum angle instead of the 1/2 inch copper tubing. This
> made the antenna much lighter. I fastened the corners together with #8
> self tapping screws. The antenna was a bit floppy, so I supported it with
> a small fiberglass rod in the middle from one side to another across the
> mast support. I use a driveway marker for the rod. The antenna is
> somewhat touchy to tune, due in large part to its small bandwidth, but it
> did get a good match slightly below the calling frequency. I adjusted the
> stub position to bring the whole antenna to resonance and then the
> feedpoint position to get a reasonable match to 50 Ohms. The two
> positions interact and there may be a better way to tune this.
>
> This loop is about 20% bigger than typical gamma matched 6M square loops
> like the lawn chair loop. The ends are farther apart as there is no
> longer any need to provide capacitive loading to bring the loop up to
> resonance. The feedpoint impedance is higher and better behaved, and as a
> result, it is less sensitive to SWR variations caused by rain or
> proximity to other metallic objects.
>
> On 2M, antennas are smaller so I thought I should get a bit of gain out
> the antenna I chose. Horizontal loops are down a couple of dB on a dipole
> and stacking them gets you only a dB or so over a dipole. I finally
> settled on a 3 element Yagi, pointed forward. I figure that I am usually
> going somewhere, there are hams there, and so if I point the antenna
> forward I can work them. If I hear someone weak, I can always pull off
> and rotate the antenna to peak their signal. Or point the car toward
> them. I used WA5VJB's Cheap Yagi 3 element design for this antenna:
>
> < http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf >
>
> with 6 gauge copper wire for the elements. I mounted it from the rear so
> that it sticks out in front of the mast.
>
> The 6M squalo went on top of the EMT mast at 11 to 12 ft above ground.
> The 2 M antenna was 2 ft down from that.
>
> How did this all work? I had the pleasure of driving through Smith
> Center, Kansas on my way back to NM to work N0LL. I took the straight
> road west out of Smith Center and copied Larry's beacons along the way.
> The 6M squalo could copy the beacons consistently out to 50 or 60 miles.
> I heard it when parked on a small hill about 90 miles away, but not after
> that. I worked K0HA and N0UNL at distances of 120 miles or so. N0KE and I
> had a nearly complete QSO in DM76, a distance of 180 miles or so. I am
> sure that we could have completed this QSO with my 2 element Yagi. So my
> conclusions are that the squalo worked fine for line of sight and
> diffraction paths out to 50 or 60 miles. It is poor on troposcatter paths
> unless the station on the other end is well equipped and does all of the
> heavy lifting and there are path enhancements. There was sporadic E on 6M
> off and on during the contest and the squalo did a good job on working
> most stations I heard. I also could run stations when the band was open
> steadily. So I pronounce the 6M square loop experiment a success,
> althoguh I will see if there is something I can do to improve
> troposcatter performance while in motion.
>
> On 2M, the 3 element Yagi could consistently copy the N0LL beacon out to
> 120 miles and I had no trouble making contacts out to this range. I
> worked W3DHJ at a distance of 90 miles on 2M, while on 6M I had to be
> much closer. Unfortunately, there wasn't much 2M activity on during the
> rove, so I didn't get a chance to get a good feel for the antenna. It
> performed well enough that I am thinking of putting up 2 back to back and
> switching between the two. Or maybe going to a 4 element version,
> although that is considerably longer.
>
> The mast is 1 1/4" EMT telescoped into 1 1/2" EMT mounted to a trailer
> hitch. It is braced with a 2" x 6" mounted to the luggage rack. I can
> raise the antennas to 16 feet or so when stopped. The antennas traveled
> fine at interstate speeds of 75 MpH when stowed at 12 ft. I can lower
> them to 8 ft or so to clear obstructions, like the phone wires in my
> fahter-in-law's drive.
>
> For the recent UHF contest, I built a symmetrical double rectangular
> (SDR) loop for 432 MHz. It consists of two loops, each 1 1/2 wavelengths
> in circumference and 1/2 wavelength high mounted vertically so that they
> share a common short side. It is fed in the middle. This is much like the
> old Skeleton slot antenna drivers and also similar to the magnetic double
> slot used horizontally on 160M and 80M. Here is my poor ASCII art
> rendition of the antenna.
>
> 1/4 wavelength
> ---------
> [ ]
> [ ]
> [ ]
> [ ] 1/2 wavelength
> [ ]
> [ Feed ]
> ---- ----
> [ ]
> [ ]
> [ ]
> [ ] 1/2 wavelength
> [ ]
> [ ]
> ---------
>
> I built this from the 1/2 inch aluminum angle using the self drilling
> sheet metal screws. This is essentially 3 stacked half waves in phase and
> a rectangular rendition of the double diamond or double delta. I mounted
> this on a 3/4" by 3/4"inch wood boom running vertically. This broke after
> 2 hours at 75 MpH and I had to splint it back together with electrical
> tape and a piece of scrap aluminum I had along. I will mount this on an
> insulated aluminum U channel in the future. I fastened this to the mast
> with hose clamps. With that single exception of the mast breaking, it
> traveled fine with the middle of the antenna at about 12 feet above
> ground. You can see photos of this antenna in action on the UHF Contest
> Soapbox page.
>
> This worked very well in motion on 432 MHz. I made contacts out to 120
> miles while in motion from the tops of hills. I also carried an 11
> element Cheap Yagi for use while fixed. An unscientific comparison
> between the two antennas by K7ICW on a 70 mile path showed that the SDR
> was down 4 to 5 dB on the Yagi that was 3 ft below it. Putting the Yagi
> up is worth it as it probably adds another 50 or so miles of range. It is
> a bit long to travel with though. Preliminary modeling shows that this
> SDR loop is better to or equal than the gain from a halo loop over about
> 270 degrees of azimuth, so you don't give away much. It is much better in
> the forward 90 degrees. And it is much simpler to feed and build than a
> loop. I am happy with the performance of this antenna. One could stack
> two more loops on top and bottom, but that starts to get pretty tall. I
> may make a 2M version, although that is getting pretty tall as well.
> There is a bit more gain to be had by making the verticals a bit taller
> and the horizontals a bit shorter. Two band versions are also possible,
> so I will explore those.
>
> So there you have it. Three different solutions for three different
> bands. I am happy with the performance of the 2M and 432 MHz antennas,
> although they could be tweaked a bit. I would like to improve on the 6M
> antenna, but nearly anything else is pretty big to put on a vehicle while
> in motion. I am considering a reversible Moxon, which may be manageable
> with some additional support while driving. Perhaps in the September
> contest. But that starts to violate my KISS philosophy.
>
> I have covered what I do for power in the rover while in motion in a
> previous post. That has continued to work well.
>
> I hope this helps someone. If it does, let me know. - Duffey
> --
> KK6MC
> James Duffey
> Cedar Crest NM
>
Hi - Duffey,
Very nice write up.
I too like you and others have the ability to rove whenever possible.
I use a '99 F150 with long bed for my rover.
In addition to 2 original Saturn 6 - 3 ring halo's that are stacked
HORIZONTALLY, 1.2:1 swr, I have installed a small TV rotator on a board in
the back (near the tail gate), and to it I have mounted a 8ft mast. I can
stack on the mast my 3 ele 6 mtr beam, a 6 ele 2 mtr beam, and a pair of 432
7 ele beams. In the future I will be mounting antennas for both a 903 and
1296. I have the whole assembly guyed to allow it to rotate while in
motion. I run the rotator off of a 750w DC-AC inverter from the battery.
When the motion stops and if I so desire, I can lower the rotator/mast assy
(on a hinge) to adjust or mount different antennas to the stack. By guying
the stack, it tends to keep the mobile flutter from the antennas down to a
minimum.
Best 73's de Howard W3CQH/r
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