[NLRS] Wanted: Rover antennas and and tower

[James Duffey]

Matt - Glad to hear that you are building a rover and planning on roving in SD. On my few roves in SD and western MN there was a dearth of activity from other rovers. I will make it back up there one of these days though. In addition to your new rover, I have a new grandson for incentive!

With two guys in the rover you can operate while in motion, which is a big advantage, particularly in June. It probably makes sense to try for antennas with a maximum dimension equal to the maximum width allowed by the highway department. That is 8 ft in most states.

For 6M it is hard to beat a Moxon. It has reasonable gain, but still fits within the width limits on most highways. I use the PAR SM-50:

< http://www.parelectronics.com/stress-moxon.php >

which may seem like a big antenna for a mobile, but I (actually my wife) drives with it at 12 ft at the 75 mpH speed limit. It was a big improvement over the loop I used previously, particularly when the band is opening or closing. One tends to lose or bend the side elements and they can only be rebent once, so I carry an extra or two. There was a picture of me fixing my Moxon in the ARRL calendar a couple of years back. I do that about every 3 or 4 times I rove, but the performance the antenna gives is worth it.

I have used WA5VJB antennas on 2M, 222MHz, 432MHz, and 1296 MHz. They are all good performers in the rover, cheap and easy to make, no tuning required, but the longest ones are still a bit short of the 8 ft width window you have. Still, they give a good account of themselves roving and can be easily repaired if he need arises. The 2M and 222MHz antennas are being replaced by W7QQ designs. W7QQ designed these antenna so that they are nearly 8 ft long, taking full advantage of the highway width allocation. He also optimized the Yagi with the element spacing so that the boom to mast clamp is positioned right at the balance point, so that they don't windmill. The Directive Systems rover Yagis are similar to Bill's design. I suggest that, without other antennas, you start with the WA5VJBs.

These are all stacked pretty closely. The 6M Moxon is on top of the stack, which can be raised to 15 or 16 ft when stopped. Ideally one would like all the antennas to be at least a half wavelength above any conducting surface. This is tough on 6M, but is achievable on the other bands. Jerry gave you some good advice on stacking. The thing to remember is that the lower band antenna is not affected much if at all by close stacking, and the higher band antennas can be a half wave apart with little problem, and even function pretty good at 1/4 wave spacing. So I usually stack the 6M antenna on top. About a foot  below that I put the 432 MHz antenna, and 18 inches to 2 feet below that the 2M antenna. That puts the 432 MHz antenna roughly a half wave below the 6M antenna and the two meter antenna a roughly a half wave below the 6M antenna. I usually put the 222 MHz antenna 18 inches or so below the two meter antenna. 

The thing to remember is that a rover is a compromise operating situation. Most modern antennas are designed to minimize side lobes, which is an advantage for lowering noise, but in a rover the side lobes are actually a bit of an advantage, helping you to hear stations off the side. Also, roving with a long Yagi is difficult as it must be pointed critically, not alway possible in a rover. One can get away with narrower patterns on the higher bands as the pointing can be done on 2M where the beam width is wider and hence less critical.

If you operate with the car stopped and the engine not running a battery booster is useful. I use the TG Electronics one:

< http://stores.tgelectronics.org/Categories.bok?category=Boosters >

Some rigs are sensitive to voltage level and start to FM on less than 12V.

The key to roving is to be loud on two, so a bit of power on that band is useful. In June it is easy to miss the local stuff when 6M is open, so monitor two if you can. I don't' have a dedicated 2M rig yet, but I think that I am going in that direction.  

Good luck, and hope to work you in June. - Duffey KK6MC/r

 
On May 7, 2013, at 10:05 PM, Matt Holden <mtholde at gmail.com> wrote:

> 
> 
> W0ZF and I are building a grid square roving machine.
> i put a beast of a cargo rack on top of my jeep, so, were thinking big.
> We're looking for a small glen martin roof top tower and beams for 50 MHz,
> 144 MHz and 432 MHz.  got any you want to part with?
> Dave and I will be at Aurora and look forward to receiving advice from you
> experienced rovers.
> The goal is to be running the beast through South Dakota in the June VHF
> contest.
> 73 Matt K0BBC
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