Rover Antenna's
Like most great discoveries I discovered this one
purely by accident. In the fall of 2001 I made a decision to further my
Microwave distance in a big way. Like most rovers the first question
is how big a dish can I take this out with me? Where can I find one? Do
I have to sacrifice my 50-432mhz (low) bands? What I found was my
50-432mhz Low Bands work better than ever! First let me tell you what
lead up to my discovery. MY old microwave configuration was a 2x4foot
dish that came out of the trunk of my van at each site. The beams were
fixed on the roof, which meant I had a 4-wheel rotator that required
gasoline to operate. Lots of set up time and poor scores.
I borrowed a 4 foot round dish in the hopes that it might help my gain.
I am sorry to say it did not help too much but I did make a 200+ mile
contact on 5ghz, which got me excited. I also got a traffic ticket for
blocking the rear center break light. So this configuration had to go.
Still had poor scores but I told myself I was having fun on the
microwaves. Something very new to me.
Now comes a bigger problem. A friend of a friend had a 6foot dish!
4foot to 6foot had quite a nice advantage in gain so I started to look
for answers. I found no one doing this. This only made me want to do it
more. I figured I might make a real leap in distance with a 6footer. I
finally had a friend tell me to strap the dish to the roof of my car
and sacrifice my low bands. Low bands being anything I could not put
into the dish, 50mhz thru 432mhz. I started to lift this 6foot dish
onto the roof when I suddenly discovered this was heavy. My brother
Robin (KK5SS) and I looked into how I could maybe use something like a
Ginn pole that we used as kids to raise a large sail boat mast. I
factored in information gathered from many people such as KJ1K, N1FGY,
WA2AAU and others. One of the most interesting ideas had to do with air
flow across the dish at 55mph. Face down it looks like a aircraft wing
so it might take off! So I mounted it upside down with the feed
pointing to the stars. This gave me a new problem. I needed new shocks
on the van since now it pushes down! At least I didn't have to worry
about it ripping the roof off my van. The end result of my 6 months of
ideas and tinkering with this was something like this:
After road testing I was convinced that it was going to stay on the
roof of my van and I started to look at the low bands. As you can see
from the picture there is no real room for beams the way I had them
before. I found a number of people like N2JMH that had solved this
problem by leaning them down over the front of the vehicle pointing at
the road or the sky. It’s a little hard to see but this is the best pic
I could find. I took it at a gas station. If you look carefully you can
see that the beams are only 1 foot or less apart from each other. On
144 and 222 this arrangement shows a loss of pattern, which seriously
curtails your usable range. It also showed some strange impedance bumps
in the smith chart I could only explain by the proximity of the beams
to each other. My old configuration was not much better than this so I
started to look into doing the same thing.
After creating a mast
and laying it on the top of the van I discovered that my beams would
have to be shortened as well to keep them from hitting the road. Maybe
a higher van would work better. N2JMH had a high standard style van and
I had a Dodge Grand Caravan I purchased to do HF in the PA QSO party
contests. I was about to give up on the low bands when I saw a cable TV
truck with some bent up pipe on top near my home. I then had the idea
to put a hinge on the mast that would allow me to have everything on
the roof and not hit the road!
Now I was cooking! Yea right. How many of you non-truck drivers ever
notice how low some of those bridges are? Especially troublesome to us
hams with beams on the roof are the low trees when your on a dirt road
attempting to get to the top of a hill. I almost gave up again until I
saw a HUGE LF log periodic antenna at the Long Island Macarthur
airport. On a repeater I struck up a discussion about it and I had my
first lesson on Log Periodic beams. Before you stop reading on, yes, I
know log periodic's have a bad reputation for performance per dollar.
Its true. When your trying to get three or 4 low band beams on the roof
of a van you have to suffer one way or another. Since I was already
borrowing many of the beams I used in the past the thought had occurred
to me to purchase new ones. Yep, big $$$ for 4 beams. I had already
priced a few. I searched the beam companies for log periodic’s and the
only thing I found was that all these companies knew was that Log
Periodic’s are poor performance (gain) per dollar. I happened to hear
about an IF rig (I needed a 28mhz IF RIG) from a friend. It was listed
on eham.net. To my surprise I saw something that mentioned KMA
antennas. I had not heard of them so I clicked. WOW ! They already had
a log periodic called a "ROVER". Only problem was that it was too big
to put on a van without assembly at each site. I struck up a discussion
with Ed Griffin (W4KMA). He was listening to my needs and designed a
better ROVER antenna. The thing that made the old one so big was 50mhz.
So we made one that worked from 144 thru 432 which includes 222mhz. It
was only 4 feet wide plus or minus which is plenty narrow for most
roads. I looked around and found that W8SMD made a halo antenna for 6
meters. Ok none of these antennas are great but I figured I could make
some of the close in contacts and even if I could not work the same
long distance stations I would be satisfied because now I had a 6foot
dish on the roof of my van! This is what the result looked like.
In the travel position (down)
In the up position:
My next contest was June 2002 and boy it was interesting. Unfortunately I blew the power supply that runs many microwave things like 28v relays and such. I made almost no microwave contacts. I did have the low bands though. So I played with them and worked a few stations over 200 miles! Even on 6 meters! I figured maybe the bands were good and I missed out on some real good contesting. The next contest was August 2002. My 144mhz IF rig died. I borrowed one the day before the contest from Sigurd (KJ1K). He is a real good friend. Again my contest had problems. Was I every going to get any luck? Rain, hail, lightening and some wind created hazards I did not know how to cope with. Its interesting how loud hail can be in a 6-foot dish facing up. I made some huge contacts as long as 280 miles on 5ghz and yes I made 289 and longer contacts on 50-432mhz. It seemed that anyone I wanted to talk to I could. Same rigs and PAs for the most part but things were good. September 2002 it was my turn to fall apart. I slipped on a wet ladder and sprained my ankle real bad. Zzzzz if you know what I mean. After I woke up I made a couple of local contacts but decided to get down the hill before I hurt myself more. I slept a little and then went to a near by medical center that was open on Sunday! Some luck! Before my ankle I had made some incredible contacts on the low bands. This is now my third trip out and this contest the bands were reported by everyone as not being great. Add to that my down time and soreness on Sunday. So how come I was doing better than ever? My score was the best I ever had (20k points) I started to analyze what I was doing over these last three contests. Here are my conclusions:
- Height, I was now at more than 14 foot above the ground and at least 8 foot above the roof of the van.
- Less interference with other antennas. I now only have the dish, log, and halo. With some fair spacing.
- The Halo was at 16 foot above the ground. Amazing 6meter contacts in all three contests.
- Rotation, Where I was fixed to the van before. Now had 360 rotations. Easier to find those other signals.
- Even my dish was higher up off the ground than any of my earlier attempts.
- Road clearance 11foot.
- Site set up time, less than 10 minutes including alignment to compass.
These factors made my low band performance much better than using
larger individual beams. The result was that my 5ghz record is now 289
miles! (FN00 to FN32) thanks to a lot of patience from a big gun
(W2SZ). I made low band contacts on all bands with every station that
had the bands I did. Even though I did not make any really tropo type
contacts it was clear after three contests that my new configuration
was not only as good as but better than anything I had before. Mostly
thanks to W4KMA for the KMA140-460 Log Periodic (See: http://www.kmaantennas.com) that
everyone said would not cut the mustard. In the case of a rover less is
more. Less set up time, less hardware, less interference and less coax.
This has really worked out well for me. I thought it would be good to
share this surprising discovery. Many of you would not have considered
it. If I don't sprain my ankle this next trip out I plan to break my
20k point score big time this year.. Look out you other rovers!
,, Tim Ertl KE3HT/r
http://www.lmrgroup.com/ke3ht/rover