I'm glad to hear that I'm not the only one who has found that a 1/4 vertical
compares very well to a loop, even with "ground wave" contacts. During the
June contest, I took both a 6 Meter loop and a 1/4 wave magnetic mount
vertical. The loop was mounted about nine feet above the truck.
Using a antenna selector switch, I often switched between the two and found
the vertical was usually better on E-skip and often as good, or nearly so as
the horizontal loop on local contacts out to about 120 miles. Considering
the often reported 20db loss that is possible due to cross polarization, I
was really surprised by the results.
To be fair, nearly everyone has said that a loop must be mounted at least 20
feet high to really perform. While that would be possible in my rover
situation, it would complicate things considerably. It might be an option
worth looking at for the January and September contests where e-skip is
rare, and local contacts become much more important. But for "Summer roves"
it would be hard for me to justify the trouble of working with the loop vs.
the simplicity of a magnetic mount 1/4 whip.
Your mileage may vary, but I was certainly impressed with the whips
performance. Local contacts out to about 200 miles were made during the June
event, and we I can't think of a single instance where we could not have
completed on either antenna. On e-skip there were often times were signals
were better on the vertical, but none where the loop won out.
This is all due to radiation angles, and would almost certainly change if
the loop was mounted higher. I see this often on my home stations, where at
times my 3 element attic mounted indoor Yagi will "outperform" my nearby
neighbors 5 element Yagi mounted on a 70 foot tower. I have to point out
that he often works DX that I can't even hear...it's just that a few times
during each e-skip season we'll both be in a pileup and my radiation angle
happens to favor that particular station.
I'm sure this is why a lot of serious Six Meter guys have antennas mounted
at various heights and a means to select them to favor a given opening. I
thought that my "Loop & Whip" selector might give me that edge for a rover
too...but the results didn't justify the effort.
On the other hand, I ran a set of stacked 2 Meter KU4AB 2 Meter loops during
the event so that I could work both "run and gun" and "point and shoot". I
was thrilled and surprised with the performance of the stacked loops on 2
Meters!
The July event is coming up fast, and I plan to run stacked loops for 2M,
and a 1/4 whip for 6. I'll also be using a rack mounted 2 Meter 10 element
Yagi, but nothing else on Six. We'll see how it turns out.
73,
Les Rayburn, N1LF
EM63nf
121 Mayfair Park
Maylene, AL 35114
--------------------------------------------------
From: "Alex" <kr1st@bellsouth.net>
Sent: Thursday, July 02, 2009 7:01 AM
To: "Jacob Tennant" <k8jwt@comcast.net>; "VHF List" <vhf@w6yx.stanford.edu>;
<vhfcontesting@contesting.com>
Subject: Re: [VHF] Another antenna question
> Hi Jacob,
>
>> After asking the overall evaluation of the current loop antennas, I am
>> thinking more along the lines of the KISS system for my mobile/rover
>> setup.(Keep It Simple Stupid)
>
> I think that's an excellent approach to many things. :)
>
>> Therefore I am now thinking about running a simple Hamstick dipole setup
>> for
>> 6 meters since a loop is nothing more than a dipole with the ends folded
>> around into a loop/square.
>
>> It should work as well as a loop, shouldn't it?
>
> If you are able to rotate the dipole (armstrong method perhaps), then yes,
> it works a heck of a lot better especially since you can get it up 20 or
> 30 feet.
>
> I used a dipole (made from aluminum tubing) at 16 feet and it worked very
> well. Since the pattern of a dipole is rather broad, you don't have to
> turn it as much either. Turning it once 90 degrees and you have 360
> degrees coverage.
>
> Someone else pointed out that a loop has a radiation pattern within a dB
> all around, but that is not really true. In the case of a halo close to
> the car you can indeed achieve this, but that is only because most of the
> energy is radiated upward. It's like pointing a flashlight upward and then
> hold a piece of paper above it and then conclude from the reflection you
> see on the paper that the radiation pattern is nearly perfectly round
> (which is caused by the reflector in the flashlight, or the car body and
> ground that act as a reflector in the case of the antenna just a few feet
> mounted of the car.)
>
> I have found that with single and stacked loops that the radiation pattern
> more that of a peanut when properly elevated. This is also discussed in
> the RSGB VHF Handbook. Front to side difference in gain can easily be 3 dB
> or so. Now if you consider that a loop already has considerable less gain
> than a dipole, and then if you'd reduce the gain of the halo even more by
> mounting it closer to the roof of the car, then yes, your proposed setup
> will be much much better. It really bocomes more like comparing apples and
> oranges.
>
> If you really want a loop with omnidirectional characteristics, then you'd
> have to build a full wave loop. See RSGH VHF Handbook.
>
> During the June VHF QP I had a 6m halo about 4 feet from the car roof, and
> a 2m 5/8 wl vertical that I used as a 1/4 wl on 6m. For close in contacts
> the halo was only marginally better than the vertical surprisingly enough.
> You'd think that the 20dB or so polarization loss would make a huge
> difference, but I guess the gain loss I experienced by having the halo so
> close to the car roof actually made the vertical a decent competitor. For
> the short Es openings that we were afforded by the propagation gods the
> vertical worked so much better (not going to quantify this w/o
> measurements) that I concluded to forget the halo next time around, unless
> I can get it at a decent height. Keep in mind that this is just a one
> person experience. Maybe others would have better results.
>
>
> Hopefully this was confusing enough. :)
>
> 73,
> --Alex KR1ST
> http://www.kr1st.com
> http://www.airlinkexpress.org
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