WB4ENE (Ken) writes:
Dear Top Band Friends,
I?m not making any claims for my MRA beyond what I have either measured or
worked. I try to avoid hype.
I am not ready for the back of QST magazine or AntenneX.
There were some questions in previous posts that I want to address:
The antenna pictured on qrz.com and my website has been in my back yard for
11 months.
Impatiently, we all wait for testing under controlled conditions, which will
happen in ?06 on the CA/Mexican border at El Centro NAF. This testing will
be at AM broadcast frequencies for the same antenna, with a slightly higher
mast and 16 tophat radials.. Transmitting at 530kHz makes Top Band a
cakewalk. This is not for USA purposes however.
EZNEC simulations were bogus, unbelievable.
Lawrence Livermore Labs is sending me NEC 4.1
There is $4,000 worth of aluminum in the MRA as shown in the picture, -->
machining extra ;) Quantity pricing of bulk aluminum will reduce that cost.
Dave, AB7E is right, it is a vertical, but he may be incorrect about the MRA
needing earth ground to work. I have one in Bahrain working on the roof of
a 4 story building. I will be installing a RX only version for the USAF
receiver site near Sacramento in 2 weeks?on a roof for SCOPE Command. If
the new one works and the Bahrain one keeps working, then we need to see if
the NEC 4.1 simulations show that the interaction of the cylinder (emitter
grid) and the trampoline (collector grid) is sufficient for ground return.
This working against its own ground plane rather than earth could well be
the reason why it works. Ground losses are minimized. Of course, mobile rig
BugCatcher antennas ?work? don?t they? Hmmm, I just worked MM0SJH on 1.848
and he gave me a 49. A SUV is similar in size to this antenna; but would it
get thru on Top Band with a 24 foot whip?
2 weeks ago I had an oyster roast for my birthday and we used the collector
grid for a table. EZ wash after the party! Nope, the MRA does not cook
food.
You can tell the neighborhood association the MRA is a ?gazebo? or a ?lawn
sculpture?, or a UFO. Just disconnect the coax before it takes off.
You can paint it urban camouflage or leave potted plants on it.
There are no radials connected to it, only an 8ft ground rod next to the
tuner. The pads under the antenna have ½? thick plastic insulators, and the
antenna rests on bricks. The LC tuner rests on bricks. The coax is buried.
Network analyzer plots were largely unchanged when adding and removing
240foot radial wires to the base.
For you antenna experts: ok, it?s a vertical, 24ft tall, with a 9 foot
radial torus as the ground plane, and at this moment, 10 capacity wires 19ft
each at
45 degrees.. To resonate the MRA on topband 1.850 I?m looking at 3100pF in
shunt (on the antenna side) with 10uH in series on the John Bliss tuner.
So, why mess with this type of antenna?? Some guys say all the antennas
necessary have already been invented. I don?t have room for a radial
field. My pecan trees are too short. I like aluminum lawn sculpture. And I
would like to make an antenna hams on high rise buildings or rocky
mountaintops could use to get on Top Band.
I would not be sad if I can prove that a capacity cylinder can add
capacitance at the base of a monopole, in conjunction with a capacity hat,
and eliminate the need for radials any longer than 3x the cylinder (think 50
ohms guys).
If you take a look at the Gap Super C antenna you will see the beginning of
a revolutionary idea. It is unfortunate that George died three years too
soon. There are 3 things you can do to improve the Super C antenna if you
have one. I have a federal patent applied (Dec04) for fundamental
differences between the Super C and the MRA. A second patent will be
applied for after the AM broadcast test, unless I decide to make the
complete design details available to the Ham community.
73?
Ken
WB4ENE
http://ken.crawley.org <http://ken.crawley.org/>
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