I think a 43 foot vertical (with sufficient radials) would make a decent
antenna on 160 meters and an excellent antenna on 80, 40 and 30 meters.
On 20 meters the antenna is a bit more than 5/8 wavelength in length and a
significant portion of the radiated RF will go nearly straight up and will not
be reflected by the ionosphere due to the high angle. This gets worse as you
go up in frequency.
Could you work people on 20 and above? Sure, but it would be on a secondary
lobe as the primary and strongest lobe of RF will be "lost in space". Above
20 meters a 43 foot vertical is really a long wire pointed straight up.
The other issue is that the required antenna coupler should be mounted at the
base of the antenna to be fully effective. Yes, an apparent match condition
could be achieved by using a coupler in the shack but that apparent match only
serves to make the rig happy. Considerable RF is burned off as heat in the
mismatched coax run to the antenna.
It would also be interesting to measure the losses in the matching unun. If
it's a ferrite or iron core those losses could be significant because UNUN's
and BALUN's are not operating within their design spec if they are operating
in an environment where the impedance is not purely resistive. RF
transformers of this type are not meant to be used in reactive circuits.
In my opinion, the antenna manufactures do a disservice to the community by
promoting vertical antennas that are longer than 5/8 wavelength. Yes, you can
get a decent SWR if you use 150 feet of lossy coax and an in-shack coupler.
Yes, you can get a decent match with a 3/4 wavelength antenna. But, having a
decent match and a decent antenna system can be two very different animals.
OTOH, I applaud the use of non-resonant antenna designs. Being non-resonant
makes for an easier job of impedance matching on harmonically related
frequencies such as we enjoy in our HF spectrum.
If you are primarily interested in 160 through 30 meters then I'd say the 43'
vertical would be a good choice. If you're primarily interested in 20 and
above then I'd go with a shorter vertical. In either case, I'd do my
impedance matching at the base of the antenna.
If you want all-band coverage and don't want to fool with an external coupler
then I'd look at an all band vertical that has traps or stubs or variable
length or *something* that makes the antenna a reasonable electrical height on
the bands of interest..
Of course, this is all opinion and worth maybe a bit less than what you paid
for it! ;-)
73,
-Doug, W7KF
http://www.w7kf.com
Michael & Sue Trussell wrote:
The weather and old age have taken its toll on my old AV5 Cushcraft 5
band vertical antenna. I am considering a purchase of another all band
MBVE-1UP 45 foot vertical by DX Engineering. Because I have been out of
amateur radio for many years the technical knowledge that I thought knew
about antennas and such has evolved so much by the various equipment
manufactures that my knowledge base has become outdated somewhat. I need
to stick with a vertical because of lack real estate and living in a
city lot!
I would like some suggestions from you who have been keeping up on the
art and technology to offer some suggestions on using an antenna like
the above mentioned MBVE-1, with my Drake MN2700 antenna tuner. I would
like to use all of the capacity of this antenna; I also understand that
the capacity of the MN2700 is limited to the standard amateur radio
frequencies. I would like to use the WARC bands that I now have the
capacity to use with my TR7 along with the L4B amp just recently
rebuilt. It works even better now with a new power supply.
Should I look for another tuner to use or purchase another MN2700 and
attempt to modify it?
Any suggestion or ideas would be greatly appreciated
Thank you in advance
Michael J Trussell KA8ASN
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