On 1/16/2012 8:56 AM, Eddy Swynar wrote:
> On 2012-01-16, at 8:41 AM, Ken wrote:
>
>> Actually this setup is covered in this month's QST "The Doctor Is In" column
>> with a couple of references to older QST articles.
>>
>> A center fed dipole with open wire or ladder line is a very good multi band
>> antenna if you have a tuner which will feed it. A half wave at the lowest
>> frequency is the classic antenna and is covered in the Handbook and Antenna
>> Book. Some people find that the high impedance of the full wave (e.g. 130'
>> on 40m) is difficult for some tuners to handle and a 100' length is a
>> popular size for 80m and up. Myself, I prefer not to give up that extra
>> length on 80m.
>>
>> Antennas like this do not have to be precisely tuned. 135', 130', 125' all
>> will give essentially the same performance. 100' will give a slightly
>> reduced performance on 80m.
>>
>> And additional plus of an antenna like this is that it will work very well
>> on the WARC bands like 60 and 30m.
>>
>> I'm currently using an antenna like this. 40' of feedline to a 4:1 balun
>> outside the house, then coax directly to the Elecraft K3. The K3's internal
>> tuner handles it perfectly on all the bands 80 through 6m.
>>
My View: If it works, go with it!
Although 300 ohm twin lead or foam filled 300 ohm twin lead is limited
in its power handling capability the two conductors in such close
proximity make it less susceptible to near by objects and much less
near field radiation. My preference would be to use a wide range tuner
for open wire/ladder line/twin lead rather than one with a 4:1 balun,
but as I said in the first line, if it works, go with it. Also, keep it
simple or the KISS approach is the best way to do most of these things.
As 160 is a half sloper I'm thinking of feeding it as an end fed line
with a simple tuner at the feed point. I don't know whether to go
resonant at the bottom end of the band and switch in capacitance as I go
up in frequency or resonant at the top of the band and switch in
inductance or go with an active tuner as the normal useful bandwidth on
160 is very narrow. I'm also planning on turning the single wire into a
fan, with maybe 6 feet of separation at the far end.
I've said all this, yet so far, I have used strictly coax. Once warm
weather gets here I expect to try feeding the slopers and particularly
75 with window line and a remote tuner. I like the idea of switching in
either capacitance or inductance for band segments rather than "fine
tuning" the remote. More often than not, antenna placement dictates my
feed line lengths within 10 to 15 feet. I can often get, or end up with,
a feed line variation between tight and straight to a big droopy loop.
Unfortunately the one to the 75 meter sloping fan dipole is just about
right to chin yourself. A good 30 to 40 feet run nearly horizontal about
4 feet off the ground so getting that up in one of the higher priorities
and it's going to be at least another 5 weeks before they let me start
climbing again...if all goes well.
73
Roger (K8RI)
> Hi Ken et al,
>
> I had mis-givings here about feeding my 160-meter half-wave inverted "V"
> dipole (50' at the apex) with foam-type 300-ohm TV twin-lead---and using it
> on all bands from 160- to 10-meters---but my cares have been quickly laid to
> rest...
>
> That sort of a multi-band tuned dipole is wonderful---and it even has the
> added bonus of some "long wire" gain on 80- through to 10-meters...this,
> despite the fact that it has good, round-the-compass coverage, what with the
> smaller, "fill-in" lobes radiated by the antenna, which increase in number
> the higher the frequency band.
>
> One thing to pay attention to, though, is the feeder length: I settled upon
> one of the recommended lengths shown in my older small-sized ARRL ANTENNA
> HANDBOOK, otherwise I simply could not tune the thing on some bands with my
> transmatch...
>
> ~73~ de Eddy VE3CUI - VE3XZ
>
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