Feeding a doublet
 

Hi all

With a bit of luck I'm finally going to get my HF doublet up in the
air in the next week or so. I'm planing on about 150ft per top 'leg',
and will need a couple of hundred feet of open-wire feeder (going to
try heavy-duty 'slotted' ribbon for starters) .

Here's the question...
Due to the geography of the site, the shack is pretty well in line
with the antenna - which will be at about 20ft above ground on 3
poles. The site slopes, so that the eaves of the shack are about level
with the bottom of the nearest pole. In all the books, diagrams show
the feeder joining onto the 'aerial' at right angles - but I'm
wondering how best ot compromise on this in my situation.

Would it be better to take the ribbon feeder straight to the bottom
of the first pole & then run it underneath & in line with the aerial
(say a couple of feet off the ground) until it meets the centre pole -
then run it up to the feedpoint ......- or would it be any better to
run the feeder at low-level but parallel with the aerial (could be
about 20-30 ft apart) and then make a right-angled turn up to the
feedpoint...?

Possibly, in terms of the wavelengths involved it'll make little
difference - and I'm quite prepared to try it & see.. but I just
wondered what opinions / experiences group members could share.

I'm planning on the doublet to make the best use of the space
available, and to reduce the possibility of TVI (we're in a weak TV
signal area and effective earths for a long-wire aren't easy because
we have very dry, sandy soil).

Thanks in advance for any suggestions / comments
Adrian G0THW
Suffolk UK

"Adrian" wrote in message
...
Hi all

With a bit of luck I'm finally going to get my HF doublet up in the
air in the next week or so. I'm planing on about 150ft per top 'leg',
and will need a couple of hundred feet of open-wire feeder (going to
try heavy-duty 'slotted' ribbon for starters) .

Here's the question...
Due to the geography of the site, the shack is pretty well in line
with the antenna - which will be at about 20ft above ground on 3
poles. The site slopes, so that the eaves of the shack are about level
with the bottom of the nearest pole. In all the books, diagrams show
the feeder joining onto the 'aerial' at right angles - but I'm
wondering how best ot compromise on this in my situation.

Would it be better to take the ribbon feeder straight to the bottom
of the first pole & then run it underneath & in line with the aerial
(say a couple of feet off the ground) until it meets the centre pole -
then run it up to the feedpoint ......- or would it be any better to
run the feeder at low-level but parallel with the aerial (could be
about 20-30 ft apart) and then make a right-angled turn up to the
feedpoint...?

Possibly, in terms of the wavelengths involved it'll make little
difference - and I'm quite prepared to try it & see.. but I just
wondered what opinions / experiences group members could share.

I'm planning on the doublet to make the best use of the space
available, and to reduce the possibility of TVI (we're in a weak TV
signal area and effective earths for a long-wire aren't easy because
we have very dry, sandy soil).

Thanks in advance for any suggestions / comments
Adrian G0THW
Suffolk UK

Why complicate things Adrian. Put the thing together and see what happens.
Work out the details later. If it works , dont fix it.

HNY

Dan/W4NTI

Adrian,
It really isn't going to make all that much difference.
Run the feed line as best you can, see what the 'problems'
are and then try to minimize them. Needless to say, at 20
feet height, on 80 meters, how you run the feed line isn't
one of the 'biggies' to worry about. That's not to say that
you shouldn't do it as 'correctly' as possible, just don't
loose a lot of sleep over it.
'Doc

HI Doc / Dan



Adrian,
It really isn't going to make all that much difference.
Run the feed line as best you can, see what the 'problems'
are and then try to minimize them. Needless to say, at 20
feet height, on 80 meters, how you run the feed line isn't
one of the 'biggies' to worry about. That's not to say that
you shouldn't do it as 'correctly' as possible, just don't
loose a lot of sleep over it.

Thanks for the comments.
I know that 20ft is a bit on the 'low' side - but the poles are going
to be close to the skyline, and there are people about the area who
might well object if the poles grew any taller.....

I had another thought today. There's a nice wooden fence surrounding
this piece of land - I could probably string about 500 - 600 ft of
wire around this in a big loop, and feed it with the open-wire feeder.

OK - so it would only be about 4ft off the ground - but it might
possibly work ....? I might try this approach first (before 'planting'
the other two 20ft poles.....

...... but not tonight - it's dark, close on freezing, and there's a
force 5 gale coming down over the paddock

Thanks again & Happy New Year

Adrian
Suffolk UK

Adrian,
Since I haven't tried an antenna like that I can't honestly
say what it might do. I'd certainly have to give it a try,
though! I would guess that it will be a 'quiet' antenna. How
much of that 'quiet' is due to it being a lousy antenna versus
too low, is another one of those 'guesses's. But I like loops
and would certainly see what happened if I had that much fence!
As for the antenna being 'skylined', and objectionable
neighbors,
put up the poles with a bird house on top of each. Tell the
neighbors
the wire is an intercom line for the birds and to mind their own
@#$%
business! Or maybe cameras wired so you can watch them... They
can
still mind their own @#$% business...
'Doc

HI Doc



Adrian,
Since I haven't tried an antenna like that I can't honestly
say what it might do. I'd certainly have to give it a try,
though! I would guess that it will be a 'quiet' antenna. How
much of that 'quiet' is due to it being a lousy antenna versus
too low, is another one of those 'guesses's. But I like loops
and would certainly see what happened if I had that much fence!

Yes - I'll give it a try.....
There's actually a metal fence 'stock fence' all round the perimiter
of the land - but the bottom end of it is securely embedded in the
earth - so I think it may be asking rather a lot for that to radiate
g. But a thin insulated wire along the fence top, that's a
possibility......

As for the antenna being 'skylined', and objectionable
neighbors,
put up the poles with a bird house on top of each. Tell the
neighbors
the wire is an intercom line for the birds and to mind their own
@#$%
business! Or maybe cameras wired so you can watch them... They
can
still mind their own @#$% business...

We do like to try to keep on good terms with our neighbours (up to a
point). One or two of them are a bit 'funny' - we had to get rid of a
cockerel because he was waking people up in the morning..... so we try
not to wind anybody up more than absolutely necessary. We're also in a
designated Area of Outstanding Natural Beauty (!) - so that tends to
raise peoples' 'sensitivity' to things like aerial farms. Never mind -
there are compensations g

Now all I need is a BIG reel of insulated wire.......

Thanks again
Adrian
Suffolk UK

On Thu, 01 Jan 2004 09:07:57 +0000, Adrian
wrote:

There's actually a metal fence 'stock fence' all round the perimiter
of the land - but the bottom end of it is securely embedded in the
earth - so I think it may be asking rather a lot for that to radiate
g. But a thin insulated wire along the fence top, that's a
possibility......

Hi Adrian,

Sounds like a combination circular Beverage antenna and fence de-icer.

As for the Beverage antenna, do it by parts (one quarter at a time) to
see if things:
a) work;
b) improve;
c) stay the same.

73's
Richard Clark, KB7QHC