| |
G0TEZ > TECH 14.09.04 10:12l 93 Lines 4303 Bytes #999 (0) @ WW
BID : 9E0222G0TEZ
Read: GUEST OE7FMI
Subj: Re: Delta Loops
Path: DB0FHN<DB0FOR<DB0SIF<DB0MRW<DB0HOT<OK0PBX<OK0PHK<OK0NAG<OK0PPL<DB0RES<
ON0AR<VE2PAK<W1NGL<W7NTF<KD4GCA<W4JAX<GB7FCR<GB7BOB<GB7HVU
Sent: 040913/2319Z @:GB7HVU.#16.GBR.EU #:52296 [Great Harwood] FBB7.00i
From: G0TEZ@GB7HVU.#16.GBR.EU
To : TECH@WW
I,m sorry, Andy (G0FTD) I have tried but I will never be able to draw
diagrams on here as well as G8MNY.
Imagine a plan view of a delta loop, a triangle viewed from above.
Inside it at a distance of 1/10 Lambda, about 1.1m on 27MHz. a little
'wall' anout 18" high made of aluminium foil, kept upright by three posts.
No wind in a loft so no need for great structural strength.
I had no way of checking the polar diagram of a delta loop, I just assumed
it was roughly circular, horizontally polarised and omnidirectional.
The reflector behaved just like the reflector on a beam. With my
background being in TV, I made it about 1/10 Lambda as that is the usual
distance for the reflector on a Yagi.
Most S meters on CB radios are roughly the same but what they represent in
terme of dB, I have no idea. Having said that, the scale IS exponential so
an increase from S3 to S9+20 is very big!
I will admit the building of it was purely empirical. The SWR adjustment
was particularly easy with the wire driven element being supported by
large , rubber bands. All I had to do in practice, was make a twist in one
side of the delta to shorten it. I had made it to the theoretical length
using the lambda=c/f schoolboy formula. I knew that the free space lenght
would be less and the reflector would lower it even further, just from
experience.
The worst part was climbing in and out of the loft as I made each
adjustment, checking my VSWR at each end of the band. My rig went from
26.004 MHz to just under 28MHz so it wasn't easy. On later projects I used
a longer power lead and took the rig and SWR meter into the loft.
There was no question of putting the baco foil under the AE. I did DX on
my full 12W PEP but that was with a half wave dipole. I always puzzled the
others because they thought the way to go was lots of power and a 5/8ths
vertical.
One other experiment I did in that same loft, was to use baco foil as a
long strip, horizontaly along a beam. I cut a slot 1/2 Lambda long and, at
the centre I attached coax. I made 'tuning bars' from the same foil to
tune the thing. The big problem, to which I found no satisfactory answer,
was that you couldn't solder coax to aluminium. I made a good, mechanical
joint, using paperclips and my old favourite,Super Glue.
Brass shim would have been far better but I couldn't find any that size,
or afford it for that matter.
Naturally, the slot was vertically polarised and behaved like a 1/2 wave
vertical. I used it for local work until everyone became blas enough to
put up 5/8th and 7/8th verticals outside.
If anyone wants to try a variation on either for HF work, I assure you
they did work. The other breakers used to think I had a "big pair of
boots" but I never used any great power. I did North America on a daily
basis. I commonly talked to Europe. In fact, as a French speaker, my
handle became
quite well known in France.
If you think a double delta is wierd. I used to listen to Americans. One
of them, who had an acre of land, had used for telegraph poles to
construct a Rhombic. He said he could do 2,000 miles, north to south under
the right conditions.
Another had bilt a 7 ele quad. I don't know what power he used but he
would ask someone in the UK roughly where they were. "Oh, Birningham,I
know where that is" and you could watch his signal fade almost to nothing
as he swung the thing to point at the midlands from across the Atlantic.
So much for all the tales of "One - Nine for the Rubber Duck, c'mon".
A lot of breakers were very knowledgeable.
*หหอออออออออออออออออออออออออออออออออออออหห*
ฬฮอออออออออออออออออออออออออออออออออออออฮน
บบ 73.Ian, G0TEZ@GB7HVU.#16.GBR.EU บบ
บบ MSG timed at: 18:04 GMT บบ
บบ on 13 09 2004 บบ
*สสอออออออออออออออออออออออออออออออออออออสส*
"The moving finger writes and,having writ,
moves on.
Nor all thy piety nor wit can lure it back to
Cancel half a line.
Nor all thy tears wash out a word of it."
Rhubayat.
Read previous mail | Read next mail
| |
