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G4EBT > COILS 17.05.09 18:02l 128 Lines 4582 Bytes #999 (0) @ WW
BID : E60775G4EBT
Read: GUEST
Subj: Re: Coils and things 'FTD
Path: IZ3LSV<IK2XDE<DB0RES<DK0WUE<GB7FCR
Sent: 090517/1555Z @:GB7FCR.#16.GBR.EU #:27428 [Blackpool] FBB-7.03a $:E60775G4
From: G4EBT@GB7FCR.#16.GBR.EU
To : COILS@WW
G0FTD wrote:-
> Thanks for the interesting info. I thought a generic reply would
> be of use to other readers (must be all of about 4 left in Packetland
> by now).
> G4EBT wrote:-
> >There's been a lot of discussion in Technical Topics over the year on
> >losses in 80M and 160M ATUs.
> Eh ? I thought TT was dead,
I'm sure it is.
Pat Hawker did a stirling job all those years.
For the 31 years I was an RSGB member, always the first pages I turned to
in Radcom, followed (in the pre e-bay era, when people used to put readers
sales and wanted ads in Radcom), by a glance down the readers adverts.
>how old is this bulletin ? ;-)
Three days old - I sent it out on 14 May 2009.
But the info was a good deal older, as I stated:
>There's been a lot of discussion in Technical Topics over the year on
>losses in 80M and 160M ATUs. TT Nov 1996, among other things, stated:
(cut for brevity)
>Jan 97 TT covered antenna loading coils and ATUs for 80/160 and developed
>the theme of "why waste your transmitting power in lossy loading coils?"
>discussing coil diameter-to-length, and suitable materials for formers.
(cut for brevity).
> Thankfully I have the complete collection on book and cd.
> Well worth the money and for once I can thank the Potters Bar Book
> Company for publishing it - as I'm sure David will agree.
Yes, I've always said that the one thing that RSGB can be praised for over
the years, has been the standard of its publications. They always tended
to be a bit dated, largely due to the rapid changes which have taken place
over the years.
The G2DAF RX/TX/Linear series of articles in Radcom was, I think, the
zenith of the home-brew era. Enough were made to justify a firm at
Loughborough - Philpotts, to make all the metalwork for those.
It was the era of Electroniques, which - among other things, made coils,
with the trimmers mounted on the end. But it as also the era when
Kenyeasuicom began to eclipse that side of the hobby, and to hi-jack
amateur radio as just another consumer electronics market.
I had a chum some years ago who started building a 6m linear amplifier and
PSU using 4CX250Bs - a design from an RSGB book. It took him many months
to get the bits together from rallies etc, but he'd bitten off more than
he could chew, and was so dispirited that I helped him finish it off.
It wasn't a project I'd have embarked on, and I did ponder on whether it
would work when finished, but in fact it worked right away and gave him so
much pleasure for many years, working innumerable countries.
> * a 70uh coil was wound on an old 35mm film cannister with two layers.
> It worked but very hot. Clearly lossy.
> * A re-wound variometer on bakelite worked superbly for matching
> purposes and variability. However the method of connecting the inner to
> outer coil just wasn't up to the job, the arcing started and melting
> occured ;-)
> * an inductor was wound on 3 FT140-61 stucks together got hot too.
Careful - you'll have Gordon Brooon (aka McVlad the Impaler) imposing a
green tax on you or something, for poking a hole in the Ozone layer!
> As an aside, the voltages on my vertical on 160m are quite frightening.
> A few years ago my thumb came close to the antenna whilst transmitting.
> It zapped across through my thumb nail, burnt a hole in my thumb nail
> and drew blood. It stung for about 2 hours too ;-)
in the late 1970s I recall that at the British Steel radio club in
Rotherham (long gone, like BSC), they'd run out about half a mile of
phone line cable - copper-coated steel telephone wire, to try to work
some DX on 160M.
By any definition, a "long wire".
As they were about to plug the antenna into the rig, a fat blue spark
about 2" long leap from the wire to the case, from static electricity
that had built up on the antenna.
After that, no-one dare try to plug it in. A brief debate ensued as to the
electrical insulating properties of leather welding gloves, and that it's
"volts that jolts and mils that kills".
Not so much an antenna as a lightning conductor!
Quote of the day;
Homebrew - or shop-bought?
"It is better for the development of character and contentment to do
certain things badly for yourself than to have them done better for
you by someone else."
(Anon).
Best wishes
David, G4EBT @ GB7FCR
British Vintage Wireless Society Member
G-QRP Club Member, No: 1339
Cottingham, East Yorkshire.
Message timed: 16:55 on 2009-May-17
Message sent using WinPack-Telnet V6.70
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