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Re: [TowerTalk] Was "43ft Vertical Feeding

Subject: Re: [TowerTalk] Was "43ft Vertical Feeding
From: jimlux <>
Date: Mon, 24 Nov 2008 06:45:08 -0800
List-post: <">>
Dennis OConnor wrote:
> Pete - right on! I am dismayed by the lack of the old ham spirit that
> I see in todays operators...

back at the beginning, we discussed the difference between homebrew and
getting an integrated unit. If you're willing to spend the considerable
amount of free time needed to design and build a unit, sure, you can do
it for a lot less.

> Pete pointed it out quite clearly... 12 relays @ $3 a pop - $36

I don't know that $3 relays (even surplus) will handle the
current/voltage in a kilowatt tuner working into a physically short

> Roll of quarter inch dia. soft copper tubing (home depot) - I dunno,
> maybe $50

Hmm.. copper prices are pretty high, and it would take a surprising
length of this to wind all those coils.

> 2X4 Sheet of .060" aluminium - maybe $50 ( I buy a half dozen full
> sheets at a time so I don't know price of small amounts)  Lots less
> if you harvest some scrap aluminium from old freezers, etc.

If your time is free, sure.

> Anyway, cobble up a test coil by winding some turns of #14 on a 2 - 3
> inch pvc pipe and get an old variable condenser and some jumpers, and
> use them to test tune each band... Measure the inductance and
> capacitance you find for each band...... Wind a coil from the copper
> tubing to the found value(s).. Make the condensers by cutting two
> plates from the aluminium sheet and spacing them apart with little
> buttons of plastic - lexan from the hardware works good - and
> adjusting the overlap of the plates for final tune... When tuned
> squirt a dab of crazy glue on the buttons to lock the plates into
> position... 

Have you actually built capacitors that can take several kilovolts (and 
that's what a kilowatt tuner into a short antenna is going to have on 
the C) with this approach?  How long do you think they will last (corona 
discharge off the edges of the plates you've cut out of that freezer, 
and treeing within the polycarbonate)..  Building durable high power 
components is certainly doable, but it's not trivial nor is it fast.

(I used to build tesla coils and other HV gear, and learned more than I 
really want to know about improvised HV components and their failure modes)

Repeat 5 more times and voila - 6 bands Another $20 for a
> covered plastic storage bin to mount the parts and relays - and for
> ~$150 you have a six band, switchable tuner, that will take ALL the
> power your amp can make and then some.... And for lots less than $150
> if you have some scrounging skills...

Even scrounging, I think parts cost will be a bit higher (you have to 
drive those relays with something, and just the copper wire from shack 
to relays will cost something).. but a few hundred dollar is reasonable.

You'll also need many, many hours of free time.  This is a reasonable 
trade, if you have time.  OTOH, if you have more money than free time, 
the kilobuck or two for a reliable and compact manufactured item might 
seem real attractive.  Ham radio, in general, is a diverse hobby.. some 
get enjoyment from scrounging and fabricating things themselves, others 
get enjoyment from other aspects.

Jim, W6RMK


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