[TowerTalk] Need Capacitors for Matching Network

[Jim Thomson]

Date: Mon, 14 Aug 2017 07:24:49 -0700
From: Grant Saviers <grants2 at pacbell.net>
To: Art Greenberg <art at artg.tv>, TowerTalk at contesting.com
Subject: Re: [TowerTalk] Need Capacitors for Matching Network

<I match my top loaded 160m T with switched series capacitors and PCB 
relays.  I run QRO (SSB QSO's with ZL's yesterday, - yea for conditions).
My match covers most all the band in four steps, no inductors, 3 series 
switched 4000pf values.  It wouldn't take much top loading to get your 
53' vertical resonant at 3.55MHz or so and use the same idea for tuning 
the entire band.  I'll send off line a note I wrote about this.

CDE CDV16 are higher rated current silver micas. 
http://www.cde.com/resources/catalogs/PULSE-MICA.pdf  However, for the 
low end of that range currents are well below QRO or circulating current 
levels.  You might try ebay for some ex military transmitter doorknob 
silver micas from Eastern Europe.

Grant KZ1W

##  Good point.  A buddy did similar for his 100 ft top load 160M T, but used
a motor driven 4000 pf ceramic vac cap.  Flat swr across the entire 160m band.
It uses elevated radials. 

##  The fellows  53 ft tall vertical is 87% full size.. on 3.840 mhz. .  Depending on how big
the OD of the tubing used for the vertical, it would be a simple matter to add a  F12  style... T bar, part
way up the vertical.   It would resemble a 10 m element.   Rough calculations show a 16 ft
T bar ele would work.  It would only have to be 16-25 ft  above the ground.  It would
resonate aprx at 3.840 mhz.   Then just a small series coil  in series with the vert, at  the base,
to shift the resonance down to 3.504 mhz.   Then the usual helical hair pin coil across the
feedpoint to transform the lower Z  up to 50 ohms...done.  

##  getting it to work on 75 / 80m is the easy part.  Getting it to work on 40M is the trick part.
3-6 uh coil is dick really.  10 or 8 gauge wire is not going to heat up anytime soon, even airdux.
But with inductance that low in value,  airdux is a waste.  A  3-6..or  even  3-8 uh coil can easily be
wound from reasonable gauge wire.   10 or 8 gauge magnet wire could also be used, with turns
almost butted up against each other.  Uh will increase at a rapid rate as spacing between turns is reduced.

##  Both the 10 and also 8 gauge polyimide magnet wire I use has 15 kv insulation...=  30 kv  between
adjacent turns.   You can also get it in 6 gauge. ( Planet wire).  In this application, V breakdown is not critical.
Edge would strap coils will also work.  .375 x .072 thick edeg wound coils are available surplus, and silver plated,
and typ in small diameters, like  2  or 2.5 inch OD.   .375 edge wound strap is the same as .25 OD tubing.  And the
unloaded Q is sky high, through the roof... like > 1000.      .25 x .072 thick edge wound strap is also 
available..and is the same as .21 OD tubing. 

##  How much current is flowing through the coil on 40m ??    If its  10-12 A,  8 gauge wire will run stone cold. 

Jim   VE7RF