[TowerTalk] Circuit Board Question

[Matt]

All comment appreciated & thanks!   I tried to put together everyone's good
ideas and just finished etching a prototype board about an hour ago - sure
takes longer for the 3oz material.

The boards are for three sets of homebrew stack matches so there are 50 ohm
traces and 22 ohm traces.  The relays are the TE/Shrack RT1 style so a bit
of a compromise/challenge to get the trace spacings to work out.

Using the on-line calculator that Jim linked me to, I ended up settling on
150 mil wide traces for the 50 ohm circuits and 300 mils for the 22 ohm
circuit based on 11A RMS and 15.5A RMS respectively.  This should keep me at
about 25C max rise.   For isolation I maintained at least 176 mils and 124
mils respectively for the 50 ohm and 22 ohm based on ~800-900V and ~550-600V
PEP.  I will tin the traces and use a conformal coatings as well for extra
insulation per your recommendations.

Rick and Steve's comments about the position w.r.t. standing waves is
certainly applicable since the boxes will be mounted midway between antennas
- but with VF should be able to shoot for 1/2 wave multiples electrically
away from the feed points.

2.25:1 un-un's are W2FMI trifillar style wound on FT240K's with homemade 22
ohm coax.  I used the 4 layers of Scotch 92 wound on 14AWG thermalize recipe
with a tightly wrapped 1/8 outer braid.  

I will test the boxes into a pair of dummy loads before installing them and
see what kind of heating I end up with...

Thanks again!

Matt
KM5VI





-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Steve
Hunt
Sent: Sunday, August 03, 2014 3:33 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Circuit Board Question

On a mismatched line - whatever the load impedance - the voltage and current
maxima are a quarter-wave apart.

Steve G3TXQ



On 03/08/2014 00:07, Richard (Rick) Karlquist wrote:
>
>
> If the load impedance is resistive, whether 50 ohms or not, the 
> voltage and current maxima will occur at the same places.
>
> Rick N6RK
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