[ARC5] [Milsurplus] SCR-183/-283 4-5 MC Coil on 75 MTRs

[Mike Feher]

Mike -

The "doorknobs" are ceramic. 73 - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
David Stinson
Sent: Sunday, June 29, 2014 11:16 AM
To: ARC-5; milsurplus at mailman.qth.net
Subject: [Milsurplus] SCR-183/-283 4-5 MC Coil on 75 MTRs

4-5 MC coil sets for SCR-183/283 transmitters
(BC-230/-430) are very common, while those that cover 80/75 Mtrs directly
can be hard to find.
The OSC section of the 4-5 MC coil set will operate down to around 3750 KC,
but the PA/Antenna coil is pretty much done at 4 MC.
http://home.netcom.com/~arc5/SCR-183/coilplate.JPG

You can get the 4-5 MC coil operational down into
75 meters with a few simple, non-destructive changes.
Move the Antenna coil tap up to the second turn from the top.  Pad the coil
from the tap down to the bottom using either a 50-100 pFd transmitting
doorknob (Thank you, Mike!)  or big, RF-rated silver mica.  
Don't use a ceramic; too lossy.
http://home.netcom.com/~arc5/SCR-183/coilpad.JPG
(yes, yes I know it's sloppy.  I was prototyping, guys!)

Assuming you use a 100 pFd RF-rated or air variable cap in series with the
output to feed a 50-ohm load, you'll find the tap for best output around
here:
http://home.netcom.com/~arc5/SCR-183/coiltap.jpg

You will get about 10-20% less power out than you would with the "correct"
3-4 MC coil, but then most of us don't have that one ;-) A working rig in
exchange for 10% is a good deal.

73 DE Dave AB5S

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