[AMRadio] Loading antenna with BC 610 E (Long-ish)

James M. Walker chejmw at acsu.buffalo.edu
Thu Jan 17 21:13:48 EST 2008

----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <amradio at mailman.qth.net>
Sent: Thursday, January 17, 2008 11:32 AM
Subject: [AMRadio] Loading antenna with BC 610 E

>I am thrilled to report that I have my R&Rd BC 610 E
> putting out lots of RF (about 370 watts) into a 50 ohm
> Cantenna dummy load.
Good show, but be advised, BC-610s are NOT regular transmitters!
First off, the relay you are speaking of is NOT an antenna switching relay,
it is a grounding relay for the output section of the plate coil, when the
transmitter is in standby. when the transmitter is placed in transmit the
relay un-shorts the link of the coil, which should already be connected to
the dual insulators for open wire, and the SO-239 connector if you are
using coax.

> I am experiencing some slight "spitting" and arcing at
> built in antenna relay. I speculate that that spitting
> is due to inadequate loading or RF transfer from the
> final tank coil to the dummy load. I am feeding the
> dummy load directly through coax connected to the two
> feed through insulators on the output.

The "E" model had a MWO, that applied the SO-239 connector to the
same plate that the two feed-thru insulators are mounted on. Check the
schematic for proper connections, as the relay contacts should NOT have
RF on them unless activated, Ie; in transmit mode, relay closes, and the
short across the output link is removed.

> I would appreciate recommendations regarding a
> "loading" device to help transfer RF from the tank
> coil to the antenna. Will installing a C2 from output
> to ground tune the reactance out of the feed line and
> facilitate loading the dummy load better or loading
> the Coax feedline to the antenna??

In the manual, for all models, it says, with a load, either antenna, or 
load connected to the proper terminals, (NOTE: when using coax ensure
the shield goes to the chassis ground in/on the RF deck.

As for loading into 50 ohms, first I must say the cantenna is fine for 
out smaller output radios, but again be advised the resistance of the dummy
load changes as the temperature in the can goes up, they used to have on
the side of the can a chart that could be related to the temperature, and 
the actual resistance. for a true test, and this depends on what liquid you 
using in the can, check the resistance of the load cold, then transmit into 
for about 3 minutes, remove power and check the resistance again, with an
accurate meter across the connector of the load, that will tell you what you 
dealing with. For a reasonablely reliable load might I suggest the ME-165,
which once calibrated holds true to accuracy if the instructions for it are
followed. Also it is rated for 600W continuous for a period in the manual.

If you want an antenna "Switch" might I suggest the E.F. Johnson TR-Switch?
I use them here and have experienced no problems with their operation, 
when I forget to turn down the audio from whatever receiver I am listening 
Feedback, is my punishment for forgetting, not into the receiver, out of the
speaker from the receiver. Also as most of the "BA" type receivers have 
ranging from 50 - 300 ohms, you can taylor the receiver connection on the
unit to provide a better match to your receiver.

As for power output, Both of the units I run (E & I) models will provide
400 watts of carrier output into a dummy load. This requires some terms
however, first the unit MUST be running properly, next the tubes should be
of good quality, starting with the Oscillator and going to the PA output.

One last word set it up JUST LIKE the manual says it will run forever,
allowing for the vagarieties of older equipment. Also the output link is
optimized for 50 ohms, you increase or decrease the loading to the
output device by adjusting the coupling to the plate coil. If you can NOT
get proper loading then either the load is not 50 ohms or the tube is 
able or dare I say it, you are doing it wrong.

As with all things radio, YMMV, enjoy the rig, I love mine!

> I would appreciate the benefit of your "actual
> experience or knowledge" to assist me in interfacing
> this BC 610 E to a feedline. Thanks and 73, John, K5PGW

"Real Radios weigh 400+ pounds, have handles, and that makes them

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