[AMRadio] BC-610 on 160


Donald Chester k4kyv at charter.net
Tue Nov 5 14:53:12 EST 2013


From: Rob Atkinson <ranchorobbo at gmail.com>


One of the articles in ER on the BC610 that appeared over the years said
that the 610 on 160, has a poorly suppressed second harmonic if you run the
rig directly into a feedline to an antenna.  According to the article (sorry
I usually only remember what something said; not author and issue dates)
it's important to run the rig into some kind
of low pass network before the feedline on 160

That's probably true for any link-coupled rig, not particularly the BC-610.
My first novice rig, 30 watts to a single 807 had a coupling link directly
to 75-ohm twin lead to an 80m dipole. When I first got on the air  with it I
got a pink slip or OO  report for 2nd harmonic right away. I ended up
building a low-pass filter and putting it in the line. The problem is that
with an untuned link directly to a flat feed line, the coupling has to be
very tight to get sufficient loading, and that doesn't have a lot of
harmonic suppression. If the link is resonated with a capacitor you get
better harmonic suppression. Better still, use an antenna tuner. I have
never received a harmonic report using a link coupled tuner to resonant
feeders. 

I don't  think the 610 would be any worse than any other rig of its type.
There is  sufficient capacitance in the tank circuit to make for acceptable
Q in the tuned circuit. Whoever wrote the ER article probably just connected
coax directly to the PA output link and fed a half wave dipole or
quarter-wave Marconi with it, with no other tuned circuitry between the
transmitter and antenna. Resonating the link with a variable  capacitor
allows for looser coupling as well as providing additional selectivity to
further reduce the 2nd harmonic.

If the link coupled final is push-pull, not single ended like the one in the
610, the 2nd and other even harmonics are inherently suppressed (or in the
real  world,  greatly reduced).

Don k4kyv



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