[R-390] Re: UnBal for R-390A

[Tim Shoppa]

Jim W6JVE writes:

> Is it not true that the unbalanced antenna connector is intended for
> use with a fairly short whip antenna, and hence may not work well with
> a longer wire?

> I wonder if you are feeding the receiver from an antenna multicoupler
> if one or the other connector is more appropriate.

I use a number of antenna configurations, including:

130 foot doublet fed with ladder line running straight into the 390A's balanced line connector

130 foot doublet fed with ladder line going to an antenna tuner to 50ohm coax, then going into the 390A in the usual way with one side grounded.

Some loops in the attic, some tuned, others untuned, fed into the balanced connector.

Other antennas without balanced line feeds fed into the balanced connector.

Far and away the best and simplest situation is the doublet fed to the balanced line connector without the tuner.

I would've thought that the antenna trimmer would have to be adjusted depending on how I match (or don't match!) the antenna to the radio, but it doesn't. It peaks in the same place no matter what. Yet I know the antenna presents a wildly varying impedance from 80M to 40M to 20M etc. So maybe the calibration is not so uniquely dependent on antenna impedance like I would've thought.

The worst situation for me is a vertical, because it picks up circa 25V to 30V of RF relative to ground from a local BCB (630 kc)  station. The doublet or the attic loops, kept balanced all the way, is picking up only a fraction of that.

Heck, a scope probe in my basement, if I touch it with my finger, picks up several volts of RF at 630 kc :-).

The lesson for me even if nobody else wants to hear it, is that a doublet fed with balanced line works great!

Tim.