RadioBanter - View Single Post - DX-160: Preselector or 9:1 transformer

January 5th 05, 07:24 PM

In article .com,
wrote:
Howard--

Thanks for the info--I'll do some reading up on both the of those
options.

One thing is puzzling me, though: the DX-160 has no coax input--only
"screw-type" terminals. So I'm guessing that some other adapter is
needed in addition to the transformer?

Somebody posted the schematic here in the newsgroup a few months back.
Interestingly simple set. It's got a tuned dual FET cascode RF amplifier.
So a preselector or pre-amp won't benefit it too much. Then a single
conversion to a ceramic IF filter (probably at 455 kHz). So it's
performance is probably similar to a Grundig FR-200 or S350.

It's probably got more sensitivity than is really good for reception if
there are any transmitters nearby. At least it's got an RF Gain control.
Looking closer, part of the RF Gain control is a 2k ohm potentiometer
right across the antenna terminals. Which go to an anti-parallel pair
of diode to act as a protection device. Ugh.

Conclusion, you want to use as little antenna on this as you need to
get the signals you want. Feed too much signal into this and, unless
you turn down the RF Gain, you'll get mixtures of strong signals and
images all over the dial.

The antenna terminals are set up so that it can use either an unbalanced
(coax) or balanced antenna. For an unbalanced antenna (a directly
connneted random wire, or coax), you hook the antenna connection to A1
(and the coax ground, to the ground terminal) and leave the jumper
between A2 and ground).

For a balanced antenna, remove the jumper and hook the two antenna lines
to A1 and A2. One such antenna is a folded dipole made of TV flatlead.
But you'd need a lot of room and it would probably only get the best
performance on one frequency band.

One antenna to try would be a small loop. Just a rectangle or circle
of wire, 3-5 feet on a side, perhaps taped to a window, and the leadin
formed by a twisted pair of the same wire, and hooked up as a balanced
antenna to terminals A1 and A2.

Damn, and I wrote this before I'd even read RHF's posting. I should
always remember to read the entire thread before replying.

Mark Zenier Washington State resident