On Wed, 05 Jan 2005 03:25:13 GMT, "Jeff"
wrote:


wrote in message
oups.com...
Hi--

I have a Realistic DX-160 in very nice conditiion I bought about 10


1) The DX-160 has an Antenna trim knob, so is a preselctor redundant?
2) The 9:1 matching impedance transformer is intriguing, but can they
be found/purchased already built?

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The trim knob is just a variable capacitor, which is somewhat what
the preselector is. The preselectors also use inductors in combo with the
variable cap. for the various bands. Personally Id use an MLB (matching
xformer) This will keep the input impedance to the radio fairly constant
around 50-70 ohms from your antenna. The better the impedance match
the more current will flow from the antenna to the radio. They have ready
made ones, I have a Watkins MLB that I dont use anymore if you are
interested.


Jeff

I agree with Jeff and suggest that if you don't want to homebrew your
matching transformer that you look at the ICE 180A. You can view this
at:
http://www.arraysolutions.com/Produc...age%20Matching

There are other out there, however I've found this one::
1) seems to have more positive user reviews than other models
2) has worked quite well for me making me a satisfied customer
3) versatile as it will match 6:1, 9:1, 12:1 and 16:1 so you can
experiment with which value works best for you.

Another option is the PAR end-fed antenna which comes with a 9:1
matching transformer that can be configured in one of two ways in
respect to primary and secondary ground. It comes with 45 feet of
flex-weave wire which is very flexible and easy to work with. You
can check out this antenna at:
http://www.universal-radio.com/catalog/sw_ant/2205.html

Quadra - I too live in LA and empathize with you regarding not being
able to put up an outdoor antenna. Another thing you might do is
install the antenna in a different room than your electronic gear and
use coax from the antenna to the radio. It probably won't remove all
your household noise but should give you some reduction. If you feel
you need further assistance drop me an e-mail and I'll try to give
more assistance.

Enjoy the radio,
Howard

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?

Thanks for the help...!

SWS

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?

Thanks for the help...!

SWS

I don't think the DX-160 is a 50-ohm input so the 9:1 transformer might
not give you the same advantage as it would on a set that does have 50 ohms.
I'd vote for a good preselector. It will improve the overload and image
characteristics of the set.

Good luck,
Bill

Correct, the DX-160 does not have an SO-239 (50-ohm) connector; it is a
high-z (500-600 ohm) connection already, and thus accepts a random wire
automatically "matched." If you had an antenna that terminated in
coax, you'd have to use a 9:1 matching tranformer "in reverse" to match
the impedance.

However, a 1:1 balun using ladder line or something similar might be
just the ticket...but the preselector idea sounds good too.
Bruce Jensen

On 4 Jan 2005 20:58:31 -0800, "
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?

Thanks for the help...!

SWS
SWS,
It's been about 30 years since I owned my DX-150A and I had forgotten
about the antenna connection scheme. Will rethink this while I read
the other responses.

Howard

On the DX-160 there is an RF amplifier after the antenna input. Its a small
field effect transistor and is easy to overload with pre-amplified input.

If I remember correctly the antenna connection is also complicated by a
switch which selects a ferrite rod for medium wave.

Later

Mark Hittinger

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

Mark Zenier wrote:

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.

Why do you think the first RF circuit in the DX-160 precludes using a
passive preselector?

In article , starman wrote:
Mark Zenier wrote:

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.

Why do you think the first RF circuit in the DX-160 precludes using a
passive preselector?

Because there are two tuned circuits, each using a segment of the
main capacitor gang, (the input transformer, and the output of the
amplifier). Both are feeding the gates of FET amplifiers, so are (or
have the possiblity of being) high impedance and therefore high Q.

The fact that there's an "antenna trim" control, (which really usually
compensates for mistracking of the two tuned circuits) indicates that
they're pretty sharp, at least for an LC tuned circuit. Likewise, the
bandspread capacitor is two sections, one in parallel with the main
oscillator tuning, the other in parallel with the RF amp output tuning
cap. So the Q must make the bandwidth narrower than the 1/2 MHz or so
that, (as I remember), the bandspread covers.

Mark Zenier Washington State resident