DX-160: Preselector or 9:1 transformer
 

Hi--

I have a Realistic DX-160 in very nice conditiion I bought about 10
years ago (for $15!). My current living situation in Los Angeles no
longer affords me the luxury of an outdoor antenna, so I am using 40
ft. of 16 gauge copper speaker wire running along the ceiling moulding
as my antenna.

(ALSO: the DX-160 is in the same room with a lot of other electronic
equipment: computer, TV, stereo, audio recording equipment, mixer,
etc.)

I've read a lot in this newsgroup about modifying the DX-160, but as my
radio engineering skills are in their infancy, I've decided on
improving my antenna situation. It seems preselectors or the 9:1
matching transformer have favorable reviews here but I'd lke to know:

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?

Thanks in advance for any input!

SWS

wrote in message
ups.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?

------------------------------------------------------------------------------

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

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?

------------------------------------------------------------------------------

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

Try this.
http://www.grove-ent.com/WR0130.html

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?

Thanks in advance for any input!

SWS

QUADRA,
..
Consider an "Around-the-Room" (Ceiling) Loop Antenna,
or an "On-the-Wall" Loop Antenna as an INDOOR Antenna
to use with your RadioShack "Realistic" DX-160 Receiver.
..
The Loops will generally be about Forty Feet plus
for an Around-the-Room (Ceiling) Loop Antenna, or
Thirth-Six Feet plus an On-the-Wall Loop Antenna.
..
1. Use Hook-Up Wire for the Antenna Wire Element.
RadioShack Catalog # 278-1225
Sixty Feet of Stranded #20 AWG Insulated Wire
..
2. Use a 'piece' of 300 Ohm TV Twin Lead as the
Feed-in-Line from the Loop Antenna to the Terminals
on the back of the DX-160.
RadioShack Catalog # 15-1174
Two 20 AWG Stranded Copper Conductors
Insulation consists of Inner Low-Loss Foam Insulation
and Outer Covering of Heavy-Duty Polyethylene
..
IMHO - Using the RadioShack DX-160 with a small size
(short length) "In-the-House" Loop Antenna; that using a
Matching Transformer and Pre-Selector are not required.
..
READ - Indoor Antenna & Lead-In = Hook-Up Wire / TV Twin Lead
http://groups.yahoo.com/group/Shortw...nna/message/75
..
READ - Try "In-Door" {Inside-the-House} Antennas First before . . .
http://groups.yahoo.com/group/Shortw...a/message/1036
..
READ - Looking for a "Silent Antenna"
Consider a {Shielded} Loop Antenna
http://groups.yahoo.com/group/Shortw...a/message/1008
..
READ - A 'look' at three MFL Antenna Turners / Pre-Selectors
http://groups.yahoo.com/group/Shortw...na/message/980
..
READ - Two InDoor "Hidden" SWL Antenna Ideas
http://groups.yahoo.com/group/Shortw...na/message/209
..
READ - The Carpet Loop Antenna
[ Sizing the Loop and Choosing the Cable ]
http://groups.yahoo.com/group/Shortw...na/message/292
..
..
iane ~ RHF
..
All are WELCOME at the Shortwave Listener (SWL) "Antenna Ashram"
http://groups.yahoo.com/group/Shortw...na/message/502
Some Say: On A Clear Day You Can See Forever.
I BELIEVE: On A Clear Night . . .
You Can Hear Forever and Beyond, The BEYOND !
[ With the an AM/MW - FM - SWL Antenna of your own making. ]
..
..

QUADRA,
..
READ - The RadioShack Realistic DX-160 Receivers
- - - - - USERS - ANTENNA - SURVEY - - - -
..
SOURCE - Newsgroups : Rec.Radio.Shortwave
From: *t (David Neece)
Date: 1998/05/20
Subject: RadioShack Realistic DX-160 Users: Antenna Survey
..
RadioShack Realistic DX-160 = http://tinyurl.com/4qzlc
http://groups-beta.google.com/group/...75e180bc56f5a4

..
..
RadioShack Realistic DX-160 and Eavesdropper Antenna Installation
SOURCE = Newsgroups: Rec.Radio.Shortwave
From: Charlie Meyer *t
Date: 1997/12/31
Subject: Advice: Realistic DX-160 and Eavesdropper Antenna Installation
http://groups-beta.google.com/group/...09bd848888d809

..
RadioShack Realistic DX-160 - Home Made Antenna Questions
SOURCE = Newsgroups: Rec.Radio.Shortwave
From: *m (Christopher A. King)
Date: 1999/09/10
Subject: Home Made Antenna Questions
http://groups-beta.google.com/group/...11f88ff0220628

..
..
iane ~ RHF
..
All are WELCOME at the Shortwave Listener (SWL) "Antenna Ashram"
http://groups.yahoo.com/group/Shortw...na/message/502
Some Say: On A Clear Day You Can See Forever.
I BELIEVE: On A Clear Night . . .
You Can Hear Forever and Beyond, The BEYOND !
[ With the an AM/MW - FM - SWL Antenna of your own making. ]
..
..

" wrote:

Hi--

I have a Realistic DX-160 in very nice conditiion I bought about 10
years ago (for $15!). My current living situation in Los Angeles no
longer affords me the luxury of an outdoor antenna, so I am using 40
ft. of 16 gauge copper speaker wire running along the ceiling moulding
as my antenna.

(ALSO: the DX-160 is in the same room with a lot of other electronic
equipment: computer, TV, stereo, audio recording equipment, mixer,
etc.)

I've read a lot in this newsgroup about modifying the DX-160, but as my
radio engineering skills are in their infancy, I've decided on
improving my antenna situation. It seems preselectors or the 9:1
matching transformer have favorable reviews here but I'd lke to know:

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?

Thanks in advance for any input!

SWS

If it were me, I'd sell the DX-160 and use the money I got for it, along with the money I was planning to spend on a preselector or mlb to buy a better radio.

I suspect a $75 Kaito or Degen 1103 would be easier to tune, more stable, and at least as sensitive as your DX-160.

For about $150 you could get a Sony 7600GR - it's one of the better portables, and has a good sync detector.

If you're willing to spend a little more, you'll have other options.

The thing is even if you added $1,000 of accessories to your DX-160, the heart of your system is still going to be a "nothing special" radio.

Making your own MLB really is easy, but with a 300 ohm antenna input, you'd want something in the range of 1.5:1 for a random wire.

I normally prefer MLB's to preselectors because I'd just as soon have fewer things to tweak, but on the DX-160, a preselector might do more for you than a MLB.

But a decent modern portable with a simple loop around the ceiling will probably give you the most bang for the buck.

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

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

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 Wed, 05 Jan 2005 12:23:44 GMT, "Merwin Dooley"
wrote:

Try this.
http://www.grove-ent.com/WR0130.html
I lokked at that and am amazed that a balun can give 5dB gain! What I
would expect is that it could help in reducing the noise floor and
thus sound like you have gain; or provide a better impedence match (at
some frequency(ies) to allow more signal to pass - perhaps. But gain,
nope - I just don't see it unless I have totally missed out on some
part of my radio education.
Howard



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?

Thanks in advance for any input!

SWS

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

Howard wrote:

On Wed, 05 Jan 2005 12:23:44 GMT, "Merwin Dooley"
wrote:

Try this.
http://www.grove-ent.com/WR0130.html
I lokked at that and am amazed that a balun can give 5dB gain! What I
would expect is that it could help in reducing the noise floor and
thus sound like you have gain; or provide a better impedence match (at
some frequency(ies) to allow more signal to pass - perhaps. But gain,
nope - I just don't see it unless I have totally missed out on some
part of my radio education.
Howard

You've missed a lot...

It ain't rocket science...

Damn.

dxAce
Michigan
USA




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?

Thanks in advance for any input!

SWS

On Wed, 05 Jan 2005 23:31:40 -0500, dxAce wrote:



Howard wrote:

On Wed, 05 Jan 2005 12:23:44 GMT, "Merwin Dooley"
wrote:

Try this.
http://www.grove-ent.com/WR0130.html
I lokked at that and am amazed that a balun can give 5dB gain! What I
would expect is that it could help in reducing the noise floor and
thus sound like you have gain; or provide a better impedence match (at
some frequency(ies) to allow more signal to pass - perhaps. But gain,
nope - I just don't see it unless I have totally missed out on some
part of my radio education.
Howard

You've missed a lot...

It ain't rocket science...

Damn.

dxAce
Michigan
USA


Huh? If I'm mistaken, which could be, at least give me a hint why I'm
wrong and I will follow up on it. I know this isn't rocket science
as I work with rocket scientists and many know little about radio.
Until shown otherwise I stand by my statement that the balun will not
add gain to the antenna - though it has other characteristics that
will improve the received signal.

Have a good one DX,
Howard
ps - I don't use a portable as my primary receiver 8-}

Howard wrote:

Huh? If I'm mistaken, which could be, at least give me a hint why I'm
wrong and I will follow up on it.

Oh, ignore our professional idiot.

You did miss something, however. The impedence mismatch makes the
energy transfer from the antenna to the receiver to be inefficient. 5
dB is just about right for any 9:1 matching transformer (from an
end-fed wire to a 50 ohm load).

I'm not going to attempt to explain the theory behind it since I will
certainly leave something out and the peanut gallery will come to life
again, but think about SWR and reflected power and how bad the
mismatch can be without the transformer vs. how bad it would be with
the transformer.

For a practiacal demonstration try (BRIEFLY) to feed a speaker from a
tube amp without using a matching transformer. (You'll want a
blocking capacitor, though.)

I know this isn't rocket science
as I work with rocket scientists and many know little about radio.

:-)

Until shown otherwise I stand by my statement that the balun will not
add gain to the antenna - though it has other characteristics that
will improve the received signal.

No, no *gain* added to the antenna, but better power transfer to the
radio from the antenna. 5 dB is what I've measured as well. I use
ICE prepackaged transformers and Mini-Circuits transformers.


Have a good one DX,
Howard
ps - I don't use a portable as my primary receiver 8-}

--
Eric F. Richards

"Nature abhors a vacuum tube." -- Myron Glass,
often attributed to J. R. Pierce, Bell Labs, c. 1940

"Eric F. Richards" wrote:

Howard wrote:

Huh? If I'm mistaken, which could be, at least give me a hint why I'm
wrong and I will follow up on it.

Oh, ignore our professional idiot.

You did miss something, however. The impedence mismatch makes the
energy transfer from the antenna to the receiver to be inefficient. 5
dB is just about right for any 9:1 matching transformer (from an
end-fed wire to a 50 ohm load).

I'm not going to attempt to explain the theory behind it since I will
certainly leave something out and the peanut gallery will come to life
again, but think about SWR and reflected power and how bad the
mismatch can be without the transformer vs. how bad it would be with
the transformer.

For a practiacal demonstration try (BRIEFLY) to feed a speaker from a
tube amp without using a matching transformer. (You'll want a
blocking capacitor, though.)

I know this isn't rocket science
as I work with rocket scientists and many know little about radio.

:-)

Until shown otherwise I stand by my statement that the balun will not
add gain to the antenna - though it has other characteristics that
will improve the received signal.

No, no *gain* added to the antenna, but better power transfer to the
radio from the antenna. 5 dB is what I've measured as well. I use
ICE prepackaged transformers and Mini-Circuits transformers.

OK, so it adds 'system' gain.

Call it what you want!

dxAce
Michigan
USA

"Eric F. Richards" wrote:

Howard wrote:

Huh? If I'm mistaken, which could be, at least give me a hint why I'm
wrong and I will follow up on it.

Oh, ignore our professional idiot.

If I'm a 'professional idiot' then I'm a damn good one!

LOL

dxAce
Michigan
USA

wrote:

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?


Some food for thought...

http://web.telia.com/~u85920178/


Which has this in it. It's hard to find, but it's there.

http://web.telia.com/~u85920178/antennas/balun0.htm

mike

MII - Thank You Very Much for this Link / URL ~ RHF
..
..
WHAT -?- "RF BALUNs" - by Harry Lythall [SM0VPO]
..
BALUN = http://web.telia.com/~u85920178/antennas/balun0.htm
..
WHY -?- Should "I" Read this WebPage / Check-Out this Link URL ?
..
READ = http://web.telia.com/~u85920178/antennas/balun0.htm
..
Elemination of Radiation from the Feeder Cable
..
Makes the Antenna Radiation Pattern Predictable.
..
Dramatically Reduces QRM, TVI to neighbours.
..
Helps to Keep RF Out of the Shack.
..
CHECK-OUT = http://web.telia.com/~u85920178/antennas/balun0.htm
..
..

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

RHF wrote:

MII - Thank You Very Much for this Link


.....blush...






mike