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Old January 5th 05, 08:24 PM
Mark Zenier
 
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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

  #12   Report Post  
Old January 6th 05, 04:25 AM
Howard
 
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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
  #13   Report Post  
Old January 6th 05, 04:28 AM
Howard
 
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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



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Old January 6th 05, 05:12 AM
Mark Hittinger
 
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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

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Old January 6th 05, 05:31 AM
dxAce
 
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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





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Old January 6th 05, 06:17 AM
Howard
 
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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-}
  #17   Report Post  
Old January 6th 05, 06:54 AM
Eric F. Richards
 
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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
  #18   Report Post  
Old January 6th 05, 12:07 PM
dxAce
 
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"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


  #19   Report Post  
Old January 6th 05, 12:09 PM
dxAce
 
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"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


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