On 1/23/10 01:28 , bpnjensen wrote:
Can the venerable 9:1 matching transformer (for matching a 500-ohm
random wire to a 50-ohm coaxial cable) also be used the inverse way,
that is, to match an incoming 50-ohm coax to a radio whose only
connection is a Hi-Z pair of screw terminals?

Further on, is there any reason why such a matching transformer could
not be installed inside said radio behind the screw terminal strip so
that a permanent SO-239 could be connected and mounted on the radio
chassis?

Thanks,
Bruce Jensen



A transformer impedance ratio is a function of the turns ratio
and the terminating impedances on each side. As long as the
impedances being transformed are the same ratio and the number of
turns on the core are the same ratio, the transformer doesn't care
one way or the other which direction it's used. So, there's no
reason you can't use a 9:1 in an inverse manner. Mounting it
internally, with proper care to minimize coupling to other hardware
within the receiver will work correctly.

The only consideration worth mentioning, is that a random wire
isn't exactly a 500 ohm impedance. Impedance of a random wire
changes with frequency. The 9:1 un-un is used to even those
variations out, more or less, to an impedance that's reasonably
uniform across the spectra in use for the receiver input to accept.

The application you're suggesting isn't going to have those
variations, and the 9:1 ratio is fairly close to the actual
impedance ratios being applied. Most screw terminal inputs are
actually closer to 300 ohm, and may or may not be balanced. And
radios so equipped, which also have a 50 ohm SO-239 are also
impedance matched from the S0-239 to the front end of the receiver
through a transformer, precisely as you describe.

So, with reservations, the answer to your questions a yes,
you can do it. And, no, there's no reason why you can't mount
internally.

The only reservations being that the impedances being
transformed are not precisely in the exact ratio as designed for the
9:1, which may result in irregular losses, and resonances--
comb filtering. Which you may or may not be able to discern in
casual listening.

On Jan 23, 5:06*am, "D. Peter Maus"
wrote:
On 1/23/10 01:28 , bpnjensen wrote:

Can the venerable 9:1 matching transformer (for matching a 500-ohm
random wire to a 50-ohm coaxial cable) also be used the inverse way,
that is, to match an incoming 50-ohm coax to a radio whose only
connection is a Hi-Z pair of screw terminals?

Further on, is there any reason why such a matching transformer could
not be installed inside said radio behind the screw terminal strip so
that a permanent SO-239 could be connected and mounted on the radio
chassis?

Thanks,
Bruce Jensen

* *A transformer impedance ratio is a function of the turns ratio
and the terminating impedances on each side. As long as the
impedances being transformed are the same ratio and the number of
turns on the core are the same ratio, the transformer doesn't care
one way or the other which direction it's used. So, there's no
reason you can't use a 9:1 in an inverse manner. Mounting it
internally, with proper care to minimize coupling to other hardware
within the receiver will work correctly.

* *The only consideration worth mentioning, is that a random wire
isn't exactly a 500 ohm impedance. Impedance of a random wire
changes with frequency. The 9:1 un-un is used to even those
variations out, more or less, to an impedance that's reasonably
uniform across the spectra in use for the receiver input to accept.

* * The application you're suggesting isn't going to have those
variations, and the 9:1 ratio is fairly close to the actual
impedance ratios being applied. Most screw terminal inputs are
actually closer to 300 ohm, and may or may not be balanced. And
radios so equipped, which also have a 50 ohm SO-239 are also
impedance matched from the S0-239 to the front end of the receiver
through a transformer, precisely as you describe.

* * So, with reservations, the answer to your questions a yes,
you can do it. And, no, there's no reason why you can't mount
internally.

* * The only reservations being that the impedances being
transformed are not precisely in the exact ratio as designed for the
9:1, which may result in irregular losses, and resonances--
comb filtering. Which you may or may not be able to discern in
casual listening.

Ah, thanks for this Peter - so, if the screw terminals are closer to
300 ohms, then a 6:1 transformer, with perhaps a 2.3:1 turns ratio,
could be a better choice?

The radio in question, BTW, is a simple DX-160 - it's front end is
pretty wide open anyway, but heck, why not? As long as I don't send a
big static charge through it, I figure I cannot do much damage :-)

BJ

On 1/23/10 12:14 , bpnjensen wrote:
On Jan 23, 5:06 am, "D. Peter
wrote:
On 1/23/10 01:28 , bpnjensen wrote:

Can the venerable 9:1 matching transformer (for matching a 500-ohm
random wire to a 50-ohm coaxial cable) also be used the inverse way,
that is, to match an incoming 50-ohm coax to a radio whose only
connection is a Hi-Z pair of screw terminals?

Further on, is there any reason why such a matching transformer could
not be installed inside said radio behind the screw terminal strip so
that a permanent SO-239 could be connected and mounted on the radio
chassis?

Thanks,
Bruce Jensen

A transformer impedance ratio is a function of the turns ratio
and the terminating impedances on each side. As long as the
impedances being transformed are the same ratio and the number of
turns on the core are the same ratio, the transformer doesn't care
one way or the other which direction it's used. So, there's no
reason you can't use a 9:1 in an inverse manner. Mounting it
internally, with proper care to minimize coupling to other hardware
within the receiver will work correctly.

The only consideration worth mentioning, is that a random wire
isn't exactly a 500 ohm impedance. Impedance of a random wire
changes with frequency. The 9:1 un-un is used to even those
variations out, more or less, to an impedance that's reasonably
uniform across the spectra in use for the receiver input to accept.

The application you're suggesting isn't going to have those
variations, and the 9:1 ratio is fairly close to the actual
impedance ratios being applied. Most screw terminal inputs are
actually closer to 300 ohm, and may or may not be balanced. And
radios so equipped, which also have a 50 ohm SO-239 are also
impedance matched from the S0-239 to the front end of the receiver
through a transformer, precisely as you describe.

So, with reservations, the answer to your questions a yes,
you can do it. And, no, there's no reason why you can't mount
internally.

The only reservations being that the impedances being
transformed are not precisely in the exact ratio as designed for the
9:1, which may result in irregular losses, and resonances--
comb filtering. Which you may or may not be able to discern in
casual listening.

Ah, thanks for this Peter - so, if the screw terminals are closer to
300 ohms, then a 6:1 transformer, with perhaps a 2.3:1 turns ratio,
could be a better choice?


That would be my thinking. Experimentation is the lifeblood of
the hobby, so I'd try it either way see what you get.



The radio in question, BTW, is a simple DX-160 - it's front end is
pretty wide open anyway, but heck, why not? As long as I don't send a
big static charge through it, I figure I cannot do much damage :-)

BJ


DX-160 is a pretty interesting radio to toy with. I've had two,
now, with dramatic inconsistencies in performance. Some, here, have
done extensive numbers of small modifications and gotten a pretty
decent radio out of it, so the raw material is there.

The front end of DX-160 is going to be close, but not really at,
any standard impedance. And it varies significantly from unit to
unit. It's very likely the scenario you first described in your
original post will be more than sufficient. Trial and error will get
you on target, but the practical differences in performance may be
trivial.

bpnjensen wrote:
[...]

The radio in question, BTW, is a simple DX-160 - it's front end is
pretty wide open anyway, but heck, why not? As long as I don't send a
big static charge through it, I figure I cannot do much damage :-)

BJ


I had a DX-150A in the early 1970s, and if I recall correctly, it
had an "antenna trim" control to peak up the input network for
maximum signal. The DX-160 may be the same -- the differences were
minimal, as I remember.

The trim adjustment would help match varying impedances to some
extent, but there could be cases where an input transformer would
help even more -- with a random impedance antenna on a wide range of
frequencies, it's hard to predict without making measurements.

Transformers work both ways, so one could add a switch for 1)
impedance step-up, 2) impedance step-down, and 3) direct connection.
Of course, an antenna coupler is another possible way to approach
the impedance issue.




With all good wishes,



Kevin, WB4AIO.
--
http://kevinalfredstrom.com/

On Jan 23, 2:09*pm, Kevin Alfred Strom
wrote:
bpnjensen wrote:

[...]



The radio in question, BTW, is a simple DX-160 - it's front end is
pretty wide open anyway, but heck, why not? *As long as I don't send a
big static charge through it, I figure I cannot do much damage :-)

BJ

I had a DX-150A in the early 1970s, and if I recall correctly, it
had an "antenna trim" control to peak up the input network for
maximum signal. The DX-160 may be the same -- the differences were
minimal, as I remember.

The trim adjustment would help match varying impedances to some
extent, but there could be cases where an input transformer would
help even more -- with a random impedance antenna on a wide range of
frequencies, it's hard to predict without making measurements.

Transformers work both ways, so one could add a switch for 1)
impedance step-up, 2) impedance step-down, and 3) direct connection.
Of course, an antenna coupler is another possible way to approach
the impedance issue.

With all good wishes,

Kevin, WB4AIO.
--http://kevinalfredstrom.com/

Mssrs. Maus and Strom, thank you! I think I will concoct a device
soon to see what happens with it.

Bruce Jensen

On Jan 23, 11:00*pm, bpnjensen wrote:
On Jan 23, 2:09*pm, Kevin Alfred Strom
wrote:





bpnjensen wrote:

[...]

The radio in question, BTW, is a simple DX-160 - it's front end is
pretty wide open anyway, but heck, why not? *As long as I don't send a
big static charge through it, I figure I cannot do much damage :-)

BJ

I had a DX-150A in the early 1970s, and if I recall correctly, it
had an "antenna trim" control to peak up the input network for
maximum signal. The DX-160 may be the same -- the differences were
minimal, as I remember.

The trim adjustment would help match varying impedances to some
extent, but there could be cases where an input transformer would
help even more -- with a random impedance antenna on a wide range of
frequencies, it's hard to predict without making measurements.

Transformers work both ways, so one could add a switch for 1)
impedance step-up, 2) impedance step-down, and 3) direct connection.
Of course, an antenna coupler is another possible way to approach
the impedance issue.

With all good wishes,

Kevin, WB4AIO.
--http://kevinalfredstrom.com/

Mssrs. Maus and Strom, thank you! *I think I will concoct a device
soon to see what happens with it.

Bruce Jensen

Another question on this subject - what core should be used for this
application?

Amidon, among others, has cores of many materials including 43 and 77,
both of which seem to get use in these applications; however, for RFI
problems below 10 MHz, Amidon recommends cores of J material, and my
RFI problems (while not confined to under 10 MHz) are primarily below
that frequency. Would use of J material be wise here, or for this
matching transformer would I be better using the old standbys 43 or
77, and then making lots of separate chokes from other materials such
as J?

Again, my sincere thanks for the advice...

Bruce Jensen

bpnjensen wrote:
[...]
Another question on this subject - what core should be used for this
application?

Amidon, among others, has cores of many materials including 43 and 77,
both of which seem to get use in these applications; however, for RFI
problems below 10 MHz, Amidon recommends cores of J material, and my
RFI problems (while not confined to under 10 MHz) are primarily below
that frequency. Would use of J material be wise here, or for this
matching transformer would I be better using the old standbys 43 or
77, and then making lots of separate chokes from other materials such
as J?




The latter course seems best to me, since the ideal core
characteristics are likely different for the two purposes.



Again, my sincere thanks for the advice...

Bruce Jensen



You're welcome; have fun with the DX-160.


With all good wishes,




Kevin, WB4AIO.
--
http://kevinalfredstrom.com/

On 1/24/10 11:55 , bpnjensen wrote:

Another question on this subject - what core should be used for this
application?

Amidon, among others, has cores of many materials including 43 and 77,
both of which seem to get use in these applications; however, for RFI
problems below 10 MHz, Amidon recommends cores of J material, and my
RFI problems (while not confined to under 10 MHz) are primarily below
that frequency. Would use of J material be wise here, or for this
matching transformer would I be better using the old standbys 43 or
77, and then making lots of separate chokes from other materials such
as J?


Without specifics on the nature of your RFI, I'd build the
transformer from the recommended materials, 43 or 77, and then build
frequency specific chokes to purpose. That way, if your RFI changes,
as it often can, you're solution is to built another choke, not to
revise your receiver's input.

Kevin makes a good point about the antenna trim control at the
input of DX-160. That covers a multitude of sins. Not unlike my
Nationals, similarly equipped.

That control showed up on DX-120, and was the reason I got
interested in this line in the first place. I couldn't afford one
until DX-150. Bought one of those, and have had two DX-160s since.
Fun radios. Not quite as selective as my S-40 and S-53 Halli's but
good for program listening on the big guys. DX-160 had less hum in
the audio, and came on immediately. After more than a decade of
tubes, by that time, I thought that was bitchin' cool. Just couldn't
justify the money at the time.

DX-160 has pretty lifeless audio. Not much above 6k, and bottom
rolled of below 150hz. You can bring a little life back to that
bottom end, by changing a couple of the capacitors. One in the audio
circuit, and one bringing the audio from the detector to the audio
stage. Which ones at this point, specifically, I don't recall, but I
think one is on a trace on the extreme right of the PCB. It's out
there by itself, easy to replace. The other is further inboard, near
the audio IC. But you can cut-and-try with a .5ufd or a .1 ufd film,
across the any of the likely candidates listening for a change. Can
make quite a difference. Although with the fact AGC, and the
generally poor audio stage, don't expect Little Jewel audio.

You can clean up the woolly audio by replacing all the ceramic
capacitors on the board with films. Better definition and clarity.
Small films will fit right in the ceramic positions, and by
selecting your components carefully, for things like thermal
coefficient, you can mitigate some of the drift. Not all, but some.

And DX-160 will drift.

Further cleaning can be achieved by replacing the electrolytics.
Not only in the power supply, but those dispersed throughout the
board. After all these years, some will have become, or have begun
to become unformed. Some my be distended, indicating impending
failure. Some may even leak. Simple replacement procedure.

Touching up the alignment will also help, and using WWV as a
frequency standard, you can do a creditable job calibrating dial
positions.

Lastly, the dial lights have decent, but not remarkably long
life. You can find drop-in LED replacements at Digi-Key, or
SuperbrightLeds.com. The warm whites look just like incandescents,
and last 100 times longer. You may have to add a small series
resistor to the dial light circuit to limit current to the LED
replacements. That's a small matter, and dramatically improves life
of the lamp without significantly altering lumen output.

Now, if you REALLY want to make this rig over, you can install
Murata filters in the IF's. But that may be a long reach for such a
simple receiver.





p

On Jan 25, 6:27*am, "D. Peter Maus"
wrote:
On 1/24/10 11:55 , bpnjensen wrote:

Another question on this subject - what core should be used for this
application?

Amidon, among others, has cores of many materials including 43 and 77,
both of which seem to get use in these applications; however, for RFI
problems below 10 MHz, Amidon recommends cores of J material, and my
RFI problems (while not confined to under 10 MHz) are primarily below
that frequency. *Would use of J material be wise here, or for this
matching transformer would I be better using the old standbys 43 or
77, and then making lots of separate chokes from other materials such
as J?

* *Without specifics on the nature of your RFI, I'd build the
transformer from the recommended materials, 43 or 77, and then build
frequency specific chokes to purpose. That way, if your RFI changes,
as it often can, you're solution is to built another choke, not to
revise your receiver's input.

* *Kevin makes a good point about the antenna trim control at the
input of DX-160. That covers a multitude of sins. Not unlike my
Nationals, similarly equipped.

* *That control showed up on DX-120, and was the reason I got
interested in this line in the first place. I couldn't afford one
until DX-150. Bought one of those, and have had two DX-160s since.
Fun radios. Not quite as selective as my S-40 and S-53 Halli's but
good for program listening on the big guys. DX-160 had less hum in
the audio, and came on immediately. After more than a decade of
tubes, by that time, I thought that was bitchin' cool. Just couldn't
justify the money at the time.

* *DX-160 has pretty lifeless audio. Not much above 6k, and bottom
rolled of below 150hz. You can bring a little life back to that
bottom end, by changing a couple of the capacitors. One in the audio
circuit, and one bringing the audio from the detector to the audio
stage. Which ones at this point, specifically, I don't recall, but I
think one is on a trace on the extreme right of the PCB. It's out
there by itself, easy to replace. The other is further inboard, near
the audio IC. But you can cut-and-try with a .5ufd or a .1 ufd film,
across the any of the likely candidates listening for a change. Can
make quite a difference. Although with the fact AGC, and the
generally poor audio stage, don't expect Little Jewel audio.

* *You can clean up the woolly audio by replacing all the ceramic
capacitors on the board with films. Better definition and clarity.
Small films will fit right in the ceramic positions, and by
selecting your components carefully, for things like thermal
coefficient, you can mitigate some of the drift. Not all, but some.

* *And DX-160 will drift.

* *Further cleaning can be achieved by replacing the electrolytics.
Not only in the power supply, but those dispersed throughout the
board. After all these years, some will have become, or have begun
to become unformed. Some my be distended, indicating impending
failure. Some may even leak. Simple replacement procedure.

* *Touching up the alignment will also help, and using WWV as a
frequency standard, you can do a creditable job calibrating dial
positions.

* *Lastly, the dial lights have decent, but not remarkably long
life. You can find drop-in LED replacements at Digi-Key, or
SuperbrightLeds.com. The warm whites look just like incandescents,
and last 100 times longer. You may have to add a small series
resistor to the dial light circuit to limit current to the LED
replacements. That's a small matter, and dramatically improves life
of the lamp without significantly altering lumen output.

* *Now, if you REALLY want to make this rig over, you can install
Murata filters in the IF's. But that may be a long reach for such a
simple receiver.

* *p

Thank you once again, Peter and Kevin - great stuff! My 160 does need
freq calibration pretty badly, and possibly (probably?) alignment as
well.

Bruce

In article ,
bpnjensen wrote:

Another question on this subject - what core should be used for this
application?

Amidon, among others, has cores of many materials including 43 and 77,
both of which seem to get use in these applications; however, for RFI
problems below 10 MHz, Amidon recommends cores of J material, and my
RFI problems (while not confined to under 10 MHz) are primarily below
that frequency. Would use of J material be wise here, or for this
matching transformer would I be better using the old standbys 43 or
77, and then making lots of separate chokes from other materials such
as J?

The different core type comes from the fact that Amidon is reselling stuff
from different manufacterers. I've used both 77 and J for transformers.
They're pretty much the same. Whatever was on the pegboard at the
(then existing) local shops. Seems to work best from 3-15 Mhz, if
you want to go for higher frequencies, like CB, try a higher frequency
(lower perm.) core.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)