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

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

The improvement would be minimal.

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 Jan 23, 4:59*am, dave wrote:
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

The improvement would be minimal.

Well, that might be true - but if the noise could be reduced at all,
it would be worth it. I live in a VERY noisy place.

Bruce Jensen

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/