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-   -   Measuring RF output impedance (https://www.radiobanter.com/homebrew/22946-measuring-rf-output-impedance.html)

Terry Given May 4th 04 11:01 PM

"Tim Auton" tim.auton@uton.[groupSexWithoutTheY] wrote in message
...
"Highland Ham" wrote:

The model number ain't gonna mean a lot to anyone as this is a very
old piece of kit (1950s) that I keep mainly out of a sense of
reverence for the past. :-) It's an old ex-RAF AVO. I have posted a
picture of the socket to a.b.s.e under this same thread title...
BTW, there's a 5p coin shown for scale, but since that won't mean much
to anyone outside Britain, the outer of the socket is approx. 1" in
diameter (which won't mean much to anyone in europe but it serves them
right for adopting the metric system.:-))

======================
Since Britain is part of Europe you probably mean 'anyone in continental
europe'

Just for your info ,the metric system was introduced /imposed by Napoleon
(eg more than 200 years ago)
For once he did the right thing ;) .


The metric system also the law here in the UK. You can't sell stuff in
pounds and ounces or feet and inches. Miles are the last bastion of
the imperial system (on road signs), with the informal exception of
pints of beer (IIRC technically it's a "large" beer and 576ml). I
don't mind working in metric units, indeed I prefer them, but if
anyone wants to stop me asking for a pint in the pub they'll have a
fight on their hands!

Oh yes, cannabis is still sold by the fraction of an ounce as it ever
was, but I don't think selling cannabis in imperial units is any more
illegal than just selling cannabis :)


same in NZ - pounds and ounces for cannabis. Everybody uses imperial for
height still, and newborn babies are in pounds & ounces...




Tim
--
Love is a travelator.




John Crighton May 5th 04 02:04 AM

On Tue, 04 May 2004 15:25:18 +0100, Paul Burridge
wrote:

BTW, I've just posted you the photo of the Sig gen. Took a bit longer
than I meant to as I've been faffing about with photo software trying
to enhance the image. Taking flash photos of shiny, black objects is
pretty tricky, I've discovered...
--

Hello Paul,
I received the picture, thanks.
Those connectors are still easy to come by.
Here is a picture of a different sig gen but with a similar
style connector to yours.
http://www.thevalvepage.com/testeq/t.../1632/1632.htm
That connector is a Pye connector.

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.

If you are a purist
and you want to keep the original RF output connector then
you can find some at Ham radio trash and treasure field days
or if you are in a hurry, check out some radio service workshops,
like taxi two-way radio repair joints. Most technicians are horders
of old stuff. They might have an old lead with connector.

If you are not a purist
in keeping old gear original but only functional, open the unit
up and see if the old fashioned RF output connector can be
replaced with a BNC connector easily.

You still haven't told me what ohm meter readings you got
when you placed the meter prods from inner to outer on the
RF connector. (sig gen switched off)
Flick the attenuator switches to all positions. You are looking
for fairly consistent readings to check if the attenuator has
been damaged by a transceiver that transmitted accidentally
or the attenuator having being connected to a high DC voltage.

Tell us. Were the readings close to 50, 75 ohms or what?

Here in Sydney the Wireless Institute of Australia, a kind
of head office for hams keeps old manuals and circuits.
There would be an equivalent office for UK hams in London
with a library of old manuals for sure. Some UK hams
on this group will tell you who to contact.

You can still get those RF connectors and if you try hard
you will find a manual for the AVO CT378B.
Do the obvious first, phone or e-mail AVO.

"The Megger office in Dover
Archcliffe Road, Dover, Kent, CT17 9EN, England."
http://www.avointl.com/common/images/DoverMap.gif
The phone number is on this map.

There you are, they are a couple of hours down the road
from you. Nearly next door. Call in with your sig gen and
ask for a photo copy of the circuit, they will probably chuck
all sorts of stuff at you. :-)

Regards,
John Crighton
Sydney


John Crighton May 5th 04 02:04 AM

On Tue, 04 May 2004 15:25:18 +0100, Paul Burridge
wrote:

BTW, I've just posted you the photo of the Sig gen. Took a bit longer
than I meant to as I've been faffing about with photo software trying
to enhance the image. Taking flash photos of shiny, black objects is
pretty tricky, I've discovered...
--

Hello Paul,
I received the picture, thanks.
Those connectors are still easy to come by.
Here is a picture of a different sig gen but with a similar
style connector to yours.
http://www.thevalvepage.com/testeq/t.../1632/1632.htm
That connector is a Pye connector.

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.

If you are a purist
and you want to keep the original RF output connector then
you can find some at Ham radio trash and treasure field days
or if you are in a hurry, check out some radio service workshops,
like taxi two-way radio repair joints. Most technicians are horders
of old stuff. They might have an old lead with connector.

If you are not a purist
in keeping old gear original but only functional, open the unit
up and see if the old fashioned RF output connector can be
replaced with a BNC connector easily.

You still haven't told me what ohm meter readings you got
when you placed the meter prods from inner to outer on the
RF connector. (sig gen switched off)
Flick the attenuator switches to all positions. You are looking
for fairly consistent readings to check if the attenuator has
been damaged by a transceiver that transmitted accidentally
or the attenuator having being connected to a high DC voltage.

Tell us. Were the readings close to 50, 75 ohms or what?

Here in Sydney the Wireless Institute of Australia, a kind
of head office for hams keeps old manuals and circuits.
There would be an equivalent office for UK hams in London
with a library of old manuals for sure. Some UK hams
on this group will tell you who to contact.

You can still get those RF connectors and if you try hard
you will find a manual for the AVO CT378B.
Do the obvious first, phone or e-mail AVO.

"The Megger office in Dover
Archcliffe Road, Dover, Kent, CT17 9EN, England."
http://www.avointl.com/common/images/DoverMap.gif
The phone number is on this map.

There you are, they are a couple of hours down the road
from you. Nearly next door. Call in with your sig gen and
ask for a photo copy of the circuit, they will probably chuck
all sorts of stuff at you. :-)

Regards,
John Crighton
Sydney


Paul Burridge May 5th 04 11:39 AM

On Wed, 05 May 2004 01:04:49 GMT, (John Crighton)
wrote:

On Tue, 04 May 2004 15:25:18 +0100, Paul Burridge
wrote:

BTW, I've just posted you the photo of the Sig gen. Took a bit longer
than I meant to as I've been faffing about with photo software trying
to enhance the image. Taking flash photos of shiny, black objects is
pretty tricky, I've discovered...
--

Hello Paul,
I received the picture, thanks.
Those connectors are still easy to come by.
Here is a picture of a different sig gen but with a similar
style connector to yours.
http://www.thevalvepage.com/testeq/t.../1632/1632.htm
That connector is a Pye connector.


Certainly looks like the one shown, I must say. I'd always thought Pye
connectors, though, had three pins, like the one in the photo I sent
you in the top LH corner. Or maybe that's a Bulgin connector. Blimey.

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.


Okay, John, just out of curiosity I will. I expect them to tell me to
get f*cked, like HP or Tek would, but we'll see what their "extended
aftersales care" is like. "What do you mean I ought to be a new model?
This one's only 50 years old!" :-)

I'll post the results later today, along with answering your other
queries.

p.
--

The BBC: licenced at public expense to spread lies.

Paul Burridge May 5th 04 11:39 AM

On Wed, 05 May 2004 01:04:49 GMT, (John Crighton)
wrote:

On Tue, 04 May 2004 15:25:18 +0100, Paul Burridge
wrote:

BTW, I've just posted you the photo of the Sig gen. Took a bit longer
than I meant to as I've been faffing about with photo software trying
to enhance the image. Taking flash photos of shiny, black objects is
pretty tricky, I've discovered...
--

Hello Paul,
I received the picture, thanks.
Those connectors are still easy to come by.
Here is a picture of a different sig gen but with a similar
style connector to yours.
http://www.thevalvepage.com/testeq/t.../1632/1632.htm
That connector is a Pye connector.


Certainly looks like the one shown, I must say. I'd always thought Pye
connectors, though, had three pins, like the one in the photo I sent
you in the top LH corner. Or maybe that's a Bulgin connector. Blimey.

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.


Okay, John, just out of curiosity I will. I expect them to tell me to
get f*cked, like HP or Tek would, but we'll see what their "extended
aftersales care" is like. "What do you mean I ought to be a new model?
This one's only 50 years old!" :-)

I'll post the results later today, along with answering your other
queries.

p.
--

The BBC: licenced at public expense to spread lies.

John Fields May 5th 04 02:21 PM

On Wed, 05 May 2004 11:39:58 +0100, Paul Burridge
wrote:


Okay, John, just out of curiosity I will. I expect them to tell me to
get f*cked, like HP or Tek would, but we'll see what their "extended
aftersales care" is like.


---
Excuse me???

I recently bought a surplus HP54659B module for my HP54602B DSO and
had trouble getting it to work, so I called Agilent for help and, even
though the scope and the module are no longer supported by Agilent,
they took the call, assigned me a case number and a pleasant
technician, and when she couldn't come up with a solution while we
were on the phone, went away to try to find some information she
needed to work on the problem. All for free. Above and beyond, I'd
say...

In the meantime, I continued to try to solve the problem and found it
was pilot error, so I called them back to let them know and to thank
them for their time. I also found out that even though one of their
instruments may become obsolete or break, they'll still do fee-based
repair and cal.

I hope you fare as well with Marconi.

--
John Fields

John Fields May 5th 04 02:21 PM

On Wed, 05 May 2004 11:39:58 +0100, Paul Burridge
wrote:


Okay, John, just out of curiosity I will. I expect them to tell me to
get f*cked, like HP or Tek would, but we'll see what their "extended
aftersales care" is like.


---
Excuse me???

I recently bought a surplus HP54659B module for my HP54602B DSO and
had trouble getting it to work, so I called Agilent for help and, even
though the scope and the module are no longer supported by Agilent,
they took the call, assigned me a case number and a pleasant
technician, and when she couldn't come up with a solution while we
were on the phone, went away to try to find some information she
needed to work on the problem. All for free. Above and beyond, I'd
say...

In the meantime, I continued to try to solve the problem and found it
was pilot error, so I called them back to let them know and to thank
them for their time. I also found out that even though one of their
instruments may become obsolete or break, they'll still do fee-based
repair and cal.

I hope you fare as well with Marconi.

--
John Fields

Paul Burridge May 5th 04 03:28 PM

On Wed, 05 May 2004 01:04:49 GMT, (John Crighton)
wrote:

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.


Okay, I've just phoned them and drew the anticipated blank, I'm
afraid. It appears all the old info; manuals, spec sheets, data etc.
on all obsolete models got thrown out years ago. They only keep info
on current models, regrettably. Still, at least they didn't try to
sell me a new one.

If you are a purist
and you want to keep the original RF output connector then
you can find some at Ham radio trash and treasure field days
or if you are in a hurry, check out some radio service workshops,
like taxi two-way radio repair joints. Most technicians are horders
of old stuff. They might have an old lead with connector.


I think the obvious thing to do from my PoV is just to leave the front
as is for the sake of originality and just put a BNC socket at the
rear and feed the mains power in via a grommeted hole likewise at the
back. Having a dirty great power lead coming into the front panel
would have looked pretty gross anyway.

If you are not a purist
in keeping old gear original but only functional, open the unit
up and see if the old fashioned RF output connector can be
replaced with a BNC connector easily.


In the 1950s? I'd certainly have thought so!

You still haven't told me what ohm meter readings you got
when you placed the meter prods from inner to outer on the
RF connector. (sig gen switched off)
Flick the attenuator switches to all positions. You are looking
for fairly consistent readings to check if the attenuator has
been damaged by a transceiver that transmitted accidentally
or the attenuator having being connected to a high DC voltage.

Tell us. Were the readings close to 50, 75 ohms or what?


70-100 ohms depending on the positions of the coarse and fine
attenuator knobs, but not nice and smoothly; jumping around a lot (I
guess noisy pots that just want a squirt of contact lube. Does that
sound right to you? I'd have expected a much greater range...

[rest noted and snipped]
--

The BBC: licenced at public expense to spread lies.

Paul Burridge May 5th 04 03:28 PM

On Wed, 05 May 2004 01:04:49 GMT, (John Crighton)
wrote:

Your connector is very similar but just slightly different.
When you contact AVO at Dover, ask them the name
of the RF connector that was used. Telling them it is
similar to a Pye should jog their memories.


Okay, I've just phoned them and drew the anticipated blank, I'm
afraid. It appears all the old info; manuals, spec sheets, data etc.
on all obsolete models got thrown out years ago. They only keep info
on current models, regrettably. Still, at least they didn't try to
sell me a new one.

If you are a purist
and you want to keep the original RF output connector then
you can find some at Ham radio trash and treasure field days
or if you are in a hurry, check out some radio service workshops,
like taxi two-way radio repair joints. Most technicians are horders
of old stuff. They might have an old lead with connector.


I think the obvious thing to do from my PoV is just to leave the front
as is for the sake of originality and just put a BNC socket at the
rear and feed the mains power in via a grommeted hole likewise at the
back. Having a dirty great power lead coming into the front panel
would have looked pretty gross anyway.

If you are not a purist
in keeping old gear original but only functional, open the unit
up and see if the old fashioned RF output connector can be
replaced with a BNC connector easily.


In the 1950s? I'd certainly have thought so!

You still haven't told me what ohm meter readings you got
when you placed the meter prods from inner to outer on the
RF connector. (sig gen switched off)
Flick the attenuator switches to all positions. You are looking
for fairly consistent readings to check if the attenuator has
been damaged by a transceiver that transmitted accidentally
or the attenuator having being connected to a high DC voltage.

Tell us. Were the readings close to 50, 75 ohms or what?


70-100 ohms depending on the positions of the coarse and fine
attenuator knobs, but not nice and smoothly; jumping around a lot (I
guess noisy pots that just want a squirt of contact lube. Does that
sound right to you? I'd have expected a much greater range...

[rest noted and snipped]
--

The BBC: licenced at public expense to spread lies.

Paul Burridge May 5th 04 03:54 PM

On Wed, 05 May 2004 08:21:07 -0500, John Fields
wrote:

On Wed, 05 May 2004 11:39:58 +0100, Paul Burridge
wrote:


Okay, John, just out of curiosity I will. I expect them to tell me to
get f*cked, like HP or Tek would, but we'll see what their "extended
aftersales care" is like.


---
Excuse me???


Sorry. Tek, then. I must have been thinking of M$ - Oh, perhaps not;
they don't even support their current range of 'products' :-(
--

The BBC: licenced at public expense to spread lies.


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