On Sun, 02 May 2004 09:04:33 -0500, John Fields
wrote:

On Sun, 02 May 2004 14:09:44 +0100, Paul Burridge
wrote:

On Sat, 1 May 2004 15:30:18 -0400, "Ralph Mowery"
wrote:

The generators are more of a voltage source. They will deliver their rated
output when loaded to the proper impedance. Load it with 50 ohms and see if
it gives the rated output. If not try 70 ohms, or another value. One of
the reasons for using a 6 db pad is that it helps isolate the impedance of
the generator and receiver.

My main sig gen states "output EMF using 6dB pad" next to the socket.
WTF is a "6dB pad"?

---
A 6dB attenuator.

---
Also, less commonly, a device used to match the impedance of a
generator to the impedance of a transmission line or a load, or the
impedance of a transmission line to the impedance of a load.

The impedance of the generator, line, and/or load are assumed to be
purely resistive, and there is always loss associated with the
transformation. Devices which exhibit the least loss are called
"minimum loss pads", and

http://www.maxim-ic.com/appnotes.cfm/appnote_number/972

gives a good description of the process involved in designing one.

The reference given to Bruno Weinschel and the ITT handbook (as we
old-timers call it) is particularly good, and if you're interested in
RF (or just about anything else...) and you can buy a copy of it you
should.

BTW, since a pad is usually rated in terms of the power it's supposed
to lose between its input and its output, the reference to "output
EMF" on your generator may be what it supposed to be with a 3dB pad on
its output.

Easy way to find out would be to build a 3dB and a 6dB pad to find
out. For a 50 ohm tee pad, here are the resistor values you'll need
for -3dB:

0dBIN--[8.55]-+-[8.55]---3dBOUT
|
[141.93]
|
GND-----------+-----------GND


and for -6dB:

0dBIN--[16.61]-+-[16.61]---3dBOUT
|
[66.93]
|
GND------------+-----------GND

The input goes directly to your generator, (assuming its output
impedance is 50+j0 ohms) a 50 ohm resistor gets connected across the
output of the pad, and you'll measure the voltage across the 50 ohm
resistor.

Use non-inductive resistors (carbon comp if you can get them) and keep
the leads short. That is, ********KEEP THE LEADS SHORT*********.

--
John Fields

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 .

Frank GM0CSZ / KN6WH

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 .

Frank GM0CSZ / KN6WH

Paul Burridge wrote in message
...
Hi,

I have a spare RF signal generator that has an unmarked output from a
type of socket I've never seen before. What's the simplest way of
establishing its output impedance? I've had a few ideas but no doubt
someone out there will know of something better, since I always seem
to end up making unnecessary work for myself.
Any suggestions?

p.
--

The BBC: licenced at public expense to spread lies.

Those ex-military AVO's were really nice g.p. signal generators though could
never afford one. Seem to remember they were 50ohms out. The o/p socket and
plug were standard 50's military chic and still available.
regards
john

Paul Burridge wrote in message
...
Hi,

I have a spare RF signal generator that has an unmarked output from a
type of socket I've never seen before. What's the simplest way of
establishing its output impedance? I've had a few ideas but no doubt
someone out there will know of something better, since I always seem
to end up making unnecessary work for myself.
Any suggestions?

p.
--

The BBC: licenced at public expense to spread lies.

Those ex-military AVO's were really nice g.p. signal generators though could
never afford one. Seem to remember they were 50ohms out. The o/p socket and
plug were standard 50's military chic and still available.
regards
john

On Sun, 02 May 2004 14:08:38 +0100, Paul Burridge
wrote:

On Sun, 02 May 2004 02:43:18 GMT, (John Crighton)
wrote:


Hello Paul,
what is the brand name and model number of your RF signal generator.
Can you descibe the socket to us.

Thanks John (and others).

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.:-))

--

The BBC: licenced at public expense to spread lies.

Go on, tell us the model number, there are a lot of us
still interested in boat anchor style test equipment.

Is this unit similar to your sig gen
http://www.thevalvepage.com/testeq/avo/sg3/sg3.htm
http://www.thevalvepage.com/testeq/testeq.htm
Unfotunately the connector has been removed and a
BNC type fitted.

I am guessing that you want to keep the original connector
on the sig gen and find a matching connector to make a
short test lead. Old Style connector to BNC.
My news group service doesn't allow me to see the group
a.b.s.e Pity. So I can not see the picture you posted.

So, what are the results of connecting your ohm meter
to the RF out put connector (with the unit switched off)
and measuring the resistance on all attenuator positions.

On one of the lower frequency ranges when you connect
up your cro via a "T" piece to the sig gen with say a 75
ohm load. Does the output level jump up to double
when the load is removed?

Repeat the experiment with a 50 ohm load. If the voltage
doubles from loaded to no load, you will be laughing.
But I don't think you will be that lucky.

I am guessing it will be closer to 75 ohm output impedance.

Try different value loads and let us know how you got on.

Cheerio,
John Crighton
Sydney

On Sun, 02 May 2004 14:08:38 +0100, Paul Burridge
wrote:

On Sun, 02 May 2004 02:43:18 GMT, (John Crighton)
wrote:


Hello Paul,
what is the brand name and model number of your RF signal generator.
Can you descibe the socket to us.

Thanks John (and others).

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.:-))

--

The BBC: licenced at public expense to spread lies.

Go on, tell us the model number, there are a lot of us
still interested in boat anchor style test equipment.

Is this unit similar to your sig gen
http://www.thevalvepage.com/testeq/avo/sg3/sg3.htm
http://www.thevalvepage.com/testeq/testeq.htm
Unfotunately the connector has been removed and a
BNC type fitted.

I am guessing that you want to keep the original connector
on the sig gen and find a matching connector to make a
short test lead. Old Style connector to BNC.
My news group service doesn't allow me to see the group
a.b.s.e Pity. So I can not see the picture you posted.

So, what are the results of connecting your ohm meter
to the RF out put connector (with the unit switched off)
and measuring the resistance on all attenuator positions.

On one of the lower frequency ranges when you connect
up your cro via a "T" piece to the sig gen with say a 75
ohm load. Does the output level jump up to double
when the load is removed?

Repeat the experiment with a 50 ohm load. If the voltage
doubles from loaded to no load, you will be laughing.
But I don't think you will be that lucky.

I am guessing it will be closer to 75 ohm output impedance.

Try different value loads and let us know how you got on.

Cheerio,
John Crighton
Sydney

On Sun, 02 May 2004 11:35:08 -0500, John Fields wrote:

On Sun, 02 May 2004 09:04:33 -0500, John Fields
wrote:

snip John helping Paul with terminology

http://www.maxim-ic.com/appnotes.cfm/appnote_number/972

Once in a while, I can post a helpful link (I've got plenty of tech
info links, but most don't usually apply to the topic at hand
whatever that may be) , but some of you guys, like Spehro, You,
etc., ... it's like you can pull horshoe out of yer asses You
must do more digging than I do.

I got a kick out of this link because I have the opposite situation.
I don't need an MLP becuse I have an SLM tha *is* 75 ohfriggin'megas
and the link dealt with ... you know.

snip John still helping but going the extra furlong or so

Use non-inductive resistors (carbon comp if you can get them) and keep
the leads short. That is, ********KEEP THE LEADS SHORT*********.
^^^^^^^^^^
advice that should be unsnipped. Er, snip the leads, though.

--
Best Regards,
Mike

On Sun, 02 May 2004 11:35:08 -0500, John Fields wrote:

On Sun, 02 May 2004 09:04:33 -0500, John Fields
wrote:

snip John helping Paul with terminology

http://www.maxim-ic.com/appnotes.cfm/appnote_number/972

Once in a while, I can post a helpful link (I've got plenty of tech
info links, but most don't usually apply to the topic at hand
whatever that may be) , but some of you guys, like Spehro, You,
etc., ... it's like you can pull horshoe out of yer asses You
must do more digging than I do.

I got a kick out of this link because I have the opposite situation.
I don't need an MLP becuse I have an SLM tha *is* 75 ohfriggin'megas
and the link dealt with ... you know.

snip John still helping but going the extra furlong or so

Use non-inductive resistors (carbon comp if you can get them) and keep
the leads short. That is, ********KEEP THE LEADS SHORT*********.
^^^^^^^^^^
advice that should be unsnipped. Er, snip the leads, though.

--
Best Regards,
Mike

On Sun, 02 May 2004 22:37:28 GMT, (John Crighton)
wrote:

Go on, tell us the model number, there are a lot of us
still interested in boat anchor style test equipment.

Is this unit similar to your sig gen
http://www.thevalvepage.com/testeq/avo/sg3/sg3.htm
http://www.thevalvepage.com/testeq/testeq.htm
Unfotunately the connector has been removed and a
BNC type fitted.

Not really similar to any of them, I'm afraid. Model number is CT
378B. I did recognise that old Advance E2, though. Had one of 'em
about 25 years ago. It was pretty ancient then!

I am guessing that you want to keep the original connector
on the sig gen and find a matching connector to make a
short test lead. Old Style connector to BNC.
My news group service doesn't allow me to see the group
a.b.s.e Pity. So I can not see the picture you posted.

Pity. Hopefully some kind soul will post it onto a web site for you. I
can't as I have no FTP s/ware installed at present. :-(
The output is just under an inch in diameter and is co-axial as you
might expect. The centre pin is about 1/16th" thick and doesn't
protrude beyond the outer. It's pretty unremarkable apart from its
size; much larger than one usually sees.
--

The BBC: licenced at public expense to spread lies.