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

A pad is usually 3 resistors in a small container. They can be a T or a Pi
type. This is the way the resistors are configured in the pad. You may
also see them referred to as an attenuator. The number 6 db is how much the
pad reduces the signal in power. You can get them from about .5 db to 20
db. They have to be used for the impedance they are rated at. They are for
reducing the signal level and also to help isolate small differences in
impedance.
For the calibration to be accurate on your generator it sounds like the
scale is calibrated so you need the 6 db pad after it. A 5 db pad will
reduce the power by a factor of 4 or a voltage by a factor of 2.

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"?
--

The BBC: licenced at public expense to spread lies.

Paul Burridge wrote:
I have a spare RF signal generator that has an unmarked output from a
type of socket I've never seen before.

Would it be a car-type output socket (deep recessed centre pin)? Would
it be an old Advance generator with the rounded corners? If so, it's
almost certainly 75R.

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.

If it has a resistive output attenuator with no DC blocking capacitor,
you can switch to maximum attenuation (minimum output) and measure Zout
with an ohm-meter.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)

http://www.ifwtech.co.uk/g3sek

Paul,
The most obvious method would be to measure the open-circuit RF output
voltage, and then measure the output voltage with a known load. The output
impedance is a simple calculation of the ratio of the voltages.
However, depending on the vintage and quality of the generator, the
impedance is likely to change with frequency, and possibly even with output
level. For source-impedance-sensitive measurements, it's generally a good
idea to put a small amount of fixed resistive attenuation at the output
(6-10 dB) in order to "fix" the impedance.

Joe
W3JDR

"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.

On a sunny day (Sat, 01 May 2004 14:19:59 +0100) it happened Paul Burridge
wrote in
:

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?

Load it with 50 Ohms, and measure output voltage, remove load and measure
again.
If it is half, it is 50, else do the math.
JP

"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?


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.

On Sat, 01 May 2004 14:19:59 +0100, Paul Burridge
wrote:

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.

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

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.

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 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.