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 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.

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.

On Sat, 01 May 2004 17:03:26 GMT, Jan Panteltje
wrote:

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.

Or double, presumably. :-)
Well there you go; I knew there must be a more elegant solution to the
one I dreamed up which basically involved taking a spread of 10 carbon
resistors of from 10 - 1000 ohms and measuring the applied voltage
across each, then arriving at power transferred in each by V^2/R;
drawing a graph of the results and finding the point of maximum power
delivered.
--

The BBC: licenced at public expense to spread lies.

On Sat, 01 May 2004 17:03:26 GMT, Jan Panteltje
wrote:

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.

Or double, presumably. :-)
Well there you go; I knew there must be a more elegant solution to the
one I dreamed up which basically involved taking a spread of 10 carbon
resistors of from 10 - 1000 ohms and measuring the applied voltage
across each, then arriving at power transferred in each by V^2/R;
drawing a graph of the results and finding the point of maximum power
delivered.
--

The BBC: licenced at public expense to spread lies.

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.

--
John Fields

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.

--
John Fields

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.

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 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