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608 output attenuator.

 

You may remember that I was concerned about the integrity of the output attenuator in my 608D. Today I checked it again the way I had calibrated it with a short cable and a pass through 50 ohm termination at the scope end. I set the frequency to 10 MHz and the attenuator to 100 mV to be sure there would be no proximity effect between the pickup coil and the output tuned circuit. With the scope reading 100 mV within accuracy spects I then removed the termination and measured 200 mV within accuracy spects. From this I conclude that my output attenuator has not been damaged by someone transmitting into it.

Regards.

Max. K 4 O DS.

Email: max@...

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Bob Albert
 

Ah you were luckier than I. My Marconi TF1066/4 not only had a broken attenuator rack (from removing from cabinet without first turning it inward) but also a burned out 47 Ohm resistor at the probe.

It required complete removal of the probe assembly, including some gear work and springs and so on.

A lot of work but now the generator output is accurate and the attenuator works smoothly. The resistor is 1/4 Watt so it doesn't take much to burn it out. Maybe 5 Volts of rf for most of a minute. A 100 Watt transmitter delivers 71 Volts; that should do it in a second or less.

Bob

--- On Tue, 12/25/12, Max Robinson <max@...> wrote:

From: Max Robinson <max@...>
Subject: [hp_agilent_equipment] 608 output attenuator.
To: hp_agilent_equipment@...
Date: Tuesday, December 25, 2012, 10:52 AM
You may remember that I was concerned
about the integrity of the output
attenuator in my 608D.? Today I checked it again the
way I had calibrated it
with a short cable and a pass through 50 ohm termination at
the scope end.
I set the frequency to 10 MHz and the attenuator to 100 mV
to be sure there
would be no proximity effect between the pickup coil and the
output tuned
circuit.? With the scope reading 100 mV within accuracy
spects I then
removed the termination and measured 200 mV within accuracy
spects.? From
this I conclude that my output attenuator has not been
damaged by someone
transmitting into it.

Regards.

Max.? K 4 O DS.

Email: max@...

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Vacuum tube site:
Woodworking site

Music site:

To subscribe to the fun with transistors group send an email
to.
funwithtransistors-subscribe@...

To subscribe to the fun with tubes group send an email to,
funwithtubes-subscribe@...

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to
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I don't have any antenna or RF impedance bridge that I trust. So the 50 ohm termination and "infinite" impedance test is all I have.

Regards.

Max. K 4 O DS.

Email: max@...

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----- Original Message -----
From: "Patrick Wong" <patwong3@...>
To: <hp_agilent_equipment@...>
Sent: Tuesday, December 25, 2012 9:16 PM
Subject: [hp_agilent_equipment] Re: 608 output attenuator.


Hi Max,

I'm not sure how this proves the attenuator is OK. If you use an oscilloscope with the option to select between a 50 ohm input and a 1M ohm input, the 50 ohm input will typically result in vertical deflection ~50% of the high impedance input.

The use of a 50 ohm passthrough adapter on a 1M ohm input, is a reasonable equivalent of selecting a 50 ohm input on the scope's vertical channel, at least until you reach a sufficiently high frequency so the passthrough adapter starts to display a reactance component.

If you have access to an antenna analyzer like an MFJ259B or MFJ269, then you can measure the VSWR of the 608 antenna output. I would say that is a reasonable test if you do not wish to remove the attenuator to physically inspect and measure the resistor(s).

Patrick Wong AK6C

--- In hp_agilent_equipment@..., "Max Robinson" <max@...> wrote:

...Today I checked it again the way I had calibrated it
with a short cable and a pass through 50 ohm termination at the scope end.
I set the frequency to 10 MHz and the attenuator to 100 mV to be sure there
would be no proximity effect between the pickup coil and the output tuned
circuit. With the scope reading 100 mV within accuracy spects I then
removed the termination and measured 200 mV within accuracy spects. From
this I conclude that my output attenuator has not been damaged by someone
transmitting into it.



------------------------------------

Yahoo! Groups Links
 

On 12/26/2012 12:01 AM, Max Robinson wrote:

I don't have any antenna or RF impedance bridge that I trust. So the
50 ohm
termination and "infinite" impedance test is all I have.

Regards.

Max. K 4 O DS.

Email: max@... <mailto:max%40maxsmusicplace.com>

Transistor site
Vacuum tube site:
Woodworking site

Music site:

To subscribe to the fun with transistors group send an email to.
funwithtransistors-subscribe@...
<mailto:funwithtransistors-subscribe%40yahoogroups.com>

To subscribe to the fun with tubes group send an email to,
funwithtubes-subscribe@...
<mailto:funwithtubes-subscribe%40yahoogroups.com>

To subscribe to the fun with wood group send a blank email to
funwithwood-subscribe@...
<mailto:funwithwood-subscribe%40yahoogroups.com>

----- Original Message -----
From: "Patrick Wong" <patwong3@... <mailto:patwong3%40cox.net>>
To: <hp_agilent_equipment@...
<mailto:hp_agilent_equipment%40yahoogroups.com>>
Sent: Tuesday, December 25, 2012 9:16 PM
Subject: [hp_agilent_equipment] Re: 608 output attenuator.

Hi Max,

I'm not sure how this proves the attenuator is OK. If you use an
oscilloscope with the option to select between a 50 ohm input and a
1M ohm
input, the 50 ohm input will typically result in vertical deflection
~50%
of the high impedance input.

The use of a 50 ohm passthrough adapter on a 1M ohm input, is a
reasonable
equivalent of selecting a 50 ohm input on the scope's vertical
channel, at
least until you reach a sufficiently high frequency so the passthrough
adapter starts to display a reactance component.

If you have access to an antenna analyzer like an MFJ259B or MFJ269,
then
you can measure the VSWR of the 608 antenna output. I would say that
is a
reasonable test if you do not wish to remove the attenuator to
physically
inspect and measure the resistor(s).

Patrick Wong AK6C

--- In hp_agilent_equipment@...
<mailto:hp_agilent_equipment%40yahoogroups.com>, "Max Robinson" <max@...>
wrote:

...Today I checked it again the way I had calibrated it
with a short cable and a pass through 50 ohm termination at the scope
end.
I set the frequency to 10 MHz and the attenuator to 100 mV to be sure
there
would be no proximity effect between the pickup coil and the output
tuned
circuit. With the scope reading 100 mV within accuracy spects I then
removed the termination and measured 200 mV within accuracy spects.
From
this I conclude that my output attenuator has not been damaged by
someone
transmitting into it.
It would be better if nobody top-posts.

That having been said; As you place and remove the 50 Ohm load, you are
mismatching THE GENERATOR, such that the signal may vary by 2:1. If you
want the test to make sense, you need to connect the generator output thru
a fairly large series resistor--say 470 ohms--to the 608 input port.
Connect your
scope thru a 10:1 probe to that same input port. Now, with that connected,
add a 51 ohm resistor in parallel with the 608 input. If the scope
reading drops
by about 50%, then the 608 has a 50 ohm impedance at the port. If it
drops by
quite a bit more than 50%, then the 608 has a higher impedance than 50 Ohms,
and there would appear to be a problem with the attenuator circuit.

BTW, if you don't have a scope, a high-impedance VTVM that will read at
10 MHz (it doesn't have to be accurate) will work similarly.

Doug, WA2SAY

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