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>
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----- 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
