On Mon, 24 Nov 2003 19:34:33 -0600 "hm" <w4lcn@frontiernet.net> writes:
> Sir:
> I wonder if you or some members here could help me with set-up
> problem or point me to some place to find the information I need?
> Some time ago I built a 4-1000 linear amplifier with tuned input and
> Pi-L output. The tuned inputs is good, and after many hours of
> trial and error tuning the output network, I have the 40 meter band
> tuned very well, and the 20 meter band somewhat close. Now to my
> problem. I have acquired an H/P 8601A sweep generator(50 ohm
> output) and also have an H/P 606 signal generator for
> centerfrequency marker, as well as a Millen grid dipper and a
> tektornix 547 scope. I would really like to be able to set the
> remaining bands using the sweep generator/scope as I think it could
> make tuning the Pi-L much easier, plus learning something new.
> Unfortunatley I don't know how to set-up the sweeper to the
> amplifier output network to do this. I think where my efforts have
> failed is with the matching the sweeper to the 4-1000 plate, or to
> the network itself. If you or one of your readers could help me to
> do this or perhaps tell me where I could find this information I
> would really appreciate it...
> thank you for you time...H. B. Moore...w4lcn...
> _______________________________________________
Hi,
Well, if you insist on doing it this way... it sounds like you have
most of the required stuff.
First tune your amp up into a 50 ohm dummy load on 40 meters where you
state that you have it working well.
Now shut it down and disconnect the amp. from the power outlet for
safety.
Obtain a Return Loss Bridge. This will allow plenty of time for the
HV to bleed down. :-)
HP 8721A or equivalent (ridiculously pricey on the used market!)
or
Build one:
QST September 1997, pp. 34-36
or
http://www.highfrequencyelectronics.com/Archives/May03/HFE0503_Kurzrok.pd
f
or
http://www.qsl.net/it9xxs/reflectometer/reflectometer.htm
Connect the RF from your generator to the bridge input and connect
your amp to the test port. Connect the vertical input of your scope,
along with a 50 ohm termination, to the sample port.
Connect the generator's sweep output to your O'scopes horizontal
input. Set your sweeper to scan 5-10 MHz or so (to cover 40 meters where
you left the amp set). Adjust the 'scope as necessary to fit the
display.
With the amplifier still disconnected from power, HV discharged, etc.
Connect a 10K carbon potentiometer between the plate of the 4-1000A and
ground next to the tube base. An old Allen Bradley Type J will be fine.
Adjust the pot. for minimum return loss as indicated on your scope.
The pot should now be set to your effective plate impedance.
Leaving the pot at this setting you should be able to sweep the other
bands and adjust your tank components for minimum return loss.
Happy Sweeping,
Marv WC6W
*
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