[R-390] HP 8640B RF Sig Gen Leakage???

[Kim Herron]

>Hi Guys!!
>
>Here is the routine: I tune up a radio, say a VHF unit, and measure
>sensitivity. Then I disconnect the generator and hook the radio to a small
>shop antenna. Presto - an on-channel carrier. Run the 8640 attenuator to
>zero, or switch off the RF, carrier still there. Change frequency of the
>8640, carrier gone... switch off the 8640, carrier gone.

    I used to have the same problem with my HP-606B.  On the higher freqs 
is where the
problem showed up.  Never did find the problem, though I suspected the line 
bypass caps and the
grounding network in the shop.  I haven't checked my HP8640B on VHF freqs 
(above 100 MHz)
but I do know that it does not do that at 30 MHz and down.  Here's a 
thought, though.  Are you using an external
timebase that has a leaking cable connected to it??  I did discover some 
cables that decided that the shielding
wasn't good in and I replaced them.


Thanks!!

Kim Herron
1-616-677-3706