Service Manuals, User Guides, Schematic Diagrams or docs for : HP 8554B-Mixer_Mods_VE3BBN

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Submitted by David Wilson VE3BBN on July 21 2007

 Here are a few pix of the modified 8554B as promised. Instead of it being the 0 to 1250
mhz range it is now a 0 to 500mhz SA. In the picture you can see the response of a FM
carrier in the 2 meter range, with 40db of attenuation in. The mods included ripping out
everything above 550 mhz (except the input step attenuator, 0-1250mhz LP filter and the
3db post attenuator. I then replaced it all with the die-cast box that has a 550 mhz LP
filter, a passive mixer, a 500 to 1000 mhz VCO, a 6db attenuator between the VCO and
Mixer and a 20 db amp which was removed because it introduced birdies. The only card
is one that takes the place of the A6 slot, and has a LM358 dual op-amp and a few
associated parts to give the VCO the sweep range and linearity. Sorry about the second
picture being out of focus as I had the camera set for close up and I moved out of range
for the panoramic shot. Hope this helps out anyone interested in resuscitating and of the
HP heads. I also made a SA of my own for the HF bands 0 to 30 mhz and it works fine. I
also have a tracking generator a marker generator and freq. readout on it. I also would say
to anyone interested that they can extend the range of a low freq. head by adding the
block that I made mentioned above.


Cheers David ve3bbn

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