HP-8554B-Mixer_Mods_VE3BBN 电路图.pdf

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 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库 RadioFans.CN 收音机爱 好者资料库