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Re: HP-8554L very low signal Solved with a VCO

 

Hi All,
The 1500MHZ LO did nor want to oscillate at that frequency, it insisted to oscillate at 1800Mhz there about.

So I decided to go another way and inject the LO signal.
HP had mounted a SMA connector on later models J2. It had a pick-up loop and was terminated with 50Ohm.

So I drilled a hole, bought a tap 1/4 x 36 (all the way from China)and made a pickup.
Bought a VCO from Mini-Circuits, the ZX95-1600W (+9dBm) and built a +12 V fixed and 0 - 18V variable voltage from the +20V line.
Good decoupling, especially on the tuning input, is necessary.

So far so good. The unit is operational again. But I miss some 10dB level. I probably can fix this with an in-line RF amp on 50MHz.
OR live with it knowing to add 10dB to the measured signal.

I'll post some photo's of this mod.

Jos PA0AMX

--- In hp_agilent_equipment@..., "Jos" <jos.raven@...> wrote:


Still trying to repair the front end of my 8554L.

The 1500MHz oscillator is in trouble, on checking the output of the 550MHz IF I had a fine 1500MHz LO signal, an hour later it was gone and never came back.
I found a weaker signal @ 1800 MHz, the oscillator is working but not tunable.

In a later version of the 8554L HP used an external 1500MHz oscillator.

I am looking for a cheap 8554L or B to replace the unit or , again, a cheap small 1500MHz oscillator with SMA connector.

Anyone have a filled junk box?

Jos
PA0AMX

--- In hp_agilent_equipment@..., "Jos" <jos.raven@> wrote:


I have found the fault for the always ON UNCAL light.

Some PO has repaired the power supply board A5 as per Service Sheet 23
Q20, Q18 and Q25 were all 2N3702.
In itself there are OK, except for the pin-out, E,C,B
I replaced the with BC556 NPN, E,B,C (direct drop-in)and the UNCAL light functions again.

No solace for the 8554L RF deck, still a very low signal.

The hunt goes on.

Jos PA0AMX
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