EMRFD Message Archive 208

Message Date From Subject
208 2006-11-26 12:42:57 jr_dakota W7ZOI Spectrum Analyzer Question/Problem
Well technically it is the Tracking Generator I'm having a problem
with ... I built up and tested all the PCB's but the last one I tested
was the TG module and I'm having a problem getting the 110Mhz
oscillator to start up ... I'll go over what I have done so far and
hopefully someone can suggest a fix

I double checked all components for proper value/placement, everything
OK there .... I removed the crystal and tested it in my rig for
matching crystals for filters and it did oscillate though not at
110Mhz obviously but in the fundamental mode .... I subbed in a 51 ohm
resistor as suggested for the 2nd LO/Mixer module (Oscillators are
very similar and the 2nd LO came up right off, no problem) and still
no go ... I did a DC voltage test of the transistor:

Voltage at R5 - 14.97V
Collector - 13.85V
Emmitter - 4.5v
Base - 5.2V

Seems to be about right to me (correct me if I'm wrong) so I finally
swapped in a new 2N5179 transistor ... a little tweak on the cap and
it came right up so I put the crystal back in ... nothing ... So I
took the crystal out and put the 51 ohm resistor back in ... still nothing

Now I'm really stumped ... on the plus side I could use a little hands
on as to how a Butler Oscillator works for my PIC n MIX and PIC a STAR
projects in the near future so this education won't be going to waste

221 2006-11-28 21:02:37 jr_dakota Re: W7ZOI Spectrum Analyzer Question/Problem - SOLVED
Got the circuit back out tonight and gave it another shot ... first I
had to fix the power supply problem which is why it wouldn't oscillate
when I removed the crystal and subbed in the 51 ohm resistor ... it
came right up at -1 Dbm so I hooked it up to my freq counter and
attempted to adjust it to 110 Mhz but the lowest I could go was 112
Mhz and the level was falling off ... so a took a little off the coil,
not much, perhaps a quarter turn and now was able to trim it to 110
Mhz (and a bit lower) so I pulled the resistor and put the crystal
back in and away we went 110 Mhz at -1 Dbm so now all I need to do is
adjust the pad to bring my level to 0 Dbm and I should be set