Tuning up any transceiver requires communications test gear
and the Syntor X is no exception. There is a scary label
inside the Syntor X that says "Do Not Field Adjust". It's
referring to the RF pre-selector which in fact will need
adjustment. At least mine did as the sensitivity for 20 db
quieting was 10 micro volts at the bottom of two meters.
However, if you have access to a spectrum analyzer and a
variable RF generator tune up is relatively easy. There is
a excellent Syntor tuning guide on
KB8ZQZ's Syntor X retuning page (dead link) and
even more information on
SYNTOR X Extended Frequency Modifications. No
need to repeat all of that here. I'll just hit the highlights.
VCO
On the Blender page there is a lengthy and
interesting discussion of how work radios in general and
specifically how the synthesized Syntor X works. Even if
you know "Radio 101" you should read this page before
tuning. Having said that, the whole discussion about VCOs
comes down to this one sentence. I quote:
However, if you want to lower the frequency coverage
for HAM use only, you can just restore the factory cut
which will probably cause some loss at the high end
frequency range.
My Syntor X locked fine on
receive all the way down to 142 MHz. The transmit would
only lock down to about 147.5 MHZ. So I followed the above
instructions and soldered in the transmit jumpers. Now I
get a solid lock through the entire two meter ham band. I
don't know where the low and high transmit lock ends as the
Xcat will not transmit out of band without jumping through
some hoops which I won't go into now.
The receive lock limits are easy to find. Just put the Xcat
in band scan and watch the unlock light on the Syntor X.
Too cool!
Pre-selector
This is where the spectrum analyzer
and frequency generator come in very handy. The generator
goes on the antenna and the spectrum analyzer connects to
the first mixer input. The Syntor need not be powered on. I
just cranked the generator frequency up and down and could
easily see where the band pass rolled off. The band pass
was from about 148-174 MHz. The KB8ZQZ page said turning
the filters in moved the frequency down. So I turned all
five in a 1/4 turn and sure enough it moved down. I
repeated this process, turning all five filters in the same
amount, until the bottom end of the band pass was around
143 Mhz. The top end came down to about 170 Mhz. I ended up
giving each of the five filters two full turns clockwise.
Injection Filter
I didn't tune this as I was happy
with the results just from tuning the pre-selector.
However, there is a bit of room for improvement and
spending the extra effort here probably would have brought
the Syntor X up to par.
Results
The band pass curve of the pre-selector had
a wide sag in the middle and peaked up a bit on the low end
before any adjustments were made. This curve remained after
adjustment. But that's not such a bad thing for ham
operation. May even cut the intermod down a few db. Before
touching the Syntor X it's sensivity on 162 Mhz was .3
micro volts for 20 db quieting and about 10 micro volts at
144 MHz. After tuning the pre-selector the sensitivity at
162 Mhz is still .3 but 144 Mhz came down to .6 micro
volts. Not red hot but good enough for our noisy hill.