The local oscillator on the XV222 will not generate a sufficient
signal level. The voltage measured at TP1 is 0.45VDC.
When first tested, TP1 read 0VDC. Seeing posts about a balky
oscillator being sensitive to L4A, I adjusted the slug while watching
at TP1. Sure enough, as the slug was adjusted, TP1 rose from 0VDC to
4.5VDC and then started back toward 0VDC as I continued to turn the
slug into L4A.
I backed out the slug until TP1 read its maximum of 0.45VDC and then
continued out until the voltage at TP1 returned to 0VDC.
When oscillating, the frequency measures at 193.995, which is well
within the accuracy of my frequency counter.
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As I don't have an XV222, I am assuming that the local oscillator is an
overtone oscillator. In most overtone oscillators there is a tuned circuit
that selects the required overtone frequency, in this case 193.995 MHz, and
I am guessing that L4A is part of that tuned circuit. If all the components
and DC voltages are OK, the result that you are getting is typical if the
tuned circuit cannot be tuned properly. It sounds as though the inductance
of L4A is reaching its maximum as you turn the slug in, but not enough
inductance is obtained, and as you continue to turn the slug into L4A its
inductance starts to decrease again.
Another possibility is an out of tolerance capacitor in the tuned circuit
which if on the low side would require greater inductance than usual from
L4A, and L4A can't provide it. A "maybe" possibility is that the crystal you
have is "sluggish" at the overtone used..
If however the LO is an oscillator followed by frequency multipliers and L4A
is in one of the tuned circuits, then what I said about the position of the
L4A's slug and the capacitor tolerance would also apply.
Metal tuning tools are a no no when the tool must connect with the slug.
Very easy to break slugs and the tool has its own effect on tuning by just
being near or in the coil.
Hope that this helps.
73,
Geoff
GM4ESD
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