Batboard

Curious if anyone has a solution for this. I recently came into an IFR 1000S that has unstable frequency generation. Looking at it's output on another monitor, the frequency error walks around anywhere from 0Hz to +1.9kHz down to -600Hz.

The 10MHz oscillator is rock-steady and I performed the front panel calibration on it, it sits at -1Hz.

Any ideas on what to look at inside?

It also seems like I can really only get accurate measurements of RX sensitivity out of the thing with the output switch in the uV x 100 position.

Any thoughts?

First: do you have the modulation sources off? It could be a bad modulator.
It could be the fine PLL is unlocked.

That is a unit well before my time, so I'm just running on generalities here.

Yes, it does it with the modulation sources off. Both PLL lock lights are lit, high & low, but they probably don't have anything to do with the "fine PLL" your referring to.

Is there anyone around your place there that might remember anything about this unit? It's in really nice shape, aside from this problem and whatever is going on with the signal generator/attenuator.

Your best bet would be Carl Engdahl, IIRC he is on here (but not as active as I am). I'll ping him when I get in to work this morning.

Wowbagger wrote:Your best bet would be Carl Engdahl, IIRC he is on here (but not as active as I am). I'll ping him when I get in to work this morning.

I'd sure appreciate any insight he can provide. Thanks for checking with him!

Did you check the variable switch for intermittent connection. That would cause drift.

The first thing to verify is that the receive is stable so if you input a known stable signal it does not show the same problem as generate.

If the RX is OK check the stability of the 54.78Mhz and 5.22 Mhz signals used to generate a phase locked 60Mhz which is then doubled to the 120Mhz IF.
Chances are the 5.22 Mhz is unstable since this is where the FM is actually generated. The 54.78 is supposed to be from an XTAL but you may a component age causing it to become unstable.

These signals are in the 120Mhz FM/AM generator module. Maybe a defective filter or coupling cap there someplace in that module

The service manual is floating around and maybe on the Repeater Builders site. Good Luck

John

Your poor RX is more than likely a blown 5.6ohm resistor that is in the RX static protect. Otherwise known as a fuse from someone keying into the antenna port

Suggestions on how to confirm/where its located/photo/etc?

the service manual has some excellent breakdowns and pictures.
In retrospect if you are having rx issues that change with the attenuator switch setting than that may be a defective CR1 in the second mixer.

The fuse can be verified somewhat by
1; doing a diode test across the RX input ...should see conduction with either polarity
2 resistance check ..should see 22K ...this may vary a bit depending on your meter current due to the diodes in parralel