IFR-1000 strange frequency offset

[AH6LE]

As I've seen other service monitor questions asked here, I though this is the best place for mine. Sorry if I'm wrong!

I have an IFR-1000A that is generating/receiving the wrong frequency.

Selected versus actual (as determined on 2 other "known to be good" monitors)

100 mHz is 1 kHz high
200 mHz is 2 kHz high
300 mHz is 3 kHz high
400 mHz is 4 kHz high
500 mHz is 5 kHz high
600 mHz is 6 kHz high
700 mHz is 7 kHz high
800 mHz is 8 kHz high
900 mHz is 9 kHz high

Seems to me this is probably a divider chain issue but I just can't wrap my head around where to look - the actual programmable divider chain or something in the reference osc. chain.

Comments would be greatly appreciated

 

[prcguy]

Sounds like a reference osc problem and that will show proportionally more offset as you go higher in frequency just like what you see. Measure the ref osc separately with a known good freq counter. The 1000 series is getting pretty old and those oscillators will drift over time.

 

[dlwtrunked]

As I've seen other service monitor questions asked here, I though this is the best place for mine. Sorry if I'm wrong!

I have an IFR-1000A that is generating/receiving the wrong frequency.

Selected versus actual (as determined on 2 other "known to be good" monitors)

100 mHz is 1 kHz high
200 mHz is 2 kHz high
300 mHz is 3 kHz high
400 mHz is 4 kHz high
500 mHz is 5 kHz high
600 mHz is 6 kHz high
700 mHz is 7 kHz high
800 mHz is 8 kHz high
900 mHz is 9 kHz high

Seems to me this is probably a divider chain issue but I just can't wrap my head around where to look - the actual programmable divider chain or something in the reference osc. chain.

Comments would be greatly appreciated

We all assume your "mHz" was meant to be "MHz", as otherwise what yous said is impossible.

 

[AH6LE]

Well...10 MHz osc. is dead on (even zero beat with WWV). I just checked

Old habit

We all assume your "mHz" was meant to be "MHz", as otherwise what yous said is impossible.

Yes I did

 

[RFI-EMI-GUY]

You should probably download the service manual from RepeaterBuilder site and verify the tuning of the reference oscillator. I think this may be a strange beast.

 

[AH6LE]

View attachment 110571
View attachment 110572

You should probably download the service manual from RepeaterBuilder site and verify the tuning of the reference oscillator. I think this may be a strange beast.

As I posted, the reference oscillator is dead on and I have poured over the SM from RB plenty! I'm still thinking that the 1 KHz increase in error per 100 Mhz must have something to do with the divider chain. Problem is, it looks as if the thumbwheels drive 3 different boards!

 

[prcguy]

I believe the problem is on the reference osc side of the synthesizer and if it were on the output side you would have the same error at all frequencies. If the master osc is divided into something else like starting at 10MHz and eventually becoming 5 or 1MHz then that divider chain might be something to look at. I would study the schematic and see what the master osc freq is and how its used in the synthesizer.

1KHz off at 100MHz is actually not that much and I can adjust the master osc in my IFR 1200S to be off by 1KHz at 100MHz and that will become 9KHz off at 900MHz. Have you tried adjusting the master osc?

As I posted, the reference oscillator is dead on and I have poured over the SM from RB plenty! I'm still thinking that the 1 KHz increase in error per 100 Mhz must have something to do with the divider chain. Problem is, it looks as if the thumbwheels drive 3 different boards!

 

[RFI-EMI-GUY]

As I posted, the reference oscillator is dead on and I have poured over the SM from RB plenty! I'm still thinking that the 1 KHz increase in error per 100 Mhz must have something to do with the divider chain. Problem is, it looks as if the thumbwheels drive 3 different boards!

I think it is odd that the procedure has you tuning WWV +1 KHz to hear a zero beat note. I have no doubt the ref osc should be tuned right at 10.00000 MHz, it just seems there is some IF wizardry afoot with other modulation and IF generation.

 

[prcguy]

If you have a big enough antenna you should be able to tune WWV directly on the IFR at 5, 10, 15 or 20MHz and use the front panel frequency meter to check accuracy. Going 1KHz off frequency will give you a 1KHz tone in SSB mode but I don't think the 1000 has an SSB mode and thats not very useful unless you specifically have a USB and LSB mode to compare the tone. You can also look up a couple of your local TV stations and tune in the ATSC pilot frequency which is almost certainly using a wicked good frequency standard.

I think it is odd that the procedure has you tuning WWV +1 KHz to hear a zero beat note. I have no doubt the ref osc should be tuned right at 10.00000 MHz, it just seems there is some IF wizardry afoot with other modulation and IF generation.

 

[RFI-EMI-GUY]

If you have a big enough antenna you should be able to tune WWV directly on the IFR at 5, 10, 15 or 20MHz and use the front panel frequency meter to check accuracy. Going 1KHz off frequency will give you a 1KHz tone in SSB mode but I don't think the 1000 has an SSB mode and thats not very useful unless you specifically have a USB and LSB mode to compare the tone. You can also look up a couple of your local TV stations and tune in the ATSC pilot frequency which is almost certainly using a wicked good frequency standard.

Read my post #5, specifically sections 5.2.2 and 5.2.3 (I think there is a typo at 5.2.3 1 MHz should be 1 Hz. ) There is implied an internal "Master oscillator" at WWV + 1 KHz.

 

[AH6LE]

I believe the problem is on the reference osc side of the synthesizer and if it were on the output side you would have the same error at all frequencies. If the master osc is divided into something else like starting at 10MHz and eventually becoming 5 or 1MHz then that divider chain might be something to look at. I would study the schematic and see what the master osc freq is and how its used in the synthesizer.

1KHz off at 100MHz is actually not that much and I can adjust the master osc in my IFR 1200S to be off by 1KHz at 100MHz and that will become 9KHz off at 900MHz. Have you tried adjusting the master osc?

IFR sure does use some convoluted engineering. Guess I'll just work my way through all this with a 'scope and freq counter

 

[AH6LE]

Read my post #5, specifically sections 5.2.2 and 5.2.3 (I think there is a typo at 5.2.3 1 MHz should be 1 Hz. ) There is implied an internal "Master oscillator" at WWV + 1 KHz.

Yea, I've been through that and it all works as they say it should. Still, things are increasingly off with increasing frequency

 

[RFI-EMI-GUY]

Just for a sanity check, keep in mind that the frequency generation of these older units is very dirty because they use comb generation and unfiltered mixing of several sources. So using a frequency counter or spectrum analyser to observe the output spectrum may be misleading. See if an actual receiver, a decent one responds to an on frequency signal.

 

[AH6LE]

As my OP said, my 2 other service monitors say it's off and actual radios also show it's off, even in generate mode.

 

[prcguy]

Do you have any adjustment range on the master osc? I've only used a 1000 once and don't know the setup but my 1200S has a trimmer on the front panel. I would generate to a frequency counter or other known good service monitor then tweak the master osc.

Does the 1000 lock up to an external 10MHz source? If so it would be an interesting experiment to do that then see if its still off freq. If that works you can get a highly accurate GPS disciplined osc for a little over $100.

As my OP said, my 2 other service monitors say it's off and actual radios also show it's off, even in generate mode.

 

[AH6LE]

Actually, I followed the procedure in the manual - set the front panel adjust to midrange and adjusted the trimmer in the Master Osc itself.

 

[prcguy]

Yes, that would be correct for a master osc that has an internal trimmer and external adjust. Tweak either one until the whole box generates on frequency then map it out from 100MHz to 900MHz, etc.

Actually, I followed the procedure in the manual - set the front panel adjust to midrange and adjusted the trimmer in the Master Osc itself.

 

[AH6LE]

Yes, that would be correct for a master osc that has an internal trimmer and external adjust. Tweak either one until the whole box generates on frequency then map it out from 100MHz to 900MHz, etc.

Exactly what I did before I started this thread. Other than this issue, the darn thing works fine!
(well....except for the AUTO thing but first things first)

 

[prcguy]

Now I'm really confused. If you were able to tweak the master osc so the 1000A will generate on frequency, then what is the problem? Is the master osc too far off to generate on frequency?

Exactly what I did before I started this thread. Other than this issue, the darn thing works fine!
(well....except for the AUTO thing but first things first)

 

[AH6LE]

Now I'm really confused. If you were able to tweak the master osc so the 1000A will generate on frequency, then what is the problem? Is the master osc too far off to generate on frequency?

What I am saying is the 10 MHz reference oscillator in on frequency (it wasn't that far off to begin with) yet the frequency error(s) I listed when I started this thread remain.

And the frequency error(s) affect both receive and generate, just as they did when I started this thread