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IFR 1900CSA Adjustment Advise and Maint. Manual Needed

This forum exists for the purposes for discussing service monitors (This includes but is not limited to Motorola, HP, Aeroflex, GD, etc). Additional topics allowed include test procedures, interpretation of test results, where to find information about specific tests, antenna VSWR, return loss testing, duplexer and filter alignment, etc.

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k7dmk
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IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby k7dmk » Thu Aug 11, 2016 5:04 pm

I have a IFR1900CSA I picked up used. I am trying without luck to find a pdf of the service/maint manual. The unit passes self tests, but the frequency calibration is off by about 1.5 KHz on both the signal generator and counter in the RX test mode at 500 MHz. By way of the internal calibration routine in the menu, the VCXO was adjusted to within a Hz by monitoring the 10 MHz reference output with GPSDO locked 53131A counter. It was not too far off. The calibration is still poor and the error increases to about about 4.5 to 5 KHz at 2 GHz. I also tried locking the unit to an external 10 MHz reference. The little blue dot next to the frequency field on the LCD iindicates the ext reference is detected, but the error persists even after a long warm up. If I recheck the reference frequency when the offset is being measured with either a locked counter in the generate mode or by feeding a locked generator into the ant or T/R input in receive mode, the 10 MHz output is dead on.

I am wondering if there is a second LO that needs adjustment to correct the error. One would assume all oscillators would lock to an internal or external reference, but that's not happening here.

All the phase lock loop tests pass in the self test. Everything else works, just the persistent frequency error.

Can anyone shed some light here? A 1900 service manual would be most helpful. I have a 1600 maint. manual, but that unit only goes to 1 GHz and appears to be a somewhat different animal. I have looked all over the net for a service manual. I willing to pay for a copy, but not what Aeroflex/Cobham probably charges, if it's even available from them.

Thanks,

Dave K7DMK

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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby Wowbagger » Fri Aug 12, 2016 4:45 am

If the master oscillator is locked, and the PLLs are locked, maybe you have a problem with the dividers, like a stuck bit? Have you reseated all the cards?
This is my opinion, not Aeroflex's.

I WILL NOT give you proprietary information. I make too much money to jeopardize my job.

I AM NOT the Service department: You want official info, manuals, service info, parts, calibration, etc., contact Aeroflex directly, please.

k7dmk
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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby k7dmk » Fri Aug 12, 2016 8:37 am

I have reseated many of the boards, but have not tried cleaning the PCB contacts or edge connectors. A divider problem certainly makes sense. If the LSB of a divider chain was stuck as you said, a small error would result.

So there is no second LO that has an independent adjustment (separate from the master osc.) that would not normally lock to the reference then.

Thanks

Dave K7DMK

jry
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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby jry » Fri Aug 12, 2016 11:56 am

what are you measuring ? Is it slaved to the same reference ?

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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby jry » Fri Aug 12, 2016 12:18 pm

just as an FYI both the 1900 and 1600 have independent gen and rx freq. loops. On the duplex screen it happens to be labeled as an offset but internally both frequency generation loops are independently generated for the most part.

The 1st lo is completely separate. Two of them ...one for RX and GEN functions .

The rx has a separate 3rd LO and the gen has the 90Mhz generate module which provides the modulation.

The 2nd LO is a fixed 1210 mhz freq and is shared to both GEN and RX... it's a direct multiple of the 10mhz ref. though.

Based on your description I would be wondering if your test source / counter reference is off.

If you can slave them both to the same reference you should remove the frequency error.

k7dmk
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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby k7dmk » Fri Aug 12, 2016 3:33 pm

Guys, thanks to everyone that replied.

This afternoon I triied re-seating all the boards and checked all the sm series connectors for tightness with no change. My setup has a 10MHz distribution amplifier that supplies "house clock" to the instruments. The 10 MHz is derived from a GPSDO and is accurate, The 53131A counter and E4000B signal gen used for testing are locked to the ext 10M reference. When the gen is set to say 500 MHz it reads to a fraction of a Hz of 500.000 when fed into the counter. When the 1900 is fed into the same counter when set for 500MHz, it reads about 1 KHz low and slowly drifts down to about 1.3 to 1.5 KHz low after an hour or so. It's about the same with and without an external reference applied. It appears the external reference is only detected at power-up. If it's applied to the rear BNC connector under power, the blue dot indicator does not come on until the 1900 is restarted. I believe this is normal behavior. For sanity, I doubled checked the setup with another counter that has it's own internal oven time base with the same results.

With the covers off, I noticed that on the module labeled 90 MHz the unlock LED takes about 15-20 seconds to go out after power up, but it does go out. If you watch the 1/4 screen analyzer display in the generate RF mode, the carrier shown drifts slightly at power-up and then locks to the center of the display at about the same time the LED goes off.

As stated before, the error increases with frequency. At 2 GHz error is about 3.2 KHz initially and about 4.2 KHz after full warm-up. So something is drifting with time or temp as the unit warms up. This happens whether locked to an external reference or not, so I don't think it is related to the master 10 MHz LO.

Bummer. Otherwise a very nice piece of gear. No sure where to look next.

Dave, K7DMK

jry
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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby jry » Sat Aug 13, 2016 8:29 am

so if you are testing the RX portion you need to check the frequencies of the 3 oscillators and see which one is off

Would be interesting to verify the GEN frequency.

The RX and GEN really only have the 2nd LO in common so if they are both off by the same amount than that would be the area to look at.

The 2nd LO is fixed though and the amount of offset should be fixed as well if that was the issue.

appears to be a first LO issue but you really need to look at the actual frequencies generated to be sure.

The only other things in common on the RX and GEN is the powers supplies and the reference. The 35V may be worth a look.

The reference switch is hw based on the ext ref input level so the it may just be that the source is checked at boot time and displayed based on that one check.

k7dmk
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Re: IFR 1900CSA Adjustment Advise and Maint. Manual Needed

Postby k7dmk » Sat Aug 13, 2016 10:00 am

As far as testing method so far, it has been with the front and rear panel connectors only. I'm not sure where to find some of these internal signals with no documentation.

I have been testing the RF Gen function by programming a freq and then monitoring the gen output present on the front panel T/R connector with the locked counter. In Gen, the external counter reads LOW by about 1 KHz. at 500 MHz. On the RCVR test I feed in a signal from the locked E4400B sig gen into either the ant input or T/R. The counter and freq error displays on the 1900 read HIGH by about the same amount (1 KHz) with the same 500 MHz freq. applied. I also monitor the rear 10 MHz ref output. Even without an ext reference the internal 10 Mhz is within a Hz when this offset is occuring. It is very close to the same offset when locked to an ext reference.

One other thing I noticed; in the RF Gen mode the last couple of digits of the 53131 counter fluctuate quite a bit when looking at the Gen output. The same counter is pefectly stable when looking at the E4400B output. This is with all modulation turned off on the 1900. Then I looked at the output signal on another specrum analyzer and it appears to have a lot of phase noise compared to the E4400B.

I do have a pdf of the 1600 service manual. I'm not sure how the 1600 and 1900 differ other than the frequency range and the cellular (CSA) stuff in the 1900. Are any of the same modules used and some of the test points the same? What got changed in the 1900 to increase it's range to 2 GHz? Probably a fair bit, I would suspect.

Again, thanks for the help.

Dave, K7DMK


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