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Author Topic: URB25 stability  (Read 6635 times)

9A5BDP

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URB25 stability
« on: October 05, 2013, 10:44:05 AM »

Hi there...first at all..topic name is wrong one..must be URM25...

I am wondering, what is frequency stability of the URM25 signal generator?

In the near future I would be in process of adjustment R390 receiver and for that purpose manual asks URM signal generator, so must have replacement unit for this purpose because I don't have it..

(P.S...how to change name of the topic after publising is maded?)

73!

Dubravko

« Last Edit: October 05, 2013, 10:54:56 AM by 9A5BDP »
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AC5UP

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RE: URB25 stability
« Reply #1 on: October 05, 2013, 11:47:41 AM »

I have a URM-25D that was drifty and had no output from the internal 400 CPS audio oscillator. Then I replaced all the tubular condensers, which is not an easy job due to the way the terminal strips are stacked in the chassis. Give yourself some extra time to do this if the generator still has the original condensers. I also cleaned & lubricated the switches and tuning drive. It's worth the effort.

Now it has modulation and is very stable after a 30 minute warm up. Whenever I want to use it for an alignment I turn it on first and have no problems with drift. I check it against a frequency counter connected to the high-level (not attenuated) output between each adjustment. Also, have you noticed in the R-390 service manual that a full performance check and 24 hour warm up is recommended before an alignment? The radio was intended for a 24/7 duty cycle and is very stable after the internal temperature stabilizes.

9A5BDP

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RE: URB25 stability
« Reply #2 on: October 05, 2013, 02:05:32 PM »

Currently I have Wavetek 166 signal generator but his frequency have noticeable drift of some 10 Hz per second and allways go down. So my big question is: is this nonstable generator good for R390A receiver adjustment..I don't think so..please correct me if I am wrong..

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AC5UP

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RE: URB25 stability
« Reply #3 on: October 05, 2013, 02:28:47 PM »

The quality of an alignment is only as good as the accuracy of the tools and skill of the technician. But... It's easier for a technician to compensate for the tools than it is for the tools to compensate for the technician.

My primary RF generator is the military version of an HP 8640B and that's one very fine generator. But it does have a bit of drift until it stabilizes after a few hours. Mine also drifts downward but at a slower rate. What I do is set the generator a bit high then watch as it drifts through the exact frequency I need. Make the adjustment and move on. It only takes a second or two for most adjustments and the generator usually gives me several at balls-on dead accurate. Try it and you'll learn how to catch the right moment.

If you miss it, adjust the generator and try again.

9A5BDP

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RE: URB25 stability
« Reply #4 on: October 05, 2013, 02:59:52 PM »

I will make tomorrow job preheating stabilisation of my Wavetek, maybe is problem only in temperature stability..couple of hours will be good for test..
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KC4MOP

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RE: URB25 stability
« Reply #5 on: October 06, 2013, 09:56:24 AM »

We called those things drift boxes.
I sprung for this:   http://www.elecraft.com/XG3/xg3.htm

Great, stable, accurate RF generator.
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9A5BDP

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RE: URB25 stability
« Reply #6 on: October 06, 2013, 11:04:53 AM »

Thanks for Elecraft info, great gadget to have..

I make my test with preheating of Wavetek and after some 6 hours of working results are:

on 455kHz drift is in range of +-20Hz
on 14Mhz drift is in range of -2kHz/hour

Maybe is preheating best approach to get useable equipment..
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W2WDX

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RE: URB25 stability
« Reply #7 on: October 07, 2013, 06:06:10 PM »

What is also important is to make sure the generator frequency is verified against a good accurate frequency counter.

9A5BDP

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RE: URB25 stability
« Reply #8 on: October 08, 2013, 11:11:16 AM »

I checked output frequency with dual measurement setup, first is Grundig UR frequency counter with special quartz time base and second one is Tentec Omni VII, and on both 'instruments' frequency drift during temperature rise is the same.
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KH2G

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RE: URB25 stability
« Reply #9 on: October 08, 2013, 05:15:38 PM »

According to the tech manual which is available on BAMA - it is +-.25% above 10MHz. Fairly loose by todays standards.
Regards
Dick KH2G
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