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Old 7th May 2012, 7:45 pm   #1
G0HZU_JMR
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Default Marconi TF2430 Frequency Counter

I've had one of these marconi TF2430 counters since I was a student and it has worked well.

However, today I took it apart for the first time to see if I could cram in a replacement oscillator to improve the accuracy.

Whilst doing this I noticed that the display PCB supports 8 characters ( 8 x 7 segment LEDs) and someone has untidily desoldered the 8th digit.

I'm assuming that this display PCB also supports the TF2431 200MHz version of this counter and maybe this display came from a 200MHz model i.e. my counter had a repair at some point maybe 30yrs ago?


Or should my counter have had 8 digits rather than 7? I'm guessing it should have 7.

Does anyone have a user manual or schematic or service manual for this counter?

Thanks
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Old 8th May 2012, 9:21 am   #2
WME_bill
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Default Re: Marconi TF2430 Frequency Counter

Marconi TF2430. The service manual shows 7 digit display. The display board appears to be numbered Z44827-549M, but there is no internal photograph of the board to compare with your version.
I have also looked at a 1979/80 catalogue. That states that the TF2430, the 80Mhz version, has a 7 digit display.
I see that the unit can be used with a 10Mhz external frequency standard oscillator. The two higher frequency models can be fitted with an internal high stability oscillator.
So I think your various surmises are correct. WME_Bill.
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Old 8th May 2012, 4:50 pm   #3
G0HZU_JMR
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Default Re: Marconi TF2430 Frequency Counter

Thanks for the info Bill

I didn't think it was ever meant to run with 8 digits because it lights the overflow LED if I inject a signal that crosses from 9.999999 to 10.000000MHz from an accurate signal generator.

i.e. the 7 digit display shows 0.000000 with the overflow LED on. However, the PCB has the artwork for the 8th digit and somebody has desoldered and removed the 8th digit. Either as a swap/repair or maybe it happened at Marconi where they converted an 8 digit display to 7 digit due to a shortage of 7 digit displays for TF2430s. Or maybe somebody tried fitting one to see if it would read with 8 digits and then removed it when it wouldn't work!

I usually run it from an external OCXO reference but I've got hold of several hi spec OCXOs recently with 2 minute warmup and sub 0.005ppm over -20 to +65degC

Ideal for a counter although having looked inside I think it will be safest to stick with an external reference as I don't have a schematic to find a suitable place to safely power the OCXO.

However, the internal HC49 crystal based reference is surprisingly good and starts off reading maybe 5Hz high if fed an accurate 10MHz but gets to within 1Hz and stays there in a stable room temperature once warmed up for >30minutes.

Last edited by G0HZU_JMR; 8th May 2012 at 4:56 pm.
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Old 8th May 2012, 4:55 pm   #4
Chaparal
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Default Re: Marconi TF2430 Frequency Counter

Here a bloc schema from TF-2431

Peter
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Old 8th May 2012, 6:03 pm   #5
WME_bill
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Default Re: Marconi TF2430 Frequency Counter

TF2430 with 7 or 8 digits.
Thanks to Peter "Chaparal" for the block diagram of the TF2431.
It is identical to that in my manual for the TF2430 except for the extra digit.
I must confess I usually accept the counter reference oscillator stability as provided.
I am intrigued as to what use you have that requires greater accuracy. You will soon be stunning us all by saying you really want a Caesium reference standard, so that you can determine whether the signal intelligence satellite wedged over Cheltenham has moved it's position by a few feet following changes of the "foreign" government in France, or USA, or Russia, or China. WME_Bill m0wpn
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Old 8th May 2012, 6:44 pm   #6
G0HZU_JMR
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Default Re: Marconi TF2430 Frequency Counter

Thanks for the block diagram

I guess I don't 'need' to have great accuracy but I do a lot of RF design up into the GHz region and it's useful to have all test equipment references nicely aligned.

So I either use a common reference or try to keep them all in close calibration. This is most useful if I want to zero beat signal generators in the GHz region (or very nearly zero beat)

eg a 5Hz error at 10MHz multiplies up to 1kHz at 2GHz.

There's always a decent OCXO on hand from a sig gen or analyser or dedicated bench OCXO unit that will outperform the oscillator in the TF2430 so I often use the external reference option on it or another counter. Usually I don't need the greater accuracy but if it's easily available I'll opt for it anyway

I use an offair standard to check them all annually (or thereabouts) but I'm sure there are going to be people on here that demand even better accuracy than this
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Old 8th May 2012, 7:20 pm   #7
Dickie
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Default Re: Marconi TF2430 Frequency Counter

Hi,

The TF2430 was the bottom of the range model at 80MHz, though it will work happily at >100MHz as I'm sure you have discovered. Other models are the TF2431 (200MHz) and TF2432 (560MHz). It was always 7 digits, though it shared the same display board as the 8 digit TF2431. If you were really keen it could be converted to 8 digit, you would need to add an extra driver transistor and the 7 segment display of course, and add a link in the right place. I have some poor scans of the circuits which are too big to post here but drop me a PM with your email address and they're yours.
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Regards,

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Last edited by Dickie; 8th May 2012 at 7:35 pm.
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Old 8th May 2012, 10:58 pm   #8
G0HZU_JMR
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Default Re: Marconi TF2430 Frequency Counter

Hi Richard
Yes, mine works to about 150MHz. It is a very nice little counter with a very clear display and simple user interface. Best of all it gives a very stable reading compared to other counters if the signal is small.

Thanks for the offer of the scans of the circuits!

Regards
Jeremy
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Old 8th May 2012, 11:21 pm   #9
G0HZU_JMR
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Default Re: Marconi TF2430 Frequency Counter

Here's a couple of images of the display board I took before I reassembled it all.

You can see the dodgy soldering around the digit that has been fitted/removed at some point in the life of the counter.

I've had it nearly 30 years so it must have happened a long time ago...
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Old 9th May 2012, 6:02 am   #10
einovaan
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Default Re: Marconi TF2430 Frequency Counter

You can get a rubidium standard from eBay. They are very accurate.
http://www.ebay.co.uk/sch/i.html?_fr...All-Categories
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Old 10th May 2012, 4:48 pm   #11
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Default Re: Marconi TF2430 Frequency Counter

I've seen those on ebay. I'm very tempted but realistically I think my homemade 198kHz offair standard is good enough for me as a daddy reference.

The ageing rate of the OCXOs in my various bits of test gear is about right for a yearly calibration to get within 0.1Hz and usually they are within 0.3Hz of 10MHz and this is fine for accurate use up to several GHz for the whole year.

Having this level of accuracy is a convenience rather than a necessity as it makes for 1st time accurate downconversion from several GHz and also keeps the analyser in agreement with the generators on narrow spans.

A Rubidium standard would be very nice but way OTT for my needs.

Thanks to everybody for the info and especially for the block diagram from Chaparal and the circuits from Richard
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