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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 1st May 2021, 12:01 pm   #1
g0hze snowy
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Default Frequency counter and CTCSS decoder.

Hi All
Can anybody suggest or point me in the right direction of a small counter as title above, i know you can purchase them for approx 15 but i much prefer to make something from the box's of bits and displays that i have in my shack.
Being retired time is of no real factor! hi hi.
What i am hoping is that i can pick up a transmitted signal thru' a small whip antenna which displays the 2 x frequencies.
As usual all advice/help pos or neg, greatly appreciated.
Stay well and away from this ruddy virus
Snowy G0HZE
If this is in the wrong section, moderators please move to correct one, TQ.
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Old 8th May 2021, 5:17 pm   #2
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Default Re: frequency counter and ctcss decoder

Quote:
Originally Posted by g0hze snowy View Post
Hi All
Can anybody suggest or point me in the right direction of a small counter as title above, i know you can purchase them for approx 15 but i much prefer to make something from the box's of bits and displays that i have in my shack.
Being retired time is of no real factor! hi hi.
What i am hoping is that i can pick up a transmitted signal thru' a small whip antenna which displays the 2 x frequencies.
As usual all advice/help pos or neg, greatly appreciated.
Stay well and away from this ruddy virus
Snowy G0HZE
If this is in the wrong section, moderators please move to correct one, TQ.
ARRL handbooks often have designs for frequency counters, the good news is that they have been proven both by the original designer and by ARRL's lab before publishing (apologies if you are already familiar wth these handbooks).

My copy of the 1993 handbook has a particularly simple design based around a 74C926, the few remaining components including a 4 digit LED display being typical of a junk box. This design may also have been repeated in the next few editions. It may be possible to find a relevant handbook on the Web, alternatively these handbooks are purchaseable for a few quid on Web auction sites (if you are prepared to watch and wait!)

Usable CTCSS decoders are much more difficult to build at home because of the typical S/N on h.f. (perhaps slightly easier on v.h.f upwards) and the closeness of adjacent tones. The simpler analogue designs tend to suffer from false triggering; more complex designs have quite a lot of analogue/digital, even software. But do you need a decoder anyway? That would just give you a CTCSS present/not present output and you don't need a freq. counter for this.

If this is just a bench experiment, I suggest feeding the output of your receiver into a sharp bandpass filter passing the CTSS tones of interest. The filter output is fed straight into a simple freq. counter. The presence of CTCSS tone would give a reasonably stable reading on the counter, good enough to distinguish eg. 100.0 from 103.5Hz

I don't understand your comment about two freqs., that sounds more like DTMF to me.

Hope this helps.
Cheers, Marty G8PCF
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Old 8th May 2021, 6:53 pm   #3
g0hze snowy
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Default Re: frequency counter and ctcss decoder

Hi Marty
Sorry if i didn't make it clear about the 2 x displayed frequencies, 1 is the TX frequency and the other is the ctcss frequency that is superimposed on the TX frequency, i have seen some advertised on the web for about 13, but they are made and imported from the far east.
I will look thru' my books as you suggest and see what i have.
Regards
Snowy
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Old 8th May 2021, 11:00 pm   #4
Terry_VK5TM
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Default Re: frequency counter and ctcss decoder

Please excuse me if I have what I think you want to do wrong, but a frequency counter won't show the CTCSS frequency and transmitted frequency at the same time.

You will only be able to measure the CTCSS tone frequency after it has been picked up and demodulated by a receiver.
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Old 9th May 2021, 7:45 am   #5
g0hze snowy
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Default Re: frequency counter and ctcss decoder

Hi Terry.

Thanks for your response to my query.

There is a small unit available on line and also a YouTube film showing both frequencies but it is from China. Having had some experience of their quality or lack of it I won't go there anymore for my purchases.

Hence the request for info.

Stay well and free of Covid.

Snowy G0HZE
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Old 9th May 2021, 11:55 am   #6
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Default Re: Frequency counter and CTCSS decoder.

Actually he is right. There are indeed rather badly specified devices on the market that claim exactly that.

They must be complete FM radios, but with no speaker!
Their sole purpose seems to be to display the frequency and the CTCSS - presumably after FM demodulation (they do not mention that).

It is not clear how sensitive they are - so not clear whether these are for telling you what you are transmitting or what you are receiving.

So what do you expect this to be used for?

A frequency meter is a fairly simple device, as modern things go. But decoding the CTCSS is a much bigger deal because first you have to demodulate the signal back to audio and then measure the CTCSS while ignoring higher frequencies. Not so easy!
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Old 9th May 2021, 12:19 pm   #7
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Default Re: Frequency counter and CTCSS decoder.

OK, learn something new every day.

Here is something I found on the net https://k3jls.net/sniffer.jpg, called the Sniffer, not exactly what you are looking for, but, if you used an FM radio (for the band of interest) and the input stage in the diagram connected to a frequency counter, it might work.

Full description here https://k3jls.net/auto_ctcss.html
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Old 9th May 2021, 12:24 pm   #8
g0hze snowy
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Default Re: Frequency counter and CTCSS decoder.

Hi GMB/Terry
Thanks for your input, i had ( at the time i asked for help) a unknown ctcss board that required adding or removing solder blobs to alter the ctcss frequency, i have thru' friends on here and locally been able to now identify said board and tell me where the paperwork was to be found, then i changed the frequency to my local vhf repeater (PE on 98.4) so all is well now.
Thanks to all that responded to my shout for help, much appreciated.
Snowy
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Old 9th May 2021, 12:32 pm   #9
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Default Re: Frequency counter and CTCSS decoder.

As the OP has found a solution it's time for this thread to go QRT.
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