Quote:
Originally Posted by g0hze snowy
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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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