FT-101 Frequency Counter and Display

Discussion in '"Boat Anchor" & Classic Equipment' started by NF1J, Jun 4, 2021.

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  1. NF1J

    NF1J Ham Member QRZ Page

    Hello all. I have been working with a RF engineer to come up with a solution for a frequency display for the 101.

    I have uploaded the project files to github.

    I am hoping that this will be a community project and if anyone makes improvements they will share with us .

    Please read DIGITAL FREQUENCY MEASUREMENT SYSTEM DESIGN in the files.

    It is in PDF and DOC format.

    You can use eagle to open the schematic and boards.

    https://github.com/granttonya/101Freq
     
    N2EY likes this.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    Just had a quick look at the explanation of how you plan to do this . . . and there are a number of flaws in your design that seems to demonstrate a basic lack of understanding how signals are produced.

    Firstly, you say that on Transmit, you can simply sample some of the RF from the transmitter driver output. That would be fine if this was an A.M. Transmitter . . . but this is an SSB Transmitter, so the readout would be constantly varying as you speak - never reading your actual transmit frequency . . . and not reading at all when you pause your speech ! Plus, if there is no signal being received, there will be nothing to make the frequency counter read.

    Secondly, you talk about sampling the Received IF signal on 3.18 MHz . . . again, this won't work, as a received SSB signal is constantly varying in frequency as the other station is speaking !

    It seems that this is a theoretical design that hasn't been tried in practice, as it clearly can't work as described.

    Roger G3YRO
     
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  3. N8YX

    N8YX Ham Member QRZ Page

    Don't re-invent the wheel.

    Study the block diagram of Kenwood's DG-5 counter...or the SB-650 equivalent used with Heathkits of the day. Adapt your design to utilize the same signals if you want a true "auto-calibrating" readout. Otherwise - as has been pointed out in the other thread - the display amounts to nothing more than a counter with preload which samples the VFO frequency and must be manually calibrated. There's really no other way around it, given variances in HFO and BFO output frequencies.
     
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  4. SM0AOM

    SM0AOM Ham Member QRZ Page

    "Those that do not learn from history are doomed to repeat it..."

    As R0ger pointed out, this scheme is fundamentally unable to reconstruct the frequency of a received or transmitted SSB signal in particular, unless long-term averaging of the counted frequencies are used.

    Similar schemes were used in some very early "digital dial" implementations, but became abandoned for several reasons, the major being the problems with spurious signals that had to be suppressed by very extensive decoupling and filtering.

    When reading the project documentation I, somewhat reluctantly, recall what a friend of mine, an University lecturer, says about "blind faith in simulators".
    It generates designs that look good on paper and which work in the simulator but usually do not stand their first contact with the "real world".

    It is a pity that "lab classes" have been more and more infrequent in favour of simulations.

    Finally, the output of any project cannot be better that its input.

    It appears that fundamental aspects of spectral and time-domain properties of the signals intended to be used for the reconstruction of the receive or transmit frequencies have been overlooked in the initial specification.

    73/
    Karl-Arne
    SM0AOM
     
    Last edited: Jun 4, 2021
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  5. N5KBP

    N5KBP Ham Member QRZ Page

    I can appreciate the time and effort you have put into this so don't take this the wrong way. This looks like a Rube Goldberg mouse trap. All you have to do is tap the VFO, HFO and BFO signals. Buffer amps would be needed but very simple to implement. Wave shape them to square waves for the digital counting circuitry. Then count each and do the math. Use a multiplexed display like the max7219 to display the result along with a one letter mode designation just for grins. ie "L 7.215.1" or "U14.250.1" or "A29.100.1" You could surmise the mode by comparing the BFO frequency in the counting/multiplexing code.
    This would be easy Using a Teesny4.0 along with the input multiplexing and waveshaping circuitry

    Pseudo code:
    Count and save VFO
    Count and save BFO
    Count and save HFO
    Deduce mode by BFO frequency
    Do math
    Display result
    Loop




    Marty
    N5KBP
     
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  6. N2EY

    N2EY XML Subscriber QRZ Page

    "If nobody does it that way, there's probably a very good reason"
     

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