14 Nov 2011

10m Chirpy Measurements

Last week G6ALB made a copy of my Chirpy 14 component transceiver for 28MHz CW. Andrew had access to some better calibrated test equipment and carried out some RF power and sensitivity measurements both on his version and on my second original unit - the first was just a rat's nest on the bench.

Both on my version and G6ALB's version the measured RF power out was in excess of 200mW, which is around 2-3dB more than I had crudely measured. The RX sensitivity on both was such that below -100dBm (around 2uV) was audible in our earpieces in a quiet room. Backwave carrier on TX was rather too high at around -10dBm. Second harmonic was also only around -6dB, so a low pass filter is really a necessity apart from casual short tests.

It does seem that the simple design is reproducible and its performance not at all bad for something this simple. The only major shortcoming is the chirp.
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3 comments:

  1. AnonymousMon Nov 14, 06:29:00 pm GMT

    Hello Roger
    For a two transistor rig the sensitivity is excellent.
    I am thinking of some circuit ideas based around chirpy.
    Thanks again for a simple design.

    73's Tony

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  2. AnonymousWed Nov 16, 01:05:00 pm GMT

    A T-50-6 should do here as well as T37-6 ??
    What do you think Roger??

    Tony B

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  3. AnonymousWed Nov 16, 02:46:00 pm GMT

    Tony B

    You can google the online calculator for the T37-6 work out the inductance from the number of turns and then recalculate it for the T50-6. and keep the tapping ratio the same. This should work just fine.
    I have just wound 20 turns of 26SWG enameled wire on a 1 inch nylon washer that dips with a GDO and 50pF variable cap at 30 MHz the circuit loading should bring it
    down to 28 MHz .
    All best with your chirpy.

    Tony

    ReplyDelete