[Lf] WOLF Test results from DF0WD]

[Andre' Kesteloot]

DL4YHF at aol.com wrote:

> Hello Jim, Markus, and group,
>
> Some on-air testing of Stewart's implementation of WOLF took place on
> sunday
> evening, which was partly successful (tnx Markus, DF6NM and Jim, M0BMU
> for
> their patience and to Stewart, KK7KA for the new software).
>
> Here is the new setup used at DF0WD:
> - An LF-transverter which was once intended to be a linear transverter
>
>   (until I blew the first set of matched MOSFETS a few months ago).
>   Transverter mixes 10.136MHz down to 136kHz and vice versa.
> - An oven-controlled 10MHz XO which feeds the transverter
>    and synchronizes the 30MHz 'master' oscillator inside the IC706
> - An old IC706 shortwave TRX, slightly modified
>  (30MHz clock 'voltage controlled').
> - WOLF signal taken from soundcard, fed to IC706 in USB mode
>  (to test amplitude shaping of new WOLF software by KK7KA).
> - TX output power about 10 Watts (a little more later with "rough
> keying")
> - Antenna 200m horizontal wire (no straight line), end fed,
>   about 8..10 meters above ground.
>   EIRP once estimated by PA0SE about 80mW with max. drive,
>   depending on WX (see www.qsl.net/dl4yhf/lf_index.html).
>
> I received the WOLF signal with the IC706 in "CW" at (10MHz+)137.500,
> using a
> the narrow CW filter.
> To transmit, the IC706 runs in "USB" at (10MHz+)135.500. The audio
> frequency
> should have been 2000.000 Hz, so the transmitted WOLF carrier should
> have
> been on 137.500 kHz (but it wasn't, see below). The soundcard's A/D
> conversion rate was once measured as 7938.086, this value was passed
> to WOLF
> as command line argument (because this is quite 'far off', I will
> verify it
> later with the 10MHz-ref divided down to audio freq. Thanks Markus for
> the
> point).
>
> To Jim, M0BMU: The "test carrier" was transmitted "CW", so it was not
> generated the same way as the WOLF signal. This may explain the
> problem.. I
> don't know how you generated the "leading carrier" before your WOLF
> transmissions a few weeks ago.
>
> One intention for the test was to compare the new 'amplitude shaped'
> WOLF
> signal. I found that with the amplifier currently use here, I can not
> generate such a 'crystal clean' WOLF spectrum like the one shown on
> Stewart's
> updated WOLF page (http://www.scgroup.com/ham/wolf.html).
>
> It seems that each MOSFET (IRF540) in the PA needs an indivudual
> carefully
> adjusted bias point, and a little more source resistance (as negative
> feedback) to make the small PA work linear. Each FET carries a
> different
> current, especially when the driving power is very low. Result: the
> damn
> thing looks like a linear when the power is 10%...70% of the output,
> but it
> does not behave linear when drive is less than 10% (because of
> different FET
> behaviour) or more than 70% (compression point).  The low-power
> linearity ot
> the PA was better, when I used the 4 "best-matched" FETS which I
> selected
> from a bundle of 50 low-cost FETS.  I blew two of these 4 FETS a few
> months
> ago when was experimenting with a slowed-down variant of PSK31 (which
> produced the sample modulation spectrum as WOLF with the option 't
> 1').
>
> The best way to drive a high-power BPSK transmitter is the way M0BMU
> described (do the phase reversal by "XOR-gating", and do the envelope
> shaping
> by "modulating the PA supply voltage" or similar).  On the other hand,
> a
> 'completely linear' concept will allow low-power experiments with
> QPSK, MT
> HELL etc. As long as I am still resctricted to the crazy power limit
> in DL, I
> don't have to care for a highly efficient TX design (there's enough
> "spare
> power" to compensate the losses in the ATU and in the cable which I
> consider
> as part of my transmitter hi).
>
>
> Hope I'll have better luck next time, and thanks to everyone involved.
>
> Also thanks to all stations active in fast CW, which will remain my
> favorite
> mode. Nice to meet you again; no matter if in CW, any kind of BPSK or
> whatever.
>
> 73's Wolf (DL4YHF).
>
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