Dear Chris, Graham, LF Group,
Thanks to G3XIZ earlier this evening for a nice RTTY QSO on 503.5kHz. I used
MMTTY with 85Hz shift, and everything worked fine - mind you, Chris is not
far from me, and is a good 599 signal.
I am currently (2310utc) sending some test calls on 503.5kHz in PSK31 using
G3PLX's Windows software - any reports/QSOs welcome.
> Hi Jim,
>
>
>
> Interesting on the system, How are you driving it ?
>
>
>
> As for 'tests' well , what's the audio bandwidth of you system ? , looks
> like most modes are in multipsk , but for rtty at 85 hz shift , mmtty
has
> that option
>
The driver is an IC 718 transmitting on 4.50x MHz in LSB mode, connected to
the PC sound card in the usual way for data operation. So the bandwidth is
about 2.7kHz, although I would not want to use it all! The HF output is
mixed down to 500 kHz with a 4MHz crystal, and also fed to a simple diode
envelope detector to recover the modulation envelope. The 500kHz output is
filtered and amplified linearly to about +13dBm, then applied to a limiting
amplifier to give a square wave "clock" signal for the class D output stage
with the amplitude modulation stripped off, but retaining the frequency and
phase information. The envelope detector output is used as a reference
voltage for a series regulator feeding the DC power to the class D PA, so
the DC supply voltage is modulated with the envelope of the original signal.
The result is the output of the class D PA looking pretty close to the
original modulated signal. On receive, the signal path is reversed, and the
incoming signal mixed up to 4.5MHz for reception by the IC718.
I have been looking at the software on NL9222's extensive download site,
there seems to be a number of feasible modes there that might be worth
trying - I will try installing some over the next few days.
Cheers, Jim Moritz
73 de M0BMU
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