----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Thursday, November 01, 2007 11:32 PM
Subject: Re: LF: EER Transverter and Linear Modes testing
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
Ok Jim,
Thanks for that , Is this a published dsesign or your own ? , Ive added a
page to the 'ng'
http://groups.google.com/group/uk500khz/web/eer-transmitting
Looks like a few stations are intrested in this , may be you can add any
links or data to the page ? what you describe looks to fit with the
general descriptions of the 'mode' , Q, do you have any problem with the
'envalope = zero' issue ?
I can see your signal at the moment (00-30 hrs) but its too low to print .
looks like a good signal at Bham , dont know about 'rtty' think we should
call it 'skippy' hih , I did see a stronger signal earlly on, which may of
printed ..
If your about , friday night , I will rig the tx up , see if we can do
anything , early in the evening , after sunset is usually the best signals
from london area ?
G ..
|
