Re: LF: WSPR without an SSB TRX ?

[M0FMT <m0fmt@yahoo.co.uk>]

Hi Jim

 

If you mix the 1500hz tone up to 500 kc/s conventionally don't you get +/- 1500hz tone as the product. i.e. upper and lower sideband? Even if a double sideband signal was acceptable on 500 it would only fit in the band exactly and the sidebands on the side bands would be out of band or have I missed something?

 

Thus the reason I suggested a Tayloe (for the want of a better description) detector in reverse which resolves the unwanted sideband issue. I dont think a straight forward product mixer will do.

 

A simple phase modulator using two 8meg xtals by G3ZJO is shown on a web page the URL in my last mail. 

73 es GL petefmt

--- On Wed, 7/4/10, James Moritz <james.moritz@btopenworld.com> wrote:

From: James Moritz <james.moritz@btopenworld.com>
Subject: Re: LF: WSPR without an SSB TRX ?
To: rsgb_lf_group@blacksheep.org
Date: Wednesday, 7 April, 2010, 23:25

Dear Chris, LF Group,

----- Original Message ----- From: "Chris Osborn" <g3xiz@yahoo.co.uk>

...>My initial thoughts were that the PC is giving out a 1500 Hz tone + / - 5 Hz.
This is used to generate USB signals from an SSB TX (?)
I was hoping to mix these tones with a stable frequency of 1400 Hz (say) ending up
with 100 Hz + / - 5 Hz - thence to an F-V converter - gain / level adjusted and thence
to the TX VCO input....>

That is probably feasible, if quite tricky - but much easier just to mix the 1500Hz tone up directly to 500kHz to generate the VFO drive for your existing TX PA; that way only a simple fixed oscillator is required (one using a ceramic resonator would be adequately stable and "pullable" over a sufficient range). You then avoid all the business of having to calibrate the f/V gain, VCO frequency shift and so on. Plus, you can tune the frequency by changing the centre frequency setting in the software, and use it to transmit all sorts of other soundcard mFSK modes, RTTY etc.,  too.

Cheers, Jim Moritz
73 de M0BMU