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Fwd: LF: Methods to transmit DFCW

To: LineOne <[email protected]>
Subject: Fwd: LF: Methods to transmit DFCW
From: Andy Talbot <[email protected]>
Date: Fri, 16 Nov 2018 15:34:42 +0000
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The Elad FDM-DUO  will Tx down to DC (well, 10kHz really),  0dBm  from a low power port and has its own internal soundcard so Tx level is always matched perfectly when using digi-modes.  You just need to add a PA.

It is certainly not a cheap rig, but is a lovely bit of kit as a modern SDR transceiver.   And of course can be locked to a 10MHz reference input.

The low power output will work up to 165MHz, so useful for 70 and 144MHz bands.   The Rx will work there, provided you bandpass filter out aliases.  Tx does not have alias problems as it uses a higher sampling rate than the Rx


On Fri, 16 Nov 2018 at 15:11, N1BUG <[email protected]> wrote:
Hi Markus,

Mine too! I would strongly prefer that every exciter and amplifier
be linear but sadly that is not the case in my station. The other
monster in the chase is frequency stability. ;-)

I do have a SSB HF transceiver and a home built downconverter for LF
transmitting. I used this for some CW and JT9-1 QSOs. Unfortunately
it is of no use for slow modes. The converter has a 10 MHz OCXO
which is very stable but the HF transceiver operating at 10.136 MHz
has a cyclic thermal drift of about 6 or 7 Hz every time my furnace
comes on and changes the room temperature! Transmitting, even at low
power will also cause problems with heat. This is no good at all. I
could try to put some kind of heater (like a crystal oven) on the
transceiver's TCXO and try to add some insulation around it. This
would not be easy due to its location on a large PCB and limited
space. I doubt I could make it good enough.

Better of course (and very interesting!) would be to replace the
TCXO with an external GPS locked oscillator but I do not know if I
am up to this challenge. It would require some very delicate surgery
I guess.

In an ideal world the HF transceiver TCXO would be replaced by a
GPSDO, the 10 MHz OCXO in the downcoverter replaced by a GPSDO, the
downconverter rebuilt to be linear, the amplifier replaced with one
that is linear, and the LO in the SDR receiver replaced by a GPSDO.
Unfortunately we do not live in an ideal world and probably none of
that is going to happen. :-)


On 11/16/18 9:18 AM, Markus Vester wrote:
> Hi Paul,
> guess my preferred method is a linear SSB exciter which can do
> all sorts of modes, including specialties like chirped Hell and
> picture transmissions, or 1-dB stepped power tests. On the other
> hand with one sitting here this is easily said ;-)
> Stefan and Tom have successfully employed a Raspberry Pi, which
> can produce modulated RF directly on one of it's digital output
> pins. This has been used for WSPR but I guess it could also make
> Best 73, Markus (DF6NM)
> -----Ursprüngliche Mitteilung----- Von: N1BUG <[email protected]>
> An: rsgb_lf_group <[email protected]> Cc: lowfer
> <[email protected]> Verschickt: Fr, 16. Nov. 2018 12:34
> Betreff: Re: LF: Methods to transmit DFCW
> Thanks Andy. I have no proficiency at all in PIC or Arduino
> programming. In my younger days I wrote some reasonably complex
> DOS programs but a lot has happened since then an the old brain
> isn't what it used to be I'm afraid.
> I am not against *trying* to learn but will consider this a last
> resort if no more complete or operator friendly system can be
> found.
> 73, Paul
> On 11/14/18 10:42 AM, Andy Talbot wrote:
>> Depends how proficient you are with PIC or Arduino or Whatever
>> programming. There are still AD9850 moduiles to be found on
>> Ebay - that are not completely obsolete or sold-out yet.
>> Write your controller code to switch between two or three (for
>> DFCWi) frequencies under control of the ON7YD software,
>> toggling RTS / DTR on a COM port interface (use an FTDI USB one
>> if necessary)
>> On Wed, 14 Nov 2018 at 11:50, N1BUG <[email protected]> wrote:
>>> I am looking for a better method to transmit DFCW for 2200
>>> meter QSOs. For my QSO with 2E0ILY I used a QRP Labs U3S for
>>> the transmitter. This worked very well for DFCW60 when I was
>>> transmitting every other night. For any QSO attempts
>>> involving quick change from RX to TX it would be difficult
>>> because of the time required to program a new message!
>>> One possibility would be to modify this method used by N1VF
>>> for JT9 QSOs with a U3S:
>>> I am a little concerned about messing up my trusty U3S but I
>>> may try that.
>>> It looks like the easy way is the old QRS software by ON7YD.
>>> This is very interesting but I don't have a suitable
>>> transmitter. Are there any published designs for DFCW
>>> transmitters which could be controlled in this way? I wonder
>>> if parts would still be available? I am guessing these used
>>> synthesizers which are not current generation any more. :-)
>>> Any other suggestions?
>>> 73, Paul N1BUG

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