Re: LF: OPDS bandwidth (was EA5DOM LF tests)

[Markus Vester <markusvester@aol.com>]

Yes, Mike is right. Zooming the spectrogram on Luis' signal did not show any central carrier, so subsequent dashes seem to have random phase. An additional problem could be the temperature drift of the master crystal oscillator (neither the common 125 MHz-clocked AD9850 modules nor the Si570 source are very stable).

Regarding a new transmitter, I would recommend starting with a stable continuous signal from an OCXO or TCXO, and applying the keying only directly before the PA, after any divider stages. As far as I can see, this is done right in the W1VD design, where the flipflop runs through and keying is applied to the FET drivers.

All the best,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Mike Dennison <mike.dennison@ntlworld.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 8 Sept 2016 12:12 pm
Betreff: LF: OPDS bandwidth (was EA5DOM LF tests)

The wider bandwidth seen on OPDS may be key clicks but I have found
it can be caused by a non-coherent signal, ie the 'oscillator' is not
continuously running. I found this, for instance, when keying a
divider chip on my GW3UEP 472kHz rig, and it was cured by keying the
PA instead.

Mike, G3XDV
============

On 7 Sep 2016 at 11:20, DK7FC wrote:

> date time call distance frequency bandwidth snr
> correlation
>
> 2016-09-07 04:35:08 EA5DOM 1398km 137519.960Hz 97mHz -37.7dBOp 100%
> 20.2dB 2016-09-07 03:35:08 EA5DOM 1398km 137519.910Hz 112mHz
> -48.5dBOp 100% 19.8dB 2016-09-07 02:35:09 EA5DOM 1398km 137519.928Hz
> 75mHz -42.0dBOp 46% 16.6dB 2016-09-07 01:35:07 EA5DOM 1398km
> 137519.926Hz 71mHz -99.9dBOp 77% 16.6dB
>
>
> Somehow the bandwidth values are quite high. Normally it is arround <
> 10 mHz. Anyway, a nice result.