Re: LF: [500] - G0MRF testing 503.70

[G0MRF@aol.com]

Hello Dave / Brian.

 

Thanks both for the report. Particually for the detailed Argo screenshot.

 

Equipment is fairly basic.  TX

A trifilar transformer with 2 diodes forming a PSK modulator ( A DBM really) driven from a DDS. Then 4 stages of linear amplification with 6 Watts out.

 

Antenna: 9m base loaded vertical.   apx radiation resistance 0.08 ohms

Antenna current. barely moving the meter.  apx 100mA

So about a milliwatt ERP !

 

Modulation is the aspect of this that has kept me busy. All modulation is on a PIC chip. The psk data is filtered by a 15Hz low pass built around an op-amp. No computer in use.

 

Having seen the spectrum from your argo shot, it appears it's the PSK synchronising signal just before the PSK31 message that is responsible for the widest bandwidth. The sync signal is a series of phase changes at 15.625Hz (+/- my timing errors) it appears to put all the energy from the TX at points seperated by 15Hz from the carrier. The PSK31 data however seems to fit reasonably well into its expected 32Hz B/W.

 

Will leave it on overnight.

 

Thanks

 

David G0MRF

 

 

 

In a message dated 16/07/2007 19:57:56 GMT Standard Time, ganymede444@btopenworld.com writes:

Dear LF, David,

Copied G0MRF PSK beacon this evening on 503.7 kHz.

Beacon text as follows:-
" PSK31 beacon de G0MRF
QTH West London IO91TK
g0mrf@aol.com "

Screenshot attached.

73, Dave G3WCB IO91RM