Re: LF: Re: 137.500 kHz ROS beacon

[Gary - G4WGT <g4wgt@tiscali.co.uk>]

Hi Mal,

Thank you for your report & comments. The mail you replied to gives all the details of equipment in use for the test beacon.

I would like to be able to have a QSO using morse but I have to admit to a complete loss of confidence as I have not used the mode for 25 years which was one year after I passed the test in 1984. Looking back, letting it go was a silly thing to do.

I do enjoy testing out these "weak signal" modes & in the report I received from Michel F5WK last night he wrote that he could not hear the signal or even see it on SpecLab but he got a complete decode. So as a weak signal communication mode it works.

Just to elaborate on the antenna, it is a 12 metre base loaded vertical with a small elevated inductor of 500uH at about 9 metres & a 1 x 3 metre capacity top with a 120uH spiral inductor. In my small garden I have no space to go outwards only upwards.

73,

Gary - G4WGT.

On 20 June 2010 13:48, mal hamilton <g3kevmal@talktalk.net> wrote:

Gary

If that was you last nite on  137.5 kcs you were strong enough for cw or qrs3 no need to struggle with decodes from elswhere.

also I had a qso with G3XIZ this morning on 137.0 kcs and got 599, he was 569.

Not sure what antenna u were using but it was putting out a fair signal to this qth. Your radiators are probably acting as an antenna above earth.

 

de mal/g3kev

 

----- Original Message -----

From: Gary - G4WGT

To: LF Group (RSGB)

Sent: Sunday, June 20, 2010 12:07 PM

Subject: LF: 137.500 kHz ROS beacon

Hi LF,

Having successfully bench & on-air tested a x2 harmonic amplifier method of driving my G0MRF Class D LF transmitter, I ran a beacon last night (Saturday 19th) on 137.500 kHz.

An extract from my previous e-mail description is shown at the end.

Using the equipment & method described below, the ERP from my 12 metre vertical antenna was around 150mW. The mode was ROS MF-1, 100 Hz bandwidth.

I received the following report from Michel, F5WK in JN18HP, a distance of 410 miles (661 kilometres) in daylight.

>> Not even a faint trace on a QRSS3 spectrum but:

>> RX1: 19:23 @ 5.9 Hz: 9 <STOP> -37 dB
>> RX1: 19:28 @ 5.4 Hz: O4WGT <STOP> -34 dB
>> RX1: 19:33 @ 5.4 Hz: G4WGT <STOP> -31 dB

The x2 harmonic low level amplifier is a simple way of driving a Class D type of transmitter which employs a divide by 2 drive chain. My limitation with multi tone drive is that my DDS VFO will only produce 2 frequencies ie. the main frequency & a CW/Rx offset which has previously limited me to 2 tones as with RTTY & DFCW modes.

Please bear in mind that it will not be suitable for modes like PSK were tones are transmitted simultaneously.

At the moment the 2 small PCB's are precariously lying on the desk, when I have cased them I will publish the circuit & pictures.

73

Gary - G4WGT.

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After a few days experimenting & bench testing a method of driving my
G0MRF Class D Tx on the 137.000 kHz band from my linear transverter I finally
constructed a harmonic amplifier producing a 274.000 kHz signal from 137.000
kHz input. An "on-air" trial was conducted resulting in a QSO with
Graham G0NBD on 137.000 kHz using ROS data mode software.
 
My thanks to Graham for his ideas & tests.
 
The mode used was ROS MF-7. The equipment used for the QSO was as
follows. Kenwood TS-440 to my LF-MF linear transverter producing the
137.000 kHz signal, followed by a tuned harmonic circuit & buffer
amplifier whose output was 274.000 kHz therefore at x2 drive for the Class
D Tx. The x2 signal is then divided by the Tx driver chain in the
normal way to provide 137.000 kHz to the PA.
 
This method should also work well using WSPR & other similar modes.

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