Friday, 15 August 2014

New Modes and New Bands

With a few days with time on my hands recently, Ive spent more time playing with the WSJT suite of digital modes, particularly more WSPR on various bands, and a play with the JT6M mode for 6m meteor scatter. As yet, I havent made a full QSO in MS, but have been received a few times, and had part QSOs. Its just a matter of refining my technique, and being more patient.

Playing with WSPR, Ive had no luck on 6m, and very limited success on 10m. I have got a bit further with Wispy though. The photo below shows the experimental parallel transistor amplifier, supposed to be 1W, on the left, and the new LPF on the right

The new 7-pole Low Pass Filter is very effective. Built as an add-on board, I can easily test the levels of harmonics before and after the filter, and it is quite clean post filtering. Ive had far less luck with the parallel transistor amp though. I can see that it is amplifying, as can be observed using the spectrum analyser, but the output is just 10s of mW! Its not even enough to raise the meter!

Why this should be I dont yet know. Perhaps its something to do with the biasing or quiescent current, or maybe its the emitter resistors and emitter bypass capacitors.

Ive also, as can just be seen in the lower right of the above picture, made a bit of progress on the receive chain. The two red components are 470nF capacitors, which due to not having that value I had to rob from Daz's Theremin project! I need another, but dont have one anywhere, I will have to try something like a 220nF in its place and hope its value isnt too critical.

One thing I noticed today about 6m WSPR is the number of stations that are only listening! Today when I was active, out of a slack dozen of stations, less than a third were actually transmitting at all! For a propagation beacon network this is poor. It relies on each station transmitting in order to establish the propagation paths.

In light of this, and after reading Roger G3XBM bemoaning the lack of stations active at MF, I have considered today looking at ways to get onto 472kHz. This is an altogether different proposal to most HF/low VHF work. The best I can manage at present is to set up my FRG-100 receiver for 472kHz, and, in the absence of a random wire for that Rx at present, Ive had to take what left of the high-Z input wire (about 2ft of 7/.32 stranded speaker wire!) and using a croc clip lead, patch it to the main doublet antenna via the center pin of the antenna switch port, and set the ATU to bypass. I also have found that the audio feed into the PC is a bad fit, but after much juggling, have managed to feed the audio from the FRG-100 to the PC.

The WSPR software is not at all happy at being fed a 24dB noise floor, and the hum is atrocious, but surprisingly some decent decodes are coming through -

2238 -23 -0.9   0.475749  0 DH5RAE JN68 23
2240 -22 -0.1   0.475684  0 DK7FC JN49 30
2240   2  0.2   0.475739  0 PA3ABK/2 27
2244 -19 -1.1   0.475641  0 DK2DB JN48 27
2244 -14  0.5   0.475653  0 G3WCB IO91 23
2244 -18 -1.5   0.475697  0 DC0DX JO31 33
2244 -12 -0.7   0.475725  1 GM4SLV IP90 23
2244 -21 -1.1   0.475762  0 G6AVK JO01 10

Best DX so far is DH5RAE at 1,141km!

Of course, ive yet to hear Roger!

UPDATE :  Managed to eliminate the hum by swapping from the USB soundcard, which it  seems doesnt like mono jacks, to use the on-board mic input. This has brought the noise floor on WSPR down to a more manageable 17dB. Unfortunately, all the messing about has upset the program, which now is crashing out a bit!

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