VK1KW novel beacon trial

[VK2OMD]

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I do feel that an alternative to WSPR is needed, one that is not as timing or frequency dependant as WSPR, one that can still allow a beacon to be on its own freq and not a shared frequency. No beacon owner realy want to have a complicated collection of equipment to maintain, most beacons are lucky to get a visit once a year.

QRSS has the potential to be that beacon mode by embracing a mixture of QRSS single tone and traditional CW. I feel that the prototype beacon mode developed by Owen and put to air by Rob deserves a wide trial within VK and beyond.

The QRSS3 extension is a very simple one to apply to a conventional A1 (amplitude modulated) for F1 (frequency shift keyed) beacon. It does not require replacement of the modulator or any later stage, just the keyer needs to be able to send a dual speed message and preferably one that repeats on a cycle of an approximately integral number of minutes. Obviously if you are hunting for the beacon with a spectrum display just a couple of hundred Hz wide, you want to know with some certainty the frequency of the beacon (relative to your own receiver)... and beacons that drift 5kHz over a day would not be good candidates, nor a receiver with similar frequency uncertainty.

On the receive side, exploitation of the QRSS3 message requires audio spectrum analysis using Spectran or the like... and lots of people already do that to find trace of weak beacons. As I already mentioned, some confidence that the receiver frequency is within say 1kHz will assist productivity.

If VK1 have a beacon that is identifiable 10-20dB lower than a conventional beacon, then it might encourage a distant station to call with a transmitter that is 10dB higher in power than the beacon, to be heard by a receiver in VK1 using an antenna with 15dB more gain than the beacon... so with 25dB total link improvement may be quite workable... even though the beacon may not be heard by ear. That might encourage more contacts into VK1 from distant stations who are able to exploit the technology!

If ZLs can detect and identify the VK1 beacon before others on the 'big island', then that might advantage ZL-VK contacts.

None of this is to restrict in any way those who want to go to work and let their WSPR station do their DXing for them... as I mentioned in another thread one 2m VK station was spotted in Europe according to the WSPR database!

Owen

[VK2OMD]

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Remembering I guess that most listening here may not be running any Pre-amps which would be a significant advantage...

I hear lots of people fret about the lack of an LNA (preamp).

The reality for many in the big smoke is that the external noise on 2m is well higher than the internal receiver noise. Under than scenario, deployment of an LNA that reduces internal noise, even if markedly, does not make much difference to TOTAL noise (ie the sum of external and internal noise).

Indeed, with inadequate LAN designs that focus entirely on delivering very low Noise Figure (NF) in a shielded room environment (good NF specifications on paper), front end selectivity is often deficient and intermodulation 'noise' experienced in the real world might not only be much greater than the internal noise implied by the LNA NF, it can quite easily be worse than the internal noise of the transceiver... ie the LNA degrades system performance.

Nevertheless, it is commonly held that an external LNA is essential to success on 2m, some even insist it must be at the masthead to 'work'.

Owen

[VK2OMD]

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If VK1 have a beacon that is identifiable 10-20dB lower than a conventional beacon...

Running the numbers for the current beacon at VK1KW, Tx power out is 25W, line loss 1dB, antenna gain 7dB (omni), EIRP=20dBW.

If a hypothetical Canberra station had the legal limit on CW (120pY, at 44% duty cycle for Morse code, 270pX), a 12el DL6WU at 15dB gain, and 1dB of line loss, EIRP=38dBW... an advantage of 18dB over the beacon.

So for a minimum S/N on CW of -6dB with EIRP 38dBW, if the beacon was observed by a distant station with S/N better than -6-18=-24dB, a contact should be feasible (all S/N figures express relative to the JT convention, 2500Hz).

Owen

[VK2OMD]

I have constructed a beacon based on the Simple Morse Beacon Keyer (http://vk1od.net/module/smbk/index.htm) using an ATTiny85 and a ULN2003 to provide 6 isolated outputs which can be allocated to inverting or non-inverting outputs using the DIP switches according to the requirements of each tx. (Keying polarity should be MARK high.)

The keyer uses a bootloader, and a common Arduino USB/RS232-TTL adapter ($7 on eBay) for field replacement of message content (or firmware for that matter).

Owen

[VK2OMD]

And a 'traditional' beacon that can be seen on the spectrum display but not copied by ear...

(Ignore the freq scales, the display is uncalibrated.)

Lacking positive ID at such weak signal level... but probably Rod's beacon under test.

Owen

[VK2OMD]

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I might prompt you all to think about Doppler, and how you can see a signal at a steady freq due to an aircraft. The signal that pops up for a little while out of the noise, and with constant freq is probably not Doppler shifted, and is a 'direct' signal rather than an aircraft reflection.

A clarification...

I wrote the above in the context of Rob's observation of VK1KW at <300km, and mine at 150km.

For any AE path, the Doppler shift will be very low as the rate of change of total distance from tx to aircraft plus aircraft to receiver is very low (eg around mid distance).

In the case of very long paths, eg 800km, the period of low Doppler shift might be many minutes, but in the case of the short paths mentioned above, it is more like a minute or two and any sustained or recurring un-shifted signal is probably due to other than aircraft.

Owen