Month: August 2008

Hi Bill,

OK on your podcast. I had a quick listen to the first portion. Yes, QRSS3 bandwidth is indeed 0.34 Hz. ON7YD has an excellent CW bandwidth reference, see –

http://www.qsl.net/on7yd/136narro.htm#Bandwidth

Clearly ‘hard keying’ of any CW (or FSK) TX will increase the transmitted bandwidth. In a practical sense QRSS transmissions key the carrier at such infrequent intervals that an odd key click every 3 (dot) or 9 (dash) seconds will be of little consequence, and especially with QRPp. Ideally however it would be best to control the carrier rise and fall times during keying. A ‘raised cosine’ / ‘Gaussian’ rise / fall time is optimal. It also seems to make ‘intuitive sense’ for those like me that do not understand the underlying math’s.

Another way to get more familiar with QRSS bandwidth requirements is to open Spectran –

http://www.weaksignals.com … Select a Mode (eg – QRSS3), then observe the “Show Controls” menu –

(22050 / 65536 = 0.34 Hz)

For QRSS10 you will see –

(11025 / 131072 = 0.084 Hz)

QRSS10 not considered unusable on HF for RX purposes, as it is impossible to keep even the most stable TX within a few FFT bins due to continually varying ionospheric conditions. RX s/n is dependent upon capturing as much energy in as few a bins as is possible.

Following some 100’s of tests over several years between DL6NL and myself, we eventually concluded that QRSS6 TX with a 5 Hz CW_FSK shift was “pretty much optimal” over long paths if you want accurate callsign ID’s. Slower obviously gives more time to “integrate” the signal, and make a ‘decision’ as to whether the portion you have just seen was a dot or a dash. The trade off (as always), is rate of information transfer. When TX’ing QRSS6 FSK_CW, the HF reception should remain as QRSS3 – use Slow Mode. QRSS6 transmissions will look fine on most grabbers.

Another factor not generally appreciated by newcomers to QRSS is that the visual ‘gain advantage’ of QRSS comes not from the RX’ers filter bandwidth, but rather from the FFT bin size (Resolution) within Argo / Spectran – namely 0.34 Hz. Narrow roofing filters can be useful to exclude strong QRM that otherwise might impact the RX AGC, but make no difference to the observed s/n ratio otherwise. (All else being equal.)

Unfortunately I think that is fairly unlikely that I will see many EU signals until conditions improve. I have caught only one EU signal so far this year. Conditions have been really poor these past 12 months or so, and the worst I’ve encountered since I started QRSS activities back in 2004, or was it 2005? When the sunspots return I’m sure I will see many new EU signals. DL6JAN has previously made it down here with 5 mW + many other stations that were running 50 mW to 200 mW or so with minimal TX antennas.

Good luck with your QRSS experiments!

Regards,

David, VK6DI.