At home in the half-million-strong city of Hannover, a 40m loop has been hanging in our huge attic for 12 years. The local QRM has increased to over S9 over the years, making it practically useless.
I was about to take it down, but then I thought of WsprNet. A digital beacon system that also serves as a scientific method for researching solar activity. Usually, you need a PC and a transceiver to operate it. And an interface for automatic band switching.
A standalone transmitter is much simpler and more cost-effective in the long run. I use a WSPR desktop from ZachTek www.zachtek.com for 80-10m with GPS and 200mW out. Now I can get an idea of the conditions myself before activating a summit. I look for my results on https://wspr.rocks/.
Insert a 13db-Attenuator: 200mW in WSPR is equivalent to 80 watts in CW. With the attenuator you get results for 4 Watts CW which - at last in my case - is more realistic to typical SOTA-activity.
The Zachtek allows also to exclude bands you dont use at your SOTA-tours vor or which you bring no rig for in the summit. For example: If you plan to use the qmx-midband just chose 40, 30, 20, 17 and 15. As a side-effect you get results on the “interesting” bands every 10 Minuten instead of every 16 minutes.
I have such a Zachtek myself and I like it very much
The minimum SNR bandwidth at 2500 Hz is CW -5 dB, WSPR -32 dB, and CW dx -15 dB.
When I transform this to a bandwidth of 100 Hz, it is CW(DX) -1 dB CW +9 dB WSPR -18 dB.
So if I use 200 mW in WSPR, that’s 23 dBm and add the difference on a -1 dB CW DX signal (100 Hz BW), 17 dB to my signal of 20 dB I get 40 dBm = 10watts.
Of course, these are only estimates, because decoding a CW signal in noise depends largely on the operator.
Hi Chris,
yes, I agree that it is very subjective and people have very different opinions on it.
Let me first quote some hams to see how different they see it and then I will try to explain why I think that “200 mW WSPR is about same like 80 W CW”, at least for me.
PA1B's QRPp Blog: Power with WSPR
PA1B says the difference between WSPR and CW is 11 to 15 db… So 200 mW in WSPR is like 2.6 to 8 watts.
https://www.voacap.com/2023/documents/VOACAP_Manual.pdf
“REQ.SNR, an internally defined value, is tied to the chosen transmitting mode. For
example, for CW, it is set to 19 dB-Hz, while for SSB it is 38 dB-Hz. All transmitting modes have internal threshold values of their own.” 19db-HZ is -17db/2500 HZ.
Ok, and now why I consider 200mW WSPR = 80 W CW to be realistic.
OK2KKW has published interesting CW-files at FT8 vs CW | ft8-vs-cw
Take for example https://olgierd.github.io/ft8-vs-cw/wav/30-to-150_CW_300hz.wav Thats -15 decode level (considered CW-DX) at 300hz. Ok, I consider myself an experienced CW-OP but - honestly - I would not stop on the frequency if tuning over the band… Well, if I see an alert showing DL1CR/p is on 7031.3 khz, looking on this QRG, listening and hearing “cq s.t. … de d.1c./p” I can assume its you but at best its readability=2-3 and I would have to ask for my RST several times… So realisticly I would only call if I get an hint that someone is calling, I know the exact QRG and I am eager working him/her.
My 200mW = 80 W sounds like this (sort of…): https://olgierd.github.io/ft8-vs-cw/wav/65-to-150_CW_300hz.wav Not a loud signal but clearly understandable, even without seeing an alert, even if I am on a windy summit, if I am tired and I think even chasers not doing CW a lot can copy me.
So now you have heard yourself the optimistic SNR Hajo uses and my - on the conservative side…) - SNR also allowing some QSB, QRM, people talking next to me and other interferences.
BTW, the required SNR also changes with the speed of your CW and also with the tone pitch you listen to: https://fkurz.net/ham/stuff/a305780.pdf
Like you wrote “Of course, these are only estimates, because decoding a CW signal in noise depends largely on the operator.”
