Date
1 - 20 of 22
Radio "limbo"
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One of my favorite pastimes over the past few years has been playing a WSPR "game" I have taken to calling "radio limbo", i.e how low in RF output power can I go and still be spotted. Since about 1540 UTC today I have had the WSPR RF output set at -10 dBm (0.1 milliwatts), hopping amongst the 40/30/20/17m bands. At this tiny RF output level, the WSPR receiving "superstations" quickly emerged - ones like KA7OEI-1, N6GN/K, K9AN, KB9AMG, etc - still spotting my signal now and then. No doubt many of them make use of the wsprdaemon software, and perhaps their owners are even active on this forum - in which case I pause in admiration your efforts in achieving outstanding WSPR spot performance. With my current setup in Michigan (grid locator EN73) I am not being spotted by the WSPR "superstations" in the northeast US simply because of terrain - there is a large hill (and the side of the house) in that direction that reduces the lower angle radiation....whereas the terrain to the NW through S is wide open. Literally - as in the open water of a small lake. Another interesting phenomenon at these tiny power levels is that the spots tend to disappear late at night - I surmise that the atmospheric noise levels increase to a greater extent than any enhanced propagation on bands like 40m. All fascinating to me.
One downside of my "game" is that you can't advertise power levels <0 dBm in the WSPR protocol, so I have to keep track manually of what I am doing, rather than relying solely on database queries. Tomorrow I'll begin reducing the power until there is but one WSPR spotting station still able to spot my signals. Likely to be at an RF power in the 25-50 microwatt range, based on my past experiments. |
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Gwyn Griffiths
Hello Bruce
Nice to read of your experiments, and I look forward to seeing the results of your 50 microwatts and below transmissions. The attachment is a screenshot of three plots from the WsprDaemon Grafana site showing time series of a) your SNR at N6GN/K (specifically at receiver GN2), your signal level in dBm, and the noise level at Glenn's GN2 receiver. Your signal level has been calculated from your SNR and the Noise level. This can be useful if the noise level changes between the times when you transmitting at different power levels. The noise plot does allow you to check whether your surmise about atmospheric noise increasing being the cause of your spots not being heard is indeed true, or, as in the case with 20 m, the band closes to your signal, and to noise propagation. I've sent you an email to your address on QRZ.com with log on details for accessing this plot. 73 Gwyn G3ZIL 
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Gerhard, OE3GBB
Hi Bruce, that is a great idea! Will have to try this also. I once have done a similar test to see the minimal power to reach a DX station. That would be an indication on how good the antenna is at low radiation angels. I remember that I needed about 50mW to get into Australia. 73 Gerhard OE3GBB
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On Tue, Oct 5, 2021 at 08:01 AM, Gwyn Griffiths wrote:
...attachment is a screenshot of three plots from the WsprDaemon Grafana site showing time series of a) your SNR at N6GN/K (specifically at receiver GN2), your signal level in dBm, and the noise level at Glenn's GN2 receiver. Your signal level has been calculated from your SNR and the Noise level...Thanks Gwyn, Fascinating plots. I just lowered my RF output power to -13 dBm (50 microwatts)....i.e. effective 1527 UTC on 5 October 2021. I've attached a screen shot for the past 24 hours at -10 dBm (100 microwatts), with 9 stations still able to spot me. By the way, the antenna I'm using is quite simple - just an EFHW cut for the 40-10 meter bands, horizontal at about 12 ft. above ground level. We'll see what happens next. 73, Bruce 
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Gerhard, OE3GBB
For info, just checked WSPR: I could receive at OE3XOE several DX stations using powers of 5 and 10 mW: 73 de Gerhard OE3GBB
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Jim Lill
what type antenna do you use on 40M?
-Jim WA2ZKD On 10/4/21 11:08 PM, Bruce KX4AZ wrote:
One of my favorite pastimes over the past few years has been playing a WSPR "game" I have taken to calling "radio limbo", i.e how low in RF output power can I go and still be spotted. Since about 1540 UTC today I have had the WSPR RF output set at -10 dBm (0.1 milliwatts), hopping amongst the 40/30/20/17m bands. |
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On Tue, Oct 5, 2021 at 02:09 PM, Jim Lill wrote:
For transmitting I am using an EFHW that covers 40-10 meters, so about 65 feet long, straight horizontal line at about 12 feet above the ground, the ends pointed roughly NW/SE directions. Since I reduced the output power to -13 dBm (50 microwatts) earlier today I have been spotted by 4-5 stations. |
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Jim Lill
If you did a NEC model of your EFHW (or most any EFHW) you'd be
shocked by how lossy they usually are. Knowing that loss, band
per band, you could further reduce your actual ERP. On 10/5/21 2:45 PM, Bruce KX4AZ wrote:
On Tue, Oct 5, 2021 at 02:09 PM, Jim Lill wrote: |
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Jim Lill
This is a pretty good article on EFHW https://vu2nsb.com/antenna/wire-antennas/multiband-efhw-antenna/ On 10/5/21 2:49 PM, Jim Lill wrote:
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On Tue, Oct 5, 2021 at 01:40 PM, @OE3GBB wrote:
Gerhard, Thanks for posting that - it's always nice to see others testing the low end of WSPR RF output. When I operate as a spotter, now and then I'll send an email to stations that are declaring their power to be 10 mW or less....just to satisfy myself that they haven't accidentally mis-stated it. For myself I verify the output power now and then, with either a spectrum analyzer, or the RF voltage measured across a dummy load using an oscilloscope. That's something I will definitely need to do for my current round of experiments, once I find the threshold power setting that yields just one spotter station in a 24 hour period. Just like to have that little extra accuracy beyond what the step attenuator tells me. Separately I will embarrass myself a bit here by admitting I have not yet used wsprdaemon for spotting. I recently set up a new KiwiSDR (grid locator EN74), and once I get another Raspberry Pi I hope to give it a try. 73, Bruce |
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On Tue, Oct 5, 2021 at 02:50 PM, Jim Lill wrote:
Jim, Yes, no argument there, and thanks for posting the link with the article on EFHW characteristics. I just find it fascinating how such a small power going into a temporary antenna setup like this can still be spotted. Bruce |
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Gerhard, OE3GBB
Hi Bruce, well, we sure have to believe the statements on power sent :-). I myself on TX am using the WSPRlight flexi and I checked the power with a spectrum analyser. The settings seem to be about correct. I did not correct for filter and koax or antenna gain. On RX I am using a raspsdr in 4 channel mode for public websdr (see OE3XOE at https://www.receiverbook.de/) and a flydog-sdr with raspPi4 and wsprdaemon as a WSPR reporter on 12 bands. I am constantly about the no. 15 of the best reporters worldwide. http://www.wa2zkd.net:8088/rank.html If you only use a raspsdr on several bands for reporting WSPR you will not be able to decode all the signals. I now have my two most busy bands decoded on the raspsdr and 10 bands on the wsprdaemon. 73 de Gerhard OE3GBB
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After nearly 24 hours running at 50 microwatts (-13 dBm), there were still 8 stations who heard me, though the total spot count and geographical diversity is narrowing. And some stations were hanging by a thread, with a just single spot for the entire day. Interestingly there is a trio of Alabama spotters, all in the same general area that are hanging in there too.
So it's time to lower the bar a bit further. As of 1600 UTC today (6 October 2021) I've reduced the power output to 10 microwatts (-20 dBm!). Stay tuned for further developments. 
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Correction and an oops...I hit the wrong button on the step attenuator when changing power a few minutes before 1600 UTC, and so had the power running 10 dB too high, at 0.1 mW, and K9AN "snuck in" there with a spot at 1058. So the real -20 dBm output level actually commenced at 1606 UTC today (6 October).
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Ouch, I hate to bombard this group yet again with a post, but my UTC timing was off off today too! I commenced transmitting at 10 microwatts 1506 UTC today (October 6). Promise this will be the last correction.
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OK, after 24 hours run time at -20 dBm output, the clear "winner" was W4HOD in Alabama (USA), spotting me twice in 24 hours. My setup is still running, and at 1742 UTC today another station in the same area "snuck in" with a spot - WA4CQG, at the same time as another spot from W4HOD. I have exchanged emails with the group of hams in that area to ascertain what is so special that's going on, since several stations in that area have been spotting me during my experiments throughout this week, all on 20m. In another words, it's not just a one time event like a meteor passing by etc. What they have in common is using beam antennas, with the one for W4HOD pointed toward Europe, so roughly in my direction. Also, W4HOD is using an Airspy HF+, a very sensitive (albeit narrowband) SDR. So those directional antennas may be a factor...although to some extent that takes them out of my notion of a WSPR "superstation", open to all directions. Nevertheless, 10 microwatts is (for me) a new spotting record, I believe.
I'll keep the -20dBm level going for now to see if any other spotters emerge outside of Alabama. And it's time for me to make some RF output power measurements to keep things accurate. Finally, since this group is about wsprdaemon, and not necessarily my low power WSPR experiments, I will say that I await the arrival of a Pi4 so that I can commence running it with the KiwiSDR I recently set up. |
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Some final comments on my "radio limbo" experiment. I've left it running since October 7th and will shut it down today (October 17th), in order to reclaim the step attenuator I've been using to adjust the output power. Over the past week W4HOD is still the winner (5 spots), though there were two additoinal stations that spotted me twice (K4COD, WD4ELG). All of the spots were on the 20m band. Interestingly, I spotted myself on 40m at (new wsprdaemon setup) 'KX4AZ/T' yesterday, about 9 miles away from the transmitter.
Lastly, the measured RMS waveform voltage on 20 meters (across a 50 ohm dummy load) was 27.5 mV, putting the actual output power into the antenna line closer to 15 microwatts (-18.2 dBm), rather than the 10 microwatts (-20 dBm) that I previously estimated...though with line/transformer losses for the EFHW antenna perhaps the actual radiated energy was not very far from 10 microwatts. |
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Rolf Ekstrand
Bruce,
It's amazing how far you can go with almost nothing. I am usually running QRO here at 200 mW -:) into an old Cushcraft R7 usually on 7 and 14 but then again there are some crafty individuals running much more. When I started with WSPR there was even a guy in W3 land running 1 Kw and now we have one just south of here running 100 W. Go figure. Congrats I see you got your Kiwi WD up and running and doing well. What antenna(s) are you using on the RX site? 73 Rolf |
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On Sun, Oct 17, 2021 at 11:16 AM, Rolf Ekstrand wrote:
Rolf, Currently I have one antenna for the KX4AZ/T WD site - a random wire dipole that is resonant at about 3.4 MHz, roughly 15 feet above ground level. I am still tweaking the matching/feedline setup, using Cat 7 ethernet cable as a balanced feedline. Earlier today I added an LNA to the KiwiSDR input which boosted the WSPR performance significantly, but I am positive that will lead to overloading later today - will need to adjust the gain. But I am certainly having a lot of fun learning & experimenting with this new setup. Bruce |
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Rob Robinett
With any kind of decent antenna and a reasonably quiet site, the Kiwi needs 10+ dB gain to get signals above 10 MHz to be stronger than the internal noise of the Kiwi RF amplifier. Of course that 10 dB gain makes Kiwi ADC overloads from local AM broadcast stations even more common, so you need an AM blocking filter ahead of the LNA. The $16 Nooelec Flamingo AMBF (https://www.nooelec.com/store/flamingo-am.html) is enough for several of my receive sites, but you could very well need even more filtering than the 20-35 dB it provides. Every 10 minutes WD logs overload events to files /tmp/wsprdaemon/..../ov.log where you can learn about OVs which happen when you aren't looking at the Kiwi's S-meter. On Sun, Oct 17, 2021 at 12:02 PM Bruce KX4AZ <bruce@...> wrote: On Sun, Oct 17, 2021 at 11:16 AM, Rolf Ekstrand wrote: --
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