LIMESDR/WSPR EXPERIMENT (Proof of Concept) …Well…I finally took the LimeSDR and connected it to a 2W - 3W wideband PA, attached the LPF I had handy and just tried beacon (transmit only, no receive) mode…The setup was VERY haybail and I connected the PA to the Lime’s TX1L port and to +13.6VDC from a very regulated power supply, the output of the PA to a LPF (30 MHz cutoff) and the then the LPF to the Station Antenna that has a nice 1.2:1 VSWR at 7.0386MHz…I used SDRAngel and setup a SSB modulator for USB transmit and setup all the audio path in advance using WSJT-X and it’s ‘Tune’ mode…Once I felt I had things working, I took to the air for the first time with the LimeSDR…During the first WSPR transmit session, I noted that the heatsink for the PA was pretty insufficient…It got hot fast so it’ll need to be a bigger heatsink later on…After the first WSPR transmit session was complete, I held my breath as I watched the reports come in…First KD6RF (1075 km) and then VA3ROM (766 km) and with the setup running 2W total power output, but later adjusted to 3W of power…I allowed the Lime to transmit a couple more sessions before I declared ‘Proof of Concept’ victory and shut off the PA and allowed it to cool down…A little later on, I switched the antenna to the RxWB1 port and allowed the LimeSDR to receive and report status on the WSPR database on 40m for over 7 hours - see pics for more details.
At this point I’m convinced the LimeSDR, along with SDRAngel, is a viable foundation for a voice or digital modes Software Defined Station…This one just needs to be designed and built for final and then the fun can begin…! More as I have it…Stay tuned…
Thanks - the ‘proof of concept’ testing just went to prove (to me) that the Lime is truly a viable foundation to work from to make a multipurpose, multiband, multimode transceiver - I’ve been on this going on 4 years and this is finally the year that the Lime will really make the jump to be that ‘go kit’ transceiver I’ve always wanted.
The published HF receive mod (on the Myriad forum here) is all that I did for the purpose of 80/75 to 70cm operation - you need not do anything to the Tx1L (Low Band) output of the Lime to make that function on HF. About 2 weeks ago I published the complete specs of the Tx1L port (and this will be the same for the Tx2L port) and it showed that the LimeSDR USB is capable - from 40m and up - to provide at least 0dBm and in some cases it’s +8dBm. Below 40m the gain falls off and about -2dBm max is possible. Again, the post shows the transmit power from 160m (1.8 MHz) to 1280 MHz. The LimeSDR’s RF output will require bandpass filtering for each band to ensure there’s no spurious or harmonics getting amplified - that’s a pretty easy task to do and I’m planning to work that next as a PWB design bandpass filtering the output of the Lime for each band, buffering it up (small PA) to drive a larger amplifier, and then putting a final bandpass after that larger PA. It worked wonderfully good on WSPR and once I get the proper heatsink for the smaller PA I’m planning to run a more extensive test on WSPR, FT-8, and voice.
Thanks for the questions and let me know if you have anything else on this, Richard - 73
The videos have all been based on my VOX RF Switch that I’ve now completed and using with WSJT-X when it enters transmit mode. When WSJT-X is in transmit mode, audio is already routed (as audio packets) to SDRAngel and at the same time there is audio being output through the headphone jack of the PC that is picked up by the VOX RF Switch I designed - that’s what keys the antenna switch to transmit taking the TX1_L port and routing the transmit RF from the LimeSDR to the antenna. When WSJT-X enter receive mode, the transmit audio packets stop and the headphone jack drops to zero volts and the antenna switch swings into the receive mode and routes the RF to the LimeSDR’s RX1_W port to be received.
Earlier videos also show the ‘TUNE’ button being depressed on the WSJT-X GUI to activate the VOX RF Switch before I had everything designed and working. Today, it’s fully operational and known good on all Digital Modes.
EDIT: The author of the SDRAngel application, Edouard (F4EXB), indicates that there’s capability to control certain functions within SDRAngel using the REST API, but I have yet to see where there is application sharing (WSJT-X to SDRAngel) or automation to make that work. In the old days (10 years ago or more) application developers would expose certain functions within their code for Dynamic Data Exchange (DDE) that would serve as that bridge between the applications if it was set up that way. I know of no exposed elements of WSJT-X or SDRAngel for DDE that would automate that process, so I went the easiest way I knew how…through hardware.
Hope this helps, and welcome to the LimeSDR forum…!
Well, that’s the ‘haybail’ setup right now - more just to get it wired up and running…More formal packaging and tests will take place today and over the next couple of days to get this a little more to a product configuration. I am planning to sell these VOX RF switches once I get things cased up and tested a little more thoroughly - I would think by June 1 I will start offering boards for sale - there are a couple of tweaks I would like to make to the PWB design and send it in for respin and build and that will be the ‘for real’ product. What I’d really like to do is incorporate bandpass filters onto the same board and just make it a VOX RF filter/switch assembly, but that will tie things up for awhile - so I’m willing to make VOX RF switches available by June 1 and then work that next issue.
Anyway that’s the report from here - keep watching this space for more developments over the month of May.
