What is LMR SDR?

See also (new post): Standalone Versions of LMR SDR!

 I have been hearing about LMR SDR during discussions among homebrewers for the past few days on 40m. Thought of learning a bit about it and my web searches told me that some of the persons behind the development of LMR SDR are YE3CIF, UT3MK and F5NPV. F5NPV has given detailed descriptions about homebrewing LMR SDR on his webpage, including videos. Even though I did look at the pages of YE3CIF and UT3MK, they seem to be in regional languages. I could not find the expansion of LMR on those pages, though I presume that it would stand for land mobile radio. LMR cables which many of us use were initially designed for land mobile radio. SDR stands for Software Defined Radio like my FT-710, which uses software to do many of the functions done by hardware in the conventional superheterodyne radio receiver.


It is interesting to note that LMR SDR covers from 160m to 10m band, that is the whole amateur radio HF bands. There are a few friends in my region also who are homebrewing LMR SDR, though I am yet to venture into it. It uses Arduino Nano microprocessor like the BITX QRP radios popular in this region. The clock or frequency generator used is Si5351. Si5351 is a programmable clock generator which can generate up to eight independent frequencies and operates on fixed crystal of 25 or 27 MHz. Frequency multipliers and dividers are used to generate the frequency of your choice with the programmable algorithm. Products listed online in this region can cover from 8 kHz to 160 MHz and cost only around 300 INR (3.56 USD). LMR SDR design by F5NPV uses only 5 integrated circuits and 5 transistors.

Output in the F5NPV design is 0.1-50mW. 30W amplifier is used along with it to provide a decent signal on the band. The final amplifier is fed by a class A amplifier providing an output of about 1W. PowerSDR and ExpertSDR softwares can be used. The VFO (Variable Frequency Oscillator) can be controlled from the PowerSDR. A computer and sound card are needed for the operation of the LMR SDR. A nice waterfall display can be seen in the computer, just as I see in my FT-710, though the configuration is different. May be after a little more learning experience, I might venture into LMR SDR, because one of the persons trying it out in my region is VU3GEX, located at just about 2km from my place!

Comments

Post a Comment

Popular posts from this blog

Building a Tape Measure Yagi for LEO Satellite Operations

Image
 The Moxon Yagi which I have been using for my LEO Satellite operations had a Moxon rectangle for VHF and five UHF Yagi elements which were passively coupled to the VHF Moxon driven element. The gain was not that high when I thought of working SO-121 QRP satellite. VU2TEK had good success with his Tape Measure Yagi which motivated me to go for one. But I don't expect the same success as he was operating outdoors, pointing the Tape Measure Yagi in the direction of the satellite pass. I am planning to use only in a mast mounted fashion which will limit its usability for satellite passes to a short period of about 4 minutes. I have chosen the DK7ZB design which I have been looking at for a quite a long time. That design has 5 elements for VHF and 8 elements for UHF with a boom length of about 1.5m. First step was to get a wooden reaper to use as the boom. Earlier it used to be available in all electrical wiring accessories shops. But now with the usage of PVC channels for wiring, I w
Read more

Six Button Wireless Mouse vs Three Button Mouse

Image
 When I started using computers long back, mouse had only two buttons, a left and a right button. Then came three button mouse with an extra scroll button. I have read that there was also a single button mouse, but I have not seen one. Now here is a six button mouse, that too a wireless mouse with a USB-A Nano Dongle and 2.4 Ghz wireless connection. In the earlier era, mouse had a rolling ball which would gather dirt and sometimes stop functioning well. Now we have optimal mouse which uses a red light source and an optical sensor instead of the rolling ball. The wireless mouse works on a single 1.5 V, AA battery with a projected battery life of one year!
Read more