Τετάρτη, 17 Ιουνίου 2015

RF Sniffing on HF bands

It was some time ago when I discovered PSKreporter and reversebeacon networks. It's all about reporting what you listen on the air to check about band propagation any given time and place. Multiple reporters exist, and most digi mode ham radio software is now reporting when you use it.
I like PSK reporter mostly because of the way they visualize everything. It's also a nice way to test your equipment, antennas, pre-amps by comparing the stations and the range you can hear.
A few months after reporting PSK and JT65 and burning my FT-920 on a thunderstorm, I decided it was time to move on. Multi band reporting using a single SDR and software was intriguing but needed some setup. The main set back, was that only Windows software exists for CW skimming and there was no way to use my existing PC's and SBC's. A few days ago I switched on my old Windows XP machine and installed all the required software, only to find out that everything was working flawlessly as described by the software authors!
A great thanks to OL5Q for providing the USRP library software for CW skimmer! Now I can use my USRP1 to listen and report from 4 HF bands simultaneously! I've picked the 20,17,15,12 meter bands mostly because my Cushcraft R5 antenna is made for those bands. Now my call-sign appears on the global top 10 chart of reporters with more than 100 different countries reported in one single day. Next is to be able to report digital modes also, and more HF bands.

I've also tried using RTL-SDR USB sticks with up-converters but the issue was that the up-converter clock was not stable enough to decode JT65. I've used both No-elec and SV1AFN up-converter. After talking with Makis, he confirmed that the clock was not for such use, and I've purchased a surplus stock 200MHz crystal from ebay to upgrade my up-converter. But, to use RTL-SDR you need one device for each band due to the "narrow" bandwidth they have, so you need to have RF power splitters for each stick. Moreover the USRP has a 12bit ADC instead of 8bit resulting in better dynamic range of the receiver. At the moment I use the LNA4HF  but I've also ordered the J310 pre amp from SV1AFN to compare them. 

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