Saturday, 14 September 2013

Homeplug

I'm using a pair of Vesenet NET-PLA-14-E power line networking adaptors to link my Sky box to the internet. I'm planning to do this wirelessly in the future but I had the adaptors spare.
They are the old standard of 14 Mbit/s, so aren't compatible with anything available now, but fast enough for downloading some on-demand TV shows (or are they?).
As a responsible radio amateur I should have never have allowed any evil power line network equipment into my home, but I had to give them a try.

I connected a laptop in place of the Sky box and transferred a large file from a network share, through the pair of devices. They were recognised as being 10Mbit Ethernet, so there was no way the 14Mbit/s was going to be reached. In fact the file transfer speed was around 540KB/s (4.5MBit/s), which is what you would get from 802.11b WiFi (11Mbit). Both devices were on the same ring main and upstairs, in different rooms. One was located in the same room as the radio equipment and the PC that was running PowerSDR.
This is lower than the internet connection speed (9Mbit, with a top download speed of about 7.5Mbit/s). But it's fast enough to watch TV through and download on-demand shows.

I picked an empty frequency to check for the noise level, at 10.544 MHz. Using AM in a 6.6KHz bandwidth, the background noise with the devices unplugged from the mains was -97dBm on the wire antenna (no ATU).
When the HomePlug adaptors were plugged into the mains, there were a few short bursts of noise which were hard to get a meter reading from, and then there was a 'click' every second, which was hardly moving the average s-meter reading. Inside the amateur bands the clicks could not be heard over the background noise, there are notches in the amateur bands.
When the file transfer started, the noise on 10.544 increased by 14dB to -83dBm. It was just as if the noise level had increased, no peaks in the spectrum could be seen. Inside the 7 and 14MHz amateur bands there was no increase in the background noise, other noise sources were large enough to hide anything coming from the HomePlugs.

When transmitting a 5 watt carrier in the 7, 10 and 14 MHz bands, it looked like there was a slight drop in transfer speed for a few seconds (to maybe 450KB/s) but then it went back up to the same as before. Probably going into error correction before adjusting the carrier frequencies used. 

If you are thinking of buying a set of new HomePlug adaptors then you might get totally different results because of the wider bandwidth used, and they will ruin any shortwave broadcast reception but these have made so little difference to the amateur bands that I've kept using them.



Monday, 2 September 2013

JT65

JT65 log from a few minutes of calling CQ on 14.076

Worked G7RNX/P tonight while he was on Snaefell (SOTA GD/GD-001), on 70MHz FM. I was using my Wouxun handheld and Garex flexi whip antenna near the sea shore on Walney.

Had a problem with the sound on my old laptop (Samsung N150 netbook) yesterday, I was setting it up to use with the FT-817 and instead of a proper data cable, I thought I'd keep it simple by using VOX through a 3.5mm jack - RJ45 cable (with some resistors to drop the level). That worked OK, once the loudspeaker volume was set to the right level (around 20%).
For receive I used a 3.5mm cable from the 817's headphone socket to the laptop's mic socket. I got the level right but then after a few seconds the meter dropped right down on the laptop. I thought there must be a bad connection somewhere. But monitoring the input through the laptop's speaker proved the signal was getting from the radio into the computer without any breaks.
If I unplugged the cable from the laptop and plugged it back in, it would work for a few seconds again and then stop.
I noticed that a message popped up on the laptop every time I plugged in the cable, telling me I'd plugged something in. I've used PCs before which have tried to auto-detect which socket has a microphone plugged in and which one has a speaker plugged in, and failed to detect it properly.
So I tried uninstalling the Realtek application which was installed when I got the laptop, is there any need for a separate application to control the sound? Probably not, unless you really must have some fake surround sound effect.
Uninstalling disabled the sound device until I rebooted, but then Windows 7 recognised it and installed the standard driver for the Realtek audio. No more auto-detecting of plugs, and it worked without cutting out.
The only thing that had changed was the levels, the output from the speaker jack was slightly higher for the same % on the slider.