Tuesday, January 29, 2013

DC into the antenna socket: Very bad idea.

Never apply DC voltage into a receiver antenna input. Never.

It should be DC blocked but this is not always the case.

Last weekend I decided to install permanently at the window one PA0RDT Mini Whip Antenna I build almost two years ago. Everything went nicely, except I double checked the DC power injector was mounted in reverse direction and anyway I connected it to the transceiver. Yes, I did it. And yes, I powered up the system. Yes, I'm stupid.

Friday, January 25, 2013

Example of bistatic radar using VOR transmitters

Observing Doppler from airplanes over nearby transmitters is an interesting way to study Doppler from meteors, because the Doppler signature from airplanes is a slow-down version of meteors.

Thursday, January 17, 2013

Receiving VOR signals for the first time

My principal transceiver in the shack is an Icom IC-746. It's coverage is from 30 kHz up to 60 MHz and 118 MHz up to 174 MHz. As you can see, no VOR band (108-118 MHz). Because recently I gained interest in receiving VOR signals to continue my experiments about radio detection of meteors and radar techniques, I had to find a solution.

Interestingly if you look in Internet about IC-746 frequency coverage, you will find two groups of pages: One group saying the transceiver covers 118-174 MHz on VHF, and a second group saying the VHF coverage is 108-174 MHz. Maybe a typographic error?

Wednesday, January 9, 2013

Detecting meteors by radio reflection in 2013

Some years ago I made meteor observations using the low VHF band TV transmitters around here with great success. Even with nearby transmitters I was able to see reflections from airplanes. Analyzing those doppler reflections some interesting info can be obtained. But with time, all those TV transmitters moved to digital at UHF frequencies so nothing can be heard now. I tried some amateur beacons but their low power and modulation are not adequate for this kind of observations.

From time to time as propagation permits I can hear some TV carriers around the usual frequencies: 48.250, 53.750 and 55.250 MHz but no meteor or plane reflections: They are too far away and their signals reach my antenna via multi hop sporadic E or F2 so they are not useful for meteor detection.

So, what are the most suitable signals for this kind of job right now?

Saturday, January 5, 2013

More eBay charger adventures: explosion and smoke

You are bored, and decided to browse eBay to see for new and interesting items. After a while you see a small 220V USB charger intended for the iPhone. The first thing you see is it is quite small, and does not have wires, only a USB socket, so it will be very easy to transport while traveling. And it is quite cheap, so you order one.

About two weeks later the small charger arrives to your home. You take it out from the envelope and gets fascinated about how small it is. So you grab a USB cable and connect your phone to the charger and the charger to the mains (220V). The phone gets into charging state, so you are happy.

Friday, January 4, 2013

eBay charger adventures: Joke or scam?

Because modern smartphones are really battery eaters, you decide to look at eBay for a car charger, just to charge a bit your battery while driving with the hope to extend battery life at least until you get home.

Thursday, January 3, 2013

Smoke from Imax B6 charger

This is the history about an Imax B6 charger who was used to charge a large 15Ah Li-ion battery. Because of the large battery capacity, the charging current was set to the maximum the charger is capable: 5 amps.

The charger was able to charge the battery nicely four or five times, but the next time, the charger went into fire and smoke.