Friday, December 20, 2013

Geminids 2013 with Baudmeteors

Last weekend I used Baudmeteors to study the Geminids meteor shower using the Graves radar. I left the computer logging data for more than 120 hours trying to catch the shower peak. And I did it:

Friday, December 13, 2013

Shielding the UT-81B oscilloscope

About three years ago I brought an UT-81B multimeter/oscilloscope. It is not a high range oscilloscope, it is more like a low range / "toy" oscilloscope but it has worked very well for me, making a great job solving problems with my Geiger counters and gamma spectrometers.

But it had a small and somewhat annoying problem: While in stand by, a pulsating signal appeared on the screen.

Thursday, November 28, 2013

FM passive radars as alternatives to Graves

Two weeks ago, on November 13, I left my computer logging meteors on Graves' frequency with the help of Baudmeteors. My goal was to catch the Leonids shower. But on November 15, around 16:40 UTC I detected one meteor and then, only silence for the next two days. Graves was turned off.

You don't realize how dependent the radio meteor detection is from Graves until you lost it. Around 20 UTC I realized there was no problem with my radio or just a very low meteor count. Graves were really off!

Tuesday, November 12, 2013

Baudmeteors: Capturing meteors with Baudline

I already knew Baudline. I used it some years ago as a simple FFT spectrum display but I didn't use it until last summer, when Iban, EB3FRN sent me a little script to automate meteor capture using Baudline. It turned out Baudline was much more than a simple spectrum analyzer display. Baudline turns out to be a powerful signal analyzer and quickly it becomes one of the most used programs in my computer.

Saturday, November 2, 2013

Impressive "dual band" feed

This weekend I've reviewing some photos taken last summer, and I found this interesting photo from an interesting dual band feed for parabolic dishes:

Sunday, October 20, 2013

HamGPS in action!

Yesterday I received a message from Eddie (ZS6BNE), who pointed me to a great video about RaDAR (Rapid Deployment Amateur Radio) operation. You can briefly see HamGPS in action, around 2:20.

According to Eddie's blog, HamGPS is a quick way to get very precise positions that can be easily send to another hams using 10 digits grid world wide locators.

Thanks for sharing, Eddie!

Sunday, June 23, 2013

Pipe cap filters for 10GHz

The most common problem in a transverter system is local oscillator leakage, this is the local oscillator signal get through the TX mixer to the power amplifier chain, becoming present at the antenna connector at some level. LO leakage is usually a sign of poor design, but it can occurs also by defective or wrong shielding or even by a metallic enclosure box.

In my case the problem was the metallic enclosure used for the transverter. With the cover removed everything was fine but once the cover was put in its place, the local oscillator was present at the output at nearly 5mW of power: Just unacceptable.

Wednesday, June 12, 2013

Using the Eyal Gal 10GHz module in a ham radio transverter

The core of my transverter project is a 10 GHz Eyal Gal module acquired in eBay the last year. These units have a receiver converter and a transmit power amplifier in the same enclosure.

Because the design frequency of the module is 10.4 to 11.7 GHz, it works unmodified at 10368 MHz, which is a clear advantage for use at ham radio.

There is not too much information about these modules except the info published by G8CUB here and herethis post from M0DTS and this datasheet. It is convenient to read all these documents before continue reading this post.

Friday, June 7, 2013

Setting the output power in Yaesu FT-911

Recently I have been using my Yaesu FT-911 as signal generator to test a 10GHz transverter's local oscillator multiplier stage (1242 x 8 = 9936 MHz). Everything worked fine, but the readings I had were not consistent. The output power was lower than expected.

When supplied at 13.8 volts, high output power should be 1W, but I was measuring around 550mW. Clearly something was wrong. Many time ago, when I purchased the walkie, I did a quick readjustment using an attenuator and a spectrum analyzer. Spectrum analyzers are fine to see spurs or relationships between carrier and harmonics but they are not good as absolute power meters, specially if you are using them at the top of their dynamic range, this is with insufficient attenuation between.

Wednesday, May 15, 2013

Repairing a Telecom AV-830 switching power supply (or maybe upgrading it)

I have an auxiliary Telecom AV-830 switching power supply I use from time to time. Recently while testing a circuit with it, the power supply explodes. The internal fuse was disintegrated and the main ICP was activated. That usually means something very bad is happening with the power supply.

Tuesday, May 14, 2013

A 10MHz TXCO master oscillator

The heart of any transverter system is the local oscillator. In practice, a transverter is as good as its local oscillator is. For my transverter project I choose a Toyocom TCO-291L2 oscillator I rescued from a UMTS board I have from surplus.

After spending a lot of evenings looking for its datasheet, I could not find it. I found the datasheet from other TCO-291 oscillators, but nothing from the TCO-291L2. Maybe it is a custom device, o maybe it is discontinued.

Thursday, April 25, 2013

Looking for the Square Law region (III)

... and all I can say is I found it!

Last weekend I assisted to a small ham radio flea market surprisingly with a lot of microwave hardware. Thanks to Andrés EB4FJV, I was able to get a DC to 18GHz Narda crystal detector. My idea was to use it as a relative measurement device, just to peak circuits at maximum output.

Sunday, April 21, 2013

DRSB-01 Geiger counter failure

My DRSB-01 ( ДРСБ-01 ) geiger counter has gone mad. Far from any source it gives up to some counts per second, when the normal rate for it in my home is around 20 counts per minute.

Once opened was easy to spot the failure: The high voltage applied to the tube was around 800 volts. The normal working voltage of the SBM-20 tube is around 400 volts, so 800 volts produces self-triggering, and therefore, the extra counts.

Monday, April 15, 2013

Counterfeit batteries

Some days ago I was given a dual SIM chinese Android phone. The LCD screen was broken and the battery was noticeably swollen, so nothing could be usable. I noticed the battery was a Nokia-like battery, even with the same prints on it, but obviously a counterfeit battery.

Friday, April 5, 2013

WiFi antennas on 2320 MHz

In the ham radio community is quite common the first experiences in the 2.3 GHz band are made using WiFi antennas. In most parts of the world the 13cm ham band is (still) 2300-2450 MHz, and the WiFi band is 2400-2484.5 MHz, so both bands overlap in a extension of 50 MHz.

But unfortunately in this area of the world narrow band work in the 13cm band is done around 2320.2 MHz, and in this frequency most WiFi antennas simply suck.

Wednesday, April 3, 2013

Singing capacitors

Today I have been repairing a 12 year old 15" LCD monitor. It had no apparent fault, everything worked nicely, but the monitor produced a extremely strong high pitched tone (around 18 kHz) enough to produce headache in only two minutes.

Usually high pitched noises come from the switched power supply. In the past I have found switched power supplies with loosen transformer cores that produced noise just like an speaker.

Thursday, March 28, 2013

Determining battery health status

Some days ago I found this 12 volts, 17 Ah battery. It was dead. It's voltage was zero volts between terminals.

The battery should be disposed away, but I took it to play. Deep discharged lead-acid batteries can become damaged, but if the battery has zero volts, it's sure it is irreversibly damaged.

The first step to play with it was to revive it in some way. I used my variable power supply and adjusted it to around 15 volts, and applied that voltage to the battery through a 1W 150 ohms resistor.

Friday, February 15, 2013

A new battery for the Yaege FC-1

I own a Yaege FC-1 frequency counter. It is around 4 years old, and recently I noticed its internal battery is dead: No more than 10 minutes of autonomy. The battery was a 18350 / CR123A, so it should be easy to find a new one.

But recently I have had bad experiences buying batteries at eBay: All the batteries I purchased were dead, with almost no capacity and very high internal resistance (in other words, useless), so I looked for a different solution.

Tuesday, February 12, 2013

ISS in Graves radar recording

From time to time, while recording Graves' signal with Spectran for meteor head echoes, strange things appear on the screen. Some of them are just "birdies" from the neighborhood, or noises from frequency inhibitors ( 142 - 144.5 MHz is deliberately interfered in some areas of Spain ). But sometimes I detect some "traces" in the spectrogram from unknown origin... until now.

Thursday, February 7, 2013

More eBay charger adventures: Now laptop chargers

A laptop power supply / charger bought in eBay. Worked fine for some months, but then started to work intermittently for some weeks, and one day BOOOM!

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.