About the HP E3611A Power Supply

After messing around some time with homemade power supplies and some of them in kit form I decided to bite the bullet and acquire a "real" lab power supply: the HP E3611A.

This power supply works like a charm. It is precise, robust, excellent stability... a real pleasure to work with. But as soon as I started to use it I noticed a small annoyance. Some times at power on, and almost all times at power off it produced a big "plop" in any speaker I had in the room. The "plop" was also heard in RF with a receiver. It was only an small annoyance so I didn't pay too much attention to the "plop".

About bulged electrolytic capacitors

In the last 20 or so years, in about 95% of my repairs the problem were always bad electrolytic capacitors. There are people who claim the capacitor plague ended in 2007, but it is 2020 and I still routinely find bulged and/or leaking electrolytic capacitors in equipment build well beyond 2007.

A bulged or a leaking electrolytic capacitor is the best thing that can happen to you. Just look around, see the damaged capacitor and replace it. Easy. But... how to find a bad capacitor still not bulged? Use a capacitor tester and measure its ESR. This is the most logical response I should obtain. It was also my first idea. And I did it.

Cleaning a Power Bank

One common option to supply the small TTGO LoRa boards is to use a small power bank. For supply small devices like these boards I use one really cheap power bank, so cheap it can be obtained for 0.80 euros from China (with no 18650 li-ion cell included, of course).

The 0.80 euros power bank

It seemed to work just fine but powering a 433 MHz TTGO board I noticed the power bank itself radiates a lot of noise in this frequencies.  UHF noise from a switching mode power supply is a new record for me!

But... Can it be cleaned?

Fuses in TTGO LoRa V1.6

Today, probably the most common ESP32 LoRa board is the TTGO V2-1.6. In a very small factor it offers OLED screen, WiFi, Bluetooth, micro SD slot, li-ion charger... and a lot of problems.

The problems seem to come from the polyfuses installed in the board. There are two of them, and each one offers a different set of problems.

The Screaming TTGO T-Beam

If you are playing with LoRa devices it is pretty sure you have some ESP32 LoRa boards, and probably a ESP32 based TTGO T-Beam. This board is quite interesting because it includes a GPS, making very easy to compute distances of messages sent and received through LoRa chips.

TTGO T-Beam ESP32 based LoRa Board

Icom IC-R7100 and its clicking noise

Some time ago an Icom IC-R7100 arrived to my shack. It's a nice receiver and works surprisingly well but almost the very first time I powered it up an annoying feature came up: every time the squelch opens or closes, It produces a clicking noise.

It is ok for the first five minutes but it can be irritating after that.

Repairing an Anritsu MS2711A handheld spectrum analyzer

One night, I was searching eBay with no especial interest when I found something interesting, a cheap non working Anritsu MS2711A spectrum analyzer. The photos shown a turned on analyzer, and some signals (noise) appeared in the LCD. The LCD had some dead lines at the bottom, but nothing serious.

A small size spectrum analyzer is very tempting. I have another two full-size spectrum analyzers but they are so big and my space so limited I rarely use them. These small units are somewhat very limited compared to a real spectrum analyzer, but I was pretty sure I would use it much more often than the two units I already have.

After a few minutes, I decided to buy it.

Repairing the OM345 hybrid module

Recently I had to repair a Marconi 2022E signal generator. It's a nice unit, relatively small, and well suited for amateur use. Talking about repairing the old Marconi instrumentation is talking about the Phillips OM345 hybrid modules. Why? Because they has a really high failure rate and old Marconi equipment make extensive use of these modules.

Considerations about the Hiland Adjustable DC Regulated Power Supply Kit‎

My "lab" power supply was a homemade one I made/upgrade some years ago. It was constructed around a LM350K TO-3 regulator and worked very well. But I really missed one function: adjustable current limit.

The LM350K regulator has a fixed current limit around 2-3 amps, but usually that is just too much current for a prototype. Many times, when something went wrong, one or more components went burnt.

Shifting to Linux

Some time ago I received a notification via Twitter about someone who installed XP on his notebook after reading my article about Linux I wrote some years ago. I think the tweet is ironical, but that doesn't matter.

The fact is I didn't remember I wrote that article, but actually I'm using Linux full time in my desktop computer. How can it be possible? How someone who ranted about Linux on the desktop ended using Linux full time?

About the CTS OCXO Board

After some time working 10 GHz with a TCXO based local oscillator I decided to upgrade it to a OCXO because stability was not as good as I would expect. It was ok for a short QSO but after some time I must search in frequency to the other station again. It was not very practical.

I decided to try a CTS OCXO Board from ZL2BKC. It is a small board with a brand new 10 MHz OCXO made to complement the ZLPLL board, and it is available in kit form for just $20: a bargain!

Determining the radiant of a meteor using Graves radar (III): the details

In my previous post I explained what we did and what results we got. In this post I'll show you the technical details behind the experiment, with some hints and tips in the case you want to replicate it. As a guide, I'll solve a meteor step by step, from the wav file to the radiant, and then, the final orbit around the sun.

Determining the radiant of a meteor using Graves radar (II)

One year ago, I published my experiences about determining the radiant of a meteor using Graves radar. If you read it (I hope you really did it) a question arises immediately: What about three receivers? Fortunately David, amateur astronomer and ham radio operator also known as EA1FAQ joined the team so we could answer this question.

Figure 1: Transmitter and receivers location

We had some doubts. Could the same meteor head echo be received simultaneously by three different stations? some calculations and simulations were made with many interesting results.

Wideband Quadrantids using Graves radar

Recently I realized one of the most limiting factors while measuring doppler head echoes is the limited bandwidth of SSB receivers. Sometimes you receive a really long head echo appearing at 3000 Hz and going down to 1000 Hz, the rest frequency when you tune 143.049 USB with Graves. And you wonder: how high the doppler can be? To answer that question I made an "special IF filter" for my FT-817. The filter is just a piece of coaxial, so I can receive the whole receive bandwidth. A dummy filter.

Simple WGS 84 - ECEF conversion functions.

One of the most unexpectedly complicated things I have found during my research into determining the orbit of a meteor using Doppler measurements is the conversion between geographical coordinates and rectangular, or Cartesian coordinates, also called ECEF (Earth Centered Earth Fixed) coordinates:

At first sight it seems easy: The earth is a sphere, so it only need a few sines and cosines. But later, when you need more precision, you discover earth is not a sphere, it is an ellipsoid, so things start to become problematic.

V2000 teardown

Over the years I have receive a lot of questions about the inners of the V2000 50-144-432 MHz antenna. I guess it is because of this. The most common question was about the capacitor values: many hams have burn them out and want to repair the antenna.

A simple PPS pulse shortener

¿How long is the pulse in a PPS signal? If you test some GPS units, you will find very different values. Some GPS produce a 100ms long pulse, but other ones produce pulses in the millisecond or microsecond area.

Usually, this is not a problem. A PPS signal works on the rising edge, so the circuit where the signal is used senses only the positive edge. In this way no matter how long the pulse is. It will work.

Determining the radiant of a meteor using Graves radar

Important
This article has been superseded by this one: http://ea4eoz.blogspot.com/2016/04/determining-radiant-of-meteor-using.html

During the last months of 2014, Iban EB3FRN and me were recording meteor head echoes using Graves. But to make things interesting, we synchronized the recordings using a PPS GPS signal. The idea was to analyze the Doppler from the head echoes and and see if something useful can be extracted from them.

Typical Graves' head echo followed by a large tail echo

A 50 MHz trap

These days I have been thinking in a new antenna experiment. If works as expected, I could install it on my roof and add one or two new bands in my shack. But for the experiment I need a trap tuned to 50 MHz.

I do not have any experience working with traps in HF frequencies, but it was obvious the main problem will be the capacitor. A trap is a parallel connected LC at the top of an antenna radiating some power, so it was obvious the capacitor would need to withstand very high voltages. How high? I don't know. Maybe 5 kV or maybe 20 kV. A very high value in any case.

Looking inside a 144 - 432 - 1296 triplexer

It has recently come into my hands a 144 - 432 - 1296 MHz triplexer. A Comet CFX-4310. I was curious, so I opened it: