Circular SWR ruler

chartLike me, you probably often needed to calculate a gain, loss or SWR when measuring powers or working on antennas. And when you are on the field, you never have the right calculator or forgot the right formula !

It's a long time i wanted to make a chart that could make me the life easier. I was thinking about a circular chart, but i never found the right tool with which i could do it easily. Until i found the GALVA software written by F5BU.

The result of my thoughts is presented below. This tool can calculate gain, loss, SWR and return loss in a second with enough precision for most amateur works.

The principle is simple, the powers are on 4 decade logarithmic scales, for a 40 dB range. The gain and return loss use the same 40 graduations linear scale and the SWR is a special scale responding to the SWR vs power formula.

To use the chart, you only have to align the 2 powers on 2 concentric disks and you read the result in a small window. There is a short explanation on the disk itself.

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Cleaning silver parts

In our hobby, we sometimes use silver plated parts for their excellent characteristics in HF circuits. Higher Q and better electrical contacts.

One drawback of silver, is that it is corroding, and getting black. This black color is mainly due to the silver sulfid (Ag2S). Silver sulfid is a much worse conductor than silver and giving a ugly look.

For one of my recent projects (VHF tube amplifier) i used an old socket which had all pin contacts very corroded. I looked for a simple and safe way to clean them.

The following method is the result of my experiences and works perfectly with things that can be found in any kitchen !

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Measuring very low R

It sometimes happens that while repairing old antennas or searching for an antenna fault, the question of tube connections quality arises. A few tenths of Ohm in traps or in between tubes can already be a problem and lead to high losses.

Measuring very low resistances is not easy with common multimeters, and if you have them it's sometimes difficult or risky to carry them on field. Often, we are in situations where we need to measure low resistances without any special equipement.(contests, fieldday, etc...)

Even the lowest range of a digital multimeter is of no help to measure resistance under a few Ohms.

The following method described here allows to measure very low resistances, in particular contact resistances between tubes or any other metalic parts.

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Regenerating capacitors

If, like me, you sometimes want to use old used capacitors, what follows might interest you !

cat aluminum050525

Why ?

When an aluminium capacitor is produced, it can't be used immediately. It must pass thru a generating process. This process consists in charging the capacitor with a very low current until it reaches its nominal voltage.

During this charging, a certain quantity of aluminium is teared off from the electrods and is deposited on the dielectric in the form of aluminium oxyd. This oxyd is an insulator that protects the dielectric up to a voltage at which it has been formed.

This oxyd layer is maintained and regenerated each time the capacitor is used by a small amount of current, called leakage current. The serious manufacterer are giving a maximum value for this leakage current.




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Unsoldering SMDs


Unsoldering SMD components can be very frustrating, time consuming and a disaster. Here is a trick i've found in a electronic magazine of which i forgot the name.

All you need is a piece of enameled copper wire of about 0.2 to 0.3 mm in diameter.

Take a length of this wire and slide it under the pins of the circuit you want to unsolder. Attach one end firmly,( because you will have to pull on it ) in soldering it on a large pad close to the circuit.



Pull firmly on the free end of the wire so it leants again the first pin of the circuit. Do that while keeping the wire as close as possible to the printed board.
Heat the first pin, the enamelled wire should slip under the pin and raise it from the board.

Repeat this procedure for each pin, taking care not to break them. Double your attention for the last one, the wire being stopped by nothing.

Make some tests on a defective board before applying this method to a board you want to repair.

The smallest SMD components can't be unsoldered this way, you can't even slide a wire under the pins !

Let me know if this could help you and/or if you have a better method.

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2 way combiner


Ilt is sometimes necessary to split the output of one transmitter in order to drive 2 amplifiers or 2 antennas. There are several ways to do that, but an elegant one is to use this splitter.

The following description is the fruit of my own experience and works perfectly.

This splitter is composed of 4 lengths of 75 Ohm coaxial cable.
During normal operation, the injected power in the input IN and split in 2 equal levels on outputs OUT1 and OUT2.
No power should be present on the 50 Ohm dummy load.

The signal available on ouput OUT2 (via a Λ/4 line) has a -90° phase, the one on OUT1 (via the 3Λ/4 line) has a phase of -270°. The signal arriving into the dummy load (via the 3Λ/4 + Λ/4 and Λ/4 +Λ/4 lines) has a phase of 180°, so is cancelled !

One advantage of this splitter is that the 2 outputs are insulated one from the other !

In case of a mismatch on one of the outputs, the other output is not (or very slightly ) affected. All the power normaly present into the output is dissipated into the dummy load. This later one should be able to safely handle half the input power.

This circuit can be used on any frequency, you only need to cut the lines to the right length.

CAUTION, the lines have to be made in 75 Ohm coaxial cable !!. Don't forget to apply the velocity factor (depends of the isolating material) when you cut your lines !

This circuit can be used in a reversed manner, for example when you want to couple 2 amplifiers into one output. In this case, the splitter is used in a reversed manner, OUT1 and OUT2 are respectively IN1 and IN2, and the output is on IN.


Works only on one frequency/band...
A bit large, coaxial lines can be long...

I hope this can be useful for you ... 

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Modification de l'ATR2400

atrr2400L'ATR2400 est un émetteur-récepteur de la marque ALCATEL, conçu à l'origine pour un fonctionnement dans la bande RADIOCOM 2000 de 414-428 Mhz.

Deux versions ont été construites, la plus répandue étant la version Duplex ATR2400 ERD avec écart de fréquence de 10 Mhz. Il existe une version ATR2400 ERA fonctionnant en alternat conçue pour les réseaux privés.

Caractéristiques générales de l'ATR2400 non modifié :

Espacement entre canaux : 12,5 Khz
Ecart duplex : 10 Mhz
Type de modulation : phase
Puissance émetteur : 2 ou 11 Watts commutable
Excursion maximale TX : 2,5 Khz
Puissance BF : variable par 6 bonds de 1 à 3 W
Sensibilité : 1,5uv pour S/B de 20 dB

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A 7el 144MHz yagi

groupe7elyagiSince almost 30 years, for my portable VHF activities, i used a F9FT 9el yagi. This one was the best i've found for this purpose, it was leigthweight, relatively cumbersome and performed quite well. Unfortunately, it broke during a contest when falling down from 7m high...

To replace my beloved antenna, i decided to build something and not to buy one. After searching some design on internet, i finally adopted DK7ZB's one. He offers several designs, and i chosed a 7 element yagi in 28 Ohms technology.

The advantages of DK7Zbs antennas are :

- Computer optimized
- Great reproductibility
- Easily assembled and dismantled. Ideal for portable operations.
- Excellent electrical characteristics, gain, pattern, F/B ratio.

The original version described on DK7ZB's page has a 3.26 m boomlength. So, i asked him if he could calculate it for a 3m boom. Aluminium tubing are sold in 6m length, and with 3m booms i would be able to build 2 antennas. The new calculated antennas have a small gain drop (about 0.35 dB)

Another advantage of this 7el is that with a 6m long alu tubing, you have enough for all elements and build 2 antennas.

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4 square vertical system

80m-4sqThis page is a short description of the four phased verticals system i've build and used. It is primarily intendend to be used on the lower bands 160m, 80m, 40m. All the principles stated here are of course valid for any other bands, but you can achieve the same game with yagi antennas easily. It is mainly built around the Collins hybrid phasing system wound on toroids.

Other feeding methods are possible and certainly better, but this one is rather simple to build and use on the battlefield. (contests, fieldays, expeditions)

Many stations use this system all around the world and it has proven his effectiveness.

  Four phased verticals on 80m (click to enlarge)

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PIC LC-meter

LCmeter finished

Here is the description of a simple capacitance and inductance meter, easy to build, based around a PIC microcontroler. Simplicity does not mean poor characteristics. The precision is very good and even better than many commercial LCmeter !

The original description has been done by Phil Rice VK3BHR on his pages. I only did adapt it to my needs.

Here are the main characteristics :

  • measures from 0 to 838 nF and 0 to 83.88mH.
  • precision +/- 1%
  • printed board eliminating any connecting wires.
  • use of common case (at least here in Europe).
  • use of common components.

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2 tone generator

2tone goodThe orinality of this description is that the tone generation is made by the use of a DDS and not a sine wave generator made with transistors or a special circuit. It also does not use any special and expensive component but only junk box components, or at least cheap ones !

The main characteristics of this generator are :

- Two tone generator 800/ 1000 Hz or 400/2600 Hz (jumper selectable)
- Single tone generator of 1000 Hz
- Ajustable output level, max around 100 mV pp on 600 Ohm, or 35,4 mV eff. in single tone or 25,0 mV eff. in 2 tones
- Spectral purity between 0,3 and 150 kHz > 50dB !
- Distorsion <0,01% (in single tone) !
- Supplied by a 9V battery, consumption 7-8 mA that gives 50 working hours with an alcaline battery.
- Automatic PTT switching at power on.

This circuit has originaly been described by DH7AHN ,adapted and translated by myself for my usage. The original description can be found here

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