G4YDM described his balun at Ham Radio – What Is a Balun and How to Make One Cheaply.
With a title like that it is sure to have wide appeal, but it isn’t anything too novel, it is simply an air solenoid of 50Ω coax cable as a common mode choke, commonly known as an Ugly Balun.
He gives some instructions for one of several constructions:
When wrapping your coax around the pipe don’t use too much force as it may damage the inner braid and space the turns away from each other by a millimetre or two. R-G-2-1-3 coax around 21 feet used with 5 inch pipe will handle 400 watts pf power.
Above is a pic of the third construction which appears to be 21′ of RG213 on a 5″ PVC former:
He gives some performance measurements adjacent to the pic above:
Using a dummy load connected to the choke and transmitting 100 watts from my transmitter indicated an S.W.R. readings of around 1.5 to 1 at 3.5 Megahertz when testing 28 Megahertz the S.W.R. reading came down to 1.1 to 1 which is an excellent match. …
The test described above seems to simply be a dummy load connected to one end of 21′ of RG213 and the transmitter with VSWR meter feeding the other end. To be meaningful we need to know the impedance of the dummy load, indeed to be meaningful it needs to be 50Ω, so lets assume that is the case. Continue reading G4YDM balun
A recent online posting gave unequivocal recommendation for the Coil32 Inductance Calculator for application to a ferrite toroidal HF current balun.
Always interested in these things, I tried to download it to evaluate it but there was rigmorol to create an account and aware that I have never downloaded a calculator that handled that specific problem at all well, I was reluctant.
They do however have some online calculators that are supposed to use the same algorithms and methods as the downloadable software, so lets review the one for a toroidal ferrite inductor.
Above is the data entry form, and warning bells sound. The “relative magnetic permeability” field is a simple scalar quantity, but the permeability of most ferrites at HF needs to be considered as a complex value (ie having real and imaginary components). Continue reading Coil32 inductance calculator
Optimal Zo for Guanella balun sections left the reader with a though exercise, a transmission line transformer used by PA0V in a 144MHz power amplifier output network.
The pair of tabs to the left are driven by FET drains, the upper pink centre conductor is grounded, the lower end connecting to C1 is the output to a nominal 50R load. The network shown near OUT is for fine load adjustment. There are two coax sections making this TLT, shields bonded all the way around and the centre conductors connected as shown. What is the optimal value of Zo for each the coax sections?
Above is a pic of the PA, and we are looking at the network to the right of the dual FET. Continue reading Optimal Zo for TLT sections challenge – a solution
A Guanella balun may have several sections, and they may be connected in parallel on one side and series on the other side so as to achieve nominal impedance transformation ratios other than 1.
The question is often asked, what is the optimal Zo for these line sections?
Several answers exist in ham lore, but the answer is relatively simple and revealed by the most basic understanding of transmission lines.
If you do not want standing waves on a line section and its associated impedance transformation, then make sure that Zo=V/I… easy as that.
(Guanella 1944) explains it with examples:
Note above that he refers to
coil systems. He did not describe for instance (b) on a single core, a shared magnetic circuit which would be a single core system, but he states clearly
two coil systems. (Sevick 2001) and lots of other hams say otherwise, but they are wrong. Continue reading Optimal Zo for Guanella balun sections
A very long time ago, I purchased a W2AU 1:1 balun on the maker’s claims that it was good from 1.8 to 30MHz.
These were very popular at the time, but as voltage baluns they achieve good current balance ONLY on very symmetric loads and so are not well suited to most wire antennas.
Above is W2AU’s illustration of the internals.
Mine barely saw service before it became obvious that it had an intermittent connection to the inner pin of the coax connector. That turned out to be a poor soldered joint, a problem that is apparently quite common and perhaps the result of not properly removing the wire enamel before soldering.
Having cut the enclosure to get at the innards and fix it (they were not intended to be repaired), I rebuilt it in a similar enclosure made from plumbing PVC pipe and caps, and took the opportunity to fit some different output terminals and an N type coax connector.
Above is the rebuilt balun which since that day has been reserved for test kit for evaluating the performance of a voltage balun in some scenario or another. Continue reading W2AU 1:1 voltage balun
Designs appearing in the ham literature and online articles tend to espouse relatively large diameter conductors, conductors that can be challenging to wind onto the toroidal cores often used.
This article analyses the copper losses in a practical Guanella 1:1 balun where a fabricated twisted pair line is used.
Total losses comprise core losses and transmission line losses. Continue reading On copper loss in transmitting baluns
In Improved cooling for the MFJ-949E I described a solution to a problem of demonstrated overheating of the ATU at rated power, indeed at a lot less than rated power.
Though I have never measured the ATR-30 temperature rise, and am probably unlikely to stress the 3kW rated ATU with a 100W transmitter, I have performed a similar cooling modification to the ATR-30.
Continue reading Improved cooling for the ATR-30
I have published a number of transmitting balun designs, and none of them use enamelled wire. I am sometimes asked why is that so, but more often advised that it is a better solution than the wires that I have used.
enamelled wire depends on an insulating coating, and its breakdown voltage depends on the wire diameter, polymer used, the minimum thickness applied, coating cure / bake processes, temperature, humidity etc.
Whilst I have seen specifications promising breakdown voltage of a single round enamelled wire in the regions of 5-10kV, and you might hope for nearly double that between a pair of twisted wires, unless you have sourced specific product, new performance may be closer to 2kV. Continue reading On use of enamelled wire in transmitting baluns
The article describes a current balun with low Insertion VSWR for operation at modest power levels. It is lightweight and well suited to portable operations, and can be made with materials readily available in Australia (LF1260 cores are a little over $1 each in packs of six.)
Continue reading Low power Guanella 1:1 balun with low Insertion VSWR using a pair of Jaycar LF1260 suppression sleeves
At Improved cooling for the MFJ-949E I described a modification to the ATU to improve its cooling using a fan and run on timer.
The run on timer described was based on a Chinese STC15F104E DIP8 8051 like microcontroller.
Because the programming tools for the STC chips work so poorly, and the lack of documentation of their protocol, there is no simple way to update only the calibration data in EEPROM. I have ported the algorithm to an ATTINY25 which doesn’t cost a lot more but had a much better development environment and a range of tools to allow EEPROM update without overwriting the FLASH image, and as well it will run my bootloader, ATB.
This article describes a generic run on timer based on an Atmel AVR chip, a ATTINY25 though the code will also run in ATTINY45 and ATTINY85.
The circuit is very simple, the DC output from the forward power detector is connected to the input pin which turns the BC548C transistor on at input voltage greater than about 0.7V. The high value of base resistor ensures very light loading of the forward power detector.
Continue reading A generic run on timer using an ATTINY25