Icom appears to delight in charging outrageous prices for all transceiver accessories, so many Hams improvise instead. A few circuits have been published for CI-V interfaces, most of which use the MAX232 IC. Here is a very simple CI-V interface, originally described by OK2WY . I’ve made small changes to the modem control signals connections. Although the circuit doesn’t conform exactly to the RS-232 specification, it does work well and has the advantage of being easily constructed inside a 9 pin D-type shell. Please note that the resistor value 4K7 means 4700 ohms. The transistor types are not critical, I just happen to have plenty of 2N2222As.
Continue readingCategory Archives: Articles
Here you can find articles I’ve cached, that are no more available in the net or are very rare to be found. Where possible credit will be given to authors.
GAP Titan DX Maintenance
I’ve installed the GAP Titan DX some years ago. Due to maintenance works on my roof, I had to put the antenna down for some weeks.
This week I’ve been able to restore the antenna on the roof. The Gap Titan DX is a vertical dipole with no traps, and with vertical elements making this antenna resonating on from 12 to 30 meters. 80 meters provided from a top capacitor, while 10 and 40 meters depends on the tuning of a cross shaped counterpoise at the base of the antenna.
I’ve already written several times about this antenna and how to tune it on several bands providing also a quick antenna reference you can seen here behind.
According to some OM there is a relation between the 20 meter stub and the 40 meter copper wire length.
Well, today after having restored back the antenna on the roof, I’ve not been able to obtain an acceptable SWR on the 40 meters.
With acceptable I mean SWR < 2.0 on the band. According to GAP this antenna shoud be able to perform well with acceptable SWR on all bands, but in the 10 years I’ve on the top of my head, it never performed on the 30 meters. SWR on 10 MHz has been always > 3.5.
Continue readingQuarter Wave Vertical Antennas
and how they operate
One of the most useful antennas in the repertoire is the
Marconi or quarter wave grounded vertical antenna. Its invention made
it possible to halve the length of antennas, simplifying communications,
especially at HF and below. This antenna is still used widely today,
especially in marine, land mobile and long distance communications. It
can offer excellent performance when installed well. There are, however,
a number of selection criteria to take into account before you buy…
Long Waves, Short Antennas
designing for MF and LF communications
When radio began, it started with low frequency communications, which it was thought was the answer to long distance communications. Since then we have seen the development of sky wave communications on HF frequencies, followed by the proliferation of communications system using the VHF and UHF direct wave and microwave. It may be thought by some that low and medium frequency communications are somewhat outmoded, but in reality they are still very much in evidence today…
Feeder Radiation
Striking a Balance
When you connect centre fed antennas, like dipoles, Vs, triangles, yagis, rhombics, loops and so on, to coaxial cable, unless care is taken, it is not difficult to end up with feeder radiation. Not only can the loss in power be quite significant, but the radiation characteristics of the antenna system will also be seriously compromised.
Continue readingFolding the Dipole Antenna
Invented by Heinrich Hertz in around 1886, the half wave dipole is still one of the most simple and practical of antennas and still very much in use today. It consists of a half wavelength long centre fed conductor. Since these early days, improvements have been made to the initial design by adding a second, and often a third conductor, joined at the two ends to form a loop. This antenna, known as the Folded Dipole, can provide improved performance over the single wire antenna when well designed, constructed and installed…
Continue readingMagnetic Longwire Baluns
Do these things do exactly what they say they do – or are they total hogwash?
Have you seen the ads? This device will match your long wire to your receivers 50 ohm input? Firstly a long wire on HF would be on 28 MHz longer than 120 foot and on the lower bands it just an end fed “EF”
We can also get rid of the “magnetic” and give the balun its true name of voltage balun. My interest in the MLB was started after a friend went out and paid ?30 for one and started to tell me how this little device will produce a 50 ohm match at all frequencies. Any aerial will have differing values of impeadence depending on what band it is used, a 66 foot wire on 80m is about 30 ohms and on 40m the impeadence is about 1000 ohms.
For any sort of balun to be able to match different impeadences to 50 ohms you need to be able to vary one or more of its components. And when you can do this, the balun will match most things to 50 ohms, but you would call this type of balun an ATU. An ATU is a variable balun.
But theory is one thing and practice is another. So mainly for some thing to do I decided to make some MLB’s and see what mystical properties they have. The first balun was made “by the book” using the correct wire SWG and ferrite ring with a type 63 core for 1 to 30 MHz. I used a friend’s MFJ analyser for the tests and a 35 foot wire aerial.
The balun did improve the match to the receiver. Only near the resonant frequency of the aerial was any match close to 50 ohms or a VSWR of 1 to 1, as you would expect. On all other frequencies the match varied from 3 to 1, to 5 to 1 VSWR. Without the balun the match was horrible!
In the real world this means I had some thing like a increase of signal from 1 to 4 “S points” on the receiver from 1 MHz to 30 MHz.
The “VMR version” MLB was made from scrap. 3 core 2 amp lighting flex and an old ferrite rod. The results are just the same as the posh version!
You need about one yard of 3 core, 2 amp flex and a ferrite rod with a length of about 6 inches or longer.
Using 3 core flex it is easy to wire because it is colour coded. Tape one end of the flex to the rod leaving 6 inches for the connections, then wind on as many turns as possible (mine has 10 turns) and again fix the wire with tape etc at the other end. Now you can just twist the wire connections together or better solder them. Connect it up as shown. Blue right hand side to Green left-hand side. Brown right to Blue left. Inner of COAX, to Brown/Blue. Braid to single Green. Aerial to single Brown. Then just bung it into a box.
So is a MLB worth having? They do produce a “better” match to the receiver but you could get an ATU kit for about the same price, which will always produce the right match. If you buy surplus VC’s you can make an ATU for under ?10. Find a couple of broken tranny radios and you can make one for free.
The main advantage of the MLB is you can use COAX to the feed point of the aerial out side and get a reduction in noise pick up from TV’s etc in your home. I would not spend money on one, but a home made MLB in a box is worth having. Because it is a pain to keep peaking the ATU as you tune up the SW bands and anything that helps to give a better match is better than having nothing at all.
160m Antenna – Inverted L
Another antenna added from the antenna plan is a 160 meter ¼ wavelength inverted L.
A 130 foot length of 12 gauge PVC covered stranded wire slopes up from the ground system to the 40 foot level of the 45 foot tall fiberglass flagpole (about 60 feet of wire length) and then proceeds about 70 feet toward the far back edge of my property. The 90 foot start-to-finish dimension just fits my city lot. At the end, the antenna wire is terminated at about 15 feet above the level of the back yard. The geometry actually resembles an inverted L that has partially fallen over – in other words, a “lazy L”. This antenna is used on 160 meters only and is coaxial cable fed.
In place of an active tuner, a 10 turn 4 inch diameter tapped coil wound of 0.250 inch diameter copper wire is used to tune the 1.8 to 2.0 MHz band in three segments.
Two vacuum relays are used to select the correct amount of the coil for a particular band segment. No coil turns are added to the top band segment, 7 turns are connected in series for the middle tuning range and the entire coil is used at the bottom end of the band. All of the base load components plus the static discharge arrestor are located in a 7 inch square weatherproof box that is bolted to the ground structure.
The coaxial cable entry point is sealed with silicone sealant to keep the spiders and moisture out. The wire that brings power to the relays is TV rotor cable which is rated to be used outside in the weather.
The transient suppressor and coaxial cable braid bus-work is bonded to the ground system with a heavy braid.
The cross-section of the metal drainage ditch that is used as the ground system for this antenna is shown below.
This metal drainage ditch is about 100 feet long and runs along the top of a five foot high concrete block wall that defines the eastern boundary of my city lot. The drainage ditch measures 12 inches wide and 12 inches deep. All of the 10 foot long metal sections are electrically bonded together along the length. This provides a very good earth ground for this 160 meter 1/4 wave inverted L antenna as well as a reflector / ground reference for the 75/60/40 meter NVIS antenna that is mounted directly above the metal ditch (see the NVIS page for more details about this antenna).
An improvement that I am considering for the ground system is to add a couple of wire radials in addition to the drainage ditch ground system. These radials will be run underground by fishing them through the drainage pipes buried under my driveway and front lawn. I think I’ll connect them with a remotely controlled relay so that I can more easily quantify their usefulness during actual on air contacts.
Another improvement under consideration is to add a number of 10 foot long ground rods along the length of the metal drainage ditch, especially near to the antenna feed point.
Since my back of the envelope calculations indicate that this antenna is only about 35% efficient (at best), these combined improvements could potentially yield as much as another 1 to 2 db of signal strength at the receiving end of my transmitted signal. Very interesting??
The antenna wire coming from the weatherproof box mounted on the metal drainage channel (lower center of the photo) first goes up to the top of the brown painted PVC pole (at the upper right of the photo),
From there it proceeds up to a point about five feet from the top of the 45 foot tall fiberglass flag pole. This places the 160 meter antenna five feet below and at about 30 degrees crosswise to the OCF Windom antenna wire to minimize interaction between the two antennas.
The far end of the antenna is attached to t he fence with a pulley and one gallon paint pail counter weight that takes the sag out of the antenna wire and allows the antenna pole to sway freely with the wind without stretching or breaking the antenna wire.
The maximum SWR at the edges of each of the three segments is less than 2.5:1. At 1.945, the frequency that I use the most, the Rs measures 33 ohms with an Xs of 32 ohms for an SWR of about 1.9:1 according to my MFJ-269 analyzer.
Since the static discharge protection is located at the base of the antenna, the coaxial feed line goes directly to the shack through a 100 foot length of coaxial cable. The antenna loads nicely and shows virtually no change in SWR when operating in either dry conditions or on a rainy day.
The antenna handbooks show that the inverted L has a more or less omni directional pattern that is uniform within about 1.5 db. The signal reports from any direction using this antenna are always as good as or better than the signal reports for other hams using top loaded verticals, full wave loops and dipoles at similar heights. This antenna is not a multi-element full size vertical array using massive towers, but it does work and works quite well. This is the one band where I often run the full power in order to overcome the very noisy band conditions that are typical at the receiving end.
160 meters is also the band where the 38 inch diameter magnetic loop antenna (pictured at the left) really shines. This loop often delivers the best quality receiving signal, especially if there are plasm TVs operating in the vicinity (see the PIXEL loop page for more details about the performance of this loop on the 160 meter band).
Article by W6SDO originally available at http://www.w6sdo.com:80/160M.html
The gamma match
The Gamma match is the most used matching device used for yagi beams.
What it does is:
A Yagi almost never has an impedance of 50 ohms. In other chapters i told that Gain, bandwith, F/B etc. all relate to eachother these figures are never all high at one point. A well designed yagi has for that reson an impedance around 20..25 ohms.
A Gamma-match can match impedance below 50 ohms right up to that 50 ohms wich your tranceiver wants to see. Continue reading
Kenwood KPG-46 programming cable
Kenwood KPG-46 Programming Cable
Suitable for the following radios:
- Kenwood TK-71 TK-81 serie
- Kenwood TK-7302 / TK-8302
- NX-700 de Kenwood / NX-800 Series
- Kenwood TM-271E
Component List:
C1 470?f 16v.
C2 47?f 16v.
C3 a C6 10?f 16v.
IC1 MAX 232.
REG1 78L05.