This article describes how to get the most out of your T-match antenna tuner. If tuned incorrectly, this type of tuner can give a lot of loss and the swr still looks ok from the shack.
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Category: Antennas
Icom tuning / ATU controls
Icom Tune Control Plug – – Credit goes to KC2WI
According to KC2WI: An easy way to put most Icom radios into 10W CW for adjusting a manual tuner is with a tune control plug. All you need to make one is a pushbutton, 10K* resistor, and 4-pin Molex connector.** Connect the 10K resistor between pins 2 & 3, and the pushbutton between pins 1 & 4.
If you add a SPST switch in series with the resistor, you can switch the radio between using or bypassing the internal tuner without having to disconnect the tune controller.
My IC-746pro will switch between internal and external tuner without power cycling the radio. When you switch the “external” tuner in, the internal tuner is bypassed, but it remembers the last setting. So you could have an antenna that is resonant at one frequency, matchable with the internal tuner on another, and matchable with an external manual transmatch on another. If your transmatch has a bypass position, you could rapidly switch between 3 different frequencies/bands without ever having to actually retune.
This may also work on some other Icoms. However, my 706 will not recognize that a “tuner” is connected unless it is connected when the radio is powered on. I haven’t tried it on other radios. See note below for the IC-7000***.
diagram created using Kunky Schematic Drawing
| Molex connector: | |
| Radio Shack: | RS 274-224 |
| DigiKey: | Connector: WM1326-ND Molex 03-09-2042 Connector Plug Housing, 4-pin Pins for Connector: WM1100-ND Molex 02-09-2103 |
*For this simple pushbutton circuit you can also modify a male computer internal power connector (from a hard drive, CD drive, power extender cable, etc.). The pin spacing is identical but the keying of the housing is different. Just snip off some of the plastic from the housing so the connector fits on the radio. It won’t have the proper keying but it doesn’t matter because the connections are symmetrical.*** So you can basically make the whole thing from junk box parts.
**Other schematics show 47K or 100K.
***IC-7000 Caution: There has been some discussion about differences between the IC-7000 and other radios, and possible dangers of using tune controls designed for other Icoms on the 7000. One main issue appears to be that improper loading of or voltage on pin 1 will cause a malfunction of the fan control circuit leading to overheating. Note that pin 1 in the circuit above is open except during the tune activation. There is also a caution that connecting pin 2 to 12V is a problem because pin 2 has snubber diodes connected to the 5V bus. See the thread at groups.yahoo.com/group/ic7000/message/30151. AD5X presents an alternate circuit which incorporates a zener diode between pin 2 and 4 to limit the voltage (seewww.ad5x.com/images/Articles/TuningIntfc706.pdf). If you build the circuit with the diode note that having a proper keyed connector becomes important. If you use it with tthe SPST int-ext switch I would put the diode between pin 4 and the switch end of the resistor rather htan direct to pin 2. Steve W3AHL has made some measurements on the IC-7000 which suggest that the resistor should be a higher value than 10K. AD5X uses 47K.
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Icom Autotuner Connector pinout:
Pin 1 is the KEY pin, when the ‘TUNE’ button is pressed, it’s pulled low by the tuner to tell the radio to start transmitting. This is the green wire on the AH-4 cable.
Pin 2 is the START pin to/from the microprocessor. Under normal circumstances the START pin is pulled high when a remote tuner is attached to tell the radio that the tuner is present. When you press ‘TUNE’ the radio pulls the pin low telling the tuner to start the matching sequence. This is the white wire on the AH-4 cable.
Pin 3 is POWER rated for 1 amp max and switches on and off with the radio. This is the red wire on the AH-4 cable.
Pin 4 is ground. This is the black wire on the AH-4 cable.
Additional Information and References:
Manual controller AT-140 but should work for AH-4
Original pushbutton circuit – pictorial diagram at http://www.hampedia.net/icom/ic-718-tune-controller-mod.php
Simple timer circuit info: http://www.hampedia.net/icom/ic-706-10-watt-tune-modification-an-icom-ic706-tune-trigger.php
Info on KG6MVB and AB2CT timer circuits: www.qsl.net/kg6mvb/tuner.html
Credit goes to KC2WI for this info. Use at your OWN risk.
What ferrite material to use for HF common mode choking appliations
LC Impedance matching networks regions of operation on the Smith chart
Here is an overview of what configuration of LC matching networks for RF applications you should use based on where on your Smith chart the load (antenna impedance) is located. Tricks: to place the series reactive element closest to where the resistance is lower. Since you know you also need a parallel reactive element, that comes furthest away from where the resistance is lowest. In most cases for HF / antenna / amateur radio applications the antenna resistance is higher than 50 ohms. However take care to correct for the impedance transformation that occurs along the feedline to the antenna.
Credit for the illustrations: VA3IUL
Here is VA3IULS PDF document:
LC, CC or LL matching circuits on the smith chart
Basic RF matching circuits
LDG AT-100PROII max C / max L
LDG does not specify either max C or max L of their antenna tuners in the “pro” series. They specify a vague “it can tune 1000 ohms”. This basically means nothing as no frequency is given and it is not given if they mean R or X or Z by “1000 ohms”. There is also no service manual or schematic available. Very disappointing from a serious (?) supplier.
Well, since LDG doent specify anything, I have measured it.
The LDG AT-100PROII is a series L, shunt C configuration.
Min L is 3uH, max L is 11,8uH
Min C is 85pF, max C is 250 pF
This is measured at 2MHz.
This shows that the capability of tuning an 2x20m doublet via “10-12m” of 590 ohm ladder line on 80m seems to be limited, and that tuning on 160m is very difficult.This is mainly due to limited Lmax. Also the limited Lmax gives limitations on other bands as well. Having the proper length of transmission line is important to overcome this limitations. You MAY also use a 4:1 or 9:1 balun. However it is important that the balun does have a very low loss. (Otherwise you you end up with a good SWR but poor efficiency).
Designing L and T antenna tuners for HF on the Smith chart
The Smith chart is a tool used a lot by professional RF engineers for solving transmission line stub matching problems and all sorts of quick calculations.
The Smith chart can also be used for quick back of the envelope L and T antenna tuner engineering calculations.
I have on the picture above plotted a T configuration antenna tuner with the first capacitor set to a so big value that it is shorted as seen by the RF voltage (large C – low |Z|). Then the configuration becomes a L tuner in practice with a shunt L followed by a series C when seen from the load in towards the generator.
I measured the Z in the shack end of the ladder line feeding my doublet antenna to be Z = (24.1 – j35) ohms at 14.200 MHz by a Vector Network analyzer. That can be plotted as a point in the lower part of the Smith chart (capacitive Z).
(1) Since we have now first an inductor (in the tuner to ground) as observed from the load towards the generator, we can use this inductance to move along a constant Conductance curve in the Y plane (upwards in the Z plane). The conductance is constant but the Susceptance varies. (We remember from the RF engineering classes at engineering school that Y = 1/Z – of course).
(2) Then we use a series capacitor to move down inside the 1.25:1 SWR circle. We dont have to hit the center because anything inside the inner 1.25:1 circle is good enough. (We move while the R part of R + jX is constant, while the X part is changing to become more negative. This means we move on a constant resistance circle in the Z plane).
Determination of component values can be done easily by hand in a tool like this while still retaining an intuitive understanding of what is going on.
Black magic! Especially with a digital smith Chart tool.
Why you should choose a lowpass configuration on your L antenna tuner
K6JCA has analyzed the needed components values for matching a load while moving on a constant reflection coefficient circle. The plot below shows that in case you select the high-pass configuration for your tuner, certain angles of the reflection coefficient will give you skyrocketing component values.
Component values for the highpass and lowpass configurations
Above you can see that the LsCp &CpLs configuration keeps the max component values quite flat. LsCp and CpLS are therefore the best engineering choices based on cost and realistic component values.
http://k6jca.blogspot.no/2015/04/notes-on-antenna-tuners-t-network-part-1.html
Repair of LDG automatic antennatuner
I blasted my LDG antennatuner some time ago. Or …. I thought I blasted it….. It appeared that it was only the resistor in the SWR detector circuit that got burned out. I replaced that resistor and now its ok again.It was easy to repair. However these small LDG tuners dont take more than 100W max. The designers have used ferrite cores, whereas it would have been a much better idea to use carbonyl cores or air core inductors. The latter doesnt get so easily saturated.
However I must say that the design of the LDG equipment I have seen so far is not very impressive. Why use that BIG chasis when you dont need it? Why use DB9 style connectors on a chassis that is supposed to be watertight? Look at that coax termination there. Both on the board and on the PL259 chassis connector. Why use RG174 teflon coax when you have such crappy terminaions? Perhaps it would be better with no coax at all 🙂 However when the tuner works it works fairly OK. Just dont trust this kind of equipment in a contest or on a dx expedition.