Antenna Controllers

There is one common caveat all antenna controllers share, and that is where the power comes from. Accessory sockets and data ports should not be used to power any load over the maximum specified by the manufacturer. For example, Icom specifies a maximum of one amp (total) for its various ports, as does Yaesu. Although these ports are fused, in most cases a circuit board trace will fail before the fuse blows, which will result in an expensive fix.

To avoid this possibility, it is good advice to use a RigRunner or similar device for the power feed to the controller, and any other ancillary device(s) in use. In most cases, the circuit should be protected with a fuse no larger than 3 amps. This protects the controller, and the antenna's motor from damage.

There is another equally important caveat to remember if you're thinking about upgrading from an Icom IC-706 to a new IC-7000. Most devices which work flawlessly with a 706, will damage a 7000 beyond repair! Here's why.

The 706, and the 7000 differ in the way their tuner port is configured. What works okay with the 706, may not work okay with the 7000. The reason is, a lot of the 706 devices place a resistor and a cap between Pins 2 (13.8 vdc) and Pin 3 (Start) as a time constant. Doing this on a 7000 causes the fan to run fast or slow depending on the value of the resistor. Further, Pin 1 (TKEY) is also shared internally with the temperature control circuitry, and must be left floating. If either condition exists, the fan may not operate correctly, which can lead to final failures!

To reiterate, devices used to mimic the AH-4, and trick the IC-706 into transmitting 10 watts of carrier are not compatible with the IC-7000. This includes the suggested circuitry from SGC, at least three of the older model screwdriver controllers, and most small tuner modules.

The only US made ones known to work correctly are from Better RF and Turbo Tuner, and only those designed specifically for the IC-7000. Their respective older units made for the IC-706 model are not compatible! Please do yourself a favor; even if your old 706 unit appears to work correctly with your IC-7000, don't use it!

There is also an Australian made "tuner upper" designed by Owen Duffy, VK1OD, which is compatible. Like the aforementioned units, it controls the radio using the CI-V port, and uses a low-power setting (about 30 watts) utilizing the RTTY mode. All of these units are powered via the tuner port.

Lastly, if you're using one of Bob Lewis' (AA4PB) Ham-Kit interfaces made before March of 2006, remove R1 (33k) entirely. This leaves Pin 1 (TKEY) of the tuner port floating which allows it to work with either radio.

SWR Considerations

Proper antenna impedance matching is a absolute prerequisite to using an SWR detecting controller. While this is covered well in my Antenna Matching article, it bears repeating here. The use of UNUNs, switchable capacitance boxes, and autotransformers have their places, but if you're using an SWR detecting antenna controller, a fixed shunt coil is the only correct solution assuming you want true, automatic operation.

Shunt matching coils are easy to make, but require some setup time for best results. If you follow the instructions in the aforementioned article, and take your time adjusting the coil's spacing (inductance), you'll find a setting that will provide an adequately low SWR (<1.6:1) from 160 through 10 meters. And do yourself a favor; buy an antenna analyzer. Nowadays, they're as important as SWR bridges were during the 50s, 60s, and 70s.

The motors and counter (reed) switches of all remotely controlled antennas operate above RF ground potential. The amount of RF present on the leads depends on several factors, especially where and how the antenna is mounted. In any case, every single one of them requires adequate RF bypassing. Inadequate bypassing will result in destroying any type of remote control. Remember too, just because you didn't have any problems with your manual control, means nothing when it comes to computerized controllers.

Digressing for a moment. RF bypassing isn't the correct term, but it is easier to understand for most folks. The correct term is RF choking. The ferrite beads discussed below are indeed RF chokes. There is a complete explanation of how they work here. As noted, the amount of choking required varies with the installation, but it is always prudent to error on the excessive side. Just keep in mind, the poorer the mounting location (trailer hitch mount for example), the more bypassing (higher choke impedance) is needed.

Most antenna manufacturers supply ferrite beads, although in some cases, they're wholly inadequate for the purpose. Separate beads should be used for the reed switch, and motor wires. Depending on the power level, at least 7 turns, and preferably 9 or more. They should be installed near the base of the antenna, and from that point to the entry into the vehicle, the leads should be shielded for further protection (see right photo).

The rule of thumb is, the choke must have an impedance of at least two magnitudes greater than the impedance of the circuit. In other words, at least 5k ohms, and perhaps 2 or 3 times this in some cases (poor mounting location for example). Mix 31 split beads are ideal for this application, but it takes about 8 turns to equal 5k ohms. Depending on the wire size and insulation, you'll need to use the 1/2 or 3/4 inch ID ones. If your antenna didn't come with RF suppressing beads, they're available from DX Engineering in several sizes.

If you're still plagued with RFI on the motor leads, and parallel line currents on the coax (common mode currents), it is a sure sign you do not have an adequate image plane under the antenna. While it sounds like a broken record on my part, it is the mass under the antenna, not along side, that counts! In extreme cases of poor mounting, shielded cable, and liberal use of bypass capacitors (paralleled .1 uF and .01 uF ceramic caps) on the output side of the chokes may be required.

How They Work, Switch Type

There are two basic scenarios used to automatically reposition the coil in all remotely tuned antennas. One, like the MFJ-1924 shown at right, is to keep track of the number of turns the adjustment shaft makes. This is accomplished by using a magnet attached to the motor output shaft to open and close a reed switch (almost all late-model, remotely controlled antennas have one built in). During set up, the antenna is parked at one end or the other (screwdrivers at the lowest position, HiQ's at their highest (highest frequency), or starting point. Then the resonant points are found (you have to do this yourself), they are stored in multiple memory locations. As long as power remains applied to the controller, a simple button push will move the antenna to a specific preset point. Some controllers, utilize the radio's data port (CI-V on an Icom for example), and reset the antenna to the nearest preset.

There are a few drawbacks to them. If power is lost to the controller, all of the memory positions go away. Obviously, you have to go through the set up process once again, so keep track of the readout numbers for each band location in case future reprogramming becomes necessary. This means you have to power the devices separately, not through the radio's accessory socket. Also, in cold climates, it is possible to draw enough starting current to lower the battery voltage down to a level which will cause some units to loose their memories.

Another basic problem with the MFJ units, is their sequential programming. In other words, to reset the position (frequency) on just one band, you have to go through ALL of the bands. Another good reason to write down the readout numbers.

Making matters worse, the MFJ SDC-103 (a sister product to the aforementioned) share a manual. The manual clearly states that all of the band memory positions are preset to on, when in fact they are preset to off! The setup procedure doesn't mention how to set the controller up for a HiQ, and assumes you have a standard screwdriver (the motors go in opposite directions). Once you get past the omissions and pigeon English, they work so-so. Their biggest drawback are their cheap push buttons which tend to double up, making programming even more difficult.

A lot of folks end up using a manual controller like the Ameritron SDC-100. Just like its automatic stablemates, proper RF bypassing is a must. Even then, the SDC-100 seems to miscount more than it should. This fact requires parking the antenna and resetting the counter.

The term parking refers to collapsing the coil of a screwdriver antenna into the mast (highest frequency position). Depending on the brand and model of the controller, and the radio is it connected to, some park the antenna when the controller is switched off. This is not an ideal situation, as it adds wear and tear to the motor assembly. Some antennas, like the HiQ, parking is not necessary, or desired.

Manual Controllers

There are so many different manual controllers on the market, it's difficult to lump them all together. Most aren't much more than a DPDT, center-off switch. Reading the SWR is left to the user.

The High Sierra i-Box isn't much more than a manual control. That said, some models of the i-Box interconnect with the transceivers tuner port (Icom IC-706 for example). When the antenna switch is operated, the radio transmits at a reduced power setting. In the case of the Icom IC-7000, you have to manually switch the radio to RTTY mode to get the requisite carrier. Here too, you need some way of reading the SWR.

How They Work, SWR Type

The other method is to (automatically) detect the SWR like the Turbo Tuner does (right photo). Although different makes use different strategies, they all use the SWR information read from the radio's data port, or a separate SWR detector. Depending on the make, a push of the radio's tuner button (or one on the controller), causes the radio to transmit at a reduced power setting. The controller then powers the antenna's tuning motor. When the preset SWR limit is reached, the controller stops the transmission and shuts off the motor.

In some cases, the antenna motor will be going in the wrong direction. Once it hits its travel limit (and the stall current preset is adjusted correctly), it reverses and goes back the other way. If the SWR limit is set incorrectly (especially on 80 meters), it will cycle through its opposite travel limit. Some units have a built in limit for the number of cycles, but all of them can cause excessive motor wear if not setup correctly. That is to say, the SWR detection level, motor stall and operating current, and motor direction settings must be correct for your installation. I emphasize your, because variations in manufacturing tolerances, and the length and wire size used make each installation unique.

It is also important to follow the manufacturers' instructions when setting the SWR detection parameters (see below). Of the 50 or so installations I have critiqued over the last four years or so, this is one of the most common problems. Some of the others are, improperly setting the motor stall current parameter, not reading between the lines in the manual (this may be facetious, but it's factual), and very poor wiring practices (both RF and DC). Remember, it pays to take time to do the job correctly the first time around, as rework is always more expensive, and it is always the most exasperating of duties.

Incidentally, the Turbo Tuner draws its power from the radio. If you have a low-power antenna, you might get by. However, as their manual points out, it should be powered directly if you're using a full-sized HiQ or High Sierra.

A Better Mousetrap

There's a new SWR detecting controller designed to mate perfectly to the Icom IC-7000. Made by the BetterRF Company in Edgewood, NM, (505-286-3333), it's based around their tune control (right photo). It has some very unique features, placing it on top of the pile.

Foremost is the fact it remembers where it was before you decided to QSY, even if it's to another band! Therefore, the motor always goes in the correct direction which reduces wear and tear. Further, it uses the SWR data from the radio so it doesn't need an external detector. When required, it uses PCM (pulse-code modulation) to slow the motor down. This reduces overshoot, and allows for a very precise stopping point. It even rechecks the SWR before shutting down, just in case there was overshoot. All of the settings are accomplished using the IC-7000's front panel controls. In other words, there are no jumpers to set. The only manual setting, is moving a jumper inside the tuner module so it knows the antenna controller is attached. This takes about 3 minutes.

Other features include, a infinitely variable SWR detection level (preset is 1.5:1) for each band, automatic motor run and stall current detection. In addition, there are two unique features.

One is a built-in bypass relay which disables the amplifier (if one is used) during the tune function. The other is a little more esoteric. The internal relays which provide power to the antenna motor, ground both of the motor leads once the antenna is tuned. This minimizes the egress of RF into the control wiring, and provides dynamic braking.

No antenna modifications are necessary, and it will work with all remotely controlled HF mobile antennas. The interconnect between the two units is a mini-stereo cable. The only addition is a 3 amp fused circuit for the DC power cable which powers just the antenna's motor. All cables are included. You can down load the installation manual here.

Odds & Ends

If you're using an RF type controller like the BetterRF unit, there is no need for the reed switch. In this case, just connect the leads directly to the antenna mast; no toroid will be needed. Remember, the reason the toroids are there is because the reed switch and the motor operate above RF ground, and must be bypassed (choked off).

If you use a separate SWR bridge with your automatic controller, be advised their readings may or may not agree. This is a direct result of measuring the SWR at different points along the feed line, and is not an indication of a problem per se.

I should mention that poor mounting locations can cause RF to flow on the outside of the coax. This is referred to as parallel line currents, or common mode currents. Either way, it's RF using the coax as an image (ground) plane instead of the vehicle. This problem is directly related to how and where the antenna is mounted. In other words, the poorer the location, the worse the problem will be.

Fully automatic antenna controllers are the wave of the future. In view of the fact that many municipalities are enacting so-called cellphone laws limiting the use of on-board telemetrics, we need to employ every device we can find that will make our mobile operation less distracting, and thus safer.

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