Q. Why use such a fancy interface? Why not just wire the tuner to the radio's connector as shown on the SGC web page?
A. The simple circuit, even the one using the resistor and capacitor, can cause reliability problems. The radio outputs a short (appox 60mS) pulse for each band change. This is intended to signal Icom's AH-4 tuner to go into bypass mode. With the direct connections, this band change pulse can cause the radio to inadvertently go into tune while changing bands. This is especially true if you step through several bands to get to the one you want. The multiple pulses can charge the capacitor to the point where it trips the radio into tune right in the middle of changing bands You wind up putting a tune signal on a randomly selected frequency which may be right on top of a QSO in progress.
In addition, the radio's tune button does not function as Icom intended when using the simple circuit. The SGC tuner does not send the proper control signals to the radio to indicate if it was able to find a proper match or not. The cancel tune and bypass functions do not work as Icom intended for the same reason.
Q. Why not just use one of those little modules that force the radio into tune when pressing the tune button?
A. With one of these, the tuner is unable to notify the radio when tuning has been completed. The radio will remain in tune until you manually cancel it by pressing the tune button again or until a time-out has occurred. The tuner is also not able to notify the radio if a match was not found. This is basically a manual device. Using the PIC interface implements the radio's tune button exactly as Icom intended.
Q. SGC says to connect the tuner to the ACC connector on the radio. You say to use the 4-pin tuner connector. Which is correct?
A. The same tuner control signals are brought out to both connectors on many Icom radios so it makes no difference where you connect to them. We suggest the tuner connector so that your ACC connector is available to connect any other devices you may want to use.
Q. Why would I want the tuner to go into bypass when changing bands?
A. Generally, the receive signals are better with the tuner bypassed so that the whip is connected directly to the radio than they are when going through a tuner that is not tuned to the band of operation. With the PIC interface, the tuner will be placed in bypass any time the band is changed, permitting better received signals until you have a chance to properly tune the antenna. With the PIC interface this function works on the SGC tuner exactly as it does with the Icom AH-4 tuner - exactly as Icom intended.
Q. Can I use the PIC Interface with other SGC tuners?
A. The new version 4.0 PCB provides a jumper plug that will permit it to work with either the combined lock/reset line tuners such as the SG-230, SG-237, and SG-239 or those with separate lock and reset lines such as the SG-231 and SG-235. The legacy version 3.0 PCB will not provide the lock function for tuners with separate lock and reset lines.
Note that the SG-237 PORTA, SG-211, and MAC-200 have no external connections for lock/hold and tuned indication so they cannot be used with the PIC interface.
It has come to my attention that the SG-239 has a 1.5K resistor in series with its TUNED line. I have therefore changed the value of R14 in the interface from 10K to 33K in order to ensure compatibility with the SG-239. This will permit the tuner to pull the interface tuned line low enough to reliably turn off Q3. Without this resistor change the circuit will perform "on the edge" and under some conditions may not terminate the tune signal as soon as the SG-239 finds a match. An indication of this problem is that the Fault LED glows dimly while the tuner is in a tuned condition instead of going completely dark.
Q. I have already built my interface. Do I need to change the value of R14 to 33K?
A. If you are using the interface with an SG-239 tuner I recommend the change. If you are using it with an SG-230 or SG-237 tuner then there is no need to change the resistor.
Q. Can I use the PIC Interface with other radios?
A. The interface should work with any Icom radio that has the standard 4-pin tuner connector for the Icom AH-4 tuner. By fitting the appropriate connector, the interface will work with Alinco radios such as the DX-70 and the DX-77. The interface will not work with any other brand of radio that I know of. Kenwood uses a completely different electrical interface which would require a redesign of the tuner interface circuit.
Q. I have heard that a 102-inch whip will not work on 75 Meters and that I should use a 75M Hamstick or something similar along with the tuner.
A. I have heard that too but could not think of a technical reason why it should be. I ran some tests comparing a 75M Hamstick to a 102-inch whip using the SG-237 tuner and found no noticeable difference in performance with my installation. A 102-inch whip on 75M or 40M presents a very high feed impedance at the base therefore it is important to minimize any capacitance between the whip and the vehicle. If the whip is mounted close to the vehicle or uses a typical ball mount or a feed wire that exhibits capacitance to the vehicle then a good deal of power can be bypassed around the antenna by the capacitive reactance. If you have too much capacitance to the vehicle then replacing the 102-inch whip with a Hamstick or any other resonant antenna with built-in loading may indeed reduce the loss on the lower bands. This is because a loaded antenna will have a much lower feed impedance so the shunt capacitance will have less of an effect on efficiency. The problem with the 102-inch whip on 75M has more to do with an improper installation than it does with any inherent deficiency in the whip or tuner. If you use a tuner like the SG-237 which is designed to feed a 102-inch whip on 75M, you mount the antenna high and clear of the vehicle, and you use a large mount insulator that minimizes shunt capacitance then you will find no difference in performance between the 102-inch whip and an antenna like the Hamstick on 75M. Note that you should never attempt to load a 75M Hamstick on 40M thru 10M as you risk the coil arcing over and destroying the Hamstick and possibly the tuner. This is because the coil turns are very close together and the thin enamel insulation may not be able to withstand the high voltages present between turns.
Q. Why do both Icom and SGC use those big ugly, expensive insulators at the base of their antennas?
A. When you use a tuner to load a physically short antenna like a 102-inch whip on low frequencies, the feed impedance becomes very high. The higher the impedance the higher the voltage for a given power output. Any length of feed line (even a few inches to a foot) will raise the impedance at the base of the antenna even more. With 100 watts output, it would not be unusual to have on the order of 1000 Volts at the base of the antenna. The big, ugly insulator is needed to ensure that it does not arc over, even with high humidity, rain, or dirt on the insulator. SGC advises against the use of the standard "CB" type ball mount which is designed for a 50-ohm feed impedance and much lower voltages. The ball mount may also exhibit excessive capacitance to the vehicle which can reduce the antenna system efficiency on the lower bands.
Q. Why can't I use coax between the tuner and the 102-inch whip in order to keep the feed line from radiating?
A. The capacitance between the center conductor and the shield will essentially bypass the signal around the high impedance antenna making for a very inefficient system. On the other hand, if the antenna is resonant on the band you are operating in (a 75M Hamstick operating in the 75M band, for example) then the feed impedance will be reasonably close to 50 ohms and the coax will work fine. In this case the tuner serves only to "trim" the match a little but you loose the real benefit of using a tuner to jump from band to band without getting out of the vehicle to change whips. If you are using a wide range tuner to match a single whip to bands where it is not inherently resonant then you MUST NOT use coax for the feed line between the tuner and the antenna. Use a well insulated single conductor wire, keep it as short as possible, and keep it spaced well away from surrounding metal.
Q. Should I set the IC706MkIIg menu 27 A-TUNE STRT to ON in order to force a retune on high SWR?
A. No. Leave this at the default OFF setting. The SGC tuner will sense a high SWR and automatically retune (even on a SSB transmission) if you leave the LOCK switch on the interface in the OFF position.
Q. Then why would I ever want to LOCK the tuner?
A. Depending on your antenna installation, the movement of the whip while in motion might cause the SWR to vary. By using the LOCK position on the interface you can prevent the constant recycling of the tuner. The interface temporarily unlocks the tuner (regardless of the switch position) when commanded to tune by the radio so it is okay to leave it set to LOCK all the time.
Q. When I connect a 50-ohm dummy load to the tuner output, it will not retune when I press the TUNE button. Why?
A. The interface always starts the tune process by resetting the tuner to bypass, connecting the radio directly to the antenna. The 50-ohm dummy load provides a good SWR regardless of frequency. The tuner sees that the SWR is good so it just stays in bypass. With a "real" antenna such as a whip, the tuner finds the SWR high when bypassed and so it performs the tuning process. Try a 100-watt light bulb as a dummy load on the output of the tuner as suggested in the SG-237 manual.
Q. When I press the TUNE button, the radio keys for a while and then quits. The red fault LED on the interface stays lighted. Is this normal?
A. No, it is an indication that the tuner was not able to find a match for your antenna. Most likely it is caused by an insufficient ground at the tuner. It is also possible that your antenna length is presenting an impedance that is outside the range that the tuner can handle. While not very likely, it is also possible that the tuner itself is defective. Disconnect the interface and apply +12VDC power directly to the tuner. Put the radio in RTTY mode so that it will output a constant RF signal. When you key the radio you should hear the relays in the tuner clicking and then the noise should stop. If the tuner is working then the SWR at the radio should be low and the TUNED wire on the tuner should read a low resistance to ground.
Q. The red fault LED never lights and the interface is not supplying +12VDC to the tuner. What is wrong?
A. The IC-706MkIIg has an internal 4-Amp fuse on the +12VDC power supplied to the interface and tuner via the 4-pin tuner connector. It is possible that someone has shorted this output to ground at one time or another and blown the internal fuse.
Q. The antenna tunes fine but as soon as I speak into the mike at full power the RED fault LED comes back on and the SWR goes very high. What is the problem?
A. The tuner is going into bypass. It could be a problem with the tuner or it could be that you are getting high levels of RF on the tuner control wires and feeding it back into the interface causing the PIC processor to wake up and reset the tuner. Try better grounding at the tuner and the radio. The 4-conductor wire between the radio and the interface should be short, certainly no longer than one foot. As a last resort, try re-routing the tuner control wires to keep them away from the antenna and try ferrite beads on the control wires at the interface end. Normally this is not a problem since the interface uses RFI filters on all of its inputs and outputs. If you are experiencing this problem it is most likely a matter of insufficient grounding at the tuner.
Q. Does the wired or kit interface come with cable to connect to the tuner?
A. No. With the SG-237 you can route the four wires from the cable supplied with the tuner thru the grommet to the terminal block on the interface PC board. With the SG-239 or other tuner that is not supplied with an interface cable, the user will need to provide a 4-conductor cable which is small enough to fit through the grommet on the rear panel of the interface.
Q. I find it difficult to put the tuner into bypass with the tune control. Is there a way to change this timing?
A. No, the timing is set by the design of the Icom radio. A very quick momentary push of the tune button when the tuner is already tuned will put it into bypass. It must be a quick push. Holding it too long will put it into bypass and then immediately begin another tune process. Note that even a quick press will put it into tune if the tuner is already in bypass. This operation may be a bit confusing at first. If the LED on the interface is lighted then either a quick press or a long press will begin tuning. If the LED is dark then a quick press will put it in bypass (causing the LED to light) and a long press will begin tuning. Note that with the SG-237, retuning on the same frequency will force a complete retune rather than tune from memory (a function of the tuner itself). This also implies that two quick presses will force a complete retune just like a long press. The first quick press puts it in bypass and the second quick press begins the tuning function.
Q. Will this interface work with a Hamstick? Do you make a high power version that can be used with a linear amp?
A. This interface is a data interface between the Icom radio and the SGC tuner. It has nothing to do with the type of antenna or power level used. The selection of antenna and power level is a function of the SGC tuner specifications rather than the interface. Note that I have only personally tested the interface with the SG-237 tuner. I have however, received second hand reports of the interface working with several other SGC tuner models. Some model tuners have slightly different features than the SG-237 so you may find things like forcing a full retune to work differently than described in the interface documentation for the SG-237.
Q. What does firmware version 3.8 do for me? Do I need to upgrade?
A. For most people, the short answers are nothing and no. Firmware version 3.8 improves operation of the interface when used with an automatic data station (typically Pactor) scanning multiple bands. Version 3.8 will offer no improvement for normal SSB or CW operation.
When operating modes such as RTTY or Pactor that transmit a continuous RF signal, the IC-706MkIIg outputs an RF signal as soon as the PTT is keyed, even when PTT TUNE has been set to ON. The SGC tuners are so fast that they often tune to this signal before the radio has finished sending the tune command to the interface. This confuses the radio and causes it to think that the tuner is not functioning. The visual result is that the Fault LED on the interface will indicate that the tuner is tuned while the Tune LED on the radio indicates that the tuner is not tuned. The radio will then not output a bypass command when switching bands. An automatic data station needs the tuner to be bypassed every time the band changes in order to improve the received signal strength when listening for possible link requests.
Thanks go to Jan, SM7ETW, for identifying this problem and taking the measurements that enabled me to develop a solution.
All units will soon be shipping with version 3.8 firmware. If you are intending to use the interface with an automatic, scanning data (Pactor) station please advise me with your order so I can ensure that you get one with version 3.8 firmware.
Note: Version 3.8 has now been replaced by version 4.1 which has all the features of version 3.8 plus the new Alinco mode.
Q. Doesn't the fact that the radio immediately puts out a full carrier mean that it is transmitting into a mismatched load?
A. Yes it does, for about 250mS until the tune command is sent. When in a data mode like RTTY, the IC706MkIIg immediately attempts to output a full power signal, even before it sends a tune command to the tuner interface. This is inherent in the design of the radio and it occurs even if you are using an Icom tuner. There should be no risk of damaging the radio because it has an SWR sensing circuit that immediately reduces the output power to protect itself from the high SWR. If you are concerned about it however, there is a simple solution for a manually operated station. After changing bands, before you key the PTT the first time just push the TUNE button. The radio will immediately enter the low power tune mode and allow the tuner to find a match. Then when you key the PTT for the first time it will be looking into a properly matched load.
Q. For an automatic station won't the automatic tuning process corrupt the data transmission?
A. Yes, the first data transmission will be interrupted by the low power CW tune signal. With ARQ modes like Pactor this should not be a problem because it will simply retry. The link should be established on the second try, after the tuner is tuned.
Q. What features does firmware version 4.1 add?
A. Version 4.1 provides all the features of version 3.8 plus it adds the ability to place the OPT-B jumper in order to switch to the Alinco mode. This version also has a test mode that permits me to perform a 100% production test using a special test fixture. The test mode is activated if the OPT-A jumper is installed during power up. Do not activate the test mode as it will drive your radio and tuner crazy!
Q. Why didn't you implement all of the Icom features on the Alinco version?
A. Features like PTT TUNE and bypass on band change require that the radio itself have that function available. It is not possible to implement them without a redesign of the Alinco's firmware.
Q. Can I modify my original interface to work with an Alinco?
A. Yes. Replace the PIC with the new version 4.1 and place a jumper at OPT-B on the PCB. Replace the connector on the radio cable with an Alinco type or build an Alinco to Icom adapter cable.
Q. Is there a way to make my interface work with both the Icom and the Alinco so that I can alternately use it with either radio?
A. Actually the Alinco interface mode will work with Icom radios as long as you don't use Icom's PTT TUNE function on any mode other than SSB voice. You can leave the OPT-B jumper in place. You can build the Optional Alinco/Icom Adapter Cable described on this web site to allow you to adapt the Alinco radio to the Icom type connector on the Interface.
Q. The interface does not work with my IC703. The tuner does not reset or tune. What should I do?
A. Some IC703s do not pull the start line (pin-2) low enough to turn off Q2 and start the reset or tune process. Changing R1 from 10K to 33K should solve the problem. New kits and wired units are being shipped with a 33K resistor at R1 to ensure compatibility with the IC703.
Q. I already ordered the parts for my interface based on the QST article. Does this mean that I have to purchase more parts in order to build the version 4.0 PCB?
A. No. You have enough parts to make the version 4.0 PCB work with the combined lock/reset line tuners. Simply omit Q6, L6, C6, and J3. Solder a jumper wire across the J3 location. Place the tuner connector to one side so that it occupies positions 1, 2, 3, and 4, leaving pin 5 on the PCB unconnected.
Q. The bypass on band change does not function when using my IC746PRO. Everything else works okay.
A. For some reason Icom did not implement the bypass on band change feature in some of their radio models. The IC746PRO and IC703 are two that we have discovered. There are probably others as well. This feature is built into the radio so there is nothing that you can do to the tuner or interface to implement it. It won't work with the Icom AH-4 tuner when used with these radios either.
Q. The fan in my IC7000 runs all the time with the tuner interface connected. Is this okay?
A. No. For some reason the presence of pull-up resistor R2 (10K) upsets the temperature sensor circuit in the IC7000. This causes the fan to run at high speed and a high temperature warning to be displayed. Remove R2 from the interface circuit and everything should work okay.
Q. I want to use the interface with other Icom radios as well as the IC7000. Do I need to add a switch to set R2 for the type of radio?
A. No. Earlier Icom radios should function just fine without R2. Just remove R2 and use the interface with any Icom radio.
Q. I do not have an IC7000. I use an earlier model Icom radio. Should I remove R2?
A. It is not necessary. The IC7000 is the first radio that has been reported to have this problem. If you want to remove R2 so that your interface will be ready to function with an IC7000 in your future then that should be okay as well.