Contents: Basics; Modular Jacks & Plugs; Interconnect Cables; Beads; Power Cables; If You Just Have To;

Basics

Being frugal is part of the game; cutting corners isn't!

Power, microphone, accessory, and/or remote cables are an integral part of every mobile installation. Most manufacturers include the first two, and sometimes the third. Remote cables are usually extra-cost items included in a remote kit along with the requisite mobile mounting brackets. When they're not included (pre-owned purchase, etc.), a lot of enterprising amateurs attempt to make their own. Nothing wrong with that, as long as you use the correct connectors and cabling.

There is one ill-advised, and dangerous practice which rears its ugly head from time to time, and that's using RG8 as a power cable. As I point out in my Wiring article, no vehicle repair is more costly than a wiring fire!

There's one more piece of up-front advice I have to offer; don't make your own power cables! Here's why. With one exception, all the new amateur transceivers use a bifurcated power cable. In other words, the wire is split so that more than one pin carries the current. I have never seen a home brew cable where the bifurcation was done correctly. When it isn't, you run a risk of overloading one of the pins. It may seem like a minor point, but an electrical fire is not!

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Modular Jacks & Plugs

A lot of the newer transceivers use modular jacks and plugs for microphone and/or remote cables. While they appear to be RJ45 telephone type jacks and plugs, they aren't! In fact, modular jacks and plugs come in about 50 different configurations. Some are designed for round cables, some for oval cable, some for flat cables, and there are different types for solid and stranded wire. There are keyed and unkeyed ones; ones with external cord grips; and ones for heavy-duty use. Selecting the correct one isn't as easy as it appears.

Adding a little insult, MFJ, and a couple of other manufacturers, use RJ45 telephone-style jacks, plugs, and even silver satin, 8 conductor telephone wire as interconnect cabling. The problem is, they aren't wired like telephone cables, and arbitrarily substituting a telephone cable will garner you an expensive repair!

The tools needed to crimp the various types are also slightly different. One designed for round cable will not crimp a flat cable correctly, and one for flat cable can actually cut through a round cable. There are some 8 different die sets to accommodate them all.

There are other considerations too. Referring to the Icom microphone jack wiring diagram (roughly 4 times actual size), you can see that the pins are very close together (approximately 1/32"). If you're fat fingered, you may not be able to properly position and hold the wires in the corresponding plug during crimping. The first time I tried it, I went through four plugs before I got it right. And note there are separate ground connections for the microphone and the PTT.

Pin 3 is the audio output on an Icom IC-706MkIIg. On the IC-7000, this pin is used as a microphone "sense" pin which tells the radio an HM-151 (stock mic) is attached. If you plug in a Heil headset designed for the IC-706, the radio thinks it's an HM-151. What's more, the requisite audio input levels are very different, so the transmitted audio will be distorted. Incidentally, Heil has a headset designed especially for the IC-7000. Its higher output does require a lower gain setting however.

Pin 6, the microphone input, has an 8V DC regulated supply fed to it (this is true of Yaesu and Kenwood as well). Although there is an internal resistor in series with this lead, shorting it to ground can cause both the series resistor and the 8V regulator to over heat causing one or both to eventually fail. Further, shorting pin 1 to ground will cause the 8V regulator to instantly fail! Either way, doing so is an expensive fix as they are both surface-mounted devices, and require special tools to replace.

Pin 2 is a multi purpose input. Shorted to ground during receive, it causes the frequency to go up. Placing a 470 ohm resistor in series to ground causes the frequency to go down. In CW mode, a 3.9k ohm resistor to ground is the dit side of the paddle (or straight key connection), and a 2.2k ohm resistor is the dah side of the paddle (information about the latter can be found on page 34 of the owners manual). There is also an audio out and a squelch switch. All of these possible uses for the jack makes it an inviting target for the uninformed. Incidentally, the maximum current for the 8V line and the sink for the squelch switch is 10 mils! The former is not intended to power ancillary equipment like TNCs.

I encourage everyone to use commercially available interconnect cables when ever possible. For example, Icom makes an adapter to convert the microphone jack from modular to an eight pin standard microphone jack for use with their SM8 and other desk microphones.

Icom is not alone in its use of modular jacks and plugs. Yaesu and Kenwood also use them especially on their mobile transceivers, and similar caveats are in order.

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Interconnect Cables

There is a very important caveat with respect to the IC-7000 (and older IC-706). Make sure the grounding screw for the remote cable is installed. It is very small (2 mm x 6 mm), and is depicted on page 16, center drawing, Figure 2, in the Owners Manual (reproduced at left). Leave it out, and you're in for major RFI problems. The 706 cable is slightly different (see page 10), but the same caveat applies.

DC cabling doesn't need to be shielded, because its impedance is very low. However, most other amateur radio cabling is shielded, and for very obvious reasons. Unfortunately, some enterprising amateurs think it's okay to use Ethernet CAT5 cable for their interconnections. It isn't. Yes, you can buy shielded CAT5 cable, but the vast majority of it is solid conductor, and should never be used in a mobile environment.

There is another little problem with CAT5, which very few think about, and that is its construction. It isn't 8 separate strands, it's actually 4 pair, with each pair separately twisted together. Depending on the use, and how it is wired (ready-made CAT5 cable assemblies come in several different wiring configurations), crosstalk between the conductors is almost a given.

Just in case you missed the point, using a ready-made CAT5 cable in your mobile just might work. Then again, it might not, and you'll be in for an expensive fix!

In some cases (Icom remote cable for example), the connectors are proprietary, and cannot be purchased, period! Attempting to extend one of these cables by splicing in another piece of wire is a good way to destroy a working cable.

The similar caution should be used with MFJ's interconnect cables, like those supplied with their ALS-500 amplifier remote kit. They are indeed 8 conductor, silver satin telephone cable, but the connectors are installed differently; they're straight, not crossed over. This is one of the very few cases where you can shorten them, and install a new RJ45 plug with a standard telephone crimp tool. That is, as long as your observe the polarity!

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Beads

Ferrite split beads are marvelous little wonders, but all too often they're misused. Once such misuse is applying them to power cables. You even see commercially made ones. The truth is, beading power cables won't cure any RFI, AFI, or EMI malady regardless of the advertising hype to the contrary. If you read the article, you'll know why.

They are of use on extension cables (for RFI ingress and egress issues), coax (for common mode current reduction), and as motor lead chokes on remotely tuned HF mobile antennas. Here's something to think about. The amount of impedance split beads add is to the square of the number of turns. For example, 6 turns through one bead is the same as one turn through 36 beads! If you're using them for common mode current reduction, it pays to keep this fact in mind.

Here's some additional food for thought. The best mix available to amateurs for use as chokes (the primary use in mobile installations) is mix 31. Depending on the ID size of the bead, the reactance per turn is approximately 70 ohms at 10 MHz. It should be evident that using them for AFI reduction (alternator whine for example) is all but fruitless.

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Power Cables

Using RG8, or any other coax, as a power feed is an accident waiting to happen. The center conductor of RG8 may be from size 10, to as small as size 13. The maximum current carrying capacity is just 14 amps, or about half that required for most 100 watt transceivers. The premise seems to be, that RG8 will miraculously cure alternator whine, or prevent RFI intrusion. It won't! Another, just as inane practice, is twisting the power cable with an electric drill, apparently for the same reason. Just for the record, most alternator whine is caused by a ground loop, typically as a result of using a mag mounted antenna. There is more about these, and other poor practices, in the Wiring article

Observing polarity is super important for power cables for very obvious reasons, and most folks are rather careful about such things. What they aren't careful about is the size of the wire.

For a variety of reasons, voltage drop should be held to less than .5 volts under full load. If you've read the Wiring article, you'd know how to select the right sized wire, and keep well within the guideline. The problem is, the connectors, like those on the rear aprons of most new miniature transceivers, won't support wire sizes required for long runs (> 12 feet). In fact, if you look at the factory supplied cables, you'll see the cable is bifurcated (split) across two separate pins. If you're adept at doing this sort of thing, fine, but there is a better solution.

As pointed out in the Wiring article, you're usually much better off using a 4005 or similar RigRunner, than to try and extend factory cables. The wire feeding the RigRunner can be as large as #8. For loads larger than 40 amps (amplifier for example), you should be wiring directly to the battery even if this takes more than one direct run.

By the way, applying ferrite split beads to DC power cables is a waste of resources, for any noise abatement problem, no matter how many cores you use. Remember, one of the conductors is at ground potential, so common mode will not occur, unless the cable in question has excessive loss. Further, ferrites are frequency dependent, and are nearly worthless at frequencies below 1 MHz. Thus, their ability to quell alternator whine is nil!

In the latter case (alternator whine), is typically caused by ground loops, and the use of a mag mount antenna is the number one cause. And, poor wiring practices add insult to injury. Lastly, if you have to resort to a brute-force filter to quell alternator whine, you'd best look for the source, and not the effect.

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If You Just Have To

I don't suggest making up your own modular extension cables in the first place as most of them are of proprietary material and configuration. Using pre-made telephone cables and splices isn't the answer either. Remember, most telephone cables flop over. That is to say, pin 1 on one end is pin 8 on the other. Ethernet cables come is straight and crossover configurations, and although their splices look like telephone splices, they're not wired the same. This is one area of amateur radio where you shouldn't scrimp, as the potential damage costs far exceeds the procurement costs of most cables. If you just can't help yourself, and you just have to try, here is a suggestion or two.

Digi-Key and Mouser sell the proper modular plugs. They are listed under Modular Connectors and Jacks in their catalogs and on-line. There are about 20 different configurations, and about 25 more they don't list.

The best type modular plugs to use, are those made by Bomar, under the trade name EZ-Plug^®. These have drilled through holes in the end of the plug allowing the wire to protrude. This helps in assuring the plugs are correctly wired before crimping. The Mouser part number, 678-300568EZ, may be used with stranded, round cable. If you use these specific plugs, use an X-acto knife to trim off the extra wire to avoid shorts.

Digi-Key and Mouser also carry the proper crimping tools and dies. At about $200 each with dies, the tools are not cheap. I caution everyone not to use the cheap Radio Shack crimper. It is designed for flat, stranded telephone cable, yet they'll tell you it is okay for Ethernet cable. It isn't! And it will not properly crimp any of the connectors when round wire is used. If you squeeze hard enough (as suggested in the instruction sheet) you run the risk of separating the insulation which can cause a short (to say nothing about breaking the plastic handles). It just isn't worth taking the chance.

Remember to check your connections for continuity and shorts. A pre-wired jack is a good tool for checking continuity. Also, make sure the wire is properly restrained by the strain relief.

There you have it, and I wish anyone making their own modular style cables a well-earned good luck. You'll need it!

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