Icom IC-706mkII Fan Mod

My mobile rig is an Icom IC-706mkII HF/2m unit that’s been doing me well for months, semi-permanently installed in the car. Lately I’ve been noticing signs of its deterioration, getting signal reports that I’m either cutting out or the audio has a sporadic “electric shock” sound. I’ve been trying like hell to track it down, thinking my custom power cables were either sub-par, that my car’s electrical system (battery, alternator, regulator) were getting edgy, or that my final transistors were starting to fry. All of those options were scary to consider.

The symptoms exhibit more strongly when it’s hot outside and I’m chatting away on a local repeater on the afternoon commute. Eventually, the radio starts freaking out and I have to sign off.

As it turns out, my radio is overheating. The internal fan’s not doing its job.

I took it inside for examination. With the covers off, I put the radio on CW mode, half power, into a dummy load, and held down the key. The fan would only run while I had the key or PTT down, and never outside of that. Even when it was key-down, the fan took a long time to kick over; the driver circuit would attempt to start the fan, but didn’t have enough voltage to push the fan blades except after a few kickover attempts. So it never gets cooling if my talk times are less than 15 seconds (and the heat builds up over the QSO). I was afraid the fan was dying, but when I removed it and drove it with 12v, it blew like a champ (thankfully). So something is wrong with the fan-control thermal circuit.

I found a few references on various radio boards where others have had the same symptom on their own Icom IC-706mkII (and the mkIIg as well). Apparently, the original Icom IC-706 was designed so that the fan would blow constantly. When they designed the mkII and mkIIg, they added a fan circuit to limit the noise and current drain. Unfortunately, once that circuit gets marginal, it stops being useful and actually contributes to the radio’s demise.

Among the references is a rework involving the addition of a 200Ω 1W resistor between L50 and J2 (on the IC-706mkII, at least) which will provide a constant voltage to keep the fan moving at a slower speed. The benefit is that the fan controller won’t need to start the fan; it just ramps up to the right speed.

Two 100 ohm 1W resistors in series for 200 ohms (identified by screwdriver tip), wired between Vcc and the fan.

I soldered a pair of 100Ω in series and shrinkwrapped all connections so they don’t contact the radio circuit (I left the body of the resistors uncovered for cooling), then flew the rework over the board between solder points. It doesn’t appear to wobble or vibrate much, and there’s enough cooling inside that hot case to keep it from frying.

Orange wire (identified by screwdriver tip) soldered to coil L50.
Orange wire (identified by screwdriver tip) soldered to hot side of fan connector J2.

It’s been a week since the rework, and the radio’s still doing OK in the car. I’m still getting spurious reports of noise, but I think my radio’s got an EMI sensitivity when I drive near electric utility substations (EMI/RFI has always been a problem with my 706). But otherwise, it’s doing alright.

It sucks when we have to modify a production device due to engineering mistakes, but thankfully we have the public resources to help us find our way and stay on the air.

Pinch To Talk

Behold my score from Austin Summerfest:

MFJ-564 iambic paddle

I’ve had an iambic paddle on my ham radio grocery list for a while, and now I have one. I guess this means I have to get better at Morse Code to be able to use it frequently. Right?

All shined up and ready to go out.

Picked it up second-hand for about forty bucks. To make it mine, I removed the 1/4″ plug and soldered my own 1/8″ plug to make it compatible with my Yaesu FT-857. Then I tore it down and gave it a complete spit-shine with alcohol wipes, eyeglass cleaner, and a lot of polishing.

I noticed this paddle is representative of the mid-grade build quality of some MFJ products: the heavy metal base is merely chrome-plated, and some of the base has small pock-mark oxidation. The nylon insulators and pivots are a little worse for wear. Some of the adjustment screws could use a dot of threadlock to keep them from walking out of their loose tolerances. But, overall, it’s still solid and highly usable.

Piiiiinch For Looooong and Shoooort Beeps Aaaauuu-to-maaaa-tic-lyyy

To operate any paddle, you simply press sideways in one direction to make a “dit” and the other to make a “dah”. What makes this “iambic” is that there are two paddles, one for dit and one for dah, and if you squeeze both at the same time, you get an automatically-generated string of “dit-dah-dit-dah-dit-dah“, much like the iambic meter you find in poetry.

The paddle itself doesn’t generate beeps. It’s just a specialized switch. You need an external keyer to take the paddle inputs and generate an output for the radio. Luckily, most radios have a keyer circuit built-in. Mine has a bunch of options like key speed and ratio between dit and dah lengths (1:3 is common).

For the record, there is no hard rule for which direction on a paddle is dit or dah. That’s up to the individual to sort out what is comfortable. Many right-handed operators choose to put dit on the left and dah on the right. It can always be reversed by crossing the connectors or using the radio’s menu if it has that option.

Now that I have all I need to send code (a paddle and a straight key), my last obstacle is myself. Knowing how to send is half the equation: I need to learn how to copy code, to hear what someone else is sending and transcribe it (speed experts do it all mentally and even recognize whole words by sound). That’s the hard part, and there’s just no way for me to do it other than with lots of listening practice.

Wish me luck.

Fat, Thick, and Dirty

I finally did it. I soldered a pair of PL-259 connectors (screw-on type) onto a 28′ (8m) length of scavenged RG-8 cable. And it works. It really, really works.

PL-259 soldered connectors RG8 coax
PL-259 connectors, kinda soldered, and they actually work.

Of course, they’re really, really dirty.

PL-259 soldered connectors RG8 coax
Dirty solder. So, so dirty.

And it took me 2 hours to f’n do it.

But it works.

Tiny, Cheap, Expensive

Picked up an RTL-SDR software-defined radio dongle. Because reasons.

After an evening of driver hell, I decided today that maybe I should read the quick-start instructions. Gosh, they’re more helpful than I imagined. Finally got the SDRSharp software to recognize the dongle and start tuning and decoding radio.

Unfortunately, my poor old laptop is just too slow. Once it gets a buffer of samples from the dongle, decodes them, processes them, runs them through several filters, displays them on screen in the FFT and waterfall views, and then finally outputs them to my soundcard, the audio is supremely distorted, as if it just can’t fill the audio buffers fast enough to keep them from looping internally. It just sounds like a cheap digital stretch of whatever audio is going in.

I’m sure the SDRSharp application could have been written to be more efficient, but my dual-core 1600MHz machine just can’t handle it. Maybe I’ll get a new laptop, or actually repurpose my music workstation tower to run my ham radio shack. For that, I need to rearrange my apartment and actually get new furniture.

See? It’s true. Amateur Radio is a hobby where you just dig a hole in the back yard and throw money into it. Nothing you get is ever enough.

Radio is hard.

Vee

Experiments with operating the radio at home continue.

Had a wacky idea to use the anchor in the tree over my balcony as the support for a 20m inverted-V dipole, fed with 300ohm twinlead for multi-band matching. Brainstormed a plan to use a pair of bamboo fishing poles, anchored by pole brackets on the balcony railing, to spread the bottom ends of the dipoles apart and keep them out away from the building.

The signals I got were certainly louder than what I got on the Slinky dipole. Loud enough to hear buzzing and static crashes. I think the static pops were probably from the trees blowing in the wind. Had to experiment with using a mix of noise blanker, attenuator, and turning off the receiver preamp (IPO). At least the high-current area of the antenna, where most of the signal emanates, is at the apex of the V and right at the level of my roofline for better clearance to the East. So there’s that.

Heard 40m surprisingly well. Tried to match the transmitter on 40m, couldn’t get better than 5:1 SWR, so I swapped my DIY 1:1 balun with my DIY 9:1 un-un. The result? Better than 1.5:1. Yes. Even 20m matched OK, enough to trigger my desk lamp with 35W. Twinlead is good about taking up some of the impedance slush of a bad match and not losing much signal in the process, which accounts for how I could match on several bands.

Couldn’t get any QSOs, not even on FT8 (but that’s kinda crowded anyway). I’ll try again later.

This was a proof of concept from existing parts on hand before I wasted any time trying to “build it right” with new parts. It proved it worked better than expected. I guess I’m learning.

I do have some refinements planned:

  • Build a proper center insulator for balanced feed (instead of my repurposed Plexiglass insulator with unbalanced SO-239), with UV resistant plastic and weather protection for long-term installation and protection from wind/tree static
  • Cut a new 20m dipole and return this one back to the tote in the car
  • Build another 9:1 un-un or 1:1 balun for mounting outside next to the balcony door
  • Trim the twinlead for slightly longer than 20m resonance so the entire antenna system can match on 40m, and find a way to run it from the balun out to the apex without getting near metal objects or itself. It’s currently 40ft of way-too-long and is probably causing some matching problems on its own
  • Make better insulators and clips for the ends of the dipole to attach to the bamboo poles
  • Run the dipole legs through the trees without snagging on limbs, in an effort to get them at a more obtuse angle for better SWR and efficiency
  • Insulate the dipole ends (the high-voltage section) to prevent arcing to the trees
  • Fix the riggings and poles so I can deploy and stow in minutes without snags

Incremental improvements.