Icom IC-211 PLL and Other Repairs...

 I've owned this Icom 211 for many years. I bought it from a friend back around 2008, and it's had a few issues over the last 13 years. To be fair, this is a mid-70's vintage rig, so some repairs are to be expected to a 45 year old radio :-)  

I leave this rig on 24/7, just so it's nice and stable when I get on 2m SSB. I came in the shack and realized it wouldn't transmit, and upon further inspection, I discovered it wouldn't receive, either. Oh well, off the table, and into the workshop it went. 

Once I got it on the bench, I realized the PLL wasn't locking up, so I began checking various voltages. I discovered the -9vdc supply was only about -7 volts, and by the time the -9vdc source made it to the PLL, it was only about -5.5vdc. I sub'd in a -9vdc source, and the rig fired up and ran. After a bit of poking around, I discovered a small choke that supplied 5vdc to the dc-to-dc converter that generates the -9vdc had failed and was only supplying about 3 volts to the converter. Once that was repaired, 5 vdc was supplied to the converter and it worked correctly. The 9vdc source was once again, as it should be. 

 The radio had been drifting more and more over the last year, and a quick thermal test with coolant and a heat gun revealed a small styrene capacitor in the PLL was failing, and once replace, it was solid and stable. Also, there was problems with the dial lights, and some noisy controls. 

On the bench, getting a good check-up.

I sampled the VCO to the freq counter via a .001 cap. Loading to the VCO wasn't too bad. 

This is where the 820pF styrene cap was located that caused all the drift...

This is the -9vdc dc-to-dc converter that caused the problem...

This is where I sampled the -9vdc that returned to the PLL...

While the radio was on the bench, I wanted to replace the meter lamps. I had some "warm white" LEDs to experiment with, from a string of LED Christmas lights. I discovered that 1000 ohms, 1/2 watt was about the right resistor value to bring the lamp to normal brilliance @ 20 mA or current, when powered from the 12vdc source. 

There's the Christmas lights I used. I'd break the clear part off, and the LED would slide right out. Easy to do, and you can buy a sting of these for $3-4 bucks. They're bright. You can see them in the meters of the radio, below. While the radio was on the workbench, it got a full alignment and is performing very well. 

 

A little work on the Heathkit SB-200 Amplifier

The Heathkit SB-200 is a very popular HF amp, and very dependable. This one belongs to a friend, and had begun to vent the filter caps from time to time. It was time for a little work, so here we go....

 

Case removed, ready to remove inner covers...

The amp was in very good condition, just had a bit of dust to get rid of :-)

With the upper inner cover removed, it exposes the tubes, filter caps, etc.

I removed and cleaned the dusty tubes. This will help the tubes run a little cooler...

It has the original Cetron 572 tubes installed from the build sometime around 1980. Here they are, clean and ready to be reinstalled...

I also used compressed air to clean the RF compartment, and the rest of the amp.

Note the filter caps. The originals were much larger and only 125uF vs. the newer, smaller caps in blue that provide 330uF. This will yield a better filtered DC supply, and take up less space than the originals.

Here, you can see the power supply board refitted with new capacitors and reinstalled. All bleeder resistors were in tolerance and good condition.

While in the amp, I included a few updates. If you notice the two diodes attached to the back of the plate current meter, this provide protection in the event of a tube short or arc. I also installed HV glitch protection, and bias protection.

 

All finished, tested, and ready for re-assembly.

Here she is, headed back to her owner. This amp is extremely well cared for, and should last many years to come!

Tri-Band Repeater Antenna Build, cont'd

This is a few more photos of the new repeater antenna build, and some observations.While tearing down a 4-bay antenna on 154mhz for parts & materials, I measured things with my MFJ Antenna Analyzer, and took note of some dimensions...

First, the larger dipoles are from the 154mhz antenna. I made a little pigtail connector for the MFJ, and took some readings. Resonance and impedance of these types of antennas is impacted by proximity to the mounting mast and the width (these are 3") of the loop. They also require at least a 1/4 wl of mast above and below for proper operation. The larger units were resonant at about 154mhz, where I expected. These dipoles are 17" per side, from the mount to the end of the loop, total 35" tip to tip (counting the 1" dia mount in the middle). The loop is 3" wide, edge to edge, and they are 3" from the mounting mast to the edge of the dipole loop. These are the dipoles I will modify for 2 meters.

The smaller dipoles are 15" per side, from the mount to the end of the loop, total 31" tip to tip (counting the 1" dia mount in the middle). They were resonant at about 168mhz. I altered the formula to calculate the proper dipole size, and it clearly doesn't track as I alter the dimensions, so I'll be doing a bit empirical testing (read trial and error, hahaha) to work the bugs out of the 220 and 440 antennas.

Another interesting observation...using DB Products RG-11 cable, the matching sections were pretty much the same length as the tip-to-tip dimension of the folded dipole elements. We'll see how this works out when I get these tuned and installed on a test mast...

I plan to use the single mast section on the right (with the rain bonnet) to install a pair of folded dipoles for 2m, 220, and 440. My plans are to keep this a compact antenna. I realize it'll be a compromise antenna, but I need to keep size down for a DC grounded tri-bander. 

RG-11 in the original installation...

154 mhz vs 168 mhz...

This pair will be modded for the 147.39 repeater.

Dave WB4IUY
www.WB4IUY.net

ARR RX Preamp Failure, 442.400 repeater...

Shortly after getting the 442.400 repeater back on the air in test mode, I discovered the receive preamp was not working. This is an ARR P432VDG GaAsFet rx preamp. It has worked well for many years, having originally been installed back around 1994. This repeater took a lighting strike when it was installed at the Zebulon site, and I had never tested the preamp. I had to replace the PA at that time, so I'm guessing that's when the preamp failed. 

I put it on the IFR and spectrum scope, and discovered that it was a "deamplifier" :-) About 34db of loss when powered up, the GaAsFet has failed. This unit is about $100, so it's certainly work repairing. A new FET is ordered, so I'll post more about this during / after repairs. In the photo below, I set the sig gen for 0dB direct, and with the preamp inline, you see the 34dB or so of loss. 

Dave WB4IUY
www.WB4IUY.net

Converting a UHF Motorola Micor to Repeater Service

I posted info on my old Motorola Micor UHF repeater on my blog, and people asked questions about how to do it. This is a fairly easy task, though it's far easier to stack two of these radios (one for receive, and one for transmit), but I enjoyed the task of repeating within a single radio. 

There's adequate isolation to do this, even when using a receive preamp, with a good set of cavities. These radios are cheap as dirt, often costing less than the crystal required for conversion to the ham bands. The nice thing, being crystal controlled, is you have no phase noise to deal with as with synthesized rigs. They are TOUGH AS NAILS! I've run them hot, it's been hit by lightning, and has operated an horrible physical conditions at one of the repeater sites. Users have locked it up for hours on end while cross-banding HF operations through it. The repeater in my previous blog has been in operation since 1994, so 26 years is nothing to sneeze at.  I'll snap some pics of the internals that I've modified, when I go back into it, to help illustrate the process. 

As I said, it's much easier to simply tune up a couple, one on the RX frequency and one on the TX frequency, wire a controller, and let'm fly. But, if you want to modify one for full duplex repeat, here's the info. I wrote the compilation of notes I accumulated and included my experiences in Microsoft Word. You can download the file, and if you don't have MS word, there's a host of online converters you can open it with for free. 

Go to my website at http://www.WB4IUY.net , mouse over the toolbar across the top of my webpage to [WORKSHOP], and click on "Schematics Manuals". You'll find Motorola Micor in the listings. Have fun!!

Dave WB4IUY

www.WB4IUY.net