WB4IUY's Random Blog

I've been in Amateur Radio since 1974, and still find new and interesting things to do. I like to build, restore, and operate on the air. This is a blog of various info about my Ham Radio operations and activities, projects, and opinions. Visit www.WB4IUY.net for the lowdown at WB4IUY.

Monday, March 17, 2014

A New CW Keying Control for Studio A...

For some time, I've been wrestling with routing the CW-to-Computer Interface,  the Straight Key, and the keyer to various rigs, depending on the rig/band I was working. I finally decided to do something about it. I built a little CW Keying Control box in one evening, totally from junk box parts. This allows me to use my keyer, CW keyboard, and any straight key with any rig in the shack. No more plugging/unplugging cables when I switch rigs. I discovered that I had to build a little interface for the IC-211, so I just enclosed it in shrink wrap and tossed it behind the rig.

The internals of the CW Keying Control are pretty simple... A 3 position rotary switch, a pair of 1/4" phone jacks for the CW-Computer Interface and external keyer interface, .01uF cap to minimize key clicks, all in an old Radio Shack enclosure that was re-purposed from a previous project.

The IC-211 @M SSB/CW rig has a goofy keying circuit that doesn't provide enough unkeyed voltage at the CW jack to allow switching by the 2N2222 transistor in the computer interface. I built a little one-off interface to take care of those keying duties, and enclosed it in a piece of clear heat shrink tubing, since it was dedicated to the IC-211 and was going to be installed behind that rig.

The control box was finished in about 1 hour, complete with a re-purposed knob from an old junker and some High Tech Redneck labeling. Even the 1/4" phone plugs were all re-purposed from various bits of scrap around the shop...notice how each is a different style.

I installed the control under the 1st shelf at the operating position in Studio A. It looks right at home with the other home brew interfaces and vintage items that are mounted there for ease of operating.

Once everything was tested, I got on the air and put it to use. Wow...what a difference such a simple accessory can make in your shack. I don't know why I waited all these years to 'get around' to building this, but I'm glad I used this rainy afternoon to build this little piece!

Here's a rough schematic of the keyer interface I designed and built for the Icom IC-221 2m SSB rig. The CW keying circuit in that rig has to be pulled down to 0vdc to work correctly, and the solid state device in my computer interface only pulled it down to .6 vdc. I whipped this up, wrapped it in clear heat shrink tubing, and tossed it behind the rig. Works great!

Sunday, March 16, 2014

W2ENY AM Filter for the IC-756

I've been looking for an AM filter for my IC-756 for many years, and just stumbled across a filter from W2ENY. I think he used to offer these, and went out of production for some number of years. He has brought a limited number of these back for sale. I emailed him, he replied almost immediately that he still had some, and I ordered one. I'm happy to have finally found one of these babies. I work AM from time to time on 160 thru 10, and usually operate one of my boatanchors due to the w-i-d-e passband on AM. His page is:


I received the 6khz AM filter from W2ENY for my IC-756. The instructions were EASY to follow and the mod was quick and simple. I LOVE it! I've been working AM on 80, 40, and 15m with the 756 and have great selectivity on AM. I replaced the 15khz filter in the 455khz I.F., and have noticed no issues with working FM on 10m, listening to broadcast stations, etc. My 18 year old IC-756 is now perfect in my opinion, and everything is working great. This is the filter the rig should have come with from the factory, as all modes are well behaved, now.

UPDATE: 3/16/14... After using the filter for about a year, I felt the need to make another change. The instructions from W2ENY mentioned to replace the 15khz filter in the 455khz I.F. with the 6khz AM filter. I found, when operating AM on 10m, it is desirable to have access to the 15khz filter to open up 

the receiver a bit for the broadcast audio often heard on AM. Also, when working 10m FM, the 9khz filter in FM narrow is a bit too narrow for good audio and clipping would occur. I never found a need for the 9khz filter in AM or FM operation, but I constantly found the need for the 15khz filter. So, I reinstalled the 15mhz filter and installed the AM filter (6khz) in the place of the 9khz filter, and all is now well. Just my $01 worth, but it sure works out better at my QTH in this configuration. 

You can visit my website at www.WB4IUY.net for more mods for the IC-756 pre-Pro (analog) model, and lots of other ham radio stuff :-)  

Thursday, March 13, 2014

Updated 60m Mods for the Icom IC-756

 60M for the IC-756 Standard

Modifying the ICOM IC-756 Standard (non-Pro model) for 60m takes a little work, but it's worth the effort. First, the transmitter has to be opened up for general coverage operation. That's pretty easy. Here's the info for the first phase of the modification...

Remove bottom cover. On the MAIN board you will see IF filters and a daughter board (DSP filter) on the right side. The W805 jumper and IC803 chip is located under the DSP board. You have to remove the DSP board (carefully) and look for the part labeled IC803 and the line of SMD jumpers (little green parts). Locate and unsolder the W805 jumper. Re-Install the DSP board and put the bottom cover back. Below is a drawing of the chip & jumper locations, a pic of the circuit board, and a pic of the jumper on my fingertip after removal.

         [W801]     |               |
         [W802]     |               |
         [W803]     |    IC 803     |
         [W804]     |               |
REMOVE== [W805]     |     CHIP      |
         [W806]     |               |
         [W807]      ---------------


When I first modified the processor, as I had seen numerous bits around the web for adding 60m, it worked 'OK', but would only put out about 50% power on 60m. I found that the band matrix is setup to use the 80m low pass filter up to 6.0 mhz, where it transitions to the 40m filter. Another ham I was talking to on the internet had the IC-756 Pro II and modified his for 60m coverage as I did, and had the same problem with low output power. He had access to some filter design software, and modeled the 80m filter to see where the problem was. He came up with a few capacitor changes to alter the upper end of the filter response to fix the problem in the Pro II. I checked the manuals and board layouts against each other, and while the filter units in the standard and Pro II are physically a little different, the circuit was the same. I ripped mine apart tonight and dove in. Change C7, C66, & C69 to 180pF disc. Change C15 to a 270pF disc. This moves the knee of the filter from 5.25mhz to 5.6 mhz. The end result was awesome...full power right up to the edge of the 60m band and no purity issues. One of the pics here is the filter as modeled in software, the violet curve is before mods, the white curve is after mods. The other pic is of the filter unit.

One last note...the internal antenna tuner isn't mapped to work correctly on the 60m band, but the rig works great with an external antenna tuner or with a resonant antenna. Hope this helps some of you with your 756 to enjoy 60 meters. The filter mods will also work with the Pro II once you use the appropriate mod for general coverage transmit. Many thanks to W6FM for the filter model work!