Archive for the ‘HamRadio’ category

Moxon

August 24, 2009

The Moxon antenna is a compact two element beam antenna with amazing specifications. Free space performance claims about 6db forward gain with around 35db front to back rejection. The antenna can be built from aluminum tubing like conventional yagis but it also easily made from wire and bamboo spreaders similar to quad construction. In fact, when compared to the quad, the Moxon can deliver the same results as a quad yet the Moxon only requires half the parts. The Moxon puts the driven element AND the reflector on one set of four spreaders. Half the parts equal half the weight allowing a smaller, less expensive rotator. Don’t need no prop pitch motors here!

The ‘normal’ Moxon orientation is horizontal. That is the elements are parallel to the ground. Even so, a vertical orientation is also possible, more easily implemented, and just as effective as the horizontal. A rope or wire is strung between the tops of two tall trees. The two shorter sides of the Moxon are implemented using fiberglass insulators and aluminum tubing forming two rigid sturctures. The sides are made from wire which is held in tension by the weight of the lower structure. The upper structure is tied to the high horizontal rope from its midpoint. The lower structure is then rotatable toward any direction and kept in place with two thin ropes attached to the ends on the lower section. Now instead of bothering to feed this antenna at the midpoint of the driven element, it can be fed at the lower corner, in an off-center fed manner similar to a windom. The higher impedance at this corner can be matched to 50 ohms using a 6:1 balun. Or just connect two 4:1 baluns in series. Take off angle on such a vertical is around 18 degrees and IT NEEDS NO RADIALS AT ALL BECAUSE IT IS A COMPLETE TWO ELEMENT BEAM. ITS VERTICAL PROPERTIES ARE DUE TO ORIENTATION ALONE.. In the example given, the antenna can be turned by hand to favor any compass direction. Since the Moxon’s radiation pattern is very broad, accurate positioning to a specific direction is unnecessary.

The Moxon is perhaps the first answer I have ever seen to the question, ‘is there a cheap and easy solution to providing a rotatable beam antenna with decent gain and front to back’?

Moxons for multiple bands can be mounted to the same four spreaders required for this antenna making it a multiband device. There is also no reason a Moxon cell could not be used with conventional directors although Moxon directors would make more sense since they are only 70percent the size of the conventional directors. Smaller size, less material, less weight.

It is also possible to use open wire line, OR 300ohm twin lead, OR 450 ohm ladder line to feed the driven element and provide multiple band operation by using an antenna tuner. In this case the antenna would work as a true Moxon at only the lower design frequency but it would provide useful coverage of frequencies above that lower band as long as the tuner could provide a match.

At this location we have been using a KLM KT-34 beam for nealy 20 years. Recently the HD-78 rotator broke allowing the beam to freewheel in the wind. The freewheeling beam broke its feedline. While attempting repairs it was noted that the capacitor caps used on the linear loading sections were deteriorated beyond repair and needed replacing. After investigating the Moxon, we are now considering modifying the KT-34 to a single band (20meter) two element Moxon allowing east and west coverage either by providing seperate feedlines and flipping reflector and driven element functions or adding a variable capacitor to a center stub on the reflector and tuning it to be a reflector or director.

A two element 20 meter Moxon requires a 9 foot boom. The KT-34 has a 16 foot boom. The seven foot left over is not enough distance to install a director for 20 meters but it is enough to install a second Moxon for 15 meters (maybe). Interaction between the 20 and 15 meter beams may be a problem. In which case we can always add a 15 meter and even a 10 meter Moxon inside the 20 meter beam. Will have to look at that and see if perhaps a third element can be added to the 15 meter cell. Adding a 10 meter cell would undoubtedly allow two 10 meter directors.

The problem with the multiple cell Moxon is that we could not easily make it directionally reversible unless we rotate the antenna. Currently we have no plans to replace the HD-78 rotator. Can’t afford it. Even if we could afford it, we are adding a small rotator to support a couple of vhf antennas above the HF beam. We figure that removing the HD-78 and reducing some weight on the KT-34 will allow us to make do with the present mast without having to add more pipe to reinforce it.

In addition to the KT-34 modifications we are adding a bi-directional 40 meter Moxon, a 20 meter Moxon vertical, and a 30 meter bobtail in place of the 40 meter reduced bobtail installed now.

The 20 meter vertical Moxon will be hung from the center of a wire support strung from between the main mast and the smaller tilt over at the east side of the house. The 40 meter Moxon can be supported on the same supports holding the 80 meter loop without interferring with the 80 meter loop.

Now, on top of all this we can set up the 20 meter Moxons to also cover 17 meters.

To sum up we will have Moxons for 40, 20, 17, 15, and 10 meters. Roatable beams for VHF and a bobtail for 30 meters. Last but not least we will also still have the 80 meter loop.

Looks like a full summer of antenna work.

Drake LED pilot lights

June 15, 2009

Next to Collins, Drake is probably the better of the old boatanchor rigs. Not better than Collins, just better than anything other than Collins.

One of the more annoying aspects of using older tube type equipment is maintenance. The equipment rarely needs maintenance but when it does good parts are difficult to find.

A dead pilot light is one of these parts. The rigs can still be used with a dead pilot light. The dial and meter can still be read but there is something depressing about a dark radio even if it is still working.

The last time I replaced the bulb was about a year ago. I found a #47 bulb at Radio Shack. A year later it is dead. The original bulb had lasted over 30 years but it was not purchased at Radio Shack.

Six months ago I bought an LED flashlight. A real bargain at $3.50 even if it did have a super stinky plastic grip. Yup, made in China and they probably made the grip out of hazadous waste. Took about two minutes to remove the grip and throw it away. The end result was a nice little flashlight sporting 20 high intensity white LEDs.

The 20 LEDs were all connected in parallel and powered off 4-1/2 vdc from three AAA cells connected in series. No dropping resistors or other parts.

The LEDs were easily removed as they were soldered into a circular printed circuit card. I first removed one ring of six LEDs.

These LEDs were wired in paralled and powered from the 6.3vac pilot light supply with a diode in series with one power lead and a 50 ohm 1/4watt resistor in series with the other lead.

The LEDs were bright enough to provide sufficient reflected light to evenly illuminate the white diffusion screen originally used in the R4C receiver.

The LEDs were mounted on .4 inch centers with the row of six centered on a peice of surplus circuit board which contained plated thru holes on .1 inch centers.

This board was then mounted to a copper bracket and attached to a custom made pilot light bracket. A third section of copper was used to tie the copper bracket and the aluminum pilot light bracket together.

The physical arrangement was such that the LEDs were aimed at the underside of the custom pilot light bracket. The underside of this bracket was covered with aluminum foil acting as a reflector. The dull side of the foil was used as the reflector because the shinnier side resulted in hot spots on the white plastic diffuser.

No attempt was made to use the blue filter originally provided with the radio. The white diffused light from the LEDs was perfectly adaquate and seemed to provide better visibility than when the blue filter was used. Without the filter the dial looked as though is was illuminated by a cool flourescent. Bright and readable. No need for any strange filtering.

The illumination for the meter and Xtal switch window was provided using three additional high intensity LEDs. The finished overall effect can be seen in the accompanying photograph.

Now to do the same thing for the T4XC. At present the transmitter has some sort of greenish filter and old incandescent bulbs. It will be good to get it upgraded and looking like a real match for the R4C.

My Drake twins will soon be twins again.

Those not willing to give up the blue light may be interested in using Blue LEDs. Note also that high intensity LEDs are also available in red, green, and yellow. When using colored LEDs there is no need for a filter.

Home Improvement Center RG6

June 2, 2009

The last time I needed 50 feet of RG6 coax I paid under $10 for it and I am pretty sure I got it at a home improvement center. That was about six months ago.

I needed another 50 feet of RG6 so I went back to the previous source and discovered the price had been increased to $17. That may have been because it had a GE logo on it. GE!!?? They don’t make cable! They just buy it from China and demand high prices for it. No thanks.

I got the grass seed I needed and left. On my way home I stopped at RS. Good old Tandy. Tandy cable holds the dubvious distiction of producing the worst coax in the universe. It as all of about 80 percent coverage on the shield. It is also priced very, very, low and still works okay.

Guess that was a few years ago. Today they want $40 for a 50 foot roll of RG6. Heck, I can get REAL coax from Belden for that price!

BGMicro has surplus 25 foot rolls of RG6 for under $3 a roll. They also have cheap connectors to connect two 25 foot rolls together and make the 50 feet I need. Unfortunately the shipping is nearly $8 for USPS and $9 dollars for UPS. Never mind that I am in the same town, shipping is going to cost as much as the cable. Then there is also sales tax. The combined cost of tax and shipping is more than the cost of the cable! No thanks.

I finally went to my old standby, All Electronics in California. Shipping at $7 but no salses tax. Not sure why local shipping is $8 when I can get 2lbs. of stuff shipped to my door from the west coast for less.

Well the total bill was $50 but that includes lots of cable, rechargable batteries, battery rechargers, audio cables and adapters, and some other goodies that I coule not resist.

It is not the money so much as what you feel you get for it. I was not about to settle for 50 feet of Tandy cable for that amount!

Drake Twins

May 31, 2009

About three months ago I installed enough screws to finally secure the top and bottom covers to my R4C and T4XC. The screws had been removed years ago and were finally lost. The radios worked just fine with the screws missing but I finally decided that secured covers were better than loose covers.

No sooner had the new screws been installed than a couple of the pilot lights went dark. I might have known something was going to go wrong as soon as I buttoned the rigs up. It always does and matters not what rig.

I have been living with the dark panels for about six months. Turns out the radios work just fine without pilot lights. Besides, I got used to working in the dark. Recently I finally bought some leds with the intent of replacing the defective pilot bulbs.

Today I open up both rigs and both of the dark pilot lights came on.

I removed all the pilot lights, inspected the sockets, cleaned everything with Deoxit, and put everything back together. Everything except the screws that hold the top covers on these radios. Those covers may never again see another screw…ever.

Still holding on to the leds. Got them in a plastic bag tucked inbetween the IF transformers of the respective radios.

Kenwood TS-120S

May 27, 2009

I believe this radio was purchased sometime in the 1960’s.

I am the second owner.

It still works but not without incident.

The first problem it has is loss of digital display accompanied by a complete loss of function. No receive and no transmit. Lifting the radio by a corner and letting it fall to the table usually solved the problem. This indicated a poor connection somewhere inside the radio.

This situation continued for over several decades. Nothing was done to correct the problem because is occurred rarely if at all.

The second problem was a hum in the audio. A loud hum. This was solved by bypassing the audio line to ground inside the microphone connector. Problem solved. Evidently RF was getting into the microphone line. Interesting to note that the hum was only present when the radio was run at power through a linear amplifier. It did not have hum when run barefoot and for a long time we thought the hum was caused by the amplifier.

The dissappearing display problem began to occur more and more frequently in the last few months. So the radio was opened for the first time and inspected.

This thing is a maze of cables, wires, and cheap connectors inside the covers. Not knowing where to start we started at one end and worked our way to the other end unplugging each connector, giving it a shot of Deoxit, and reconnecting. Then we turned it over and did the underside.

We let that first application sit for a day and did it all over again the following day. The radio was then powered up with the covers still removed and seemed to work just fine.

That was two months ago. The covers are back on and it has been working fine. We use it at least two hours a week. So far the maintenance has been successful. No more loss of display or other malfunction.

It is a good rig. Works on SSB and CW. The receiver is okay. Mine narrows down to 500hz bandwidth when in CW mode. Power is a solid 100watts OUTPUT on all bands. It needs a good match to a decent antenna to work well. SWR above 2:1 will drastically reduce the power output. It will still work but you won’t be heard as well. It has a built-in fan that only comes on when the finals get hot. That only happens on long transmissions at full power.

It only covers the old ham bands. No WARC bands and no hope of doing so without designing and building a transverter.

Does not do well with SWR greater than 2:1. That might be a plus. You should not be running an SWR higher than about 1.5:1 into the radio in the first place.

Audio sounds tinny. That may also be a plus. With more of the lows removed, the audio is easier to understand under adverse conditions.

Drake Case and Cover Screws

February 18, 2009

Now that I am completely done with the upgrades, mods and repair on both the R4C and T4XC, I figured it was time to install the screws connecting the bottom cover and top covers to the main chassis of each piece of equipment.

Takes #6-32 pan head, black oxide, plain slot, machine screws that are 1/4 to 3/8 inch long. Need 24 of them, 12 per radio.

I found lots of screws on the internet (pun intended). One outfit had the exact type of machine screw needed and was willing to sell in box lot quantities. Trouble was their ‘boxes’ held 10,000 screws and cost over $100. Not a prudent solution.

After a search of the ‘junk box’ I did find several dozen nickle plated, phillips head, 6-32 machine screws of sufficient length to do the job. They are now doing the job.

Not original but they actually look better. At least now you can tell if the screw is installed because they show up very clearly with their bright silver finish.

All I need to do now is find spares for the tubes used in these two radios and I will be set for quite some time to come.

T4XC AM Mod

February 18, 2009

I saw this modification on the web somewhere but don’t remember exactly where. Google on T4XC AM Mod and see what you get.

The mod is a simple matter of replacing the 220 ohm cathode resistor on the 6AU6 am modulator with a 1K pot. Then the 1K pot is adjusted to give 20 to 30 watts carrier output with the transmitter in AM mode and keyed on the air via the microphone.

Why do I need this? My thought exactly. I had always known that the T4XC had an AM function but why bother with it when it has such a good SSB feature?

I probably still will not bother with the AM function but this mod makes the AM function much more functional. You see the transmitter goes to ‘controlled carrier’ mode when doing AM. Carrier output is only about 10 watts or so when unmodulated in AM mode (dead mike). Power out increases when you talk up the mike but for those periods of silence between sentences the signal appears to disappear as the power level goes to QRP.

So, by increasing the bias resistor value from 220 ohms we can get more carrier output with a dead mike and the signal does not disappear as much. Carrier output increases to 25 to 30 watts. You could probably get more but it makes it hard on the finals.

The mod has you installing a 1K pot in one of the extra phono jack holes on the rear apron of the transmitter. After I figured out my pot would not fit such a small hole, I used a small PCB mount trim pot soldered to heavy wire extensions from pins 2 and 7 of the 6AU6 socket.

While working on the socket trying to remove the wires and one resistor lead off pin 2, I ended up breaking off the solder lug part of the tube socket pin. While it is not impossible to replace the socket, it is a major undertaking that I was not interested in undertaking. I ended up removing a pin from a surplus 9 pin socket and inserting it in place of the broken pin. I pushed the new pin down into the socket with the 6AU6. It worked and the wires and resistor were far easier to remove off the broken pin now that it was out of the radio.

Once the pot is installed, you tune up the transmitter for max power out in the tune position, switch it to AM making sure the SSB switch is in the XLSB position, and monitor your power out while adjusting the new pot. I set mine to output about 30 watts. Have not tried it on the air yet but it sounds okay on the receiver. Then it sounded okay before the mod too.

One last thing about the mod. You don’t need to leave the pot installed. Measure the resistance of the pot after the adjustment and replace the pot with a fixed resistor of that value. Note that the original 220 ohm cathode resistor is left with one end remaining soldered to pin 7 just in case someone wants to remove the mod and return the transmitter to stock condition. I figure if it is a mod worth doing, it is a mod worth keeping. Still, my T4XC now has an extra unused 220 ohm resistor hanging off pin 7 of the 6AU6 socket.