Archive for May 2007


May 29, 2007

Ever wonder about owning gold. No, I do not mean jewelry. I mean owning gold bullion or at least double eagle coins or krugerands.

Every now and then you will hear ads on the radio about what a really good investment gold can be. The perfect way to diversify your investment portfolio.

What they do not tell you is that gold is a commodity. Buying gold makes as much sense as buying sacks of coffee beans or cocoa beans. Same opportunity to make money. Same requirement for storage. Same security requirements so it does not get stolen.

You see, gold is not really an investment. Oh, gold does increase in value over time, but so does real estate, so does coffee, so does sugar, so does cocoa. Why? Because of inflation. Why do you think an automobile that cost 5 thousand dollars twenty years ago now costs 20 thousand dollars? The product did not improve that much over time. The problem is that the dollar lost its value over time.

Now that may not be all that is at work here regarding gold, but I suspect that more than half of the inflated cost of gold is due to the eroding value of the dollar.

Gold does not earn interest, pay dividends, or demonstrate significant growth. Stocks, bonds and even savings accounts do.

Gold merchants are fond of the story about the 20 dollar gold piece. Seems that a 20 dollar gold piece would buy a very nice suit back in the 1800’s. That very same gold piece will still buy a very nice suit today. True, but they don’t tell you the whole story. Had that 20 dollar gold piece been invested in a simple savings account two hundred years ago, it would have earned enough interest to buy the entire clothing store today.

Not convinced? Okay, here is how gold ownership works. You pay for the gold with taxable income. That is income you earn that is left you after you pay income taxes on it. You have to secure the gold somehow in a safe place. Most people use a safe deposit box at a bank. Safe deposit boxes are not terribly expensive but they are an expense that you do not incur with many other real investments.

So you hang onto the gold for ten years. During that time the price of the gold doubles. You decide to take your profit. You sell the gold and find that the proceeds are treated the same as income for tax purposes. In fact, you are required to give your social security number out to the gold exchange before they can pay you for your gold. So, you get taxed on the proceeds at your normal income rate. That could be a serious problem if you are in a high tax bracket or if you have enough gold to place you into a high tax bracket. Could be you may find that your ‘investment’ in gold did not double in final value to you because you had to share your gains with the IRS. At a 50 percent tax bracket that would mean you did not get ahead at all. You did not even break even because you had to pay for a safe deposit box at the bank for ten years.

I think everyone should own some gold. A very small sum. Perhaps one ounce for every member of their immediate family.

Still not convinced? How often do you hear ads on the radio trying to sell shares of Apple computer stock? Evidently Apple computer stock does not need to advertise. Probably because it has more than enough buyers. Now how often do hear ads on the radio trying to sell gold? I hear at least one every other day. Evidently gold is not as popular an item as Apple computer stock. I wonder why?

Invisibility Suit

May 25, 2007

I recall how neat is was to see the alien in Terminator to pop in and out of view using his invisibility shield (or whatever it was called).

Before long our military will be able to do just that.

Sony has developed a thin flexible TV screen that can be worn like a t-shirt. All that is needed now is for someone to develop one that can be worn as a uniform.

Linear Amp Tuned Input

May 20, 2007

The biggest single improvement that can be made to the simple GG RF amplifier is the addition of a tuned input.

The tuned input improves linearity while also reducing the drive requirements.

I recently found a tuned input design by ZL1AXB that does this as well as eliminating the filament choke required by tubes using directly heated cathodes.

A full description of an HF amplifier using this tuned input circuit can be found HERE.

The single 813 amp shown is designed to cover only 40 thru 10 meters. So the specifications for the input circuit will not work down to 80 meters. However, all that is required is to increase (probably double the turns) the inductance of the input coil to cover 80 meters.

The input is deceptively simple. For the original design, the input coil is composed of 7.5 turns of 3/16th inch copper tubing wound on a 1 inch diameter form. A length of teflon insulated #12 wire is threaded through the tubing to form the second connection to the filament. The tube filament pins are connected to the tubing and to the #12 wire at the tube socket. Three turns down from that provision is made to insert driving power through a 0.01mf disk ceramic capacitor. Claims are made that such a tap provides a 50 ohm input across all bands.

At the other end of the input coil, the tubing and center conductor are connected to the secondary of a center-tapped filament transformer. The center-tap is grounded to provide a return for the plate current. Both filament leads at the transformer are bypassed to ground through 0.01mfd disk ceramic capacitors.

A 1000mfd variable capacitor is connected across the tubing coil to allow tuning 40 thru 10 meters.

A 2.5kohm 2watt resistor is connected across the variable capacitor to reduce the Q of the input circuit.

It seems like a very neat and painless way to significantly improve amplifier performance while eliminating the need for a filament choke. The only down side is fabricating the tubing coil and threading the center conductor through the tubing. Obviously the center conductor should be threaded through the tubing before trying to bend the tubing into a coil. That should help prevent collapsing the tubing during bending and also simplify installation of the center conductor.

An even simpler approach might be to use coax in place of the tubing and center conductor. After all, the tubing and center conductor are really just a length of homemade coax.

A length of RG8 with solid dielectric should work well. The smaller coaxial cables like RG59 and RG58 may not handle the filament current very well. A single 813 needs 5 amps at 10 volts. A quad of 811s require 6.3 volts at 16 amps. Or 12.6 volts at 8 amps depending on how they are wired. In either case, the #20 center conductor of the smaller cables may not be sufficient to handle the current.

For an 80 meter application, approximately 14 turns of RG8 will be required. At a 1 inch diameter this amounts to 42 inches of cable. The capacitance of the center conductor to the shield will not be inconsequential and it may cause problems when trying to tune the 10 meter band but it should work without problem across frequencies below 10 meters. Running high power on 10 meters is usually not necessary in any case so that should not cause any real problem.

ICOM 737 Problems

May 18, 2007

About five years ago or more I bought a used ICOM-737 for less than half the price of a new one. It has worked fine for over four years and I would consider it the best of any transceiver I have ever had the privilege of operating.

About a year ago it began to demonstrate a nasty habit of shifting frequency by about 50 hz or so. It usually happened when I was transmitting. The shift was not serious enough to loose contact. It merely changed the pitch of my voice on SSB and it did not occur all the time. Only on very rare occasions. At first. Recently it has become more and more frequent.

Then, the other day, it began to have trouble with 160, 80, and 40 meters. It just quit working on those three bands. It still worked on 20 meters and up but the lower three bands were dead. No signals, just noise. The condition went away when the radio was powered down and left overnight. The next morning all bands worked as they should for about fifteen minutes, then the lower three bands would fade off into never never land.

I was convinced that it was a power level problem. The 8 volt regulator was a little low running at 7.25 volts. Or so I thought. Turns out that my voltmeter was off but before I discovered that, I replaced the regulator with a new LM7808. A standard LM7808.
The regulator that ICOM used had the mounting tab insulated. The standard LM7808 had an uninsulated mounting tab. No problem. Tab goes to ground anyway, so I just mounted the new regulator with the uninsulated tab to ground. When power was applied the display remained dark. I re-installed the old regulator, powered up and everything returned to normal. I still had the problem of loosing the lower three bands but at least the display was lit and everything seemed to be working on the bands that were still active.

That is when I decided to see if there were any service notes on ICOM on the internet. Yup, sure were. Most had to do with frequency instability caused by defective plastic trimmer capacitors. The notes recommended they be replace with ceramic trimmer capacitors.

I have not done that yet but I am sure that when I do, the problems will be solved. The parts involved are primarily C294 and C205.

I vaguely recall that the ICOM-735 suffered similar problems which were also caused by plastic trimmer capacitors. My guess is that the difference in price between plastic trimmers and ceramic trimmers might be as much a 5 cents, maybe. You would think that the manufacturer would have learned a lesson about trimmer capacitors from the problems with the 735 model, but noooooo… they needed the those 5 cents far worse than they needed satisfied customers. Well, they better find some part that gives them more than just a 5 cent boost in profit because I am not buying anymore ICOM junk.

I figure if they cannot do the right thing and build in the quality that I deserve in an expensive radio, then I don’t need to do business with them anymore. Besides, I don’t want to find out the hard way the trimmer capacitors were not the only parts they cheaped out on.

By the way if you have one of those trashy ICOM transceivers, I can replace the faulty trimmers for you for a flat fee of $100 plus shipping (both ways, of course).