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Computer Turns Itself Off

Sometimes my computer problems are software related but most often they are caused by hardware problems.

Recently I experienced a problem where my desktop was turning itself off. This destop is somewhat a cludge. Its top is off and one of three drive ports contains two SSD disks, one for windows, the other for debian. The operating systems are selected by moving the data cable from one drive to the other. In order to accomplish this the drives have extra long cables to allow their mounting tray to be removed for access.

After accessing the drives the tray is pushed back into the computer. The last time this was done the longer cable got jammed against the blades of the CPU fan. When the CPU overheated, it would turn off the computer.

Antenna Switches

Over time I have used a number of tower based antenna switches. They all worked but were never able to select between morew than four antennas.

These switches were controlled through the coax feedline by using chokes and capacitors to isolate the control voltages from the RF energy. This seemed to work even at high transmitter power levels but the additional components required to do this would certainly have an adverse effect on reliability over time. I did not need another toy to repair at some future date so I decided to run a separate control line to power the relays used in my antenna switch.

By using a tower mounted antenna switch I need only one coax feedline from the shack to the tower and I have relatively short feedlines runs from the switch to the five antennas. Otherwise I would need five long feedlines into the shack, one for each antenna. The antenna switch more than pays for itself in money saved buying coax. The main downside is that you can only use one antenna at a time.

So if you own more than one ham rig, you can’t use that other ham rig on the antennas connected to the antenna switch when they are in use by the main rig. That is actually a good thing. Two rigs in close proximity and running power could easily blow each others front ends.

There is one valid reason for running more than one feedline to the shack, diversity reception. That is using two receivers one one a vertical and the other on a horizontally polarized antenna to enhance reception.

My antenna switch uses three 12 volt 30 amp SPST relays and a four conductor control line. Two of the relays have thier coils wired in prallel to act like a DPDT relay. They are wired just like the Heathkit four position antenna switch but use an additional SPDT relay. The extra relay takes the normally #4 antenna selection and translates it into #4 and #5.

The control cable is an old landline phone line. It has red, green, yellow, and black conductors and is dirt cheap. Power to the relays is 14 volts provided through diodes and a rotary switch at the operating position. The diodes isolate the five selections needed to provide proper sequencing of the relays.

Kenwood TS-850

Ever since I repaired a TS-850 for a close friend I have been wanting a TS-850 of my own. I do have a TS-950 and the TS-850 appears just as good and considerably lighter in weight. On top of that I know how to keep it running.

Like many Kenwood radios, you can get them with or without certain options. The ATU is one such option and raises the price of the radio. Is an antenna tuner really needed? It is only needed if you don’t have antennas and feedlines that ensure an impedance match to your radio. The ATU will ensure a match to the feedline at the operating position. That keeps the transmitter happy but could make the operator unhappy as the power is dissipated as heat in the transmission line.

You are much better off using well designed, resonant antennas. They radiate better, more efficiently and also ‘hear’ better and you don’t need an ATU to use them.

Depending on condition the 850 is worth from $500 to $600 if it is electrically perfect. Trouble is, even new out of the factory, some of these radios were not perfect. That makes their value on the used market below $500. Unfortunately most sellers of this radio do not agree and ask prices that take them out of the used equipment market.

Recently I have come to the conclusion that it is more enjoyable to play with new radios than to try and repair some sick broken toy that no one wants.

Sure, I can repair it and make it work but it is still an old toy looking for a place to die. It is just not worth the time it takes to keep the old stuff working when the new stuff works better and does much more.

SWR and Power Meters

Is it worthwhile to pay extra for a power meter that can measure up to 2000 watts and beyond?

If we want to measure and monitor the output of a powerful amplifier we would need such a device.

Perhaps a better question would be, ‘Why do we want to measure the output of our amplifier’?

Have we received reports from long time ham friends that our signal has become weaker? Maybe we just want to check and make sure our tubes are not soft. Whatever the reason, an accurate measurement of the amplifiers output is not going to improve the signal. In addition, a truley accurate, high power, watt meter is going to be expensive. You would be better off spending that money on new tubes if you suspect the old ones to be soft. Besides, you can get a pretty good idea of the power level by noting the plate current and voltage under load. The product of plate current and plate voltage times .6 is a good indication of power out.

Tubes are not the only thing that can go soft. Plate voltage can droop due to aging electrolytics in the plate supply. A lower plate voltage will result in lower plate current as well.

You may also want to make sure you are not expecting more output than your amp can deliver. Don’t confuse output with input. Most amp manufacturers prefer to quote power input and list it in PEP. PEP is normally about twice what you can expect from a key down CW condition and to be linear an amp can only deliver about 60% of the input power at its output. That means a 600 watt PEP input amp is only capable of delivering about 200 watts constant carrier key down output.

Input only sets the cost of running the amp. Output is what is useful to the amateur radio operator. The benefits of knowing precisely what that output is do not justify the cost. So, no, you should not pay extra for a high powered watt meter.

Getting ahead of myself, I will also state that you don’t need a high power SWR meter either. A low powered simple resistive bridge can be built with very short lead lengths allowing its use up through the UHF region.

Also you don’t need a dual meter dual pot sensitivity adjustment. A single meter with sensitivity pot in the return lead of the meter will work just fine if it is switched from the forward circuit to the reflected. First, reading forward, you adjust for full deflection. The you switch to read reflected. If the reflected reading is at half scale the SWR is 3:1.

I already have a decent SWR meter, but, if I were looking for one today, I would buy the least expensive CB meter I could find, gut it, and install a resistive bridge for a pickup. I have seen prices as low as $15 on Amazon. That is less than you would have to pay for a meter, switch and case.

50 Percent Off !!

Why is this offer only extended on stuff I don’t need?

I can’t save money by buying stuff I don’t need.

I can save money by ignoring the offer.

So when I see that offer I take 100 percent off.

I guess I am just a greedy old fart.

More Bazooka Dipoles

Nearly a year ago I invested in a Unidella trap antenna kit. It included two 40 meter traps, two end insulators, and a center insulator/balun. The resulting trap dipole ended up being somewhat narrow banded favoring the cw portion of 40 meters and the 75 meter ssb band.

The antenna seemed to work reasonably well on 75 and 40 meters but did not cover other bands as well as my home brew 80/40 trap dipole. That was not a problem as I had other antennas covering those other bands but I did want a 40 meter capability that would favor the entire 40 meter band.

So why not build another 40 meter bazooka, hang the traps off that antenna and add wire to cover 75 meters. The traps would not care that the 40 meter portion was a bazoola.

It also turns out that the bazooka does not care what coax you use to build the two quarter wave stubs as long as they are 40 meter quarter wave stubs, they will work. So I ended up using some surplus RG62 to build the quarter wave stubs.

Antenna Pulley System

The current problem is one padeye being used as a fulcrum for a halyard with too much weight on the halyard making it difficult for the rope to pass through the halyard fulcrum.

The heavy weighted halyard would pass through a properly configured pulley with roller. The pulley with roller would easily pass through the padeye fulcrum.

This works well but the pulley needs to be attached so that it does not slip on the line.

The bazooka modification has the 40 meter portion SWR best at 7.074. Need to take about 6 to 12 inches off each leg.

Now I have a 75/40 meter trap dipole that covers the entire 40 meter band with a 1.2:1 SWR and allows me to transmit on 75 meters as well.

Stand Alone Soft Start

This would be neat if it could be made to work. The trouble is that in order for this to work, an on/off switch has to be located at the soft start relay and the on/off switch in the equipment has to be on and configured in a way that allows the impedance condition of the primary of the power transformer be reflected to the soft start circuit. Otherwise the soft start relay will engage immediately taking the current limiting resistor out of the circuit before the current surge has abated.

The short version of this story is ‘stand alone soft start does not work’.

If we can agree that a soft start feature is good, we might also agree that an external soft start might also have merit.

All soft start devices I have seen are added internally to the target equipment. This requires digging into the device, finding room for the circuitry, coming up with an acceptable mechanical installation and deciding if two soft start mechanisms are needed, one for filament and one for high voltage.

All of these concerns disappear when we build an external soft start device. The external device is built into a cast aluminum enclosure. The proper power socket is mounted onto the enclosure and the current limiting resistor and soft start relay is mounted inside the box. A line cord and strain relief exits the box. The line cord is plugged into the power connection on the wall. The equipment is plugged into the the soft start box.

For it to operate properly, the equipment needs to be left turned on. It needs to be on such that the turn-on load will be reflected back to the soft start box. This means there can be no relay switching of power inside the equipment. The transformer primaries must be a continuous circuit to the power connector of the equipment. Otherwise the soft start relays will engage immediately bypassing the current limiting resistors and the equipment will see the full startup current surge.
This also requires that the equipment to be protected be energized by a switch mounted in the startup box. One switch per circuit. These switches need to be rated at the current limit level. For instance, if the current limiting resistors are 100 ohms and the line is 120 vac, the startup current would be limited to 1.2 amps and a 2 amp toggle switch would be adequate as an on/off switch.

These considerations may not be realisable in all aplications but where they can be used we have a portable and universal soft start feature.

Meter Shunts

shunts0411.jpg

There is an easy way and a hard way. First the hard way otherwise you would not appreciate the easier way.

The hard way requires lots of arithmetic and knowing the internal resistance of the meter.

Secure a voltage source. A regulated supply is fine or get a battery. Lets say you found a 9 volt battery and it is actually 9 volts. Now lets assume our meter is a 1 ma current meter. Actually all meters are current meters. Volt meters are current meters with series resistances.

Now, using ohms law E=IR we find we need a 9k ohm resistor in series with the 9 volt battery to make the 1 ma meter read full scale. So hook it up and verify that the meter reads full scale.

Now, select a potentiometer. A 10k would be a good choice. Wire the wiper of the pot to one of the fixed terminals and connect the pot across the meter. Adjust the pot until the meter reads half scale. Remove the pot without disturbing its setting and measure its resistance. That resistance reading is equal to the internal resistance of the meter coil. Why? Because it shares the current equally with the meter. Two equal and parallel resistances take an equal and half share of the current previously conducted by only one of the resistances.

Now you can use that value to calculate the shunt you need.

Now for the easy way. An example will be used to explain the process. I had two meters. They were both 1 ma meters. One needed a shunt allowing it to read grid current as high as 200 ma. The other needed to read plate current as high as 1 amp.

These meters were to be used to measure plate and grid current in a linear amplifier I had built around four 811As. This amp’s relay supply was being provided by an old PC supply that was delivering +5and +12 volts. The PC supply was being used in normal fashion and was at home in the computer case that was being used to house the new amp.

I had just finished setting the band switch taps on the tank coil and had removed the 50 ohm resistor across the output of the pi network. This 50 ohm resistor was now employed in series with the regulated 5 volt supply to ground to generated a current flow of 100 ma.

I had previously purchased a bag of 50 1.8 ohm metal film resistors at a very low price and decided to use these to build the meter shunts I needed. I verified the 100 ma current flow with my $3 Harbor Freight multimeter. Then I placed one of the 1.8 ohm resistors in series with the 50 ohm current limiting resistor. I placed the meter across the 1.8 ohm resistor and noted the meter deflection. Too high. So I added a second 1.8 ohm resistor in parallel with the first. The deflection was now 17 divisions on the meter scale. 100/17= 5.88. Each division was was now indicating 5.88 ma for a full scale of 294 ma for the 50 divisions. My goal was to measure 120 ma which would be about 20 divisions or 0.4 on the meter scale. Close enough. The additional range would come in handy for use with other finals. I had purposely set this amp up to use other tubes as they became available.

For the plate shunt I kept adding 1.8 ohm resistors until the 100 ma current source deflected the meter to 5 divisions. 100 ma X 10 = 1000 ma or 1 amp. 50 divisions full scale divided by 5 = 10. Thus full scale translates to 1 amp on the 1 ma meter.

Done. Accuracy so – so. Ten percent would be fine.

Installing meter parts to tiny single hole solder lugs is an unpleasant task. That is why I mount the parts to circuit boards that can be installed to the meter terminals with two nuts. Wires soldered directly to the printed circuit board pads.

Select a fairly thick cicuit board scrap and drill two holes to fit the meter studs. Use a dremel tool to cut away a strip of copper on both sides creating isolated pads. Now solder, surface mount style, all the required parts across the isolating gap.

Once done, solder the meter leads to the pads and mount the assembly to the meter.

Using Obsolete Computer Hardware for Ham Equipment

I am suggesting the use of old computer cases to house communications equipment. Primarily for the housing of linear amplifiers. In a recent project I used a mid sized tower case to house the parts of a four tube 811a amp.

A small tower case measures 7 x 15 x 13 inches. The case I found measured 9 x 15 x 17 inches and was just barely large enough to house the required parts. To prepare the case I cut the cover into three parts using a metal cutting blade on a table saw. The sides of the original cover were used for the top and bottom plates of the resulting cabinet. What used to be the top of the case became the front of the amp. The bottom of the case became the rear wall of the amp. What used to be the front of the computer case became the right side of the amp after the plastic computer front was removed.

A shelf used originally to support the mother board was mounted to the bottom of the five inch hard drive enclosure and supported about two inches above what ended up being the new bottom of the case. This shelf was cut out to receive the upper half of a filament transformer which further stabilized the shelf. The plate transformer was a spare for a Heathkit SB-220 and fit nicely into the five inch drive enclosure.

This particular tower case had provision for two standard computer power supplies. I think it was an either or sort of deal instead of providing for two supplies at the same time. In my project I used both locations. One to house an old Dell supply to provide relay power, 5 volts dc, and 12 volts at up to 15 amps for powering an exciter or other lower power equipment. The second supply location was used to house an empty PC power supply case that was used to house the rectifiers and the filters for the HV supply. Both PC power supply cases have fans to exhaust air from the case. A third fan blows air into the case over the tubes.

I am not too hopeful that all the parts could be fit into a more normal sized case. The more normal dimensions are 7 x 15 x 13. In my case the 7 inch dimension would become the height. Seven inches is not enough to accomodate an 811 standing up. Of course you don’t have to lay the case down on its side. There should be no reason not to use it in its original ‘tower’ c0nfiguration.

Universal Linear Amplifier Design

Primary Features

The grids are directly grounded.

Uses cathode bias generated by a series string of forward biased diodes

Fused cathode circuit. Fuse and diodes paralleled with high value resistor to provide cutoff bias should the fuse fail.

Both primary power leads are fused.

Soft start limits inrush to 5 amps for filament and plate supplies. Inrush can be limited further by increasing current limiting resistor values.

Makes use of computer power supply to provide 5 and 12 volt relay control voltages and auxiliary power for exciter. The computer power supply fan exhausts hot air from the cabinet.

A computer power supply empty shell is used for additional fan cooling and safe housing of the high voltage rectifiers and filters.

Filament transformer is rated at 400 watts.

Plate transformer is rated at 2kw and selectable 1000 or 1200 vac secondary via primary taps.

All band capability.

Equivalent to the 30L1 when using 811 tubes.
(Plate supply is robust enough to properly run a quad of 572s in a 30L1 configuration).

Equivalent to the SB-220 when using a pair of 3-500 tubes.

Equivalent to the Loudenboomer when using a single 3-500 tube.

Desktop unit.

Grid, plate, and output metering.

Input tuned circuits allow use of solid state exciters at full power.

Plate tune and antenna load controls use 3:1 velvet vernier dial mechanisms.

Plate current meter switchable from plate current to RF output.

Wired for 120 vac operation. Can be wired for 220 vac operation.

PTT only. No QSK for CW.

Keying line at 12 volts 100ma.

Universal High Voltage Power Supply

This power supply design is intended to support the Universal Linear Amplifier. The entire system is designed to provide from 500 to 1500 watts OUTPUT ( that is power available at the feedline to the antenna) using a variety of transmitting tubes. The only solid state devices are the silicone rectifiers used in the power supply, bias circuitry, and relay inductive spike suppression.

Tubes under consideration include the 811, 813, 572, 3-400, and 3-500. These tubes are listed in an ascending order of cost with the 811 being the most economical.

The universal power supply uses a circuit that can be configure as a bridge or full wave voltage doubler. The plate transformer for this supply is intended to supply 800, 1000, and 1200 vac at up to 1amp. Output voltages from this design are 1120, 1400, 1680, 2240, 2800, and 3360 vdc.

The ac plate supply voltage is adjusted by using a tap on the primary of the plate transformer. The plate transformer is selected for operation from 120 vac or 240 vac.

The amplifier is designed with a removable tube plate. A number of identical plates can be fabricated to allow the use of any of a number of the tubes listed previously.

The most economical and well supported solution is the 4×811 amp operated at a plate voltage of 1680 volts. 1680 volts at 1 amp is 1680 watts input which at 60 percent efficiency results in 1000 watts output to the antenna.

Filament power is supplied by a modified 400 watt transformer. The normal secondaries were removed from this transformer and replaced with one layer of stranded #12 insulated wire with center tap to provide 6.3 vac under the load of four 811 tubes. It is estimated that should that load current be increased to 24 amps (as requored by two 3-500s) the voltage would drop to around 5 volts. If the drop is less than that the voltage could be dropped further to ensure 5 volts at the tube pins by adding a sufficient length of small gauge wire. Note that at 400 watts the transformer is capable of supplying up to 80 amps at 5 volts. The secondary voltage of the filament transformer increases by 0.5 volts per secondary turn. Thus it takes about 12 turns to generate 6 volts.