Archive for April 2007

Regenerative Receiver Hints

April 13, 2007

You don’t know what frustration is until you have tried to use a marginally functioning regenerative receiver as a communications receiver. Then I guess marginally functioning equipment of any type would frustrate the user. It is just that regenerative receivers have so much more to become frustrating.

Drift, hand capacity effects, flakey regeneration control, dial setting jumps when you touch it, headphones are uncomfortable, not sensitive enough normally and when you increase sensitivity, you can’t keep the signal tuned in. Those are just a few of the ‘fun’ experiences you are opening yourself up to.

Here are a few tips on how to deal with these frustrations.

Choose your tuning capacitors and dials very carefully. Ball bearing capacitors and zero backlash dials are best. If it is good enough to be used in building a VFO, it will probably work fine in a regen.

Wooden cabinets are fine but the front panel needs to be made of metal and connected to ground to prevent hand capacitance effects to the circuitry. Any part of the circuit could be effected by hand capacitance, not just the coil.

You don’t need RF amplification but you could benefit from RF isolation from the antenna. A grounded grid triode amp at the input will prevent the antenna from loading down the oscillator.

A triode makes a decent regenerative detector but a pentode makes an even better detector and allows smooth control of the regeneration threshold by varying the screen grid voltage.

The screen grid voltage to the detector needs to be well regulated. Using a VR tube here is a good idea.

Although a pentode detector has good output, it is not good enough to drive a headset under all conditions. Follow the detector with at least one audio stage before the headphones.

If you want speaker volume, then add another audio stage (maybe a 6V6) after the first.

If you have kept up with the tube count we are now up to five tubes. We might want to re-evaluate the design. Maybe go with a single conversion heterodyne.

Run the radio off batteries or a separate AC power supply. With the high sensitivity of the detector it will be nearly impossible to keep hum out of the radio if the power supply is built into the radio case.

You probably decided on a regenerative receiver thinking it would be a simple project. It can be simple but to get decent performance the regen becomes as big a project as a simple heterodyne.

Also, the same problems you experience using a single conversion heterodyne at higher frequencies also plague the regenerative receiver. At the very least, stability will suffer. Even so, both of these receivers can do very well on 80 and 40 meters. There is absolutely nothing wrong with using a crystal controlled converter, making the system a dual conversion, regardless of whether you decide on a single conversion heterodyne or regenerative.

Used Ham Radio Equipment

April 13, 2007

Is it worth screwing with used ham radio equipment? YES! Most definately, but be careful.

Hams are a cantankerous lot. They don’t get rid of stuff that is useful unless they are dealers. Now it could be that the equipment is just old and they are tired of it. If the stuff is new to you and works, it might take you longer to tire of using it.

On the other hand, the stuff could be junk that has been hosed down and dried off so that it becomes presentable.

Unless you can have the equipment demonstrated under actual operating conditions, maybe make a few contacts and get some signal reports, don’t pay more than salvage value.

Even before you make an offer, pay attention to the conditions under which the item is being offered. Don’t make an offer on the stuff if you are confronted with any of the following:

‘I am selling this for a friend’
Could be his ‘friend’ does not even know he has it.

‘It worked the last time I used it’
That might have been 30 years ago when he first bought it new. Chances are good that if it was working, he would not be trying sell it.

‘It is in mint condition’
If he is not a dealer presenting you with brand new equipment with factory manual, box, and warrantee, he is lying to your face.

‘Complete with copy of the original manual’
If it does not have the original manual, it has been orphaned and probably more than once.

‘Power supply and mike are not included’
Might only have had time enough to steal the rig itself.

‘Very rare collectible’
If you are looking for collectibles at a hamfest, you are out of your mind!

You will just not find highly desirable equipment on the bargain table at a flea market or hamfest. That does not mean it cannot be useful but its usefulness will vary from person to person. It all depends on what their needs are.

Lots of old equipment began life in kit form. Make sure if that is the case for the item you are considering that it had life after assembly. An unusually frequent problem is that kits that never worked are being offered as valuable collectibles. Unless you are a junk collector, you may not be interested in such equipment.

Store Brands

April 13, 2007

Certain grocery items can be purchased as store brands. For instance, in the case of a can of peas, the store brand may have Kroger on the label instead of Libby’s.

Store brands are generally less expensive offering five to ten percent savings. Unfortunately, when you open that can of peas, you may discover what was done to offer you the savings over the brand name.

If the item is to be used as an ingredient in a recipe and is just one of many with most of the many being herbs and spices which are mainly responsible for the ultimate flavor of the dish, you may never realize that a store brand was used.

If, however, the store brand item is it, meaning it is the dish itself, there may be greater potential for disappointment.

Some store brand items that have been disappointing have been mustard, pre-cooked sausage patties, some condensed soups, and canned vegetables.

The store brand mustard was thinner, more acidic, and had a funny taste when compared to French’s.

The store brand sausage patties had more fat content and a decidedly gamey taste when compared to Jimmy Dean patties.

The store brand condensed mushroom soup did not seem to be as condensed as the Campbell brand.

Lastly, the store brand canned peas were decidedly inferior to LeSueur brand peas. That may be an unfair comparison. LeSueur peas are the caviar of canned vegetables.

1GIG USB Stick

April 7, 2007

I remember when I considered myself lucky to own a 100mb hard drive. I just can’t remember exactly what year that was but I definately recall that it was NOT FREE.

I just redeemed a card for a FREE 1GIG USB Stick at the Micro Center. One Gigabyte!!!! That is 1000 mb or ten times the size of my 100mb hard drive.

It is hard to understand how they can stuff that much memory into such a small space. The thing is about two inches long and three-quarters of an inch wide. I just hope none of those bytes fall out. I would never be able to stuff them back in again.

It even works on my old win98 machine. Formated out to 967mb. I don’t even feel cheated that it did not format out the full 1gig.

My very first hard drive was in an IBM PC. It was only 10mb worth of storage and cost over $300. It was also the size of a small shoe box and took up a full sized 5-1/4 inch drive bay. That was around 1980.

Had someone told me then that I would be getting a free 1000mb USB memory stick that could fit in my pocket, be portable, and work like a hard drive but not have any moving parts, I would have thought they were nuts.

Shrimp Sauce

April 6, 2007

I have been putting off posting this because I don’t have the pictures ready yet, but this stuff is so good I decided not to wait any longer.

First off, you have to like shrimp. If not, forget it.

The sauce is thick and full of shrimp, both whole and cut up. It is intended to be used as a topping for noodles but works on rice too.

Start off by cooking up some shrimp. I buy a big bag of 30-40 medium sized raw, in the shell, shrimp. They have been de-vained and cleaned but are still in the shell. Dump them all into a big pot of boiling water. No need to thaw. Let them cook until they turn pink. Don’t over cook.

Pour off the water and save it. Strain the water to remove any shells and other unwanted debris. Then save the water and use it to cook rice or noodles. You will be surpised at how shrimpy the rice and noodles taste when they are cooked in shrimp water.

In a large sauce pan, prepare the soup stock for the sauce. One can of condensed mushroom soup, two cans of water, half an onion (diced), and six to twelve garlic cloves, fresh and minced or finely diced. Stir well to mix all that stuff together and let it simmer while the shrimp are shelled.

Shell the shrimp. There should be about three to four dozen shrimp. Take half the shrimp and cut them into smaller pieces and add them to the sauce. Add the rest of the shrimp later but leave them whole.

Season the sauce with salt for taste, pepper, and basil (if you like it). Add some more water if the sauce is too thick. You don’t want the sauce to stick and burn, so add water if needed. Simmer the sauce on low to medium heat for a one to two hours or until the onion and garlic is cooked into the sauce.

If the sauce is too thin at the end, add some flour to thicken it. Don’t just dump in the flour. Mix a tablespoon of flour at a time in a cup with water. Then add the mixture to the sauce. The sauce should be hot and close to the boiling point as you add the flour. The heat will cook the flour and thicken the sauce. Mixing the flour with water before adding prevents clumping.

This recipe makes enough sauce for four to six generous servings. Use it immediately or pour it off into jars for later use. I find that two salvaged Prego jars are enough to hold and save one recipe.

811 Triode

April 1, 2007

The 811 has to be the most useful of all higher power transmitting tubes.

I got started in ham radio in 1959. That year the December issue QST had an article on the use of four 811s to build a medium power linear. The basic idea was to have one RF deck with the four 811s, one power supply, and five separate, switch selectable, pi-net output circuits covering 80 thru 10 meters.

Now, nearly 50 years later, that is still the most logical, economical, and reasonable approach to high power.

The 811 is still in production. At least in China and it is one of the tubes the Chinese know how to make.

Used to be you could get NOS, American made, 811s for five bucks each. Today they cost you fifteen bucks each and are made in China.

Over the years I have homebrewed linears, used linears made from kits, and also owned commercial amps. This equipment used 813s, 811s, 4-400s, 572Bs, 4CX300s, and 4CX1000s. Out of all of these choices the amps using the 811s were the most reliable, most inexpensive, and easiest to operate. Here is why.

811s are perfectly happy running at 1500 volts on the plate. The lower plate voltage reduces power supply cost and allows less capable components to be used in the pi-network of the plate circuit.

Filament requirements are easily met. 6.3vac at 10 amps is more than sufficient to power a quad set of 811s. You don’t need to wind a special filament transformer or buy a special 5.0 volt high current transformer.

Each tube requires a 4-pin socket which is a fairly inexpensive and standard item, mounts with two screws, and does not require any special sized chassis hole.

Cooling 811s is easily done using simple fans. No need for high volume blowers. Some applications (like the Tiny Tim) can be implemented without need for any forced air cooling at all.

A set of four 811s will easily run a 1KW input without need for a special 220vac line connection.

811 linears are easy to homebrew because low cost parts are still readily available.

Of the commercial 811 linears the Collins 30L-1 is the best by far. Quiet and strong it is a marvel of good engineering and reliability. It is also very fairly priced and can be purchased, used, in good condition for as little as $600.

In contrast all the 4-xxxx series of tube linears fall far short of the 811s benefits by requiring higher plate voltages, higher voltage components, special cooling considerations, expensive hardware and sockets, and special biasing and driving circuits. In short all the things that make the 811 so desirable are missing in the 4-xxxx series of tube linears.

Probably the most significant thing is the missing lower cost. While four 811s will set you back about sixty bucks, you could easily spend ten times that on a 4-xxxx tube equivalency.

I still have four linears. One is a dual 811 Tiny Tim. Another is a Yeasu FL-2000B running a pair of 572Bs. A third is an underpowered pair of 4-400s in a short rack mount cabinet. A fourth is a desktop pair of 813s. All four of these are all-band, band switching linears. I am seriously considering turning the Tiny Tim into a 75 meter only amp, converting the 4-400 amp to a quad of 811s, and setting up the 813 on 20 meters permanently.

That still leaves me with one all-band amp and allows me a higher degree of operating convenience. At least on 75 and 20 meters.

A Little Power

April 1, 2007

Last weekend I was keeping my weekly sched on 75 meters using reduced power and a non resonant dipole match with an antenna tuner.

The reduced power was being used because on 75 meters the non resonant antenna was presenting an impedance that was developing too high a voltage for the Z-match and I was getting arcing between one of the main coils and the pickup loop wound around it.

Signal reports were dissapointing. Somewhere between s-6 and s-9 even though I was running close to 200 watts output to the antenna. I was beginning to suspect that the new 88 foot non resonant dipole was just not going to cut it.

I got he arcing problem solved by using rg-58 coax for the pickup loop. The insulation on the coax allowed me to run a full 500 watts out to the tuner as I had done with the 80/40 meter trap dipole.

This weeks sched on 75 resulted in a 20 over 9 report. I guess the new non resonant antenna is working after all.

I would not have thought that increasing the power from 200 watts output to 500 watts output would make that much of a difference. I am still not convinced that is all that is at work here. For the last two days we have had continuous rain and the ground is about as soaked as it will ever get. I think that might have some effect on antenna efficiency.

Unfortunately it never occured to me to reduce the power to the 200 watt output level and get a report. Oh well.