Amateur Radio - WARC band fan dipole

Welcome back to the Cly Institute for Radio Repair subsidiary of the Imp Barn. The institute wants to be capable on as many bands as we are licensed to operate on.

The WARC bands are three portions of the shortwave radio spectrum consisting of 30 meters (10.100–10.150 MHz), 17 meters (18.068–18.168 MHz) and 12 meters (24.890–24.990 MHz). They were named after the World Administrative Radio Conference, which in 1979 created a worldwide allocation of these bands for amateur use. The bands were opened for use in the early 1980s. They can sometimes be ignored by ham operators, but possess good opportunity for DX under the right conditions. My manual tuner works HARD to make my transceiver happy on these bands with my existing equipment for very poor efficiency, and very few contacts.

In researching the availability of antennas for these bands I found very little. Verticals are available from the usual sources, but the cost is prohibitive. (I didn't want to include 60m in this design either since my radio doesn't do 60.) The bands are nice and narrow bandwidth with little need to strive for obtaining wide bandwidth capability in a design. I normally run a commercial "fan" dipole which Alpha-Delta refers to as a "parallel" dipole for 80, 40, 20, 15, and 10 meters. What was needed was a simple wire solution. I was inspired by an article by W4DAN for this fan dipole design. The solution was simple, create a fan dipole for the WARC bands using first principles where the calculation is 468 / freq in Mhz = total length in feet for a half wave dipole.

 To reduce interactions between elements, I spaced them 6 inches apart. This may be excessive, but works fine. The center is an old 1:1: balun I found at a hamfest.

With the longest element of just over 23 feet in the center, the next longest on top and the shortest on the bottom.  A Dacron rope makes up the difference between the 17m and 12m element to reach the last spacer.

30m just over 23 ft

17m just under 13 ft

12m just over 9.5 ft

Here's a shot at dusk before the tuning process got fully underway.  We did all this work by flashlight in the dark.  This has few advantages, but at least the neighbors don't stare.  Its SCIENCE folks!

When tuning this antenna, I put the center up on a thin bamboo pole supported by my son's wooden swing set, and supported either end so that I could reach up at the end and grab it.  After getting the wire in hand I could walk hand-over-hand bending the bamboo pole down to reach the end of the element for tuning.  This was rather more like an Inverted-Vee arrangement which will result in slightly shorter lengths and will be ideal for mounting where there are no high objects to tie to.  At the recommendations of my elmers, I started with the 30m elements and tuned them to under 1.5:1 SWR.  Progression was to adjust 17m and then 12m elements.  I noticed little interaction between those elements while tuning.  I did jump back and forth once between 17m and 12m to get the tune just right.  The bamboo pole worked well for a temporary tuning setup.  A final mounting location is yet to be determined.

Using my VK5JST analyzer, we were able to get the tuning reasonably close.  I discovered that a simple technique to keep me from cutting too much off the elements.  It didn't seem to affect the tuning and I would encourage others to take advantage of this trick to enable you to re-tune an antenna in its final installation for perfect matching.

I folded the element back on itself and used a cable clamp to secure it.  The loop can be adjusted easily by loosening the cable clamp and re-tightening.  The element wire in the loop didn't seem to matter much, but I kept it to a minimum without too much wire involved in the loop simply for fine tuning.

Good high quality T-B ty-wraps were used to keep the spreading spacers taut with the 30m elements, and with the spreader near the feed point to keep everything aligned.  The ty-wraps can be adjusted slightly if needed but provide a good solid way of keeping the spreaders in place.  This is what Alpha-Delta uses, so why not!

Catch you on the WARC bands!

Amateur Radio - 1924 Crosley 52

This beauty was found at our club swapmeet.  It is a nearly complete radio.  The power switch was missing along with a few of the knurled screws.  The case is in nice shape too.  I brought it home for nearly market value and discovered that the tubes were also good.

The schematic revealed that the Crosley 52 is a basic regenerative receiver.  The first tube does all the RF work.  The second and third tubes are for audio amplification only.
https://www.radiomuseum.org/r/crosley_52.html

The grid leak resistor was also found to be open-circuit.  It is supposed to be 3 megaohm, so hiding a modern resistor under the grid leak resistor holder, was easily done to maintain proper operation.

The chassis is held rigid by the thick wiring to the tube sockets.  The cloth-covered wire of the tickler coil is all intact.

After the dirt was cleaned away from the chassis, and the tube sockets cleaned, all the filaments did not glow.  I had to solder a short between two of the windings on the filament rheostat.

All the wiring was intact.  This radio was probably forgotten on a shelf somewhere for many years and not abused.  The front of the radio was easily cleaned from years of dirt.

Replacement of the power switch was going to be a difficult matter.  The switch operates by pulling the stem out.  I found a piece of brass rod, put it in the lathe and turned it down.  A plastic sleeve fits over the stem, and a steel ring makes the contact.  The rear of the stem is drilled and tapped for a screw, which holds on a washer keeping the whole assembly from popping out of the front.  Only an expert is going to spot that it isn't original.  The point is that it works and I haven't done any modification that isn't reversible if I do locate an original switch assembly.

This radio was intended to run from batteries, but since Burgess has long been out of business, there's no ready source of period-correct batteries.  I want to run it off the mains anyway, so I need to build a power supply.  The power supply has to produce +5vdc for the filaments and +45vdc and +22vdc for the tubes.  Normally this would be done with 4 No. 6 dry cells and a B+ battery like the 10308.  I felt that No. 6 dry cells were pretty big, so I started looking for alternatives like a 2FBP dry cell.  Searching the internet for resources led to a page to which someone has kindly scanned in a set of battery boxes from these old dry cells.  BINGO!  However the scans weren't good enough quality to simply print out.  I spent basically a whole day re-creating the artwork for these Burgess dry cells in Inkscape vector drawing software.  The results a reasonably good.  The cells look good sitting on the shelf next to the Crosley radio.

Arts and Crafts

Filling the mockup dry cell with a block of wood and instant concrete yields a reasonable weight.

All that was missing was a speaker.  There were plenty of Atwater-Kent speakers to choose from, but I felt that a reasonable Crosley speaker would be the only acceptable solution.  The swap meets didn't yield any results, so on ebay I was able to find a good working example of a Dynacone Type F.  This has a field coil that can be powered up by the A+ supply.  I wasn't able to get exact specs, so using only 5 volts with a 500 ohm coil seemed a good limitation.  If someone can find better ratings for this field coil, I would be happy to know.  I tested the speaker using a LM385 amplifer driving into an impedance matching transformer.  It worked, but sounded terribly over-driven.  I hoped that driving it from a tube would yield better results.  Otherwise it would mean tearing the speaker down for an overhaul.

The last step was to make a power supply battery eliminator.  This will be built into a mockup 10308 Burgess battery.  Testing the radio for the first time the power supply was just built as a breadboard circuit.  The transformer puts out 190 volts center-tapped at 25 mA.  Using 22 volt zener diodes each step of voltage is available to power this radio.

The audio wasn't particularly strong, and I believe the power supply needs a larger filter capacitor to clean up the hum.

With the radio chassis sorted, the battery eliminator case needed designed.  This housing was to be a Burgess 10308 B+ battery.  This battery is quite large and will easily house the entire power supply.  An additional connector will be used for the filament voltage and hidden out of view near the 120vac cord.  I decided to make the box out of acrylic glass and finally adhere the artwork to it when everything is finished.  The scanned artwork wasn't clear enough for my liking, so I re-drew the whole thing in Inkscape for a crisp clear final product.

Attaching the artwork was done with some 3M "Super 77" spray contact cement.  The acrylic glass was first scuffed with a Scotchbrite pad so the adhesive would stick better.  The result is a nice battery box.

"Recognized by their stripes; Remembered by their service."

The circuit board and transformer was affixed to a wooden block.  The rear of the box has to allow the cord to leave through a hole in the bottom, and I decided to put a lighted power switch in it.

The fahnestock clips were installed and another test was done to insure all was right.

All was not right, however, and the speaker had to be stripped down for some adjustment and cleaning.  I ended up taking the whole thing apart and cleaning it out.  The adjustment screw needed lubricated anyway.  After that was done the volume could be adjusted much louder.

The whole setup was moved to the shack and re-assembled on a shelf for display and use.  I need to obtain some cloth-covered wire for aesthetics.  That concludes the overhaul and restoration of this fine surviving specimen.