The Florida Boys Contest Filter Project

In addition to the Florida Boys contesting from their club station at the American Red Cross in Melbourne, Florida, many of the Florida Boys contest from their homes as SO2R and one is now playing with SO3R. One item we found we all needed were contest filters. There were some already available on the market but the group felt it would be fun to design our own filters for the group.

AF4Z did a basic design using the ARRL Designer program. Several designed were tried but finally selected a top C-couple design that reduced the circulating RF currents and provided power margin so the higher power transceivers could use the filters without damage.

Once the design was done, parts were ordered and the paper design was turned into hardware. Plots were made and parameters were measured to insure the units were performing as designed. To insure the design, tests were run using 300 watts at a 50% duty cycle for 1 hour. There was minor heating of the unit which was expected but no change in performance.

Now that the designs were done and tested, the needed components had to be located for the kits. Parts were found locally and in catalogs. The cost of building sets of filters was then determined. It was decided the best way to do the parts purchase was to offer the filters in either a 5-Bands Set (80-10) or a 9-Band Set (160-10 with WARC bands). Some wanted just the 5-band set while others wanted the full set of 9 filters.

Aluminum box material was all found locally. Some of the other hardware was available locally and some was ordered from catalogs. Most all the electronic parts were ordered from catalogs except the coils. The coils were made from copper wire obtained from the local Home Depot and wound on a home made coil winder. K4PX built a coil jig that allowed him to wind the coils both left and right hand allowing the coils to be made in sets. This allowed each side of the filter to be made as mirror images of each other and cause less confusing in assembly. AF4Z designed the PC board used in the filter. It was made of a piece of G-10 glass board material and was designed such that it could be made in minutes with a razor and a soldering iron. This saved having to have custom circuit boards made.

On two different days after our weekly Florida Boys luncheon, we all got together at K4QD’s house and cut the material and drilled and punched holes to make up the Filter cases. We would each take a task and had an assembly line going for cutting, drilling and filing.

Once all the ordered parts were received, we again met at K4QD’s house and had a Kitting Party. All the hardware, caps, coils, PC board, mounts, cases and covers were all put into clear plastic bags as kits. Most everyone who was purchasing the kits came over to help bag the kits. Each kit also contained a sheet of paper with all the detail information that would be needed to assemble that kit like the capacitor values, Number of turns of the coil, tuning frequency, etc. This made the kits easier to understand and tune.

AF4Z had written the instruction manual and details on how to avoid problems but as well as some things are planned, there are problems. The problem that occurred the most was soldering the tap on the coil in the correct place on both coils. Several times it was found that filters would not tune properly and after looking closely, most every case, someone had their tap on the coil correct on one side and wrong on the other.

To date, several people have not had time to build their filters. Most have completed their units and are pleased with their results. One set is on it’s way to Haiti for a workout with K4QD and I’m sure the Florida Boys will be using them in upcoming RTTY , CW and SSB contests.

If you would like more information on the AF4Z HF Contest Filters, you can email Don Winn (AF4Z) at: af4z@cfl.rr.com or go to his website at http://www.af4z.com.