IMPORTANT NOTE: I have written permission to use all of Annecke's original publications and pictures on my web site. This permission was granted by Fred Annecke, Alfred Annecke's son.
[ Type 218 ]
The Annecke Differential - Transmatch
(Type 218) was a very small machbox based on the Differential-T-Network circuit.
This tiny 100w matchbox was well suited for matching antennas which were "supposed to be 50 Ohms" (but were not). Applications include 80m dipoles, trap beams, Windoms, etc. Anything which is near 50 Ohms but due to narrow bandwidth of the antenna or other reasons was less than perfect SWR across the band.
Of course it could also match longwire antennas up to about 2000 Ohms. Though its matching range was not quite as wide as most classical T-Network matchboxes, this still covered a broad range of antennas.
- Bands: 80 - 10m
- Power Rating: 100w
- Impedance Matching Range:
- 50 to 200 Ohms Coaxial
- Up to 2000 Ohm Longwire Antennas
- Size (Width/Heigth/Depth): 20 x 8 x 18cm (8" x 3" x 7")
The Matching Range specifications are unclear to me. I see no reason why a higher impedance on the coax could not be matched, other than you really would not want to have more than 4:1 SWR on a coax-fed antenna. If you do, then maybe you should fix your antenna.
The beauty of the Differential T-Network, in contrast to the more popular T-Network, is it is much easier to tune. There is only one combination of settings which gives you the lowest SWR and this coincides with the most effecient setting. This makes it much easier to use in mobile applications where tuning should be quick and easy.
I used this matchbox in my RV for matching the mobile whip, which especially on 80 and 40m did not have much bandwidth. It was perfect for that task. Once the match was found, you could QSY up or down the band using only the roller inductor to keep the antenna matched. There was no need to re-set the variable capacitor. Unfortunately when I sold my RV, I forgot to remove the matchbox and now it's gone.
The instruction manual was very brief - just 2 pages.