THE END FED ZEPP

 

W4ULD 08-19-2009

 

 

In the early days of Ham radio the Zeppelin, Zepp, or end fed Zepp was a popular ant-  enna. It is diagrammed in Figure 1 for 7.1 MHz. as modeled with EZENEC+4 antenna program. The Zepp got it’s name from it’s use as a trailing antenna on Zeppelin airships. Thus it is an end fed antenna usually cut for 40 M. For Ham use, it was originally fed with a ¼ WL of open wire line of about 600 ohms. At its fundamental frequency the flattop is about ½ WL long and the feeders about ¼ WL long. It  was originally tuned with the balanced tuner described under Antenna Tuners. Series tuning (a capacitor in series with both feed lines) was employed when the antenna system was electrically too long and thus contained inductive reactance which had to be tuned out. When the system was electrically too short or contained capacitive reactance. A parallel capacitor across a tapped inductor  was required as an antenna tuner. Thus to properly match the total syatem to the transmitter, one had to select parallel or series tuning and select the proper taps on the inductor. This was initially tedious but once selected could be recorded for each frequency used. An RF ammeter in each feeder was adjusted for maximum and equal current.

 

Open wire line is still the best feedline; however, modern day “450” ohm window line may be used with a modern broad band T-network tuner with a 1:1 or 4:1 balun at the end of the feedline. Most tuners have a good balun already installed. However, when the internal balun is used, some feedline radiation will be brought into the shack. It is usually best to use an external balun outside the shack and run a good grade of coax to an unbalanced input of the tuner. The coax length should be no more than 10 ft. to keep losses down.

 

The 40 M Zepp, just like the center fed Zepp, can be used on all bands; However, feedline radiation will be almost cancelled on only 40M and  odd multiples. The antenna can also be used on 75-80 M. The total wire in the system (the flattop plus the feed line) is ½ WL on 80 M so the system can be tuned to 75-80M as long as one is willing to accept the feedline radiation and the reduced gain on 75-80M. The horizontal radiation pattern on 40 M is shown in Figure 2. This is the typical dipole pattern with most radiation straight up. Therefore the plot is made at 45 degrees elevation. The broadside gain is 6.34 dBi. The 80M pattern is shown in Figure 3. Maximum gain was also straight up so the plot was made at 45 degrees elevation with a gain of 2.61 dBi or 3.73 dB less than 40 M. This is less than one S unit, so the 40M Zepp is fairly good on 80M. for a half size antenna.

 

As seen by the current patterns in Figure 4, the currents on the feed line almost cancel at 40M and at 15 M (an odd multiple of 40M, Figure 5 but do not come near canceling on 10 M, an even multiple of 40M, Figure 6).

 

To complete the picture the horizontal radiation patterns at 20M, 15M and 10M are shown in Figures 7, 8, and 9.

 

When I was first licensed and living in Waynesboro, Va., the end fed Zepp was the most convenient antenna to use. The 40M CW band was very popular, so I bought an ARC5 transmitter which covered the 40M band and a surplus BC-348 receiver. At that time the 40M band was 100% CW. The only phone station in the band was Radio Moscow. Everybody used their frequency to “tune up on”. I link coupled the ARC5 to the end fed Zepp and used the pencil technique to tell when RF was going into the antenna. The pencil technique consisted of placing the point of a lead pencil on the plate cap of the 1625 finals and drawing a spark. The antenna coupling was being adjusted during this procedure. When one could no longer draw a spark, the antenna was “tuned” because the RF was going into the antenna..

 

40M CW was great back then. At sometime during the day or year, one could work any place in the world.. The end fed Zepp worked beautifully. When I advanced to Class A after the required one year as a Class B, and I had bought a Viking II, I found that the 40M Zepp would load on 75M; so I started checking into The Virginia Phone Net with no difficulty.

 

So I am convinced that the end fed Zepp is a good antenna, at least for 40M and 75M. I don’t remember using the antenna on bands below 40M. About that time I moved to Seaford, DE, and had to use an end fed long wire. But that’s another story.