Terminated End Fed Vee Antenna (TEFV)
Figure1 – Terminated End Fed Vee antenna
It is a travelling wave antenna, which has a constant current distribution along its length. Antennas usually used by radio amateurs are resonant standing wave types like dipoles. It is built to a specific tuned length so that a standing wave is set up on the antenna element. This is efficient and narrow band, only works on the fundamental frequency. In a traveling wave antenna there are no standing waves on the antenna element as the power that would be reflected back from the end of the antenna is absorbed by the terminating resistor. Typically this is 25% of the power applied to the antenna.
The polarization of the TEFV is a mixture of vertical and horizontal that results in a kind of elliptical polarization. The main advantages of terminated end fed V antennas are its broadband nature and no tuner requirement. It provides a non-resonant antenna with exceptionally wide bandwidth, matching a 50 ohm coaxial cable transmission line with a VSWR of less than 2:1 from 1.8 MHz to 30 MHz.
The critical parts in TEFV antenna are 9:1 unun transformer and terminating resistor. Main problem was in constructing 9:1 Unun with correct size wire for windings. Winding with wrong wire size resulted in poor impedance transformation and high through loss. The resistor value should be 10% higher than the transformer output impedance. So for a 9:1 transformer (50 ohms to 450 ohms) the termination should be 500 ohms.
Length of antenna
As per John Fisher, The lengths of antenna aren’t critical…A smaller length one will cover the same frequency range, except it will be less efficient on the lower bands. 90 feet is a good length for this antenna. Any length is extremely broadband, LF to VHF continuous coverage. Longer length gives better performance on the lower frequencies.
Thick Film Power Resistors work well up to 30 MHz. Ceramic tubular or ceramic slab resistors designed for RF use are good. For low power, 2 or 3 W carbon composition or carbon film resistors work well…A bunch of them can be stacked in parallel for higher power capability.
You mileage may vary using this antenna, but as a general coverage antenna for ham and shortwave broadcast, the simplicity can’t be beat even though an individual dipole on a specific band may out perform this broad band dipole.
Figure2- Terminated End Fed Vee Antenna (TEFV) with ground rods at both end
Figure 3 -Terminated End Fed Vee Antenna (TEFV) with counterpoise
Figure 4 – Terminated End Fed Vee Antenna Approximate gain figures
(Image courtesy & Source – John Fisher)
Bill, W9HJ did a side by side receive comparison of an End Fed Half Wave multiband antenna and a Terminated End Fed Vee broadband antenna
Frequently asked questions on TEFV – From facebook group answered by John Fisher
1. What’s the wattage of the 500 ohm resistor?
30% of the transmit power…So for 100 W, need a 30 W resistor.
2. What are the height parameters for the counterpoise? Could it be buried?
It can be ground mounted with a buried counterpoise…Ground rods at each end help too…Could put more along the length of the counterpoise.
3. What is height above ground for counterpoise? Is it critical? Can I run counterpoise just on terrace between both points?
It’s not critical…It can be mounted right on the ground if you want.
4. Is it vital the antenna is earthed at the unun end ?
It works better if it’s grounded…It will still work without a ground with counterpoise.
5. Can we use wire wound resistor as terminating resistor?
Wire wound resistors aren’t suitable, since inductance of wire wound makes it unusable.
6. Does the counterpoise need to be elevated above ground?
No it can run along the ground…Two ground rods without a counterpoise may work too if the soil conductivity is good where you are
7. Is the counter poise required if using good ground rods at both ends? UNUN from wire to ground at one end and wire to resistor to ground at the other. Running a counterpoise from ground to ground isn’t practical in my situation.
If you have good ground conductivity it probably won’t make much difference if you use a counterpoise or not…Use 10 ft. ground rods at each end.
8. Did any of you measure the field strength of this antenna. Sure, the SWR seems OK, but is it radiating, and what is the efficiency?
Depending on the length of the antenna and the band used, some of the power is converted to heat in the resistor. The losses in the resistor are always reasonable…Worse case is 30% of the transmit power…That’s the maximum power rating of the resistor…Losses are lower than that at most frequencies…Even at 30% loss, that’s a drop in signal of 1.55 dB, about 1/3 of an S-Unit…It’s like the difference between a 100W transmitter and a 70W transmitter.
9. Is it critical to have equal lengths of wire on both sides of the apex?
It may cause directivity on certain bands depending on how far off centre it is. Refer below image
Fig 5 – Terminated end fed antenna directivity
10. The resistor gives a low SWR across a wide frequency range. What’s the tradeoff in performance?
There is no tradeoff in performance…The performance is better than most ham antennas…The termination only absorbs power on frequencies where the SWR is high…On other frequencies where the SWR is low, that power is radiated…The maximum loss in the resistor is 30%…That’s what it is rated.
Best case scenario would be the antenna is resonant without the resistor could be as low as 12.5% power wasted. The tradeoff is no or little reflected wave coming back down the feed line. This type of antenna to me is most useful on the bands where a Tuned Resonant antenna has to narrow a bandwidth.
11. Do you use a tuner with your TEFV?
No…It just works everywhere, 1.8 to 54 MHz continuous coverage without adjustment.
12. Provide suggestions for resistors suitable for terminated end fed antennas.
Thick film power resistors and carbon tubular or carbon slab non inductive resistors…Thick film resistors require a suitable heatsink…Carbon noninductive resistors don’t need a heatsink, but the surface temperature runs around 180’C (350’F), so this must be taken into account when mounting. Terminations can also be made by stacking 2 W or 3 W metal film resistors.
I tried terminated end fed antenna with ubitxv3, gave good results. My setup is ubitx+PA150 W linear+ATU100, 9:1unun+70feet inverted v wire+470ohm power resistor(made using ten parallel 4.7k 2watt resistors). Only issue noted is CMC at high power.
Figure 5 – TEFV – SWR plot by VU3DXR
1.TEFV Facebook group – (1) Terminated End Fed Vee Antenna | Facebook