Terminated Delta Loop @ DL4EAX and DM4EAX in April 2021
Picture of my setup, you can see the box with the resistor on the top and
the box with the balun at the lower part of the mast.
HFLINK (search for BBTD Inverted V Delta Wing): http://hflink.com/antenna/
Based on a discussion with Tom, (DF5JL) at the HAMRADIO in 2019 about the T2FD, I got curios.
After moving to the new house, I remebered this dicussion and began to look for T2FD antennas.
To get as much wire as possible into the air and to avoid usage of spacers with a high wind load,
I thought about a terminated loop. However, the BBTD Inverted V Delta Wing looked more promising
with regards to the mechanical realization. Tom told me it would not matter if the resistor is on the top
or not, I should do what I could build better.
Mast hight: 9m
Base space: 28m
Due to the nauture of a terminated antenna, the size does not need to match excaclty.
Get as much wire into the air as possible. As long as the wire length is equal or greater
than one wavelength at the lowest working frequency it works with a quite good efficency.
So with a circumfence of 50m, there will be a performance drop on 80m, not to talk about 160m.
With an output power of 100 Watts, a resistor of 50 watts should be sufficient.
For example "RTO 50F 1,0K Thick-film resistor, 50 W, TO220 - 1.0 kOhm, 5%".
I have taken 4 thick-film resistors with 30 W each to be on the safe side.
Maybe this is a bit heavy on the top of the tower and I will change to a single 50 W resistor later.
I am using a 1:16 Unun in combination with a choke balun.
Mechanical realization for resistor and balun:
The challenge is to get the resistor and the balun into a waterproof housing and to keep the
mechanical forces away from the electrical connections at the same time. So I remembered the
housing of mast preamps that are used on VHF and UHF.
Anything will do as long as it survives the mechanical forces and does not have an excessive resistance.
Since I do not have the space to do additional guying of the mast, I have chosen DX-WIRE Premium since
it has the strength of a guy wire, good electrical characteristics and is nearly invisible.
Measurement of SWR and R, X and |Z| done with a RigExpert AA-54:
0 to 54 MHz:
Already before doing the measurements, I had the feeling that the antenna works very good on 20 and 40m.
On 80m, the TX performance in SSB is for sure below a full size dipole. However digimodes and CW work very well.
Due to the nature of a closed loop in combination with a termination, the antenna is very quiet compared to dipole.
So doing CW is a real pleasure now and SSB signals are much better to understand due to the better signal to noise ratio.
It is expected that digital modes will also benefit from that.