[QCWA] Terminated folded dipoles.

[Jeffrey D Angus]

I think it's doing moderately well.
<http://pskreporter.info/pskmap.html>
If you fill in / pull down the options at the top of the page.
On 20m show signals rcvd by the callsign wa6fwi using PSK31 over the 
last 24 hours.

To recap the antenna installation:
It's roughly 20' above ground running from North to South above the East 
wall of the
shop in Ranger, TX. It's 123' overall length with a spacing of 12" 
between the wires
and terminated with an 800 ohm 100 watt non-inductive resistor and fed 
with a 16:1
current balun. There's roughly 50' of RG-214 coax running from the 
antenna to the
Icom IC-761 transceiver. The software used is Ham Radio Deluxe in the 
Super Browser
(I.e. NSA vacuum cleaner mode) and updating information to the 
pskreporter.info site.

L.B. Cebek W4RNL SK, did a write up on the terminated folded dipole:
<http://pe2bz.philpem.me.uk/Comm/-%20Antenna/Info-907-AntennaBasics-Advise/ModelingTheT2FD/t2fd.html>
It was his comments that made me go with the 800 ohm termination and 
16:1 balun.

The 123' length was based on the assumption that the door in the middle 
of the shop
was indeed in the center. It was not. It's about 7' closer to the front 
of the building. So
the antenna ended up being 123' rather than 137' long.

That being said, the "calculated" bottom frequency of the antenna is 
roughly 2.75 MHz
which puts it far enough below to not appreciably affect power 
absorption at 3.5 MHz.

The SWR as measured with the transmitter putting out 25 watts was a 
consistent 2:1
to 1.5:1 over the entire range from 1.8 to 30 MHz. The internal 
auto-tuner in the IC-761
has no problem trimming that down to 1:1 on all bands. A greater than 
four octave span.

As a receiver only antenna, it appears to be functional from 500 KHz to 
150 MHz. For a
greater than 8 octave span.

Mike Gregory, KB3IYQ, ran the "as built" antenna through NEC for me and 
as we suspected,
at the height it's at, it acts like an Near Vertical Incident Skywave 
antenna. It also appears to
be fairly omnidirectional.

Previously, I had worked three stations on PSK31 on 20 meters, two being 
to the East in
Tennessee and Kentucky, and one being to the North in Missouri. I am 
waiting on some
new hardware to arrive to get the station back in the transmit mode with 
the HRD Suite.

As predicted, the "noise floor" on the IC-761 is about 2 S-units below 
the same receiver
at the house using the 102' doublet with 450 ohm window line and an LDG 
Z-11 Pro II
tuner. This would be similar to putting a 12 dB attenuator in series 
with the feed line.
For example, an S7 noise level and an S9 signal would be an S9 noise 
level and S9 +12 dB
signal level at the house with the other antenna. There doesn't appear 
to be any appreciable
improvement in signal to noise ratio between the two antennas.

Commercially, the terminated folded dipole is available in both 90' and 
45' lengths and
uses a 450 ohm termination and a 9:1 balun. They also vary in price from 
$300 to $1300.

In my opinion "Is the terminated folded dipole" the "Whiz bang DX and 
tactical antenna"
the commercial vendors claim it is? In a word, no. There are certainly 
better antenna
designs out there. However, as a "no tune" broadband antenna that works 
surprising
well? A definite yes.

Jeff-1.0
wa6fwi