T2FD Antenna

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From: Rogerio Gonzaga (gonzaga@med.up.pt)
Date: Thu Jun 27 1985 - 06:03:30 EDT


Hi, Bill (K3AS), Dave (W0CH), and all the guys,

About the T2FD antenna discussion, it is, I believe, a quite popular aerial
in the land-based Portuguese Navy Stations. A similar aerial is manufactured
by Yaesu under the name of YA-30, I think it is the very same antenna, with
a small difference of the Navy stations, in that it apparentely has a 12:1
Balun at its feeding point, enabling to feed it with 50 ohm coax. I suppose
it is not directely intended for ham use, so it can have to be specifically
ordered in an Yaesu dealer. I am aware of this because indeed I own one and
use it as a secondary antenna, and have my opinion about it.

The accompanying literature is very scarse, and the type of balun (12:1) and
the loading resistor (600 ohm) have been deducted by me after some research,
as they are not stated on the leaflet. It is basically an aperiodic antenna
pretending to cover 2 to 30 MHz with less than 1:3 SWR in any frequency and
less than 1:2 under the 17 MHz, without the help of any ATU. I have been
using it for a while, and I can confirm that it accoplishes the SWR
specifications. In the higher frequencies (lets say, over 7 MHz) it performs
quite nicely, but performance seems to drop in lower frequencies (although
the SWR drops as well, in the 80 and the 160 meters being virtually 1:1). It
is rated to 150 W PEP (in my search I found that the loading resistor should
be able to dissipate half the transmitting power, so I think it is probabily
rated to 50 to 75 watts). My antenna measures about 25 meters which,
according to my search, should allow its use until the 75 meters band (it
should be supposed to have one third of the higher working wavelenght). This
could explain why I am not very happy with it on the 160 meters.

Mine is mounted as a flat top at about 12 meters high, and it is used as a
secondary antenna as I have an homemade FD4-type Windom hanging as an
inverted-V at 18 meters AGL (with an huge 6:1 brand-new surplus military
balun) and a Marconi, also slooping to 18 meters, for the top-band, and
those perform obviously much better (the higher the better...); however, the
T2FD performs quite nicely (specially in the higher bands), and has the
advantage to be always acceptabilly tuned for a fast response, lowering the
SWR to 1:1 being possible with an ATU for more prolonged working periods.

Sorry by the bandwith, and I hope the information is usefull. The usual
disclaims (I have no interest in Yaesu, and so on), and best 72/73 de

Roger, CT1ETT


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