The DX Engineering Thunderbolt antenna includes a means to resonate and
match the antenna using a series inductor and a shunt inductor. *It does
not require a balun*.
See the manual:
https://static.dxengineering.com/global/images/instructions/dxe-160va-1_jj.pdf
An EZNEC model shows it to be resonant at 1825 kHz with an input impedance
of *4.0 ohms*. Adding 2.5 ohms of GND + coil loss it shows a 2:1 VSWR
bandwidth of 40 kHz. This agrees with the DX Engineering SWR graph on page
43. If your installation has 2.5 ohm base referred GND/coil loss the
radiation efficiency will be ~60%.
Dave KH6AQ
On Sat, Dec 5, 2020 at 5:39 AM Wes <wes_n7ws@triconet.org> wrote:
> Or reduce the loading to present a capacitive reactance at the feedpoint
> and
> shunt it with an inductor. Functions as a step up L-network and presents
> a
> ground at DC. That's what I do here.
>
> Wes N7WS
>
>
> On 12/5/2020 7:35 AM, Rudy Bakalov via Topband wrote:
> >
> > P.S. If your vertical has a good set of radials, you will see about 35
> Ohm feedpoint impedance. You may want to wind your own unun using Jerry
> Sevick’s cookbook
> >
> >
> http://www.introni.it/pdf/Amidon%20-%20Transmission%20Line%20Transformers%20Handbook.pdf
> >
> > or buy a readymade 35 to 50 Ohm unun from balundesigns.com
> >
> > The third option is to build a coax transformer per PA0FRI.
> >
> >
> >
> > Rudy N2WQ
> >
> > Sent using a tiny keyboard. Please excuse brevity, typos, or
> inappropriate autocorrect.
> >
> >
> >> On Dec 5, 2020, at 8:37 AM, David Aslin G3WGN <david@aslinvc.com>
> wrote:
> >> I'm building a contest station and the time has come to make a choice
> of 160m TX antenna. Looking at DXE Thunderbolt I note that the capacity hat
> extends to a significant distance down the vertical section. It's my
> understanding that will shield some of the radiation from the upper part of
> the vertical. Alternatives like a vertical tee would not have this issue.
> >> Is my understanding correct?
> >>
> >> I'm considering a commercial antenna as high strength telescoping
> antenna tubing is unobtanium in UK. My QTH is an exposed windy location so
> strength matters!
> >> 73, David G3WGN M6O
> >>
> >>
> >>
> >> Sent from my Galaxy
> >>
> >> _________________
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