All,
Thanks for the comments & suggestions.
The current solution is built using a 6m telephone pole topped by a 12m
spiderbeam pole with a 1m whip addition. This approach has survived the
worst weather has thrown at it but the price for that is it is very bendy at
the top - there is no way it'll support an isolating coil for 80m nor top
hat capacitance wires. I've tried top hat wires using very light gauge wire
and it's a non runner.
The fundamental issue for me (from a practical standpoint) is mechanical
survivability. As EI7BA will testify, we get hammered here by North Atlantic
gales in the Winter. If the antenna doesn't stay up, then I can't work
anything at all :-)
The antenna is a good performer on 80m, but base loading it on 160m has led
to pretty poor results so far. I think I need to re-engineer the existing
design so I can insert an isolating coil at the top and attach top load
wires...
BR & HNY to all
Cormac, EI4HQ
On 28 December 2010 03:40, Scott MacKenzie <kb0fhp@verizon.net> wrote:
> Absolutely - That is what I do
>
> ------------------------------
> *From:* topband-bounces@contesting.com [mailto:
> topband-bounces@contesting.com] *On Behalf Of *k8gg@voyager.net
> *Sent:* Monday, December 27, 2010 9:26 PM
> *To:* Cormac Gebruers
> *Cc:* topband@contesting.com
> *Subject:* Re: Topband: 80m quarter wave on 160m... can support guys be
> used to provide capacitance loading?
>
>
>
> Cormac, EI4HQ wrote:
>
> >
> > I've an 80m vertical that
> I want to use as my transmit antenna for
> > topband.
> >
> It's about 20.5m high.
> >
> > For reasons of weather
> survivial and because of the antenna construction
> > my
> >
> plan is to base load for 160m with all the inefficiences/compromises that
>
> > flow from that decision. However, I've been wondering about
> something;
> >
> > The antenna is supported by three
> non-conducting guys. The guys are
> > connected to the antenna at
> 13.5m above ground. They are angled downwards
> > at
> >
> about 45 degrees to support points on the ground. This leaves 7m of the
>
> > antenna above the guy support point.
> >
> > 1.
> Could the guys (replaced with conducting material of course and
> >
> insulted before connection to ground anchors) be used to provide some
> > kind
> > of capacitance loading on 160m i.e. to provide a
> capacitance "skirt" as
> > opposed to a capacitance
> "hat" and thereby reducing the size of coil
> > needed
>
> > at the base for 160m?
> > 2. Would this be any more
> efficient than a well made high Q coil at the
> > base?
> >
> 3. Has anyone done this? How did you deal with practicalities like
> > taking
> > the guys out of the circuit when the antenna is
> being used on 80m?
> >
> > --
> > Regards
> >
> Cormac (EI4HQ)
>
> Cormac, et.al.,
>
> I would suggest
> leaving the 80 meter antenna as described and not using the guy lines
> as loading wires for 160 meters...
> I belive one is better off making
> a heavy duty 80 meter trap for the top of your vertical and then adding
> one or more top loading wires to bring the antenna to resonance on 160
> meters. The trap will add about 5 meters/16 feet of inductive
> loading, so a single top loading wire would be only about 14-15
> meters long... 3 or more toploading wires would probably be about 9
> meters long each, assuming they are nearly horizontal or slope down at
> less than 30 degrees. Steeper sloping means longer top loading wires
> to get the effective length(s).
>
> Otherwise base load the
> vertical as you describe and consider two coils in series to get the 50
> ohm match at the antenna.... one in series with the antenna to get the
> loading and one across the feedpoint to ground to bring the impedance up
> to 50 ohms... Alternately, resonante the antenna at about 1800
> KHz or lower and put a shunt capacitor across the feedpoint to ground
> to get the 50 ohm match up in the band.
>
> I like the two coil
> approach as it is a short curcuit for lightening.
>
> YMMV 73 and HNY 2001
>
> George K8GG
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
> ------------------------------
>
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--
Regards
Cormac (EI4HQ)
[Cork/UTC+] NNNN++++
http://ei4hq.shacknet.nu/
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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