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 <[email protected]> wrote: > Absolutely - That is what I do > > ------------------------------ > *From:* [email protected] [mailto: > [email protected]] *On Behalf Of *[email protected] > *Sent:* Monday, December 27, 2010 9:26 PM > *To:* Cormac Gebruers > *Cc:* [email protected] > *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 > > ------------------------------ > > No virus found in this message. > Checked by AVG - www.avg.com > Version: 10.0.1191 / Virus Database: 1435/3342 - Release Date: 12/27/10 > -- Regards Cormac (EI4HQ) [Cork/UTC+] NNNN++++ http://ei4hq.shacknet.nu/ _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
