Don't worry Wayne I have a 80 foot tower with a tribander mounted on the top that I use shunt fed on 160. i have been able to operate in contests with KP2MM using the triband while I am blazing away on 160. (I use Beverages on RX) On the three bands that use the tribander, that are also hot with 1KW on 160, I measure about .3 watts on a Bird wattmeter on the cable coming from the tribander. Most of the time, and this should not be a problem on two meters, there is no IX at all. In the few cases I just put a 160 meter quater wave open stub on the transmission line with a Tee connector coil up behind the 20-115-10 meter radio. The length of the RG-58 A/U or RG-8X stub cable is determined by dividing 1.825 into 234 times the Velocity Factor of the cable. In the case of plain RG-58 that turns out to be .66 and with foam cable it is a higher amount. A small box with a variable cap and coil inside was also considered for the construction of a 160 meter trap. I found about 30db reduction with the 1/4 wave stub and that shoulod be ample for your two meter operation on the same tower. It may also be helpful to ground the 2 meter transmission line shield to the tower at the base. Some prefer winding coax in a choke but the added feedline length loss may not be to your liking.
Herb Schoenbohm, KV4FZ On 4/15/2012 11:49 AM, Wayne Rogers wrote: > Maybe a bit off topic, but I'm hoping someone can give me some insight. > > I use my 90' tower as a vertical on topband. It's base is grounded, and I > feed it with a gamma match. Works great. OK so far. > > I want to put a two meter vertical on the tower which will be used for ARES > (packet, continuous 24/7 connected up to the two meter radio. > > My concern is protecting the two meter radio when I'm transmitting 1500 watts > into the tower on 160 meters. Would like to hear from anyone who is doing > this - will a simple high pass filter at the input to the two meter radio > suffice to protect the radio from 160 meter RF? > > Also - on the antenna installation. Typically the two meter vertical's outer > conductor will be grounded to the tower at the base of the two meter antenna. > I could also keep the two meter antenna insulted from the tower for its > entire length up to the lightning protector just before it enters the house. > What's the recommended practice? Ideas? > > Thanks, Wayne N1WR (160 op and also AEC Calvert Co. MD) > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
