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
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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