Topband: Topband Tower Antenna With Two meter Vertical

[Herb Schoenbohm]

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)
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