Topband: no response to query: feeding phased verticals at half wave spacing

[ZR]

----- Original Message ----- 
From: "Rik van Riel" <riel at surriel.com>
To: <topband at contesting.com>
Sent: Thursday, November 24, 2011 10:59 AM
Subject: Re: Topband: no response to query: feeding phased verticals at half 
wave spacing


> On 11/22/2011 08:06 PM, Gerry Treas, K8GT wrote:
>> Hi Dale,
>>
>> I'm no antenna expert, but certainly read as much of the experts 
>> publications as I can get my hands on, but having a Teflon brain, it 
>> doesn't stick very well.
>>
>> That said, the ARRL Antenna Book has a page that shows the patterns of 
>> various spacings and phasings of vertical antennas, which I found very 
>> enlightening.
>>
> Enlightening, but also somewhat misleading...
>
> The patterns in the ARRL Antenna Book are correct if the
> current in both elements is the same.
>
> However, if you feed an array of antennas with delay lines,
> those delay lines will act as impedance transformers for
> the antenna impedance of each element (like all feedlines do).
>
> This can result in each element getting different currents,
> and the pattern no longer being what it was.
>
> This makes feeding a phased array with delay lines much
> trickier than one would imagine at first glance.

For 2 elements coax phasing is sufficient if 15dB or a bit better F/B is 
acceptable especially when using low noise receiving antennas. I was more 
than satisfied with a pair of sloping wires on 160 (NE/SW cardiod, NW/SE 
figure 8) and was happy to not be wasting power in a dummy load.
I used a noise bridge and the rig to cut the lines to exact lengths and 
about 18dB FB was the norm, sometimes a bit better or worse but I could also 
load it up to about 1950 in a contest without wasting more RF in a tuner.

Carl
KM1H