> Garry wrote:
>> Years ago, Bill Orr wrote a book titled
Wire Antennas. On page 104 in
>> this book, he described an
inverted-L type of antenna called a Twin Lead
>> Marconi built
using TV win lead in the L section with a length of single
>>
conductor wire making up the last 17 feet of the L with a few radials.
>> It was suppose to give a reasonable match to 50 ohm coax. Has
anyone on
>> this forum ever built this antenna and what were
the results?
>>
Herb, KV4FZ wrote:
>> Gary,
For portable use this is a fine antenna IMHO. This is precisely
>> the antenna I used for numerous DX-Peditions from South America
and rare
>> Caribbean Islands in the 60's. I was compact to
pack along with the
>> gear and was easy to get to work with a
nearby palm tree on the beach.
>> The twin lead Marconi (mine
was 1/4 wave of 300 ohm twin lead over the
>> entire length)
was an easy match for my Drake's T-4XC Pi network which
>> fed
the antenna directly sloping out of the cottage window to the
>> highest palm tree on the beach. For portable or vacation use
antenna
>> worked well and I was able to give many new
countries to those chasing
>> DXCC on 160.
>>
>> I do recall however that the theory that the ground losses were
reduced
>> by a 4 to 1 base impedance multiplication factor
has been disputed. I
>> always carried along some small 1/4
wave bell wire radials which
>> terminated at the rig ground.
The twin lead Marconi may improve on the
>> rigs ability to
match the antenna with a built in tuner but you can
>> raise
the impedance by making a single wire the antenna longer like 180
>> feet. This antenna can be generally brought to resonence by a
series
>> variable capacitor to remove the inductive reactance
it imposes.
The problem with a 180 foot long inverted-L
antenna is that over half of the wire is horizontal so the majority of the
radiation is nearly vertical. A series capacitor with a 150-160 foot
long inverted -L, preferably at least 70 foot up and the rest horizontal
will give a reasonable match and a lot less sky wave, with the high
current point 20-30 feet above ground.
>>
>> The
twin lead is two close spaced for much bandwidth improvement and the
>> ground loses are a factor of the radial system. But for certain
>> applications it is a good antenna to consider.
>
73
>
> Herb, KV4FZ
>>
Again, use as
many radials as possible. at least 30, each 65-70 feet long is a
reasonable minimum per ON4UN's many Low Band DXing books.
73
& GL,
George K8GG
>
>
>
>
>
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