I have had two requests for the Telrex 3L Yagi dimensions
so here they are for anyone interested. Tom N4KG
>>>>>>>>>>>>>>>>>>>>>>>
The standard Telrex 3L20 is model 20M326 on a 26 ft boom,
3 inches o.d. with 3.5 inch sleeves at each element.
MY Telrex 3L20 is a special design on a 24 ft boom that was
used for "Luxemburg Effect" studies (ionospheric Intermodulation)
at Syracuse University. The antennas were sold in 1962 and I
purchased 5 of them from the University in 1972.
The elements are mounted through the boom with 12 inch sleeves
of 1.5 inch o.d. at the center of each element. The DE is offset
10 inches toward the DIR and the T-match is offset 7 inches
toward the DIR (3 inches from the DE). The element tips have
'coronna balls' 1-1/4 inch in diameter, tapered down to a 3/4 inch
o.d. shaft that inserts into the end of the last section of tubing.
Spacing is as follows:
REF to DE 154 inches (12 ft 10 inches) center to center
DE to DIR 136 inches (11 ft 4 inches) center to center
Element dimentions measured from boom center are as follows:
REF:
72 inches by 1-3/8 inch o.d. (don't forget the 6 X 1-1/2 in. overlap at
center)
68 inches by 1-1/4 inch o.d. (last 5 inches tapered to 1 in. o.d.)
73 inches by 7/8 inch o.d. including the 1-1/4 in. corona ball at the end
DE:
72 inches by 1-3/8 inch o.d. (don't forget the 6 X 1-1/2 in. overlap at
center)
68 inches by 1-1/4 inch o.d. (last 5 inches tapered to 1 in. o.d.)
66 inches by 7/8 inch o.d. including the 1-1/4 in. corona ball at the end
DIR:
72 inches by 1-3/8 inch o.d. (don't forget the 6 X 1-1/2 in. overlap at
center)
68 inches by 1-1/4 inch o.d. (last 5 inches tapered to 1 in. o.d.)
55 inches by 7/8 inch o.d. including the 1-1/4 in. corona ball at the end
These are the dimensions I have written from my notes.
I notice that the dimensions on one that I have on the ground
are slightly different (REF tip 72 in., DE tip 60 in., DIR tip 55 in.)
Notice REF / DIR lengths approximately 10% difference.
de Tom N4KG
>>>>>>>>>>>>>>>>>>>>>>>>
Telrex 15M317 (3L15 on 17 ft boom)
Common center element piece 72 inches by 7/8 in. o.d.
REF 66 1/4 inches by 3/4 in. o.d.
DE 62 1/4 inches by 3/4 in. o.d.
DIR 56 1/4 inches by 3/4 in. o.d.
T-Match 47 1/2 inches by 7/8 in. o.d.
Boom 2 inch o.d. with 2.5 inch o.d. sleeves at each element.
Elements are mounted through the boom.
Spacing not recorded.
Assume DE offset toward DIR.
Notice REF / DIR lengths approximately 8% difference
de Tom N4KG
>>>>>>>>>>>>>>>>>>>>>>
Telrex 10M313 (3L10 on 13 ft boom)
Common center element piece 72 inches by 5/8 in. o.d.
REF 53 inches by 1/2 in. o.d.
DE 49 inches by 1/2 in. o.d.
DIR 40 inches by 1/2 in. o.d.
T-Match 41 3/8 inches by 1/2 in. o.d.
Boom 2 inch o.d. with 2.5 inch o.d. sleeves at each element.
Elements are mounted through the boom.
Spacing not recorded.
Assume DE offset toward DIR.
Notice REF / DIR lengths approximately 13% difference
for greater % bandwidth required on 10M (28.0 to 29.6)
de Tom N4KG
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