[NLRS] 70-cm Antenna Dilemma

[Carl Estey]

In the Spring of 2005 I obtained a used 16-element 432-Mhz yagii of un-known
design.  When I got it up on a 40’ tower and fed it with 65’ of LMR-400 I
found performance over a 50-mile path very poor.  Last week I put up a 48’
piece of Andrew 7/8” Heliax and a 15’ LMR-400 Ultraflex jumper at the
antenna the best I can do on a fifty mile path with 100-watts at both ends
is 20-24 db above the noise – somewhere there is a loss of 40-50 db!!
Physical exam of the antenna shows nothing wrong, which makes me think the
balun is the problem – and it is a ½ diameter six-inch long tube that is
sealed (soldered) on the end with the female N-connector.  One the opposite
end of the balun from the N-connector are flat zig-zagged metal straps that
go to several of the elements.  Does anyone recognize the design of this
16-element antenna and have any specs on it?

 

Yesterday someone loaned me a 25-element 17’ 5” long K1FO-style yagii.  I
tried the same path with similar poor results.  Adjustment of the T-match
failed to provide proper SWR at 432.1 and the lowest point was at 430 Mhz
despite a large amount of re-adjustment.  The measurements (made mostly in
the dusk so forgive small errors) are as follows:  

 


70-CM K1FO-style Yagii Measured Dimensions


 

 

 

 

 


Element

Length

 

R to DE

4 1/4


R

13 1/2

 

DE to D1

2 3/4


DE

13 1/4

 

D1 to D2

3 3/4


D1

12 5/8

 

D2 to D3

5 1/4


D2

12 1/8

 

D3 to D4

6 5/8


D3

12 1/8

 

D4 to D5

8 1/8


D4

12    

 

D5 to D6

10 1/8


D5

11 7/8

 

D6 to D7

10 1/8


D6

11 5/8

 

D7 to D8

10 1/8


D7

11 1/2

 

D8 to D9

10 1/8


D8

11 3/8

 

D9 to D10

10 1/8


D9

11 3/8

 

D10 to D11

10 1/8


D10

11 1/4

 

D11 to D12

10 1/8


D11

11 1/8

 

D12 to D13

10 1/8


D12

11 1/4

 

D13 to D14

10 1/8


D13

11 1/8

 

D14 to D15

10 1/8


D14

11 1/8

 

D15 to D16

10 1/8


D15

11 1/8

 

D16 to D17

10 1/8


D16

11 1/8

 

D17 to D18

10 1/8


D17

11 1/8

 

D18 to D19

10 1/8


D18

11 1/8

 

D19 to D20

10 1/8


D19

11 1/8

 

D20 to D21

10 1/8


D20

11 1/8

 

D21 to D22

10 1/8


D21

11 1/8

 

D22 to D23

10 1/8


D22

11 1/8

 

 

 


D23

11 1/8

 

 

 


 

 

 

 

 


Total Boom Length = 15 ft 5 in.

 

 


 

All Dimensions in inches.

 

 


 

T-Match 12-ga wires for DE = 4 3/4" L  

 


 

Spacing of T-Match wires to DE = 3/4"

 

 

I have two questions –

1)  Does this appear to be a true K1FO-style antenna?

2)  Does anyone have a drawing with dimensions for the antenna?  I have
looked at the Directive Systems Website and the antenna I have seems similar
to their DSFO432-25, although I believe it is a home-made copy.  The T-Match
arrangement on my antenna is very similar to that which Directive Systems
shows in their “The Ins and Outs of T Matches” article.

 

73

Carl Estey WA0CQG

wa0cqg at arrl.net

(952) 250-3110 (Cellphone)