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[TowerTalk] Effects of less than 80% guying (long)

To: <towertalk@contesting.com>
Subject: [TowerTalk] Effects of less than 80% guying (long)
From: k6ll@juno.com (David O Hachadorian)
Date: Fri, 20 Jun 1997 14:06:09 EDT
On Fri, 20 Jun 1997 01:25:53 +0000 "Sean McCarthy" <wx8l@akorn.net>
writes:

>Hello all,
>My lot (105' x 310') will accommodate up to 80' of tower guyed at 80% 
>"by the book". What compensation would I have to make if I were to 
>sneak it up to 90 or 100' (72 and 65%) ? Would the extra 10 or 20 
>feet be worth it?
>The tower will be 25G with a TH7 at the apex and 40-2CD 12' above.

Here's a little comparison of 80 vs 100' on 40 thru 10.
It shows that you gain about 1.9 dB at the lowest angles
by adding the height. But, you lose a lot at the higher
angles. If being loud in the USA is important to you, even
80' is too high for your 10 meter antenna. It's time to
start thinking about stacking something lower, at about 40
or 50 feet. Angles up to 20 degrees are useful on 10 thru 20,
and sometimes even higher angles work. One interesting
possibility for you would be to use 100' of Rohn 45 or 
preferably 55, and engineer it such that it 
required guying at only two levels. If you guyed it at 95'
and 47', you would have room to rotate another TH7 on a
sidearm or ringrotator at the 48' level, even if the
anchors were only 65' away at ground level. This approach
would also give you another 2-3 dB at the low angles, plus
a lot of flexibility.

The following data is from a little spreadsheet program that
I use. The "ERR" entries are where the program falls apart
because of some divide-by-almost-zero errors, and in those
cases the total gain is less than minus 20 dB.
-----------------------------------------------------

height in feet: 80              height in feet: 100
frequency, Mhz: 7.15            frequency, Mhz: 7.15
wavelengths:    0.581           wavelengths:    0.727
ant gain dBi:   6               ant gain dBi:   6

        tot gain                tot gain
        reflection/             reflection/
angle   antenna         angle   antenna
-       -               -       -
1       -11.92          1       -9.98
2       -5.92           2       -3.99
3       -2.43           3       -0.52
4       0.03            4       1.91
5       1.91            5       3.77
6       3.42            6       5.24
7       4.68            7       6.45
8       5.75            8       7.47
9       6.66            9       8.33
10      7.45            10      9.05
11      8.15            11      9.67
12      8.76            12      10.20
13      9.29            13      10.65
14      9.76            14      11.02
15      10.18           15      11.33
16      10.54           16      11.57
17      10.85           17      11.76
18      11.12           18      11.89
19      11.35           19      11.97
20      11.54           20      12.00


height in feet: 80              height in feet: 100
frequency, Mhz: 14.2            frequency, Mhz: 14.2
wavelengths:    1.154           wavelengths:    1.443
ant gain dBi:   9               ant gain dBi:   9

        tot gain                tot gain
        reflection/             reflection/
angle   antenna         angle   antenna
-       -               -       -
1       -2.97           1       -1.05
2       2.97            2       4.86
3       6.38            3       8.20
4       8.71            4       10.43
5       10.43           5       12.03
6       11.75           6       13.19
7       12.77           7       14.02
8       13.55           8       14.58
9       14.15           9       14.90
10      14.57           10      15.00
11      14.85           11      14.89
12      14.98           12      14.56
13      14.98           13      14.01
14      14.85           14      13.19
15      14.59           15      12.07
16      14.18           16      10.55
17      13.61           17      8.46
18      12.88           18      5.45
19      11.94           19      0.50
20      10.76           20      -12.87


height in feet: 80              height in feet: 100
frequency, Mhz: 21.2            frequency, Mhz: 21.2
wavelengths:    1.724           wavelengths:    2.154
ant gain dBi:   9               ant gain dBi:   9

        tot gain                tot gain
        reflection/             reflection/
angle   antenna         angle   antenna
-       -               -       -
1       0.48            1       2.39
2       6.34            2       8.16
3       9.60            3       11.27
4       11.72           4       13.17
5       13.17           5       14.32
6       14.14           6       14.89
7       14.72           7       14.97
8       14.98           8       14.57
9       14.93           9       13.63
10      14.58           10      12.04
11      13.89           11      9.49
12      12.81           12      5.14
13      11.24           13      -5.33
14      8.95            14      ERR
15      5.43            15      ERR
16      -1.14           16      ERR
17      ERR             17      ERR
18      ERR             18      ERR
19      ERR             19      ERR
20      ERR             20      ERR


height in feet: 80              height in feet: 100
frequency, Mhz: 28.2            frequency, Mhz: 28.2
wavelengths:    2.293           wavelengths:    2.866
ant gain dBi:   10              ant gain dBi:   10


        tot gain                tot gain
        reflection/             reflection/
angle   antenna         angle   antenna
-       -               -       -
1       3.92            1       5.80
2       9.66            2       11.39
3       12.71           3       14.16
4       14.53           4       15.56
5       15.56           5       16.00
6       15.98           6       15.57
7       15.85           7       14.19
8       15.15           8       11.47
9       13.80           9       6.08
10      11.52           10      -20.62
11      7.66            11      ERR
12      -0.71           12      ERR
13      ERR             13      ERR
14      ERR             14      ERR
15      ERR             15      ERR
16      ERR             16      ERR
17      ERR             17      ERR
18      ERR             18      ERR
19      ERR             19      ERR
20      ERR             20      ERR

Dave Hachadorian, K6LL
k6ll@juno.com

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