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Coax Stub Calculations
by Bob Brehm, AK6R
Modified 7/30/01 to add WARC bands and allow portrait printing of web page
(Thanks Lee, KH6BZF).
| Stub |
Length |
End |
Band |
Top Ten |
80 |
40 |
20 |
15 |
10 |
| A |
45' 2" |
SHORT |
80 |
J1 |
P |
N |
N |
N |
N |
| B |
21' 11" |
SHORT |
40+15 |
J2 |
|
P |
N |
P |
N |
| C |
21' 10" |
OPEN |
20+10 |
J5 |
|
N |
P |
N |
P |
| D |
10' 2" |
SHORT |
20 |
J3 |
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P |
|
N |
| E |
10' 1" |
OPEN |
10 |
J4 |
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N |
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P |
| F |
45' 0" |
OPEN |
40 |
J6 |
N |
P |
P |
P |
P |
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Notes:
P = PASS,
N = NULL |
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Stub |
Notes |
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A |
.25 on 80, .50 on 40, 1.0 on 20,
1.5 on 15, 2.0 on 10 |
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B |
.25 on 40, .50 on 20, .75 on 15,
1.0 on 28 |
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C |
.25 on 40, .5 on 20, .75 on 15,
1.0 on 10 |
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D |
.25 on 20, .50 on 10 |
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E |
.25 on 20, .50 on 10 |
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F |
.25 on 80, .5 on 40, 1.0 on 20,
1.5 on 15, 2.0 on 10 |
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Phone |
VF=.66 |
VF=.66 |
RG-213 |
CW |
VF=.66 |
VF=.66 |
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| Band |
Freq |
1/ 4 L |
1/2 L |
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Freq |
1/ 4 L |
1/2 L |
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| 10 |
28.4 |
5.7 |
11.4 |
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28.05 |
5.8 |
11.6 |
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| 12 |
24.96 |
6.5 |
13.0 |
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24.91 |
6.5 |
13.0 |
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| 15 |
21.3 |
7.6 |
15.2 |
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21.05 |
7.7 |
15.4 |
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| 17 |
18.139 |
9.0 |
17.9 |
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18.084 |
9.0 |
18.0 |
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| 20 |
14.2 |
11.4 |
22.9 |
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14.05 |
11.6 |
23.1 |
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| 30 |
10.125 |
16.0 |
32.1 |
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10.125 |
16.0 |
32.1 |
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| 40 |
7.2 |
22.6 |
45.1 |
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7.05 |
23.0 |
46.1 |
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| 80 |
3.8 |
42.7 |
85.5 |
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3.55 |
45.7 |
91.5 |
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| 160 |
1.85 |
87.8 |
175.5 |
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1.805 |
90.0 |
179.9 |
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Tune |
Test |
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| Stub |
Length |
Freq. |
Frequency |
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| A |
45' 2" |
3.55 |
3.55/7.1/14.2/21.3/28.4 |
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| B |
21' 11" |
7.1 |
7.1/14.2/21.3/28.4 |
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| C |
21' 10" |
7.1 |
7.1/14.2/21.3/28.4 |
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| D |
10' 2" |
14.2 |
14.2/28.4 |
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| E |
10' 1" |
14.2 |
14.2/28.4 |
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| F |
45' 0" |
3.55 |
3.55/7.1/14.2/21.3/28.4 |
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| Band |
Stubs |
Effect |
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| 10 |
C,E |
pass 28.4, nulls
7.1, 14.2, 21.3 |
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| 15 |
B |
pass 7.1, 21.3,
nulls 14.2, 28.4 |
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| 20 |
C,D |
pass 14.2, nulls
7.1,21.3,28.4 |
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| 40 |
B,F |
pass
7.1, 21.3, nulls 3.55,14.2, 28.4 |
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| 80 |
A |
pass
7.1,14.2,21.3,28.4, nulls 3.55 |
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| 160 |
not used |
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| Stub
Effects |
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| Length |
End |
Functions as |
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| 0.25 |
open |
short at input - null at F |
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| 0.25 |
short |
open at input - pass at F |
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| 0.5 |
open |
open at input - pass at F |
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| 0.5 |
short |
short at input - null at F |
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| To
cut: - keep open, measure at .25L, add short, measure at 2F |
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Use the Stub Effects table above to determine which stubs you need for a band
to pass the band frequency or null an interference frequency. You can cut
shorter stubs for the phone portions and add pigtails for cw but I don't find
this effort worth it. All coax is RG-213.
For my SO2R installation, the coax stubs are placed on the output of the
amplifier (and switched by an Icom 627) and I use Dunestar
600 Bandpass filters plugged into a Topten
band decoder box plugged into the ACC2 rear of the transceiver (switching
daisy-chained with the Icom 627). Note the Icom 627 is plugged into my
Icom 775 and auto switches the bandpass filters and the coax stubs at the same
time and I don't have to worry about using the wrong stubs on the wrong band.
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