about yaa trap

COAX Stub Filters for MM Contest Station,

So Called “YAA Trap”Key Points of Multi Band Trap

using Coax Stubs

JA1CTB (JA7TNO) Tetsu Tanizawa “Aki”

113年11月18日月曜日

About YAA Trap

• Original Article was introduced to Japan by QST through CQ Ham Radio(JP) in 60’s

• JA7YAA, Club Station of Tohoku University, tried this idea in 1975, because it looked easy and not expensive for university students

• It gives good isolation for band to band in Multi-Multi Contest Operation

• So far, JA7YAA has become very active in contests, and this Coax Stub has become known as YAA Trap amongst the Japanese contester HAMs


Basic Implementation and Theory

• Open Ended 1/4 λ Stub shows Short condition (Zero Impedance)

• Short Ended 1/4 λ Stub shows Open condition (Infinite Impedance)

• Combinations of above are used

• These Stubs give a null condition or no effect at the connecting point depending on the Observed Frequencies

• The null points will appear in every 1/2 λ from the stub point along with the main


Z-Chart of Open & Short Stub

• Open Stub

• Impedance = ∞ at (2n)/4 λ for n = 0, 1, 2, 3, 4, ...

• Impedance = 0at (2n+1)/4 λ for n = 0, 1, 2, 3, 4, ...

• Short Stub

• Impedance = ∞ at (2n+1)/4 λ for n = 0, 1, 2, 3, 4, ...

• Impedance = 0at (2n)/4 λ for n = 0, 1, 2, 3, 4, ...

-300 j ohm

-250 j ohm

-200 j ohm

-150 j ohm

-100 j ohm

-50 j ohm

0 j ohm

50 j ohm

100 j ohm

150 j ohm

200 j ohm

250 j ohm

300 j ohm

0 0.0625 0.125 0.1875 0.25 0.3125Stub Length at f [λ]

Short Stub f Open Stub fShort Stub 2f Open Stub 2f


Examples to Understand Basic Theories and Physical Structures

• 28MHz Trap for14MHz TRX --- basic

• 28MHz Trap for14MHz TRX --- extension

• 21MHz Trap for 7MHz TRX--- extension


28MHz Trap for14MHz TRX --- basic

14MHz 1/4λShort Stub

~

14MHzimpedance = ∞

=> Z0 with coax Q

28MHz impedance = 0

=> null at 28MHz

14,1000

→ ANT

Hot Point!Vmax << COAX VmaxShort Ended

Stub must be here !

Hot Point!Vmax << COAX Vmax

Voltage Standing Wave Distribution on a Stub in Different Frequencies

V = max




↑ 28 null ↑ 28 null ↑ 28 null↑ 28 null


28MHz Trap for14MHz TRX --- extension

Center Feed14MHz 1/4λShort Stub

~

14MHzimpedance = ∞

=> Z0 with coax Q

28MHz impedance = 0

14,1000

Stub must be here !

14MHz +j50ohm14MHz -j50ohm

28MHz impedance = ∞

Short Ended

Open Ended

Parallel Resonancegives impedance = ∞

28MHz impedance = 0

=> null at 28MHz


→ ANT

↑ 28 null ↑ 28 null ↑ 28 null↑ 28 null






28MHz

28MHz TRAP for 14MHz Operating Point in Z Chart

-300 j ohm

-250 j ohm

-200 j ohm

-150 j ohm

-100 j ohm

-50 j ohm

0 j ohm

50 j ohm

100 j ohm

150 j ohm

200 j ohm

250 j ohm

300 j ohm

0 0.0625 0.125 0.1875 0.25 0.3125Stub Length at f [λ]

Short Stub f Open Stub f Short Stub 2f Open Stub 2f

~

14MHz 1/8λ Short Stub

14MHz 1/8λ Open Stub




28MHz14MHz 14MHz



21MHz Trap for 7MHz TRX extension

Offset Feed7MHz 1/4λShort Stub

~

7MHzimpedance = ∞

=> Z0 with coax Q

21MHz impedance = 0

7,1000

7MHz +j90ohm7MHz -j90ohm

21MHz impedance = 0

Short Ended

Open Ended

21MHz impedance = 0

=> null at 21MHz


Parallel Resonancegives impedance = ∞


→ ANT


↑ 21 null ↑ 21 null↑ 21 null


↑ 21 null


Short Stub f Open Stub f Short Stub 3f Open Stub 3f

-300 j ohm

-250 j ohm

-200 j ohm

-150 j ohm

-100 j ohm

-50 j ohm

0 j ohm

50 j ohm

100 j ohm

150 j ohm

200 j ohm

250 j ohm

300 j ohm

0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 0.225 0.25 0.275 0.3 0.325Stub Length at f [λ]

21MHz TRAP for 7MHz Operating Point in Z Chart

~





7MHz 7MHz21MHz 21MHz


Implementation Examples

• For 3.5MHz TRX, trapping 7, 14, 21, 28MHz

• For 7MHz TRX, trapping 3.5, 14, 21, 28MHz





For 3.5MHz TRX, trapping 7, 14, 21, 28MHz

• 3.5MHz 1/4 λ Short Ended Stub∞@3.5MHz, Null@7, 14, 21, 28MHz

3.5MHz 1/4λShort Stub

~

3.5MHzimpedance = ∞

=> Z0 with coax Q

7, 14, 21, 28MHz impedance = 0

=> nulls1213年11月18日月曜日

For 7MHz TRX, trapping 3.5, 14, 21, 28MHz

• 3.5MHz 1/4 λ Open Ended [email protected], ∞@7, 14, 21, 28MHz

• 7MHz 1/4 λ Short Ended StubNull@14, 28MHz, ∞@7, 21MHz

• 7MHz 1/4 λ Short Ended Stub with Off Set Null@21MHz, ∞@7MHz

3.5MHz 1/4λOpen Stub

~


~

21MHz 1/4λOpen Stub

~7MHz 1/4λ Short Stub

with 21MHz 1/4λ Off Set1313年11月18日月曜日

mailto:[email protected]




• 7MHz 1/4 λλ Open Ended StubNull@7, 21MHz, ∞@14, 28MHz

• 14MHz 1/4 λ Short Ended Stub with Center Feed Null@28MHz, ∞@14MHz


~

7MHz 1/4λOpen Stub

~


~14MHz 1/4λ Short Stub

with Center Feed1413年11月18日月曜日





• 7MHz 1/4 λ Stub + Off Set 7MHz 1/4 λ Short Stub Null@7MHz, ∞@21MHz

• 14MHz 1/2 λ Short Ended Stub Null@14, 28MHz, ∞@21MHz


~

7MHz 1/4λ ~


~








• 7MHz 1/4 λ Open Ended StubNull@7, 21MHz, ∞@14, 28MHz

• 14MHz 1/4 λ Open Ended Stub Null@14MHz, ∞@28MHz


~

7MHz 1/4λOpen Stub

~


~




about yaa trap

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