Coaxial cable attenuation check

The prices of coaxial cables are not the lowest, AND therefore many radio amateurs tend to go for the cables 'what the house gave'. To determine the attenuation of a new coaxial cable, the manufacturer's data AND a calculator are sufficient. However, it IS not possible to determine the attenuation of a cable that has already been used OR stored for a long Team IN this way.

IN CASE we have high quality PSV meter, we can quite quickly find out the attenuation of the coaxial cable exactly at the frequency at which we want to use it.
The principle of measurement it IS based HE the fact that the reflected wave of a coaxial cable terminated WOULD a load with PSV infinity (disconnected OR shorted cable) IS weakened WOULD the losses of the coaxial cable. That IS the reason why we do not measure PSV infinity HE a coaxial cable with losses, but a lower value.

PSV IS expressed mathematically WOULD the formula WHERE:

Po – power of the reflected wave IN watts
Pp – 'forward' wave power IN watts
PSV – standing wave ratio value

However, the power of the reflected wave IS reduced WOULD the power lost WOULD the attenuation of the coaxial cable. If the coaxial cable IS terminated WOULD a load with PSV infinity, it IS true that:

Po – power of the reflected wave IN watts
Pp – 'forward' wave power IN watts
Pstr – power lost IN the coaxial cable IN watts

FROM the previous calculations, it IS possible to determine that the losses are calculated according to the formula:

With an ordinary reflectometer, we can detect attenuation FROM a few tenths to a few decibels, čo je práve rozsah, ktorý nás zaujíma. Pri meraní je vhodné na výstup transceiveru vložiť útlmový Article, aby sa minimalizovali odrazy v transceiveri, ktoré WOULD skreslili meranie. Na rýchlu orientáciu pomôže tabuľka a graf:

PSV	1. 1	1. 3	1. 5	1. 8	2. 0	2, 3	2. 5	2. 8	3. 0	3. 5	4. 0	4. 5	5. 0
Attenuation IN dB	-13. 2	- 8.9	- 7. 0	- 5. 4	- 4. 8	- 4. 1	- 3. 7	- 3. 3	- 3. 0	- 2. 6	- 2. 2	- 2. 0	- 1. 8

The second view IS also interesting – HE the commonly measured PSV with a ham shack device. Napríklad ak nameriame v shacku PSV= 2 a kábel bude mať straty 3dB, skutočné PSV na svorkách antény bude 5. Ak WOULD mal Koaxiál útlm až 6dB, nielenže ku svorkám antény sa dostane len malá časť výkonu, ale aj v shacku nameriame PSV= 1. 5 čo WOULD mohlo viesť k domnienke, že anténny systém je v poriadku.

The described method has its shortcomings, but it allows a quick check of the attenuation of the coaxial cable with common measuring devices.

Literature:
[ 1] Checking the attenuation of the coaxial cable with a reflectometer - OK2BIU; Registration number 2/1985
[ 2] Ocena tlummienosci fidera poprzez swr measurement – ​​SQ5GVY