Author Topic: swr question (Read 743 times)

duldog · « **on:** August 23, 2011, 05:29:18 PM »

gud day po sa lahat!

nagsetup ako ng f23 antenna (20ft high) using a very long rg58 coax(around 40meters, more or less), the antenna is not new, gamit na po bigay lang sa akin

ang swr reading nya is about 1.5 sa 140 mhz, 1.2 sa 146 mhz, 1.4 sa 150 mhz, using a 1/2 meter long rg58 patch cable from the radio to the swr meter

assuming that i had it set right, nagputol ako ng cable ng around 15m, so bale nasa +/-20meters na ang cable papunta sa antenna

i was surprised when i rechecked the swr naging 2.2-3.0+ na ang reading

i checked to make sure that the connectors were soldered correctly, pero ganun pa rin ang reading

using a straight connector, i connected again the previously cut 15 meter cable after that bumalik na ang 1.2-1.5 swr reading nya

is it possible na ang antenna is not yet tuned properly and i am just getting a wrong reading due to the long cable? any ideas po? tnx!

Philippine Electronics Forum · « **on:** August 23, 2011, 05:29:18 PM »

stcboy · « **Reply #1 on:** August 23, 2011, 11:40:13 PM »

sir duldog try nyo cut ang coaxial to the 1/2 wave multiple base sa operating frequency nyo .at kung maari gamit kayo at least RG8 for vhf na longer run cable. Maaring ng mahaba ang run ng rg58 na-attenuate nya ang return signal kaya mababa ang vswr at nang magputol kayo ( hence mas mababa ang attenuation ) tumaas ang vswr dahil hindi na masyadong attenuated ang return signal at yun po ang tutuo na vswr reading nyo. eto try nyo . Lagay kayo nang 50 ohms load to end antenna side connector at subukin nyo ulitin test.

Philippine Electronics Forum · « **Reply #1 on:** August 23, 2011, 11:40:13 PM »

Ikasamoko · « **Reply #2 on:** August 24, 2011, 01:14:07 AM »

RG48 at 40 meters? paktay tayun dyan...kahit Belden pa gamitin mo...

Philippine Electronics Forum · « **Reply #2 on:** August 24, 2011, 01:14:07 AM »

duldog · « **Reply #3 on:** August 24, 2011, 06:10:22 AM »

ok mga idol salamat sa info, palit cable nalang tapos re-tune ulit, tnx!

Philippine Electronics Forum · « **Reply #3 on:** August 24, 2011, 06:10:22 AM »

du1vss · « **Reply #4 on:** August 28, 2011, 11:46:04 AM »

The problem here is that you got a false reading by the SWR meter. Remember that 40meters of RG-58 already attenuated the reflected power before it was read by the SWR meter. By the time you cut half of your RG-58, the attenuation was reduced that is why the SWR goes up to 1: 2.0. Try to fix the F23 antenna and when reading SWR use a shorter cable if RG-58 is used. Lesson learned, NEVER USE RG-58 WHEN MORE THAN 15METERS AT144MHZ COZ THE ATTENUATION LOSS IS APPROX. 3dB, thats half of your transmit power. 73 de du1vss

Philippine Electronics Forum · « **Reply #4 on:** August 28, 2011, 11:46:04 AM »

duldog · « **Reply #5 on:** August 29, 2011, 10:10:39 AM »

thanks for the info boss!

bravokilo · « **Reply #6 on:** November 08, 2011, 05:40:20 PM »

Du1vss hi. Question: I have these cable in the house, never used, braided sya medyo green and kulay size ng RG8, Wala siya plastic outer skin. We bouth this from AVesco noon, better daw than the RG8. ano kaya ito?

Thanks....

BK

du1vss · « **Reply #7 on:** November 15, 2011, 07:23:40 AM »

sorry for the late reply sir BravoKilo anyways i have no idea about that kind of coaxial cable. Look weird to me since the outer conductor (braid) was exposed.. i wonder if moisture already contaminated the entire length of the coax.

Philippine Electronics Forum · « **Reply #7 on:** November 15, 2011, 07:23:40 AM »

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