| Author |
Message |
    
Mpuckett
| | Posted on Monday, September 29, 2003 - 11:44 pm: | 
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I got my CB radio installed, and finally got around to getting a SWR meter (just didnt transmit before), discovered my SWR is off the scale! Furthermore, it would change when i moved the coax cable (got it to 1.1, but i'd sure be a weird driving position :-) ) Anyways, from what i read, that meant that the signal was coming back down the coax shield. I took a multi-meter and checked for continuity between the wire of the coax, and its sheild, and discovered it was connected. However, after some more messing around, i found out its only this way when connected to the SWR meter. Should this be happening? I get no continuity if the coax isnt connected to anything, none if its only screwed into the antenna, and none if its only connected to the radio. Bad SWR meter or is something else happening? Thanks |
Kc0gxz
| | Posted on Tuesday, September 30, 2003 - 1:11 am: |
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Mpuckett
Some antennas will show continuity from shield to center conductor and some won't. If it's capacitance grounded, (mag mount) it will. Very poor grounding there.
What kind of antenna and what kind of mounting system are you using. The information you provided didn't help much.
Jeff, kc0gxz. |
Mpuckett
| | Posted on Tuesday, September 30, 2003 - 9:08 am: |
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Its a radio shack whip antenna, and a stakehole mount i bought online.
I know that isnt the best setup possible, but I working on my ham license so im trying to save alittle money for that. However, i should point out that this continuity exists *only* when the SWR meter is involved. Thanks
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Tech808
| | Posted on Tuesday, September 30, 2003 - 9:36 am: |
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Mpuckett,
Simple test, use your Volt/Ohm meter to check meter coax connectors (check both).
Place 1 lead in center hole and other lead to threads on connector.
It should show OPEN "No" continuity, If it shows continuity it is shorted out and meter is bad.
Then check Center hole to Center hole for Continuity and outer threads to outer threads.
This "SHOULD" show continuity.
It could be minor re-solder job or a blown diode or resistor problem.
Lon
Tech808
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Mpuckett
| | Posted on Tuesday, September 30, 2003 - 1:23 pm: |
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Thanks, thats exactly what happens. I guess i'll be getting another meter. I guess thats what i get for using radio shack stuff, but as far as i know, its the only shop around :-( |
Mpuckett
| | Posted on Thursday, October 02, 2003 - 3:46 pm: |
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Well i went to exchange it for another one today, and all 3 of the ones they had failed this same test! Be warned if you buy one of these, because if the store i went to is any indication, they arent taking them off the shelf. Basically the person I talked to seemed to think that I was miss informed and there was "no way all 3 could be bad, thats impossible!". So if you buy one be sure and check it before you leave the store (usually they have a multimeter behind the counter). I guess i'll be buying online now.
Mpuckett |
fancypants
| | Posted on Friday, October 03, 2003 - 12:00 pm: |
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As a general rule, the Radio Shack swr meters are one of the best buys / most accurate swr meters on the market for the money. I would trust one of these over most anything that you are likely to find in a "generic" radio shop or at a truck stop. If anything, the Rat Shack meters tend to show a slightly lower swr reading than what you really have. Given the type of installation that you have and knowing how poorly most antenna systems work when mounted on the bed of a pick up truck, you better start checking things out before you do damage to your radio. |
Bigbob
| | Posted on Friday, October 03, 2003 - 8:53 pm: |
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It all depends on which lead you put where,if you put the redlead of volt meter on redlead of ohm meter and black on black the volt meter moves backward,funny aint it 'cause the supply of ohm meter is backward to color code on purpose so you can measure semi-conductors according to their markings,thus if you switch the leads on your swr meter you will still get a reading,but it should register some resistance either way.In an swr meter you have a diode hooked foward for forward power and one hooked backward for reflected power.The diodes rectify the rf(AC)into DC to power the simple circuit to drive the meter movement,simple!? as that.The ohm tester never falls to zero when testing one of these unless the swr meter IS shorted or you have an extremely CHEAP tester. |
Bigbob
| | Posted on Saturday, October 04, 2003 - 10:55 pm: |
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Boy did I goof,I forgot about the swr BRIDGE,it isolates the center conductor,so remember one other thing,DO NOT touch the test leads of ohm meter or you will be measuring YOUR BODY'S resistance not the test subject,this may have been the problem with the radio shack swr meters.And Tech 808 is RIGHT ON. |
matthew puckett
| | Posted on Sunday, October 05, 2003 - 12:16 am: |
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Bigbob, im afriad you went over my head alittle there :-) In the meters i tested, the two center wires of the posts were connected, and the outer rings of the two posts were connected. This makes sense to me. However, the cetner wire part, and the outer ring were connected also (in other words it was making a connection between the coax wire, and the coax shield). |
Mikefromms
| | Posted on Saturday, February 07, 2004 - 9:44 am: |
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The rad shack might be a good swr meter but I know the power readings are wrong. Why even bother with putting that function on the meter? I'll never buy another rad shack radio, antenna, coax, meter. Maybe the tvi filter for tv and little stuff.....I think it should be renamed computer shack or cellphone shack. Radios are not their interest any longer.
mikefromms |
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