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SWR Meter

Discussion in 'General Ham Radio Discussion' started by spider87, Aug 9, 2010.

  1. spider87

    spider87 Member

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    #1
  2. mackmobile43

    mackmobile43 Jock Supporter

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    If it's dummy load is near 50 ohms it should work just fine for you.
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  3. spider87

    spider87 Member

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    Thanks for the reply. How can I tell if the load is above 50 ohms? Should I just ask the seller or is there a way by looking at the pictures or something?
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  4. Robb

    Robb Yup

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    The guy who owns this meter said he tested it with a 50 ohm dummy load. The load doesn't come with it. You don't need that yet.

    That meter will work for you just fine.
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  5. spider87

    spider87 Member

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    I don't mean to pick but I'm just curious, is this just assumed when someone says dummy load? Because I can't find where it says that in the description?
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  6. Robb

    Robb Yup

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    From eBay:

    "...This auction is for a vintage Lafayette SWR meter with some scratches and scuff marks (see photo). There is a scratch in the plastic meter face see photo). I tested it with a CB and a dummy load and it works OK. Item is sold AS IS but will guarantee not to be DOA and as described. I currently ONLY SELL AND SHIP TO USA BIDDERS. Shipping and handling actual shipping to your zip code for 1 lbs. Payment by PAYPAL ONLY..."

    This meter will be just fine for your needs...
    #6
  7. spider87

    spider87 Member

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    I know, I just meant the 50 ohms part. I don't know what that part refers to. Sorry.
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  8. Robb

    Robb Yup

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    When an antenna is being transmitted thru; it needs to have an impedance (that is resistance from an AC circuit. Radio freq's are 'AC") that matches the output of the final transmit transistors. 50 ohms is what your radio would like to see and to work without heating up. The SWR meter is used to check what kind of impedance your antenna is presenting to the radio's output transistors. Adjusting the height of the antenna whip (either up or down) will change this impedance value; the meter is used to dial it in the zone. You will need to tune the antenna manually - usually with a small Allen wrench - to get this adjustment correct.

    The antenna subsystem is the most important part of your CB system. It's tuning can make you or break you. When checking the SWR or the "Standing Wave Ratio", you will be hooking up a simple form of a directional watt meter between your antenna and the CB radio.

    The meter measures Forward power to the antenna system and then compares it to the reverse or reflected power from the antenna system. Instead of showing you power, the meter is calibrated to show the RATIO of coupling from radio to antenna system. If there is all forward power and no reflected power the antenna system has a one to one (1:1) ratio with the transmitter.

    By checking the SWR at channels 1 and 40 on your CB, you will have a good idea if the antenna is too "long" or too "short" for the center of the desired band. You will also be able to evaluate your system performance and troubleshoot problems. For instance a SWR too high (over 3:1) all over the band can be an indication of a bad part or junction, poor ground or poor location. An SWR too low over the whole band (1:1 for all 40 channels) can indicate a low efficiency antenna or lossy component.

    Safe operation of your CB should be with an SWR of 2:1 or less. Most people would prefer to be 1.5:1 or less. A good quality antenna and proper installation (location very important) should easily result in an SWR of less than 1.5:1 and for most long antennas it will be that low across all 40 channels (plus a few). Shorter Antennas tend to be more narrow banded and may have as high as a 2:1 at the top and bottom of the band. Here's one of the places you can evaluate your antenna. We EXPECT a high quality "short" antenna to be narrow banded. If you have an antenna that's say, three feet or less, and the SWR tunes great (less than 1.5) across all the channels than maybe your antennas feedline coax or the antenna coil is "lossy".

    In "Lossy" I mean that maybe the design or construction material is inferior and is wasting some of your energy as ground losses or increased heat dissipation. This causes both the forward and reflected power to be partially absorbed, thus showing a lower SWR on the meter.


    What the meter shows on an SWR meter reading - is the amount of power being reflected back into the radio. Too much 'reflected' power is what can damage a radio; that is why we told you that it is important! We want to adjust that antenna so that it reflects very little power back into the radio - and on to the antenna will it will transmit better. A SWR reading of 3 to 1 or above is considered unacceptable. A SWR reading of 1.5 to 1 or less is considered desirable - and that is the target to reach. Sometimes you will not be able to get it to 1.1 to 1; so you must get it as close as you can.

    Read this completely; than ask some more qustions about it:
    SWR
    #8
  9. mackmobile43

    mackmobile43 Jock Supporter

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    It means you radio has to see a 50 ohm load to operate properly, I did not see that this meter does not have a dummy load (MACK needs to pay more attention to ads) and is not necessary for tuning an antenna.

    Be sure to use 50 ohm coax with your setup.
    #9
  10. nat19

    nat19 Active Member

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    Again this is a very important part. If you go the cheap route and buy a swr meter that gives incorrect readings such as, it says you swr is 1.5:1 when it is really way higher than that, then you may blow the final in your radio. As long as that meter is accurate it should work though.
    #10
  11. Hutch

    Hutch Active Member

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    Before you depend on a used meter from ebay I suggest you test it against a known good meter that maybe one of your friends has.
    #11
  12. spider87

    spider87 Member

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    There's a cb shop up the road... maybe I'll just give him a call and see if he'll help me tune the antenna until I am in the position to buy a $44 dollar swr meter brand new...

    Another question, my radio loses the previous channel and the memory presets each time I turn off the power to it. Is there a battery somewhere in these I can replace generally or is it more like just a rechargeable battery inside? I have opened it up and I don't see anything but maybe I'm looking in the wrong place?

    I'm fairly certain it's either an in-circuit rechargeable battery or just doesn't have anything because I can't find anything...
    #12
  13. Robb

    Robb Yup

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    You could do it that way too. It might cost more to have them do it that for you to get your own and learn how to do it...

    That radio might have a computer/motherboard type of battery in it. That CB shop would know about that too...
    #13
  14. W5LZ

    W5LZ Crotchety Old Bastard

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    This is an old meter, notice the "vintage" part? I would guess that it's older than you are (maybe). All things considered, I might give that $5.00 -IF- the shipping was free. You get what you pay for if you are lucky! Which in this case is not much, unless you collect old stuff. Pass on it.
    - 'Doc

    (They weren't much thought of when they were new, and that was over 40 years ago.)
    #14
  15. nat19

    nat19 Active Member

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    Like I said the old vintage meters seem to either not work or be very inacurate. It is really not recomended that you transmit on your radio until you check the swr. In another thread I noticed yu bought a cheap antenna. Chances are you will have trouble with your swr since you bought one of those "junk" antennas.
    #15


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