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Thread: modulation pots

  1. #1
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    modulation pots

    Can anyone tell me which is the modulation pot on a 1997 cobra 25ltd classic? I have awfully low audio output on this radio and am trying to figure out why.
    Gasman

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    VR5. That should be the modulation pot

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    That's what I thought 222. I opened up the radio, found it turned all the way to the right. I turned it all the way to the left and it only got worse. this radio was peaked and tuned when it was new. I have very low modulation even running it with a palomar 225. Do you or anyone else have any ideas what I can do to rectify this? Thanks for the info 222.
    Gasman

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    Not without the proper test equipment. I know it's not what you want to hear, but without a good meter to measure the modulation, then you are just guessing. If you want to run and amp you have to suppress the am carrier, you can do tins with the cap and resistor mod or the TIP120 mod. The resistor cap mod is the easiest way, keep your dead key at at around 1.5-2 watts max. But you need to have a way to do all of this, an oscilloscope or at least a good watt meter and dummy load, a watt meter that can measure modulation.

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    gasman (06-29-2014)

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    O.k. 222 any recommendations on what type of meter or o scope I should look into? My backround is in appliance repair so I am well versed in reading diagrams and using a multi-meter. I imagine this will be along those same lines. I have an astatic pdc2 swr/power meter, however I get the feeling this will not accomplish what I will be attempting to do. Thanks for your input and any recommendations.
    Gasman

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    sell it and get a older side mic cobra or uniden .

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    gasman (06-29-2014)

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    This is an older side mic cobra. 1997. Do I need to go older than that? I bought this radio new. I used it for a number of years. then I stored it in the original box for close to ten years before I dragged it out and set it up in my p/u. Running it with a roof mounted Wilson 1000. Apparently the palomar 225 isn"t helping it any. I was talking to a local who is maybe a mile away and he said he could barely hear me.
    Gasman

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    That amp doesn't like a dead key above 2 watts. I have one, it's has 2 sd1446's in it, a uniden 980 works well with it. They don't like to be over driven, and if your radio has had the golden screwdriver in it, it's going to make the issue worse. Also, check all your connectors, jumpers and antenna coax as well. If you have a newer wilson 1000 with the 2 piece connector on it, that would be the first thing I would replace, then I would check all my connectors on my coax jumper from the radio to the amp. And last, have you checked the swr reading with the amp out of line to tune the antenna properly? Like said before, you need a good meter that can set modulation to 100% maybe a bit less, an oscilloscope would be best. Idk which one to tell you to get, but would think one that measures to 1-100mhz would work. Check eBay out, there are a bunch out there!!

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    Thanks again 222. Right now the amp is out of the circuit. Swr is 1.3-1.7. According to the radio meter deadkey is 1w with the mic gain turned up. It's not even swinging to 2w. The antenna coax does have the two piece connector, however there is no issue with my connex 3300 on the same setup. (minus the amp)
    Gasman

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    also, don't know if it matters but I am running a ranger noise reducing mic on the cobra.
    Gasman

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