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  1. #1
    Join Date
    Jan 2002
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    Pyefleet
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    Default vhf 'weak and feeble'...

    according to the coastguard who were kind enough to listen to me and report back. Measured on an av-200 VSWR meter SWR is 1.25, measured power out of the radio 25 watts. I've just remade the pl259 connections. Nothing is short circuited. Am I missing something?

  2. #2
    Join Date
    Apr 2006
    Location
    Portsmouth, UK
    Posts
    2,643

    Default Re: vhf 'weak and feeble'...

    Perhaps one of the pl259 connections was not fully mated...
    Even though you might have done them up tight, did you realise that there might be 4 dimples in the so239 socket edge into which fit four little peaks (if that's what you call them) on the pl259 plug inner bodies.

    Turn the plug body slightly as you tighten the knurled part to ensure they align.. sorry if you know that already.

    I've never tested the power loss when badly screwed together but I'd not like to transmit any more than 25w if not mated correctly.

    vSWR might be measured 1.25 even if the antenna is bad.. It could perhaps be absorbing and not reflecting the signal power. Did you measure at the base of the mast as well or only at the back of the radio?

  3. #3
    Join Date
    Apr 2006
    Location
    Portsmouth, UK
    Posts
    2,643

    Default Re: vhf 'weak and feeble'...

    It's late.. But thinking again, it could be the modulating circuitry within the radio that's faulty. Your meter will be measuring the carrier power... Since it's FM (frequency modulated) then the carrier will be at a constant 25 watts (measured) with the voice effectively overlaid into the carrier by modulating the frequency...
    So you could well be transmitting a good 25 w carrier, through a good antenna system but just be badly modulating the voice signal.

    To check that then I'd suggest trying a known good rig (VHF radio) plugged into the current antenna.
    Or your radio on another antenna.

  4. #4
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    10,776

    Default Re: vhf 'weak and feeble'...

    Quote Originally Posted by Martin_J View Post
    It's late.. But thinking again, it could be the modulating circuitry within the radio that's faulty. Your meter will be measuring the carrier power... Since it's FM (frequency modulated) then the carrier will be at a constant 25 watts (measured) with the voice effectively overlaid into the carrier by modulating the frequency...
    So you could well be transmitting a good 25 w carrier, through a good antenna system but just be badly modulating the voice signal.

    To check that then I'd suggest trying a known good rig (VHF radio) plugged into the current antenna.
    Or your radio on another antenna.
    Yes agree or try getting someone to transmit while you listen on another set. Weak modulation can be slightly overcome by shouting into the mic but will be seen as a strong quieting of the receiver with squelch open but weak actual voice.
    A bad mic or modulating circuit will sound weak no matter how close you are to the receiver. olewill

  5. #5
    Join Date
    Jan 2013
    Posts
    210

    Default Re: vhf 'weak and feeble'...

    Quote Originally Posted by Martin_J View Post
    It's late.. But thinking again, it could be the modulating circuitry within the radio that's faulty. Your meter will be measuring the carrier power... Since it's FM (frequency modulated) then the carrier will be at a constant 25 watts (measured) with the voice effectively overlaid into the carrier by modulating the frequency...
    So you could well be transmitting a good 25 w carrier, through a good antenna system but just be badly modulating the voice signal.

    To check that then I'd suggest trying a known good rig (VHF radio) plugged into the current antenna.
    Or your radio on another antenna.
    Exactly the problem I had with my ICOM 505, corrected FOC by Icom on a 9 year-old set. Checked both ways - receive with a known rig, it worked with squelch turned right up, but still put out a very small signal.

  6. #6
    Join Date
    Jan 2002
    Location
    Pyefleet
    Posts
    4,351

    Default Re: vhf 'weak and feeble'...

    Thanks all for these very helpful replies. I should have thought of vSWR at the mast foot. Doh! I'll check that. To be honest the radio is a 20 year old Navico 1400 so if it's not the antenna I think I'll just replace it - I can get a Standard Horizon kit for under £200 it seems.

  7. #7
    Join Date
    May 2007
    Posts
    28,130

    Default Re: vhf 'weak and feeble'...

    What is the co-ax like?
    If the braid is anything other than shiny, the loss can be very high.
    Often while giving a good VSWR.

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