Wolfgang Decker wrote:
>Dene, > >you should be able to use your CB radio SWR meter for VHF as well. These >things work by coupling a conductor parallel to the RF cable (they are not >connected) and through a diode setup you switch the measurement between >forward power and reflected power. The total amount of power that couples >into the meter depends on frequency, but the coupling factor is the same for >forward and reflected power, and since you only want to measure the ratio >between the two it does not matter. It might be, though, that you are not >able to tune to a full 100% in the forward setting, in which case you need >to adjust the reading for the reflected power. > >If you want to measure the actual power going to the antenna, then you need >to have a tuned meter, such as the Bird Wattmeter with a respective insert. > >Greetings from the still cold Western Pennsylvania, > >Wolfgang >N1YM > >-----Original Message----- >From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net]On >Behalf Of AVLEC >Sent: Monday, February 26, 2007 4:35 PM >To: KRnet >Subject: KR> antennae tuning > > >Hi KR radio heads >This one is for the radio literate. I have just installed an antennae into >an aircraft made from coax only. I left the radiator and counterpoise too >long on purpose so that I could tune it to length in the aircraft using a >SWR meter and a handheld radio. Here is where my confusion starts. >I have in the past built a number of antennae for CB radio and have tuned >them with one of two SWR meters that I have and they worked fine. >Today I spoke to a guy that has built a few airband antennae and he says >that the SWR meters suitable for CB radio freq are not suitablr for >airband?? As far as I know all a SWR meter is is a voltmeter so why should >the freq make any difference? He also told me that a handheld radio does not >put out enough power to be able to get reliable readings??? Sounds really >obsurd to me. >Comments from those in the know would be very much appreciated. > >Regards >Dene Collett >KR2SRT builder >South africa >Whisper assembler >See: www.whisperaircraft.com >mailto: av...@telkomsa.net > > > Here's the details about the - Bird Watt meter - Notice the different incerts for different ranges... and the further you get from the center of the range the less accurate the measurment will be. http://www.radiodan.com/Henry/misc/bird.htm Frequency ranges: A = 25-60 MHz B = 50-125 MHz C = 100-250 MHz D = 200-500 MHz E = 400-1000 MHz H = 2-30 MHz . Examples: (full scale power) 25A = 25 watts 25-60 MHz 500C = 500 watts 100-250 MHz 2500H = 2500 watts 2-30 MHz -dave KB8SSA
