PMR446 Antenna Length

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PMR446 Antenna Length

Postby AshtonMobileScanner » Sun Jun 02, 2013 1:58 pm

Ive got a telescopic antenna and ive been using it at 70cm long running pmr446, am i doing this wrong.

please help guys.

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Re: PMR446 Antenna Length

Postby m0lsx » Sun Jun 02, 2013 3:07 pm

The VSWR is probably through the roof & the radiation resistance is also probably very high, so you are suffering a double loss & a tripe loss if your radio is choking back due to high VSWR. The calculation of frequency to wave length needs to be a real world one, not just a 300,000m per second one as that does not take into account a radio waves real speed.In the real world it's velocity is different.
So your antenna may work, but it will not be efficient & it could damage your radio.
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Re: PMR446 Antenna Length

Postby m0lsx » Sun Jun 02, 2013 6:13 pm

As an after thought, the terms given to amateur bands, broadcast bands etc etc, are to describe the area of spectrum in round figures & none are the exact length of the antenna required...CB as an example is described as 11 meters as the amateur band above it is called 10 meters..However legal UK CB is in fact at the top end of the 10 meter wavelength. The amateur 40 meter band is actually 42 meters, 160 meters is 166 meters & so it goes on..
Last edited by m0lsx on Mon Jun 03, 2013 2:50 pm, edited 1 time in total.
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Re: PMR446 Antenna Length

Postby Staffs Paul » Mon Jun 03, 2013 1:22 pm

70cm is basically what they call the UHF ham band from 430 to 440 a catch all for the band.

446 is actually a little higher so the wavelength is a little shorter at 67cm
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Re: PMR446 Antenna Length

Postby Martin » Sat Jun 22, 2013 1:55 am

19''1/4 inch length brass rod 4mm OD from B/Q soldered with a so-239 and x4 157mm long radials 4mm brass rod and small battery connectors soldered into the rod and you will get a vswr of 1.1 and thats good for the 446 pmr channels :thumbup:
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Re: PMR446 Antenna Length

Postby rich83 » Sat Apr 09, 2016 7:05 pm

Martin wrote:19''1/4 inch length brass rod 4mm OD from B/Q soldered with a so-239 and x4 157mm long radials 4mm brass rod and small battery connectors soldered into the rod and you will get a vswr of 1.1 and thats good for the 446 pmr channels :thumbup:


Sorry for the necro post but what would this look like?!
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Re: PMR446 Antenna Length

Postby Chris P » Sun Apr 10, 2016 6:51 am

It would look like a quarter wave ground plane for 149Mhz ( one hundred and forty nine Mhz) with undersized radials , which is almost like a three quarter wave whip with undersize ground plane for 449 Mhz ( a minimum quarter wave radial length is required to give an effective ground plane) :biggrin:

ps Ashtonmobilescanner if you are using a telescopic for transmitting you are operating illegally as it could exceed the allowed ERP as would be using any antenna not as that supplied on a legal 446 radio ie removable rather than fixed not that anyone has yet been prosecuted or likely to be :rolleyes:
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