[aprssig] 433 MHz operation

Stephen H. Smith wa8lmf2 at aol.com
Wed Feb 15 13:24:20 CST 2012

On 2/15/2012 1:12 PM, Scott Miller wrote:
> Hi all,
> I've been playing with some half-watt 70 cm data transceivers lately. I'm 
> currently testing at 434 MHz, and with the standard crystal they should cover 
> about 430 to 439 MHz.  I'm not really familiar with the 70 cm band plan and 
> figured I'd check here and see if people consider that a reasonable part of 
> the band to be working in.

Traditionally weak signal SSB and CW, including moonbounce,  have been done in 
the segment  432.000 to 432.5 or so.  This the segment where serious arrays of 
high-gain long-boom yagis (horizontally polarized) and ultra-low-noise RX 
preamps are routine.  (This is a historic legacy of the early 1950's when you 
got to this band by using the third harmonic from a traditional 
crystal-controlled frequency-multiplier class-C RF chain on the low end of two 
meters from 144.000 to 144.100 or so.    I.e.  144.05 x 3 =  432.15, etc  )

Above this, traditionally has been  ATV country from 433-439 (single 6-MHz-wide 
NTSC TV channel) , while FM/repeater activity has always been 440-450 (due to 
ham FM activity beginning with surplus land-mobile radios retuned downward from 
450-470 MHz) .     In recent years, some FM activity has been spreading 
downward to the 438-440 segment, due to many newer ham FM transceivers now 
having coverage from 438-450 MHz.

In populous active areas like southern Cal or the north-eastern US, the range 
420-430 (i.e. below the "bottom of two meters x 3) is used extensively for 
remote control links for systems on other VHF/UHF bands or even for repeater 
links for multiple systems in the 440-450 range. (20-25 MHz away is enough to 
keep repeater tx at 445 from desensing link receivers at 425 or so.)

Note that in most other parts of the world, the "UHF band" for hams is only 
430-440 MHz (or less), rather than the vast 420-450  MHz spread that we enjoy 
in North America.   The result is that in these areas,  the "low end" of the 
band is busy with the kind of strong-signal FM/repeater operation that we (in 
North America) do on 440-450.



Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
Home Page:          http://wa8lmf.net

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