[OZAPRS] Brisbane APRS

Glen English VK1XX glenlist at pacificmedia.com.au
Sun Oct 29 17:59:49 AEDT 2017


Andrew, there are a few checkpoints to this

1) I gather you know precisely what frequency error your spectrum
analyser has.

2) I gather your spectrum analyser , if FFT / digital  type, has
sufficient resolution bandwidth to tell a non aliased story.

3) It is not usual for station's TX  PLL /synthesisers to not be fully
settled during the keyup phase, and take 30- 100mS to establish fine
frequency lock .

4) I would expect +/- 5ppm for most radios, that being about +/- (5 x
145.175 Hz)

5) It's probably not going to hurt much until +/- 1kHz, and not really
hurt until +/- 2kHz, depending on the TX deviation. (IE how far outside
the Receiver IF filter the modulation protrudes, as the received signal
will be asymmetrical in the receiver's IF passband, the higher the
deviation, the greater the extremes)

How far out are they ?

-glen


On 29/10/2017 5:51 PM, vk4tec at tech-software.net wrote:
>
> Hello
>
>  
>
> I just had a quick look on 145.175 MHz on a spectrum analyser.
>
>  
>
> I can see stations off frequency
>
>  
>
> I can see transmitters shifting frequency on keyup
>
>  
>
> Andrew
>
>
>
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