[OZAPRS] Brisbane APRS

[Glen English VK1XX]

yeah, I  used to do TX key-up freq chirp characteristic /amplitude
envelope fingerprinting in the mid 1980s with a microbee and parallel
port ADC...

cheers


On 31/10/2017 2:55 PM, Carlos Peco-Berrocal wrote:
> Hi Glen,
>
> The transient at the beginning/end of the transmission is unique. I
> even compared two portable radios and differences in battery level and
> temperature made them drift differently during the transmission
> period.
>
> Those transients can be recorded and then new transmissions are
> correlated with the entries in your database. There are standards for
> that database so you can share fingerprints with "your mates".
>
> I found a couple of photos, I don't know if the link to imgur will work:
>
> https://imgur.com/a/kTJ4S
>
> That repeater was off frequency few hertzs, you can see the vertical
> pink lines (markers).
>
> The last image was HF, there are lots of interesting details in the waterfalls.
>
>
> If you monitor Canberra Approach you'll see the air traffic controller
> in the center (GPS disciplined radio from some Germans you know) with
> the aircraft appearing at the sides. The automatic simultaneous
> transmission detection available in the current generation of ATC
> radios from the same German brand exploits that: if two simultaneous
> transmissions occur, it is highly likely that their instantaneous
> frequencies will be few hertz apart so they will appear as two peaks
> in the FFT of the complex envelope.
>
> https://www.youtube.com/watch?v=Y983aZelEkM
>
> Back in the days of CB27 in AM you could hear a beating tone when two
> transmissions happened at the same time and had power levels in the
> same range (if one transmission is MUCH stronger than the other,
> you'll hear nothing but the strongest transmission).
>
> Sorry for the long post, I hope you find it interesting. Happy to take
> some toys to your place so you can tinker a bit with this.
>
> cheers
> Carlos VK1EA
>
>
>
> On 10/29/17, Glen English VK1XX <glenlist at pacificmedia.com.au> wrote:
>> hmm
>>
>> how much sag is that  in kHz, or even better Hz/sec ?
>>
>>
>> On 29/10/2017 6:35 PM, vk4tec at tech-software.net wrote:
>>> http://59.167.159.165/aprs.jpg
>>>
>>> -----Original Message-----
>>> From: OZAPRS [mailto:ozaprs-bounces at aprs.net.au] On Behalf Of Glen English
>>> VK1XX
>>> Sent: Sunday, 29 October 2017 5:00 PM
>>> To: ozaprs at aprs.net.au
>>> Subject: Re: [OZAPRS] Brisbane APRS
>>>
>>> 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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