[OZAPRS] Brisbane APRS

Tue Oct 31 16:37:29 AEDT 2017

actually Carlos, I wonder how useful the frequency chirp is now with the
advent of fractional-N synthesisers with their MHz wide loop bandwidth,
the radios are generally well and truly settled by the time the TX is
turned on....

On 31/10/2017 3:48 PM, Andrew Rich wrote:
> I used to check RADAR encoders with a logic analyser 
>
> And change valves 
>
> I used to work MIR on C64 and a Baycom modem 
>
> Those were the days before SMART phones
>
> Andrew 
>
>
>> On 31 Oct 2017, at 2:09 pm, Glen English VK1XX <glenlist at pacificmedia.com.au> wrote:
>>
>> 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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