[OZAPRS] Concerned about 10.151Hhz LSB

[Chris Hill]

Hi Hamish,

I think two things come out of this:
1.  USB is better than LSB, when trying to operate legally on the
international 30m HF APRS frequency
2.  Higher TNC modem tones are "safer" than lower tones, when trying to
operate legally on the international 30m HF APRS frequency

Consider the following two cases:

+------------------------------------------------+

Firstly, let's take the case of:
- a standard HF SSB rig, with a TX passband of 200Hz to 2800Hz
- TNC (eg MFJ1270) generating 1600Hz and 1800Hz tones
- Trying to operate on the international frequency of Tone_1=10149.2kHz,
Tone_2=10149.4kHz

LSB operation:
- Suppressed Carrier freq = 10149.2 + 1.8 = 10151.0 MHz
- Significant output power available from 10150.8 MHz to 10148.2 MHz
[Audio
from 200Hz to 800Hz is TXd out of band]
- Suppressed Carrier being transmitted (at very low level) at 10151 MHz
[Out
of Band]
- Suppressed USB signals being transmitted (low level) from 10151.2 MHz to
10153.8 MHz [Out of Band]

USB operation:
- Suppressed Carrier freq = 10149.2 - 1.6 = 10147.6 MHz
- Significant output power available from 10147.8 MHz to 10150.4 MHz
[Audio
from 2.4kHz to 2.8kHz is TXd out of band]
- Suppressed Carrier being transmitted (at very low level) at 10147.6 MHz
[In band]
- Suppressed LSB signals being transmitted (low level) from 10144.8 MHz to
10147.4 MHz [In band]

+------------------------------------------------+

Now consider the case of:
- a standard HF SSB rig, with a TX passband of 200Hz to 2800Hz
- TNC (eg PK-232) generating 2110Hz and 2310Hz tones
- Trying to operate on the international frequency of Tone_1=10149.2kHz,
Tone_2=10149.4kHz

LSB operation:
- Suppressed Carrier freq = 10149.2 + 2.31 = 10151.51 MHz
- Significant output power available from 10151.31 MHz to 10148.71 MHz
[Audio from 200Hz to 1.31kHz is TXd out of band]
- Suppressed Carrier being transmitted (at very low level) at 10151.51 MHz
[Out of Band]
- Suppressed USB signals being transmitted (low level) from 10151.71 MHz
to
10154.31 MHz [Out of Band]

USB operation:
- Suppressed Carrier freq = 10149.2 - 2.11 = 10147.09 MHz
- Significant output power available from 10147.29 MHz to 10149.89 MHz [In
band]
- Suppressed Carrier being transmitted (at very low level) at 10147.09 MHz
[In band]
- Suppressed LSB signals being transmitted (low level) from 10144.29 MHz
to
10146.89 MHz [In band]

+------------------------------------------------+

I don't have enough information on key click / keying transient
characteristics to meaningfully comment.


73 Chris vk6kch





-----Original Message-----
From: ozaprs-bounces at marconi.ics.mq.edu.au
[mailto:ozaprs-bounces at marconi.ics.mq.edu.au]On Behalf Of Hamish Moffatt
Sent: Wednesday, 3 December 2003 6:58 PM
To: ozaprs at marconi.ics.mq.edu.au
Subject: Re: [OZAPRS] Concerned about 10.151Hhz LSB


On Wed, Dec 03, 2003 at 01:09:25AM +0800, Chris Hill wrote:
> Recipe for HF APRS happiness;
> 1.  Look up the specs on required spectral purity for out of band
> transmissions (varies from one country to another, but at least -40dB or
> better)

Well, are you sure that your USB signal is entirely below 10.150 MHz?
When you're on 10.151 LSB your suppressed carrier is out of band, but
your audio signal is more likely to be within the band.

> 2.  Estimate (or measure) the Signal to Noise ratio of the audio you are
> feeding from your TNC into your HF rig.  Don't forget to add power
supply
> noise, alternator whine, keying spurii from the modem chip, etc etc

Key clicks are likely to extend out of band from your USB signal..

Hamish
--
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>
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