[aprssig] Need help testing 30m HF APRS in the Northwest

[Ray McKnight]

Well, the *actual* frequencies of HF APRS are subjective.
There's the 10.151MHz we all know and love, but that
is actually never what you tune your dial to, *usually*.

I hear several claiming an *exact* or actual dial readout to use.
This is bunk.  Every radio/TNC combination can be different.
Your problem of not getting to a DIGI might be either:
not being on the correct frequency, or
not having sufficient radiated signal

To determine how your radio/TNC display your actual transmitted
frequency you need to know:
what your TNC tone pairs are - MOST tnc's are different!
How your radio handles the display, if it has a "digital" or "packet" mode
that attempts to add/subtract the *assumed* TNC tone from the center
frequency.

As an example, my FT-1000D has several different settings to adjust the
displayed dial freq to try and match the sideband offset of various TNC's.
If I have that set incorrectly my dial freq could be several hundred Hz off.
It also has a true center freq mode, so I can simply do it myself knowing
what the offset is.

On HF, your radiated output can be almost NOTHING, even with
hundreds of watts, but in your case with only a few watts you need to
make sure you're getting out!  If your antenna stinks the output power
is meaningless.  You can load up a light bulb and the transmitter might
be perfectly happy but no one except your next door neighbor will hear you.

You've made no comments as to what your antenna is and how it's mounted.

Make SURE you're on freq first, then work on the antenna issue.

For all digital modes in the USA, LSB is the standard, BUT most
rigs will not be happy with that since the offset will SEEM to place you
outside the band edge and the rig's CPU will prohibit TX.  So you can
still go USB and subtract to get where your dial needs to be.

With only a few watts you SHOULD be getting out most of the time,
even with poor propagation these days, so I'd guess you're not on freq
or the antenna isn't doing it's job.

What TNC did you say you had and what's the tone pairs?
And you rig?
----- Original Message ----- 
From: "Ben Jackson" <ben at ben.com>
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
Sent: Sunday, July 30, 2006 19:10
Subject: Re: [aprssig] Need help testing 30m HF APRS in the Northwest


> On Sun, Jul 30, 2006 at 09:18:11PM -0400, Stephen H. Smith wrote:
> >
> > The actual mark and space frequencies for 30M HF APRS are 10.149.2 and
> > 10.149.4 .
>
> Yes, I'm doing direct FSK at 10.149.200 and 10.149.400.
>
> > Because of the very narrow receive passband of most TNCs
> > on 200 Hz shift on HF,  you MUST be within 10-20 Hz absolute of the
> > correct frequency on transmit.
>
> Well, the transmitter and receiver have to agree within about 20Hz.
> How do HF gates generally maintain that <2ppm accuracy?
>
> It may be that a mobile HF APRS beacon is impractical.  If so, I'm
> learning it the hard way.
>
> -- 
> Ben Jackson AD7GD
> <ben at ben.com>
> http://www.ben.com/
>
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