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[aprssig] Good 30m Reference?

Stephen H. Smith wa8lmf2 at aol.com
Sun Feb 4 20:12:37 UTC 2007


jmaslak-aprs at antelope.net wrote:
> On Feb 4, 2007, at 11:14 AM, Bob Bruninga wrote:
>
>> You are correct that many HF recommendations are wrong and do not 
>> help the network while helping the user.  But the answer is simple 
>> and was always the same, going back to the original APRS HF operation 
>> in 1993. (except for updating to GATE,WIDE1-1 instead of GATE,WIDE.
>
>
> Wouldn't GATE,WIDE2-1 be preferable?  I'm assuming the vast majority 
> of people who can put up decent fixed 30m antennas and gear should 
> have no problem putting up a 2m antenna that can hit a decent digi.
>
>
>
> I'll be on the road mostly during the day, so this is perfect.
>

The greatest DX of all occurs via "grey line" propagation; i.e. when it 
is twilight (sunrise or sunset) somewhere between where you are and 
where the other end is.   Here on the west coast in Los Angeles, I 
routinely hear stations from the midwest and Florida in the late 
afternoon Pacific time (when it is already after sunset on the east 
coast) and just before sunrise Pacific (when it is already daylight in 
the east).     

Once as an experiment, I beaconed from my car parked outside my office 
in East Los Angeles from noon to about 5:00 PM in November (where local 
sunset was at about 4:50).    This was done with an FT00 and it's 
matching ATAS-100 mini-screwdriver antenna; i.e. not a high-performance 
antenna on 30M.   I then repeatedly hit findu to see what station had 
gated me to the Internet and where they were located.     Over the span 
of 6 hours  the sequence of entry points was:

San Diego ,     Bakersfield,   Salt Lake City,  Boise, Denver,  Omaha, 
Saint Louis,  Chicago and then back to Denver and Salt Lake City.   

You can watch the daily variation of HF propagation on my UIview APRS 
webserver at:

      < http://wa8lmf.dyndns.org:14439 >    

This is 30M monitored live off-the-air 24/7 in Pasadena, CA with a 
horizontal dipole made of two 30M Hamsticks about 15 feet off the ground 
broadsiding the northeast.  Bear in mind that I have an absolutely 
HORRIBLE noise level here (leaky digital cable TV trunk at the back of 
my yard that generates a continuous broadband S9 white noise level 
across all of the HF spectrum. ) that severely limits what I hear.  As 
soon as I get away from my own neighborhood, I can hear about 5 times 
the activity from my mobile!]

>    
> I
> Speaking of implementing things, I'm thinking of adding a "mute" 
> switch to the IC-706 stock microphone - has anyone already done that?  
> I imagine all I have to do is add a super small toggle switch in line 
> with the microphone element.  (my stock mic plugs into the 706 head in 
> my installation, but the tracker will plug into the 706 main unit, so 
> I need a way of muting things to stay legal - and I don't like the 
> idea of unplugging the mic every time I want to use APRS.)
>


I assume you are feeding the tracker into the rear-panel 6-pin Mini-DIN 
"data" connector (the perfect place to do it since you get audio in, PTT 
and a receiver squelch indicator that can hold off transmit if the 
channel is busy).    If so, I don't think you need to mess with the 
mic.   On most radios that have the 6-pin Mini-DIN connector, asserting 
PTT from this connector automatically mutes the front panel mic input to 
avoid exactly this problem.     Details on the Mini-DIN connector's 
functions are here:

  < http://wa8lmf.net/miscinfo >     

Look for the file      MiniDIN6-Packet.pdf    

Actually, a more important issue for HF packet/APRS is frequency 
accuracy and stability.    Like anything transmitted via SSB, the pitch 
of the recovered audio (i.e. packet tones) is affected Hz for Hz by 
frequency setting errors on the transmitting  or receiving radios 
(unlike VHF FM where the PITCH of recovered tones IS NOT affected by RF 
frequency errors).  The audio tone detection filters of the receiving 
TNC on the 200Hz-shift 300baud packet used by HF APRS are EXTREMELY narrow.

You must be able to set (and keep) your radio to within 20 Hz or so of 
the correct frequency long term for reliable results.   Especially with 
a dumb tracker, you are setting your frequency and transmitting "in the 
blind" with no way to confirm you are "on-channel" by receiving other 
stations.  A radio with a TCXO high-stabilty master frequency standard 
is almost essential for successful HF operation.






--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

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