[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Re: [sarex] What am I doing wrong...?]

Guido Gazzadi wrote:
> n4xeo wrote:
> > I would tend to say that your local aprs stations are running HIGH
> > deviation.  This is what I've seen from running a bbs for 15 years. The
> > users just don't have the equipment to set the tnc for 2.8 to 3 khz of
> > deviation. Not to mention most radios out of the box now a days are running
> > over 5khz of deviation. Just add a tnc and look at what you have.
> >
> > 73, Bill N4XEO
> >
> I full agree with the need to set a correct TX deviation, but what is the way
> (for an average ham...) to measure it ???
> I have a Tek 100 MHz scope, HP old (and nice:-) HF-VHF-SHF signal generators
> and frequency meter, and the usual shack stuff.
> Someone can explain a technically-correct procedure ?
>                                                  thank in adwance, 73 de Guido,

I could go into first bessel null crap and all sorts of geek-speek , but
hey I am just a radio tech who knows what works , and your oscilloscope
will give you more help when you need it than just about anything , so
don't discount its value !
I would love to have a 100MHz Tek scope at home ( I do at work ) .....

Ok , this is not the "do-all" answer but it works for most folks :)

You need some sort of reference to be able to do a good deviation
setting without a service monitor , so the best bet is to have a known
radio that is set properly ( like a local node ) and use that as your
reference , then you need a seperate receiver (like a scanner or such )
and a ac voltmeter  ( or in your case your scope ) .

Then what you do is connect the ac voltmeter to the rx audio output of
the scanner and tune it to the local node frequency and measure what
kind of audio level you are getting from the node during long duration
transmissions write this level down and without changing anything on the
scanner , with your own radio/tnc setup on a dummy load set it up so
that it can transmit actual text ( not mark or space only ) on the same
frequency  and make it transmit enough so that you can get a good
measurment on your ac voltmeter and set your tx level until it matches
the level that you wrote down for the local node .

This of course is rather crude , but for 1200 baud afsk it does get you
alot closer than setting by ear and if you don't have a service monitor
it will suffice .

But it must be stressed that your "reference " must be transmitting the
proper deviation to begin with or you will only be as accurate as it is
, so make sure before doing this .

You could use test tone , but that would require having control of the
"reference" xmitter to be able to put it into align mode :}

I am sure that someone will shoot holes full of this , but it has worked
many times in the past for lots of folks in the inland northwest
washington state where we don't have service monitors and hi paid
techies to let us use them ;^}

I am one of the lucky ones who has test eqpt. that I can use at work :|

Hope this helps .

Douglas Cole   N7BFS
AMSAT#26182 , K2 # 544
Registered Linux user # 188922
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org