[amsat-bb] NO-84, what is the secret?

Jerry Pixton jpixton at shentel.net
Tue Dec 8 19:51:21 UTC 2015

NO-84 listeners want-a-bees,

Mark asked a good question for beginners (aren't we are all beginners 
with a new mode?):

On 12/6/2015 11:43 PM, Mark Lunday wrote:

> 1.	What's the secret to receiving PSK31 on FM?  I never tried that
> before.

Given your 70cm FM radio, you will want to get an audio output that you 
can connect to a sound card in your computer. You are looking for the 
type of low level audio output that maybe you would feed to a rtty 
modem, etc while is a SSB mode. Some radios might have special audio 
connections for 1200 or 9600 baud FM packet - this is not what you want. 
The audio connection you are looking for might be called AFSK or maybe 
DATA - one that gives you the full 3KHz of bandwidth. Worse case, you 
can use high level Speaker audio through an attenuator so as to not 
overdrive your sound card.

Once you get the audio connected to your sound card, then probably the 
easiest PSK31 program to start listening with is DigiPan. I find the 
waterfall view very helpful to find signals to work. There is a good 
picture of what to expect on the apps.org/psat.html web page. The 
signals you will be able to decode are those vertical lines. In the web 
picture you see the signal of DK3WN at about 1000 Hz. And you see the 
beacon at 314 Hz. The slanted signal is a signal that is not being 
doppler corrected - either ground based or trying to call thru NO-84. 
These are much harder to decode.

So with your radio in FM, keep it tuned to the NO-84 downlink frequency 
of nominally 435.350 MHz, remembering that at the beginning of a pass 
the UHF signal is going to appear closer to 435.360 MHz, move through 
435.350 at closest approach and leave you around 435.340 MHz all due to 
the doppler shift. If the radio has a Narrow FM mode, that might help to 
recover a stronger audio signal.

Once you can comfortable see some signals and decode them, you can then 
move on to the transmit side. Probably DopplerPSK, by K0SM, is the 
easiest way to start. Here you are using a USB HF signal which may be 
more familiar to most hams as the standard setup for working PSK31 on 
the HF bands.

Give it a try. NO-84 PSK31 is a challenge but doable.

73, Jerry, W6IHG

Dr. Jerry R. Pixton, PIXOS Designs
jpixton at shentel.net

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