Re: Very low iGate reception


Bill Brown
 

I forgot to copy the GPSL group in my reply to Zack but here are some thoughts:

The HX-1 audio needs to be superimposed on a bias voltage going into the module and the p-p audio level should be low enough as to not overdeviate it. I will have to check my design notes on my other computer but what I recall is that I usually start out with about 200 mV p-p audio level and start with 2.5 volts bias but usually end up around 1.7 volts bias into the HX-1 to allow you to center the frequency onto 144.390 (or 144.800) depending on your country's APRS frequency.

Also a horizontal dipole antenna swinging around will cause some very bad fading unless you use something like a Big Wheel, Turnstile or HALO antenna (but then you end up with that pesky cross-polarization hit). But it you run a big wheel on the chase vehicle as well, then it will be a good thing for simplex telemetry but not digipeaters but having an iGate ground station with horizontal polarization might be a good way to solve that. I concur with another post that bending the vertical radiator about halfway in a 45 degree angle does indeed help with the null below the balloon.

I did a 10 mW flight on 434 MHz once using a vertical dipole and a whip on the car. I had great reception until I got within a 10-mile radius of the balloon's position while it was over about 60,000 feet. The signal rapidly faded out to almost nothing until I drove 10 miles to the other side of the balloon and then it suddenly ramped up dramatically in signal strength.

- Bill WB8ELK



-----Original Message-----
From: Zack Clobes zclobes@... [GPSL]
To: Group GPSL
Sent: Mon, May 25, 2015 2:11 pm
Subject: [GPSL] Very low iGate reception

 
I just got done with our flight 2015c which went up to 87k'.  It was a HX-1 300mW transmitter that was tied in to a decent whip antenna laid horizontally from the capsule.  I expected to take a small hit from the cross-polarization, but as you know horizontal antennas don't exactly stay horizontal up in the sky.

The capsule was airborne and within iGate range for at least 96 minutes (yes, a short flight), beaconing every 20 seconds, for a total of 288 potential packets being captured.  According to APRS.fi, only 28 packets were gated this morning, for less than 10% capture rate.  


Direct RF reception from the trackers was pretty poor as we were sitting directly under the balloon for much of the flight, but I still captured 111 packets (over ~40% capture - I didn't start logging until 8 minutes into the flight).  I don't see any indications that the transmitter wasn't operating during these blackout periods.


The APRS path was disabled above 2000m MSL, so all of the packets gated were direct.


Any ideas on why we had such low copy rates?


Zack Clobes, W0ZC
Project: Traveler
www.projecttraveler.org

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