Re: APRS reception concern Huntsville

Bill Brown

hi Mike,

  Our local chase and recovery team are really experienced at retrieving payloads from trees and forests but we will try to land in open fields.

  Not a bad idea to start planning APRS time slots and frequencies for the balloons that will be flying.

  I will have one APRS Skytracker on a Pico balloon and one on a latex balloon but those have a time dither algorithm which shifts the transmit time up or down by 5 seconds plus or minus for each transmission on a random number generator basis.

  They also transmit on 144.39 AND 144.34.

  I plan to put an iGate on 144.34 on my mountaintop location 20 miles south of Huntsville.

We've had no problems with APRS coverage however when we fly balloons from Huntsville.  My mountaintop digi (WB8ELK-1) tends to fill in the gaps. I don't have it on most times but usually only during balloon flights. 

- Bill WB8ELK

-----Original Message-----
From: Michael Hojnowski <kd2eat@...>
Sent: Sat, May 20, 2023 9:56 am
Subject: Re: [GPSL] APRS reception concern Huntsville

More iGates is definitely a help for retrieval, as we have a better chance of getting  beacons closer to the final landing spot.  Personally, I love it when there's an iGate right in the predicted landing zone.   If we do get a few portable iGates on offer, having one camping on a hilltop near the "average landing zone" for the duration would be helpful.  I'm running into some glitches, but I hope to have a mobile iGate running for the flight, so I'll be in the recovery area iGating some frequency or another, depending on needs.  I don't expect to fly an APRS tracker, so I can help fill in with whatever frequency is most helpful.

In some previous GPSL's we've actually done both frequency AND time based coordination, taking advantage of those trackers that can designate the second upon which to transmit.  With a 5 second gap between xmits, we can easily accommodate 12 APRS balloons on 144.390 each beaconing once/minute.  That said, 144.390 will be a balloon-a-palooza for the flight duration.  Using alternate frequencies helps relieve the congestion on 144.390, reduce the instance of cranky hams in the area who will complain we're misusing APRS, and also helps address trackers that can't synchronize transmissions at a particular second.

Honestly, looking at the map, I think we'll be really lucky if our landing zone isn't in the forest.  To that end, I'm planning to launch a payload that I don't love much.  If it's in a bad recovery zone, I'm just going to abandon it.  I have a LoRa test I want to try that is a great candidate for "Fire and Forget" mission.

Should we start a table of frequencies and time slots for the APRS flights?  I'm happy to help organize that.

Mike / KD2EAT

On 5/20/23 01:57, Mark Jessop wrote:
Is more iGates operating on the same frequency going to solve the issue in this case?
Isn't the issue more about too many transmitters trying to use the same channel at the same time? If they transmit at the same time, and there isn't a significant enough difference in their transmit power for one to be 'captured' over the other, they're just going to collide resulting in no decodes?

It seems like the solution is spreading out in frequency (which will require more igates... though on other frequencies).

On a related note - how many simultaneous payloads are currently planning to be in the air? I'd like to make a GPSL 2023 dashboard on, but I'll need to know the callsigns of what'll be in the air.

Mark VK5QI

On Sat, May 20, 2023 at 2:32 PM Lynn Deffenbaugh <kj4erj@...> wrote:
May I ask what an " reporter" is?  Is that injecting the decoded packets into the APRS-IS for global visibility by any APRS-IS client application or some sort of direct reporting to which is only a single website?

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 5/20/2023 12:21 AM, Phil Karn wrote:
Do you guys need to add iGates? I have a turnkey receive-only igate configuration that will run on a Pi (or other small Linux box) with a low end SDR front end such as an Amsat UK Funcube dongle. It's all my software: a multi-channel SDR, AFSK/AX.25 decoder and reporter. If you're using WB8ELK's tracker that transmits on both 144.39 and 144.34, it listens on both channels simultaneously in case there are a lot of collisions on 144.39.
On 5/19/23 15:53, Mark Garrett via wrote:

Thank you for your comments.  I hope the I-Gates and nodes will be able to handle the traffic on 144.390  in the Huntsville area.   I believe others will be flying balloons & operating portable I-gates and other frequencies such as 144.340 and to help reduce congestion.  The good thing is that the congestion if any will be only for around a couple of hours at most. Once the balloons are aloft other I-Gates should be able to receive and handle the traffic.  Currently watching the W8BI-11 & 12 that were launched from the Hamvention today and that area is probably the most active area in the world right now.


On Thursday, May 18, 2023 at 08:31:16 PM CDT, Carlton Corbitt via <ccccrnr@...> wrote:

Hi Mark,

I don't have much airborne experience in Huntsville, but of any sizable city i've lived in since adding APRS to balloons the greater Huntsville area has the worse ground tracking of APRS i've come across.

my FTM-400 leaves a good bread crumb trail of my car everywhere else, but very hit or miss in the greater north alabama area.
I've heard several other hams also complain about APRS here versus where ever we came from, but alias we haven't actually done anything to fix the problem.

So given the limited i-gates with good reception around Huntsville, my concern is that they could get overloaded between all the balloons and all chase cars all packeting rapidly on Saturday of GPSL.


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