Re: Inter-balloon crossband repeater with Dallas

Andrew Koenig


Unfortunately we couldn't scramble the payload together in time for GPSL. Michael, Chris and I have prepared a secondary payload of just a simple crossband repeater using a DJ-580T. The backup payload is in the ballpark of 600 grams.

There were two main things working against us, and I'm sure we would've had some other road blocks as integration continued. The issues we had were strictly related to interfacing the repeater controller, an Arcom RC210, to the various handheld radios (RX, TX, remote base). It boiled down to two issues:

1) RFI. The Arcom seems to run fine in its rack enclosure, but was not a happy camper without adequate shielding.
2) Logic Levels. For unknown reasons, the shift registers in the Arcom couldn't seem to pull down the PTT line enough to trigger the 220 HT. Although buffer circuits are an option, these controllers are borrowed and can't be modified to that extent.

The RFI was a very interesting issue. I learned that the Arcom RC210 does not have a ground layer in the PCB; it appears to just be a simple 2 layer PCB. At a repeater site in a rack enclosure, this shouldn't be a big deal, but when we're running 2 HTs less than 12" from the controller, it just was overloaded. The most common symptom was a persistent digital clicking sound coming through the transmit audio, likely from the shift registers being clocked out. We were able to modulate the various RFI artifacts in the audio by moving the HT around in relation to the Arcom.

The logic levels were quite quirky, and I was never able to conclude why the Arcom was unable to trigger PTT on the 220 HT. I believe the output shift registers are open-drain, which indicates that it shouldn't have an issue pulling the PTT line to ground. On the bench, we never saw the Arcom pull the PTT line below .6v. Unfortunately the required buffer circuitry modifications to overcome this one goes a little beyond the scope of what these controllers were loaned to accomplish.

So with these two things working against us, and given the time constraint, we've opted to just fly two "island repeaters" and see about linking them via crossband repeater on the ground. The UT Dallas ARC has a nice satellite station, and we'll see about aiming it up towards Kansas since the DFW-area balloon can likely be hit off the side of the beam. This depends on the TM-V71a being cross-band capable with some very odd splits.

Anyway, sorry to get your hopes up. We'll definitely look into trying this experiment again with some better hardware and more time to prepare. I believe we might have another chance later in the summer with a geographically diverse series

73 de KE5GDB

On Mon, Jun 5, 2017 at 6:44 AM, BASE <basedepauw@...> wrote:

BASE DePauw can fly your repeater payloads.  I do not have my repeater operating at this time and have other tasks on our schedule for the early summer.

Please let me know the payload weights (or masses).  If I need to bring a larger balloon, I can do that.

See you in Hutchinson.

Howard, KC9QBN

On Monday, June 5, 2017 2:35 AM, "Michael West michael@... [GPSL]" <GPSL-noreply@...> wrote:

Hi all,
On June 17 the Plano, TX amateur radio club (PARK) will be launching a balloon near Dallas with a crossband repeater (440 RX/140 TX). We’d like to try and use a 220 HT as a half-duplex remote base to link this with another balloon repeater at GPSL. Any transmissions heard on 440 by either balloon would be simultaneously broadcast on 140 and 220. The other balloon would listen on 220 and 440, and repeat transmission on 140. Talk in Texas, be heard in Kansas, and vice versa! 😊
We’re looking to collaborate with anyone at GPSL who has either space for an extra payload or plans to fly a crossband repeater. We can provide whatever hardware is needed, just let me know.
Andrew KE5GDB came up with the idea and will be helping with the PARK launch. Chris N5CMR and I, W5MAW, will be at GPSL and can bring up the hardware from Dallas. Chris and I didn’t plan to launch a balloon and it might be a little difficult to try to put one together in time for GPSL, so hopefully we can find someone to help.

Michael West

Andrew Koenig

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