FEEDACK PLEASE: Smaller Antenna and No Pointing -- Lower Bitrate

In the next few days, we’ll be experimenting with putting the existing power into a smaller channel. This has both pros and cons. The pro is that pointing should be even easier. Our eventual goal is to let a user simply place the receiver flat on the ground and receive packets. But in order to do this right now, we the result will be to reduce the bitrate.

Question: Would you prefer something like a GPS antenna that requires no pointing–at a cost to bitrate? Or would you prefer higher speeds with some degree of pointing?

How much reduction in Baud rate are you proposing. Currently we get I believe 20 MB a day?

Assuming you can reduce the size of the antenna then I imagine you will then want to market a lantern the size of a mobile phone.

At the moment, is the current Lantern Wifi Hotspot getting enough solar power to receive and process a Outernet signal for 24 hours?

Unless the E4000 tuner and the Chip computer has a massive reduction in size and power requirement, I cannot see a smaller Lantern running for very long without recharging.

My feeling is get the current system working with the best download rate. Miniaturizing the system for me is not that important.

I think the current Solar powered Lantern if It can be tweaked to work 24 hours continuously as a solar Hotspot is a very good solution.

Possibly you could make the pointing easier by having a internal GPS chip and compass chip and then have RED(port side) led on left and green (Starboard LED) on the right. The GPS calculates the position relative to the Inmarsat satellite and then the CHIP either tells the left or right led to flash indicating which way to swivel the lantern.

For elevation setting, both leds could flash fast for too flat. and flash slowly when to low. No flashing when aimed correctly.

If you dont want to put a GPS chip in you could Just have the E4000 decode the L-Band GPS signal that is coming to the Lantern L_Band antenna. ( I acknowledge the current LNA SAW filter may be blocking the the GPS frequency)

What cost to bitrate? Are you proposing 19Mb a day instead? Or 3Mb? How large the reduction is matters to me.

The current solar panel won’t run the lantern for very long at all. I’d suggest spending £15-£20 on a proper external panel if you want that to work

If this makes the signal easier to access it might be worth it. I haven’t been able to get the signal even pointing it, so it would seem to me that a signal of any kind is better than one that doesn’t exist.

Your right, Sam. I gave up on solar charging and use a 2 watt USB wall wart to run the Lantern. I believe we would need a 15 watt solar array to run and charge the Lantern to get 24/7 out of it, but am not too sure the 5300 mAhr Boston Power lithium ion will keep it going at night. I haven’t tried that yet. Ken

Syed said a lantern should run at [2watts](http://discuss.outernet.is/t/lantern-power-budgets/2265] so 0.4 amp at 5v.

Without cable loss etc the 5300ma shoul run it for around 13 hours. So probably 8-10 in the real world?

I think that ease of use of the device is more important at this point than bitrate. It appears that the data is just compressed with gzip now, so that leaves a lot of optimization yet. Usability is key, and optimization to increase the real data throughput still can be done.

The current data rate is 2.1kbps. Moving to a lower symbol rate would bring the data rate to about 1.2kbps.

The purpose of reducing the size of the antenna is not to make the device smaller (though it might). The main reason is to allow reception by an omnidirectional antenna, which requires no pointing. A GPS receiver has an excellent user experience.

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That’s great. When will the tests begin? I have a number of GPS antennas that I’ll try out.

Later this week. They will be short tests. We should definitely try regular GPS patches, but they are usually tunes to L1. The ceramic patches we have were retuned down to our center frequency.

I thought GPS antennas were heavily by pass filtered to only allow the GPS signal at 1575.42 MHz
as opposed to Outernet 1545.95 MHz. Is 30 MHz outside the bypass filter of a gps antenna?

Are all three Inmarsats going to reduce the Symbol rate or just the one covering the Americas and the Outernet office?

GPS receivers do have really sharp filters, but that happens after the passive antenna. The antennas are usually designed for at least a few megahertz of bandwidth, and they can always be retuned to a slightly different center frequency.

The lower bitrate service will probably only be tested on 25E.

There is a simple modification for active GPS antennas. I’ve been able to receive signals from Inmarsat although a bit stronger ones: AERO and EGC signals. Here’s the link:

http://wiki.muc.ccc.de/iridium:antennas#modified_active_gps_antennas

My miscommunication. I meant if we were to offer the antenna, it would be similar to a GPS-style ceramic patch, but the element would be tuned for our band.

I’m good either way. I didn’t find pointing the Outernet patch to be all that critical or difficult. :smile:

I’d suggest reducing bitrate to increase the rx power.
Perhaps then look into increasing the amount of data compression. If that can’t be done, I’d suggest prioritising transmissions of weather etc.
Then perhaps down the line in the future if finances allow a 2nd channel could be used to increase the data rate.

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Personally, I would prefer a higher bitrate with some pointing needed. This isn’t like trying to aim a satellite television dish… This is much easier!