Team Prometheus help wanted with NBTV link

[Monroe Lee King Jr.]

The JAVA app only works for receiving end we need the transmitting end on the spacecraft. to run on linux

[Steve Anderson]

A suggestion...

Rather than trying to source ready-made software for a rather specialist application - especially on Linux (I use Linux, don't worry)...perhaps a alternative approach is worth consideration?

I realise weight, size and power consumption are all issues, that having been said..

Why not use a standard 525/625 camera and down convert it to the specific format you wish to use. Several simple low-power versions have been published and in fact I'm working on one now...

Just a suggestion...

Steve A.

[DrZarkov]

...and I always thought NBTV is no rocket science...

[holtzman]

Thank you for sharing such an interesting project!
It seems very unusual for our days to go back to analog transmission. I am not electronics engineer, and have not enough expertize to give you any advice on the subject. But for mere curiosity, I want to know what can be the reason for going so much back in technology in the days when we can watch movies on smartphones and to make video calls on them via skype? Of course the quality is not perfect, but I used to think if it was analog, it would require much more energy to transmit and the quality would be even worse...
And if you want to transmit it in analog way, so why to use any software at all? It's better to make it all-analog, at least there will be no lag.
From my experience with NBTV, I was surprised how long the lag is. I connected a webcam to PC running Gary's software, and connected my 60 line monitor to the audio line out. And my pC is not weak. The lag was less than 1/2 a second, but I am not sure it was good for flying a plane...

[Steve Anderson]

This is somewhat off-topic, but about nine months ago I showed a friend (he's not in the electronics industry) around an operational TV station. After a few minutes he said, "Isn't picture quality amazing! But but why do you use 4:3 monitors for HD?.

When outside I said, "That was a 625 studio, it will be decommissioned in a month or so."

He couldn't believe it. What we get at home is a poor facsimile of what originates from the studio. An uncompressed serial HD signal requires 2Gb/s. So broadcasters compress the crap out it so the they can get a number of channels delivered where there used to be only one analogue signal. Hence all the artifacts you see these days. One plus-point, cross-colour has gone.

There are plus and minus points with both systems, it depends on the application.

Steve A.

[Monroe Lee King Jr.]

To answer the question:

Bandwidth and signal to noise ratio. NBTV can travel a lot farther on less power and for a space application it makes a LOT of sense.

We have had some success with WBTV but the range is not nearly enough to make it into space especially on the amount of power we have available.

I'm working with Gary now on a software solution thanks for all the help in that direction fellas.

Yes a hardware analog solution is in the plan! Software will work fine for the preliminary testing of the idea in general. This way we wont waste time developing something that may not work.

There are some very exciting other possibilities we can work on if this works out as we expect it too. There are some SDR things we are working on as well.

You know doing this amateur space work I have discovered the cheapest way is the old way in many ways!

Balloon launched rockets for instance. It makes absolutely no sense to me to waste a perfectly good rocket only to make 100,000 ft when a smaller cheaper rocket can actually make it all the way to space launched from that balloon at 100,000 ft.

Van Allen did this in the 50's!

NBTV will go farther on less power same thing- follow?

[Harry Dalek]

Good thinking Monroe and good luck !

Do let us know how its going ,i am sure Nasa only used SSTV so you would be doing pioneering work with NBTV on this project.

[Monroe Lee King Jr.]

Well not exactly NASA did use NBTV they did use more bandwith at 500khz then we will be using. The resolution form the moon landing was higher rez than we are attempting.

Just for fyi I've worked out the transceiver we will be using for the test. We will be downlinking on 433 and uplinking on 144 using crossband full duplex.

This is for the initial test work. We are working on an AM eSSB solution for future use.

For now we are working with AX25 protocol for the uplink.

[holtzman]

"We will be downlinking on 433 and uplinking on 144 using crossband full duplex"
Sorry I am totally confused, are you going DIGITAL or ANALOG? In the previous post you wrote about analog advantages, and that you are going to use it. Here it seems you are still aiming to digital format.
Actually, it seems to me digital is still better. All the history and real life experience tells me this.

Russians made it analog way when they took pictures of the far side of the Moon. They used slow speed telecine scanning a developed on board film. The results were inferior to those transmitted digitally from Amarican spacecraft, both in terms of speed and quality.

When television became digital in my country, they told it's for making it cheaper. Less transmitters are needed, of less power. And by the way, the quality jumped allthough we receive on a small cheap converter with tiny in-house antenna.

Again, with the wireless phone using DECT technology, I hear better with range increased by factor of two at least, while it consumes less battery power.

So where is the point? Sorry if my questions sound stupid

[Harry Dalek]

I think NBTV is less than 100 lines Nasa used 320 lines what they call NBTV and what we call NBTV is confusing .

In the 1930's i am sure they would of taken 320 lines like HD is today ...When i talk NBTV i mean true NBTV our NBTV NASA never used our system at all or close to it .
You could fit a fair few channels in their bandwidth.
Believe me your a pioneer if you use our system .

[Monroe Lee King Jr.]

Our uplink is digital. Right now we have chosen AX25 to make things easy. We don't need to send video to the spacecraft.

Your forgetting about bandwidth/SNR again. Digital will require more than we can afford.

Once we decide on a format that we find sustains our minimum requirement we can announce it.

we are shooting for the 6-12khz range we can go as high as 25khz for the FM system.

Once we switch to eSSB we are limited to 12khz max and that's a limit I'm setting.

Digital uses less power on a larger bandwidth so again it is a trade.

There are some other factors involved as well the final platform should be using the propeller II processor. We are using the R Pi for now because it's an easier swap for now.

We don't have 30 meter dishes on our ground stations

The farther along we get here the more optimistic the team get's so I'm pretty sure this is going to work.

digital is an option if conditions allow use to use it we are starting with analog that's for sure

You have to consider man power and man hours as well we are limited in both as well as funding.

If you have any of the above to spare you are welcome here!

[Monroe Lee King Jr.]

Ok here let me put it this way.

The narrower the bandwidth the less space there is for outside signals to interfere. In a wideband signal there is a lot of space for outside interference.

Therefor the more narrow the bandwidth the more signal your always going to get. So the SNR is always better with narrow bandwidth.

It's harder and harder to pack digital information in such a narrow bandwidth so you have to make a trade off.

So we want to trade resolution (bandwidth) to get the better SNR for much longer range.

So far I believe we have traded so much bandwidth for range I don't think we can do any better with a digital signal. In other words at some point you can get an analog signal in there with enough BW to get an image but not enough for a digital image.

Does that clear things up?

[holtzman]

"It's harder and harder to pack digital information in such a narrow bandwidth so you have to make a trade off"

Well, I doubt this. Attached here is a AVI file weighting mere 184 kb. It is in color, 64X64 pix resolution, 23 sec length. As far as I can remember, in 56k modem days, it was possible to download about 7k per second via telephone line bandwidth. This means it would have been possible to watch this movie almost in real time at 5kHz bandwidth (roughly)! Now take in consideration that for black and white NBTV signal of such a resolution format, you'll need something about 25kHz bandwidth (roughly again).

I appreciate your taking the time to reply, indeed your opinions are very interesting!

[Monroe Lee King Jr.]

http://en.wikipedia.org/wiki/Signal-to-noise_ratio

We are testing for now with a max 25khz (if we need it) but the goal is 6 khz and you not going to get anywhere near 56k baud at long range over the air with that.

We hope 1200 baud is possible.

[holtzman]

Thanks, now it seems I am getting the idea. You mean for 56k speed you need a very clean, noise-free channel given a narrow bandwidth is used? It was more than 10 years ago, I remember how often I cursed the connection, the low speed etc. and called for phone technician to fix the line... There was slight noise sometimes which corrupted everyting...
And CDs that do not play...the same problem I guess.
Fascinating!