Portsdown Filter Modulator board stock

The place for announcements on the latest stock items and for your feedback on items that you would like to see in stock
g8gtz
Posts: 1104
Joined: Wed Apr 07, 2010 6:26 pm

Portsdown Filter Modulator board stock

Post by g8gtz » Fri Nov 30, 2018 12:15 pm

As of today we have only 7 built Portsdown Filter Modulator boards left and will NOT get any more in before Christmas, so if you were intending to get one for "Dad's Christmas Present" please buy now before it's too late.

We have sold over 200 of the units in the last 18 months but things have changed since we started to develop it 2 years ago. Therefore we are in the middle of evaluating if it makes sense to order another 60 units - the minimum quantity we can buy - as there are several alternative commercial solutions available, such as Lime SDR, which are more flexible and available for a similar price (you wouldn't need the ADF 4351 and Lo filter).

Whatever decision we make we will continue to support members who have bought the current filter modulator board and will ensure that there is an easy and cost effective route to get on the air with DATV.

73

Noel - G8GTZ

G8PEF
Posts: 106
Joined: Mon Oct 30, 2017 6:42 pm

Re: Portsdown Filter Modulator board stock

Post by G8PEF » Fri Nov 30, 2018 1:05 pm

Hi, Noel

Having just read this, and your mentioning LimeSDR etc, it set me thinking...
Can "someone-who-knows-about-this-stuff" give an outline of what's required of an SDR in order for it to be useful for DATV? (Obviously, a TX /and/ an RX path are required if you wish to transmit, which rules out some of the SDRs available, but what else is required?)
For instance, would a HackRF One (or one of its cheap Chinese clones) be suitable? Either way, which features are the important ones that determine suitability or not?
What about other platforms? Maybe if we got enough info together here, we could add it to the wiki?

All the above, based on the assumption that I'm not going too blind in my old age, and that it isn't already covered in the wiki, of course... And if it is, please accept the apologies of a blind, daft old bat, and could you post a link to the relevant page(s) please ;)

John PEF

g8gtz
Posts: 1104
Joined: Wed Apr 07, 2010 6:26 pm

Re: Portsdown Filter Modulator board stock

Post by g8gtz » Fri Nov 30, 2018 1:44 pm

Hi John,

The majority of SDR hardware types could potentially be useful for DATV - but the major task is writing the software applications to run on them and as ATV is a bit of a niche, there are only a few dedicated people such as Dave, Evariste and Charles who undertake these tasks.

AFAIK, to date we have only really seen the Lean DVB rxr application written for the RTL dongle and integrated in to Portsdown and the DVB-S and 2S transmit applications from Charles and Evariste which are implemented in Lime, DATVexpress, RpiDATV and Portsdown.

If we do decide to use another hardware platform, for support reasons it will only be one type and there's a clue as to the possible choice in the above post!

73
Noel

User avatar
M5TXJ
Posts: 175
Joined: Wed Jul 05, 2017 8:34 pm

Re: Portsdown Filter Modulator board stock

Post by M5TXJ » Sat Dec 01, 2018 10:08 am

Ha ha,

I went for BSB when Sky became dominant, this time I've got a Pluto and BATC are going Lime...

One day I'll get it right!

73 Dave.

g0mjw
Posts: 763
Joined: Sat Sep 20, 2014 9:15 am

Re: Portsdown Filter Modulator board stock

Post by g0mjw » Sat Dec 01, 2018 11:53 am

Pluto works fine with DATV-Express, as does the lime. Pluto has on-board CPU and may be able to take some of the load of the PI in the portsdown, but it's a complicated thing to do

Mike

G8PEF
Posts: 106
Joined: Mon Oct 30, 2017 6:42 pm

Re: Portsdown Filter Modulator board stock

Post by G8PEF » Sat Dec 01, 2018 12:16 pm

Thanks, Noel. I have an original Lime SDR, looking for something to do, and when I ge the time I intend to get it doing something DATV. Noting that the the Lime Mini works with DATV Express, does the 'full' Lime also work?
M5TXJ wrote:
Sat Dec 01, 2018 10:08 am
Ha ha,

I went for BSB when Sky became dominant, this time I've got a Pluto and BATC are going Lime...

One day I'll get it right!
Haha, you and I, both, Dave with the BSB... And I also went with V2000... Oh, and I also have a Pluto, so will be interested to see how developments in that area progress.

Noel, could you expand a little on what the difficulty is with writing software for other SDR platforms, please (I'm not much of a programmer, so I have a tendency to gloss over these things...) I /thought/ that the software was principally concerned with generating the IQ data streams from the video source (and recovering the video from the received IQ data, of course) - which to my non-'softy' mind seems independent of the hardware... Perhaps I've massively misunderstood; it sounds like it (and I certainly wouldn't be the first time ;) )

John

G8GKQ
Site Admin
Posts: 1174
Joined: Sun Mar 22, 2009 1:21 pm

Re: Portsdown Filter Modulator board stock

Post by G8GKQ » Sat Dec 01, 2018 2:34 pm

Hi John

We have now got to the stage where generating the I and Q signals needed to transmit DATV from an SDR is fairly easy. The difficult bit is controlling each SDR to modulate those signals at the correct baseband level with the correct baseband filtering on to a carrier at the correct frequency and outputting that at a controlled level.

Each SDR is different in how it is controlled, and while there are some standards out there, the standards tend to add complication and extra processing load.

The Portsdown will very shortly be able to properly control a LimeSDR Mini or a LimeSDR USB. This is mainly thanks to Evariste's work on the "glue" to connect the I and Q signals to the LimeSDR; I must also acknowledge Charles G4GUO as the original author of much of the code used to generate the I and Q signals.

The reason that the Pluto or other SDRs have not been supported by Portsdown so far is that no-one else has come up with a proof of concept demo of the RPi3 driving a Pluto for DATV. I do hope to make this work one day, but there are simply too many other projects in the queue for my time to say when. If someone could provide a demo, I would be more than happy to modify it and integrate it with Portsdown sooner.

I hope that provides some insight into the issues with DATV transmission using SDRs. Receiving DATV presents even greater difficulties as the error-correction algorithms are beyond the capability of most domestic computer hardware - it needs specialist FPGAs.

73

Dave

g8gtz
Posts: 1104
Joined: Wed Apr 07, 2010 6:26 pm

Re: Portsdown Filter Modulator board stock

Post by g8gtz » Sun Dec 02, 2018 10:13 am

Ha ha,

I went for BSB when Sky became dominant, this time I've got a Pluto and BATC are going Lime...

One day I'll get it right!
Don't despair (or sell it) - I've got one as well and I'm sure it will rise to the top of Dave's list one day!

Plus as Mike says you can already use it as a DATV generator using Charles' excellent DATV-Express PC software.

73
Noel

g0mjw
Posts: 763
Joined: Sat Sep 20, 2014 9:15 am

Re: Portsdown Filter Modulator board stock

Post by g0mjw » Sun Dec 02, 2018 10:32 am

I will mention it again - the Pluto can transmit 333ks DATV all by itself with the right software loaded. It's very capable and works up to 6 GHz. Pity the USB interface is so slow.

Mike

G4GUO
Posts: 609
Joined: Tue Feb 16, 2010 12:51 pm

Re: Portsdown Filter Modulator board stock

Post by G4GUO » Mon Dec 03, 2018 5:12 pm

I had thought about how to allow faster DVB-S/S2 on the Pluto
rather than sending 32 bit IQ data to the Pluto it would be possible to send an index
into a constellation table (8 bits), the Pluto would then take that index and turn it into
32 bit IQ data on the Pluto itself, immediately you get a 4x speed up and for QPSK
potentially a 16x speed up.

There is a guy in France (call escapes me) who has got applications running directly on
the Pluto but he has had to drill holes in the Pluto case to cool it down!

Unfortunately a lot of work would be involved and there are more interesting things to work on.

- Charles

Post Reply

Return to “BATC Shop”