One time rant, get it off of my chest.. then the DigiLite from BATC

Well, now that you can tell that I only am posting short messages once every three months or so, that life has gotten in the way of my other plans... including ham radio.

I've not been on the air since June or so, and had severe house and antenna damage in early July that-- although the monetary loss was minimal, took a lot of my SUMMER free time to fix.  I would often operate from the W0CXX club station at work, but they are re-roofing the building, and there are no usable antennas there either for quite some time.  So ham radio has been on hold.

I'm probably back to operational on 40m (at least with a low dipole), pretty sure I'm operational on 20-15-10m. My previously poor 75/80m tower feed can be fixed.. but with the 'spots being what they are lately I'm not in a hurry with that.

I want to complete my 12m/17m Moxon/Yagi combo that I've been building out of an old 10m Cushcraft beam. (When I prove that it works I'll post a 'blog entry on it here with an overview at Amateur Radio.com.)   I have a 6m 5 element beam ready to put on a roof tower on the opposite side of the detached garage from where I have the tower.  It will be a little lower in elevation but should be fine.  This has been in the works since spring.  I was also going to put up two verticals phased on 40m (and eventually load it for 80m) but I don't see that happening in 2011.  Sigh.. for a while there I was really productive with the hobbies.  I lost my wire 1/2 square for 40m when a tree fell through it, so it would have been nice to get the phased ones up.  Maybe next year.  If I don't move and put up everything for auction.  That's a different story though not related to the 'blog.  But it's sad.. I'm getting upset that I never have time for anything fun anymore.  I'll mention this once and try not to use the excuse I'm too busy anymore but it has been the truth.

The TS-590S I bought at Dayton has had ZERO transmit time on it.  And maybe a couple hours of RX.  BOGUS AND SAD!


I also started to gain some weight after hitting "bottom" with the gastric bypass.  It became obvious that I'd need to start working out to go from a "stick" (literally, people were telling me that I was looking bad) to at least gaining some inevitable weight back as muscle.  Okay, they *tell* you that 30-minutes of exercise a day is enough.. but it's not... really 4-5 times a week for about 1.5 hours at a time is what I found I need to benefit from it.

Rockwell Collins Rec Center Zagrata 5K 9/2011

But that's, what?, 8-10 hours a week less to do building and operating.  But it sure beats going back up to 350 lbs, .... that is for sure.

I even missed the Iowa QSO Party today because I couldn't get home early enough on Friday not to be exhausted with the 9AM start and everyone else in the family had other plans.  Only in Iowa would someone think that running a contest from 9AM to 6PM  on a Saturday was a good idea.  Hell, it would have been nice to have some after dark 40m/75m contacts, right?  I work 8AM-7PM during the week.  It's not fun to do that on Saturday.   If it would have been 9AM to 9AM or noon to midnight or something logical I would have done it.  But by the time I got home, and then got to bed at 3 AM I couldn't do the 9AM-6PM thing.. oh well.  I suppose the 3AM thing was my fault but as it is it was for a good cause..  I started on it well after 10 PM but I actually had the enthusiasm to do so for the first time in months.. maybe ham radio isn't over for me after all.

So maybe someone who has their crap together much better than I do can tell me how you can be a productive working age adult ham operator and work full time+, have four kids, a wife, and have to work out?  I don't want to quit but I starting to think I have to.  I now understand why ham radio is becoming a "retiree's" hobby.

Anyway, why was I up to 3 AM?  I received a care package via "Royal Mail"  on Friday.. and it's something that was designed almost the same way (actually more clever in many respects) that I had been thinking of doing for close to 10 years.  

British Amateur Television Club "DigiLite" DVB-S serializer and modulator, top side 3/4 done

Bottom side, probably more than 3/4 done

Anyway.. one comment of pride:  I haven't yet ordered parts for this board.  About a year ago I started to buy parts kits from (mainly China and Thailand but) all over and stocked up modern useful parts for a fairly low cost.  Needless to say I have the board 3/4 done from my parts kits.  I did identify an issue where I need to stock chip tantalum capacitors or chip electrolytic as I have had more than one case of not having them when I needed them.  Okay.. I cheated slightly in that I paralleled a couple of 0805 capacitors to make an equivalent of the called for 1206 value.. and I used 0805s for most of the capacitors (which fit) since it's easy to get good quality kits of 0805's from Sure in China but no one has or normally uses 1206/1210's in industry so you won't see cheap kits on e-bay.  I think I was lucky to find a US source for a 1210 chip resistor kit (which ultimately was from China).

Chip resistors are typically less than 1 cent bought that way.  Newark wants upwards of 15 cents/ea for one.  It makes sense to stock up on chip components for the coming apocalypse -- it's typically cheaper to do so than to order specifically for one project!

Chip caps, too.. maybe slightly over 1 cent.  The 0805 0.1 uF caps I bought a "lifetime" roll of 1000 of them for $20 delivered from China.. they are name brand and are good quality, too.  The "Sure" caps are of OK quality but at low RF levels and low DC levels they are perfectly fine.

 The DigiLite is based on the "Poor Man's DATV" by F4DAY.  The project has been updated for modern computers by using a 2 channel FTDI USB serial port chip (which is the "why didn't I think of it?" part of the design) and a closed-source (unfortunately) DSPic33 and Windows PC software to capture data from a "e-bay special" several year old Hauppage PVR-150, 250, 350 (and probably PVR-USB2) analog capture card.  Which are cheap now (about $30 for US NTSC) on e-bay since they only have analog tuners, and many were pulls from OEM PC equipment.  What is special about them for this project is an Conexant MPEG-2 encoder hardware chip.  Newer computers will soon be able to do MPEG-2 and H.264/AVC MPEG-4 in their CPU hardware, so these older chips for now are the only cheap way of easily and quickly doing digital video for this system.  Actually.. I wish there were hardware H.264 encoders out there for a reasonable amount.. but likely there will not be except for embedded stuff because the PC's will handle it in real time without the ASICs.

The BATC's solution of using an inexpensive PIC and the FTDI serial interface is a maybe slightly kludgy but awfully clever solution of inexpensively and simply pumping data to the QPSK modulator chip.  Coming up with an exact kludge like that kept me from this project for 8+ years.  The only disadvantage to it is that they can only do Symbol Rates (SR) up to about 6250Ksym/s.. but for ham use at this time.. that is more than enough!  It's an awesome start!

The modulation used is DVB-S, which is the older digital standard used by most of the world for satellite transmissions.  I've been playing with LEGAL Free-To-Air satellite for many years.  The majority of what is left unencrypted on C-band and Ku-band FSS satellite is receivable on an inexpensive (from $30 used DVB-S to $130 new DVB-S2 high definition PVR type units) set type box and/or PC receiver card.  This same receiver can take in 950-2150 MHz signals as an IF (with a converter and/or a LNA in front of the IF) in Amateur use.

The disadvantages to DVB-S for ham radio is that it is QPSK with Convolutional Encoding and Reed-Solomon FEC..  Meaning that it's about 3 dB "weaker" than the more "modern" BCH/LPDC codes used in DVB-S2 and that it's QPSK -- optimized for weak signals, but pretty weak when it comes to handling multipath.

Current Analog NTSC AM TV doesn't handle multipath well either ("ghosting").. so those who already do ATV are using Yagi beams other directional antennas for their front-to-back and front-to-side directivity more so than the secondary benefit of gain.  Experiments with DVB-S for terrestrial Amateur TV/Data links show that the same antennas work to fix many of those issues.  Hams will likely use beams at these power levels anyway.

One great advantage to DVB-S for ham use-- and overwhelming one in my opinion is that the bandwidth and data rates, even the video and audio coding the the MPEG-2 Transport streams are pretty much completely up to the link user.  DVB-T in Europe and ATSC in the US is only setup for 6/8 MHz channels and IMHO there is no reason for hams to use this much bandwidth in 2011 for ATV.

Experiments by the BATC and others show that the digital signal is much more usable and stable than equivalent bandwidth analog ATV and it just gets better with reduced bit rates.

They seem to do okay with D1-ish video quality (PAL is 625 lines so it's already "more HD" than NTSC) at 1.5 MBPS-2 MBPS with 1/2 FEC for a net of 1.5 - 2.0 MHz of bandwidth.  I will argue that eventually even this simple modulator could be redone to do the more modern DVB-S2 standard, with more advanced audio codec (more compression) and H.264/AVC type data.  We are not far off of that.  I could see with DVB-S2 and H.264 that 1 MHz wide studio SD (D1) could easily be possible and to boot the C/N ratio to decode these signals can almost be 3 dB less, or even more advanced modulation like 8-PSK could be used to further reduce the bandwidth for a 4dB or so hit over Mpeg-2/DVB-S.  Is it possible for 500 KHz FS video?  Probably but the consumer grade Set-Top-Boxes might not be able to support it.  Most can be coaxed to do 2000 Symbol rate or even 1500... I've heard of some doing 1000.

Ho, Hum?  ATV?  who cares?  Well.. see.. it's not really just that, is it?  The data on DVB-S is transmitted as  as Transport Stream (of 188 byte packets) but there are protocols such as DVB-IP that can do internet over DVB modulation.  There are $20 e-bay boards capable of receiving this as a native computer network interface.  If we can write a data driver to go the other way... half and full duplex multi megabaud links could be done for the price of a Digilite and a TwinHan or SkyStar (or even cheaper like old Broadlogic) DVB-S cards and the supporting RF amplifiers and preamps.  That would have to be a boon for things like emergency communications... and maybe even getting a packet radio network up again.

Oh, and supposedly the newer FET based Mitsubishi power modules seem to be much more linear than the older Mxxxxx series bipolar modules.. so generating a few watts of linear PSK seems to be quite doable for reasonable cost at 70cm (but is it legal in the US?  Our OUTDATED data rules on that band seem to say no even though bandwidth can be reduced by a factor or 6-8 for more reliable digital signals!), 902-928 MHz, 1240-1300 MHz and probably even beyond.

So this is the start of an interesting project for me that I've wanted to do forever.  Hopefully it will turn out well and can be revolutionary.

The bad thing here.. is going back to the rant.. the other project from last year will have to stay in it's current state a little longer.