70CM DVB-C/DVB-T/DVB-S

[zg3409]

Hi all,

I am involved in ATV in Dublin Ireland and we are considering an ATV repeater(analogue & digital) I understand all the analogue and I have spent the last 2 weeks investigating the Digtal side. I am aware of what has been done elsewhere and I would like some advice and feedback based on my enquiries.

Quick summary:I am thinking of broadcasting DVB-C on 70CM as some new TV's in Ireland have a built in DVB-C tuner that covers 70cm and there is lot of old DVB-C cable receivers from ex NTL UPC (nicknamed dodgy boxes)

My main aim for a repeater is to reduce the cost for people trying to receive the digital signal to rock bottom prices. (The poor man's receiver) The cost of the transmitter is not really relevant for now. I think the main reasons people don't get involved in ATV is the receive equipment costs (both 23CM antenna, pre-amp and receiver) and the homebrew necessity.

A secondary problem is in Ireland 23CM is from 1240 to 1300 (not 1320). This gives a problem for in-band (rather than cross band) repeaters. Some sites use frequencies assigned to Satellite etc (1290) while others use 2 different sites linked on 10 Gig 3CM (1 site 1249 in, another 1276.5 out) Recently we have been granted 1300-1304 0dBW (1Watt Max) for repeater outputs, which is not wide enough for an analogue repeater and very little power for a digital one.

I am also aware that 70cm has better coverage potential and that some set top boxes can cover 70cm without the need for up/down converters/ nor pre-amps.

23CM/70CMs
Having looked at the options I think it will be cheaper for users to receive digital on 70CM

DVB-T

I looked at the possibility of broadcasting DVB-T on 70CMs and here are the main problems:
1) Irish digital receivers generally do not cover that frequency (down/up converter need)
2) Receivers that do cover the frequency normally are limited to 7/8Mhz bandwidth in software/hardware
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The main good points for DVB-T on 70cms
1) Can be received by some USB dongles if correct dongle and PC software used (say £30 +pc)
2) Can be received by some PCI PC cards if correct card and software are used (say £50 +pc)
3) SR-Systems sell a receiver that can do the 2Mhz bandwidth (cost 170+Mpeg decoder)
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DVB-S

I looked at the possibility of broadcasting DVB-S on 70CMs and here are the main problems:
1) Irish sat receivers generally do not cover that frequency (DVB-S receiver and up converter needed)
2) No off the shelf tested up converters found (does anyone know of any?) (homebrew type linked below)

The main good points for DVB-S on 70cms
1) Standard free to air sat box can be used with up converter
2) Same receiver can be used for the home TV (in ireland BBC is picked up on DVB-S on a dish)
3) Setup is good for portable use on 70cm and 23cm -World standard

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I looked at the possibility of broadcasting DVB-C on 70CMs and here are the main problems:
1) Irish digital receivers (DVB-T) generally do not have DVB-C tuners -some have it by accident
2) A fancier (more expesive) TV is needed (such as Samsung L32C530-F1WXXU) (May not be sold in UK)
3) DVB-C uses 64 QAM (like AM) which is not good for portable use nor with multipath reflections (designed for cable TV systems)
4) Range may be far less than other modes/amplifiers are unknown (AM ike signal?) 70CM beam may be needed or TV antenna.
I see from this post:
http://www.batc.org.uk/forum/viewtopic. ... 1039#p1039
F3YX has DVB-C gear. I will try contact him. He notes DVB-C is for local use (50-80KM)

The main good points for DVB-C on 70cms
1) A standard new TV for DVB-T in Ireland also happens to have a DVB-C tuner which covers 70CM (nothing else to buy) (DVB-T tuner does not cover the freq)
2) Same receiver does MPEG2 and MPEG4 so we could upgrade to more quality/lower bandwidth/more channels later
3) There are lots of nearly free DVB-C boxes (such as the Nokia D-Box 2) and other starview and other makes that no-longer work and are un-unused (dodgy NTL/UPC boxes) -Hundreds of receiver boxes that don't need a pre-amp nor converter and are being dumped. No 23CM aerial to buy either.
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Some get-out clauses
-I have not tested a low bit-rate DVB-C transmitter with the TV nor the set-top boxes although they seem to cover the frequency and the bit-rates needed
-It will be at least 1 month before I can get a DVB-C transmitter
-The TV I spoke about may not be available in the UK (The Irish DVB system has different specifications to the UK so TV's might have different tuners/sw)
-I know that the world DATV standard is DVB-S for many valid reasons and it's probably best to stick to it.
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Regarding the 70cm transmit frequency Frequency 436.0 MHz Symbol Rate 2 M S/sec seems to be used for simplex DVB-S DATV but that is the satellitle portion and I don't think suitable for a repeater output. 430 to 432Mhz would seem to be a better location but these are the current Amateur Users

430.0125-430.0750 MHz Internet voice gateways (TX?)
All modes 430.1625-430.1875 MHz Experimental MPT1327 Base TX
430.4000-430.5750 digital links
430.6000-430.9250 430.8000 MHz RAYNET 7.6 MHz talkthrough - mobile TX
430.8250-430.9750 MHz 7.6 MHz split repeaters – outputs
430.9900-431.9000 MHz Digital Communications
431.0750-431.1750 MHz Internet voice gateway (6 dBW max)(12.5 kHz channels)

Let alone military users (in the uk?) - I don't think there are any in Southern Ireland

or 438 to 440Mhz which is wide-split repeater inputs, 438.4000 EmerComms 7.6MHz talkthrough - base TX. Naturally having interference on repeater inputs would probably cause trouble.

The signal could be horizontally polarised and beamed down towards the city, (Voice repeaters are verical), low power (10W over 2Mhz), I could also use a corner reflector to block out signals towards Wales, England, Scotland.

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So my questions are:
1) Has anyone got a DVB-C trasmitter in the UK or further afield that can test for me? (I can post receive equipment)

2) Has anyone got an off the shelf DVB-T tuner to work on 70cm as all the ones I have found don't cover that band or else only have 6Mhz bandwidth?

3) Has anyone a DVB-T PC based tuner card or dongle that works 100% that is low cost and a practical alternative? -should we use that system?

4) What do people feel about trying DVB-C -Am I wasting my time & money on a transmitter?

5) What do people feel about a 70CM crossband repeater (23CM input) that would transmit a 2Mhz wide signal on 70cms from Dublin

Backround and links
Irish Digital Terrestrial DVB-T
-Different to the UK
-Receivers MUST have MPEG-4 (some channels not broadbcast in MPEG2)
-Receivers must have MHEG TV guide capability (not the same as MPEG!, not used in the UK)
-Receivers must receive on VHF Band II as well as UHF (This means tuners may cover 70cm, or TV's may have DVB-C tuners)
-Most UK High definition receivers from the UK will work (MPEG4) but TV guide won't -depending on software in the unit
-BBC not being broadcast over Irish System. Most people use a free to air dish (DVB-S) for BBC
So basically most people already have DVB-T and DVB-S tuners but none cover 70cm
More info:
http://www.saorview.ie/products-retailers/

Irish Analogue Television Repeaters (23CM) -Not 100% correct
http://www.superiorsignals.co.uk/hamatveire.htm

23CM Ireland Bandplan showing 1300-1304 1W repeater output
http://www.comreg.ie/_fileupload/public ... eg0945.pdf

Cavan (Far North of Dublin) 70CM Voice Repeaters and TV repeater frequencies in use
http://www.iatc.ie/newgallery2.html

70CM Simplex Digital ATV standards:
http://www.g7lwt.com/datv.html

70CM DVB-S upconverter modifcations (pre-amp still needed)
http://m0dts.co.uk/datv_converter.htm

Australian TV Receivers that work on DVB-T 70CM
http://www.vk3rtv.com/atvrx.html
HOWEVER THEY ALL NEED WIDE BANDWIDTH TX so no good for UK
These cover the required frequencies, just not the bandwidth settings

70CM transmitter with DVB-C, DVB-S, DVB-T options
http://d-atv.org/D-ATV-Modulator.pdf

70CM UK Bandplan
http://www.rsgb.org/spectrumforum/bandp ... n_2010.htm

http://en.wikipedia.org/wiki/DVB-C

http://en.wikipedia.org/wiki/DVB-T

http://en.wikipedia.org/wiki/DVB-S
Please help me and give me some feedback on your thoughts!
Thank you for your time

Daniel Cussen
EI9FHB Dublin Ireland

[KenW6HHC]

Hi Daniel EI9FHB,

One of the questions that you asked was "4) What do people feel about trying DVB-C -Am I wasting my time & money on a transmitter?"

Allow me to share my thoughts about DVB-C for ham DATV:
(1) Commercial DVB-C modulation is designed to operate in a "noise free" and "strong signal" environment. These are NOT the characteristics of most ham radio DATV situations.
(2) The robustness of complex 64QAM modulation in DVB-C would be far out-performed by the robustness of QPSK modulation in DVB-S.
(3) Choosing DVB-C negates the usefulness of a large amount of DATV resources that are available if you choose DVB-S. Europe is loaded with experienced DVB-S DATV users who can share their knowledge and provide solution(s) to convert incoming 70CM signals to be received by DVB-S STB's.
(4) I have not heard of anyone else who is actually using DVB-C for DATV transmissions. But, SR-Systems in Germany makes a DVB-C exciter for hams...you might contact Stefan DG8FAC directly for his thoughts on this topic.

Hope this helps...73...de KenW6HHC

[zg3409]

Just to update everyone. I have jet been unable to obtain a DVB-C transmitter. S-R systems is out of stock of encoder.

I have asked the commincations regulator in Ireland if we can use more than 1 watt power on 1300 to 1304.
I have also asked them if we can use 1300 to 1308Mhz to give better bandwidth.

I note that the newer S-R systems units can transmit DVB-S, or DVB-C or DVB-T on 70CM or 23CM without by changing the settings (milliwatts out) so if we end up changing from DVB-C to DVB-S it shouldn't require new hardware. The main manual on the site does not detail this.

I am also researching DOCSIS which is a data over cable standard that can be used over wireless which can combine video and computer IP data. The computer replies on the uplink frequency which in a normal cable modem is at least 200Khz wide in the range 5 to 54Mhz.

[F6DZP]

Hello,
2 years ago I used DATV transmissions in DVB-C with a Dektec DTA-115 PCI cards in my PC ( this PCI card can modulate DVB-C and DVB-T on any interband frequency. I used 437Mhz or 438 Mhz)
For receiving we can use a little USB dungle plugged in a notebook ( Cinergy HTCusb XS HD) . With the notebook we could receive and decode SD or HD in Mpeg2 or H264.
( even if not USB dungles are not marked "HD" they can receive H264, it's just a problem of codec installed in you PC).
When transmitting with my PC, I can use any video camera in SD or HD, or webcam in real time. ( just by creating a graph- nothing to program)
There is also a tool to play .TS files already encoded.

73

Jean Pierre F6DZP