DIGILITE at 437MHz

[F1CJN_alain]

My Digilite is now alive and well !

It runs with at 437 MHz with a modulator based on the U2790B circuit using :
- the Digilite video filter only (without the video inverters, without the levels and bias adjust circuits)
- a résistive fixed divider to get the right vidéo level on the I and Q U2790B modulator inputs,
- a capacitive coupling to the I and Q modulator inputs. The Inot and Qnot modulator inputs are grounded with capacitors.
- an external 437 MHz oscillator with a single ended input.

The symbol rate is 3000Kbit/s at the moment but it is just for test. For the air 1000K will give a less generous spectrum !
Thanks again for the very nice description
Alain
F1CJN

[G4EWJ]

It's good to hear that it's all working.

It will be interesting to see how you get on at SR1000. I've found that it's not completely stable at that SR. I haven't found out why yet. Maybe it's just the receiver.

It's fine at at SR1250 and SR1333. SR1250 is not in the DigiLite Config SR list, but it is possible to set it.

Brian

[F1CJN_alain]

The receiver configuration
Silvercrest SL 65/12 with a DirectTV BBC converter (2400Mhz - 437 MHz = 1963 MHz)

The transmitter
Hardware Digilite with the "wideband" video filter (3 MHz at least ) and the U2790 modulator.
I have modified the direct.ini file from GB-PVR to have 800k and 1500k Peak in low resolution.

Everything is correct and stable at a 1000k/s symbol rate except for the 1/2 FEC.
At the 1/2 FEC and 1000k :
- it is not stable during the reception
- I have some issues with the PCR lag (negative values and resets). I suspect the GB-PVR configuration.

SR 1333k is right at all FECs.

Alain

[G4EWJ]

I would recommend setting constant bit rate rather than variable, as any surges in data rate are likely to make the PCR figures go negative, but it is worth experimenting to see if a lower average rate with a variable bit rate can give a better result overall.

800k and 1500k seem too high for SR1000 FEC 1/2. DigiLite Config gives 590 as the bit rate. Also, try it with FEC on PC.

I am using an HVR-1300 at the moment and it seems more stable than the PVRs at SR1000. I can run SR1000 FEC 1/2 with bit rate 590 and everything is stable. Unfortunately the HVR-1300 produces a stretched picture with 352 as the horizontal resolution.

I'll put the PVR150 back in and try these tests again.

Brian

[F1CJN_alain]

Hi Brian
The reception is now ok with at a 1000 k/s with a 590k video stream from the PVR-150 and at 1/2 FEC.
It runs fine with either PC or serializer FEC.

I am using a fixed video stream in all my trials.( The peak video stream figure was just annotated in the direct.ini, just in case .... because I am not yet very familiar with the GB-PVR program!)

Alain

[G4EWJ]

Good. Maybe it's just my receiver that doesn't like SR1000.

Brian

[G4EWJ]

I was slightly out with the bit rate for 1MS. It should be 570 instead of 590. Small changes make quite a difference at low symbol rates and 590 brings the Pad% too low for comfort.

Do you use audio with low symbol rates? There is a facility in DigiLite Transmit to remove the audio from the transport stream to allow more video data. It is not selectable by the user at the moment, but at 1MS, it would allow the bit rate to be raised to 760.

Would it be worth having this facility in a future version?

Brian

[OH6MQM]

Hello

Hard to find out 70cm receivers.

Where i could find receivers

[G4EWJ]

I don't know of any DVB-S receivers that cover 70cm, but many people are using one of these:

http://www.ebay.co.uk/itm/B-Band-Conver ... 3f065b5ced

See here for conversion details:

http://www.m0dts.co.uk/datv_converter.htm

Brian

[OH6MQM]

I don't know of any DVB-S receivers that cover 70cm, but many people are using one of these:

http://www.ebay.co.uk/itm/B-Band-Conver ... 3f065b5ced

See here for conversion details:

http://www.m0dts.co.uk/datv_converter.htm

Brian

Thanks from info.

Just one check. How much was bandwith is needed for this.
Starting from 437 MHZ.
In Finland Band end up at 438 Mhz