Success Stories

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
g0mjw
Posts: 2330
Joined: Sat Sep 20, 2014 9:15 am

Re: Success Stories

Post by g0mjw » Mon Jun 05, 2017 6:17 pm

Hi Dave,

In the end I just soldered wires to the bottom of the PI PCB. Fixed the low voltage warning issue immediately at the cost of slightly less convenience in servicing.

Mike

M0YDH
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Joined: Sat Dec 31, 2016 5:59 pm

Re: Success Stories

Post by M0YDH » Tue Jun 13, 2017 9:44 pm

I've made it to this topic! Great relief too. Thank you very much everyone especially Noel, Dave and Colin.
My wife Ann-Charlotte is making her DATV debut below. Now I can help Dave G7MEG with his Portsdown set so there are 2 of these a mile apart.
73
David M0YDH
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G4WIM
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Joined: Thu Jan 29, 2015 8:36 pm

Re: Success Stories

Post by G4WIM » Mon Jun 26, 2017 8:11 pm

Here's a few photo's of my attempt at a Portsdown.

It has both the rtl rx dongle and EasyCap built into it, but no RF switch yet....

The front panel has the HDMI and composite + audio sockets easily accessible and no screw heads in sight - just need to get it engraved now.

The rear panel has connections for ethernet, USB, linear control (9 way dsub), DC input + fuse, RTL dongle RF in and RF output switch PCB (yet to be fitted).

I was a little concerned about heat build up but have had it running most of the afternoon in a fairly warm shack with no excessive temp rise.

In hindsight, not sure it was a good idea to build in the RTL dongle and EasyCap but if the worst came to the worst heat wise they are easily removed.

To help manage the heat issue, internally there's a 3mm thick base plate 'chassis' which supports the right hand chassis plate for the LO and filter and the rear panel for PSU and RF switch PCB.
The display and band switch PCBs are held to the base plate chassis by means of extrusion.
The RTL and easycap dongles are held in place by simple brackets attached to the base plate.

The modulator has its own 7V SMPS while the LO and filter are powered from another 7V SMPS. The RPI has its own 5.2V SMPS

I suspect because of the construction using fairly heavy aluminium plates to spread the heat and only 7V supplies the internal temps are adequately low.

I'm yet to test it with my DATVExpress - but so far so good.

Next project - linears for 70 and 146MHz.

Well done to everyone involved in creating this excellent bit of kit and 'putting up with' the barrage of questions from those of use who should spend more time RTFM ;-)

73 Tim
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g0mgx
Posts: 31
Joined: Sat Dec 31, 2016 7:57 pm

Re: Success Stories

Post by g0mgx » Thu Jul 20, 2017 7:14 pm

Thanks to G4OHV, we have successfully tested my Portsdown, filters & PA on 146.5 MHz:

https://g0mgx.blogspot.co.uk/2017/07/fi ... plete.html

https://youtu.be/WOJDfWt-jjM

I'm feeling rather delighted! :D

Mark
G0MGX

M0YDH
Posts: 264
Joined: Sat Dec 31, 2016 5:59 pm

Re: Success Stories

Post by M0YDH » Mon Feb 05, 2018 1:31 pm

Hello all.
I've made an accessory unit to house all the items that connect to Portsdown transmitter but don't fit in the case because I adopted the G4KLB example early on. I'm really happy with it BTW. This means my Portsdown is in a small Farnell case.
20180203_125051 Portsdown DATV companion unit (Small).jpg
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The 19 inch rack case used to contain some class of low frequency function generator. There's a 5 foot stack of these in our radio club room which I assume are towards club fundraising. I purchased a mains powered unit and cut off the function generator.

I had a Plugable powered USB hub left over from Raspberry Pi 1 days so I made the circuit from the LM2756-ADJ datasheet because I have the parts to hand to power it and it takes 32VDC input from the mains unit large capacitor. I made a diode switch from two 3 amp rated diodes to select the highest voltage and connected battery input line to one side of this and 32VDC to the other. I made another regulator like the first for 12v service to the rest of the contents.
20180203_125046 Portsdown DATV companion unit (Small).jpg
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It's a home for my Minitiouner and converter with DISEqC switch. I've used a mini to USB B panel mount lead in 2 places for data. Also the relay sequencer circuit is housed and under Portsdown control.

Everything seems to work showing up on the Info menu item and across bench transmission were successful on pattern and Pi camera. MPEG2 view on the touchscreen worked but no pictures were seen on the Minitiouner. One to work on later. I saw the spectrum scope and it showed activity on fm calling frequency so RTL dongle is working. How do I test audio please? I recycled part of the front panel of a scrap PC to get the pretty audio fascia and socket unit. The accessory unit draws 100mA. 1.5A is needed total to also power the Portsdown. That's fine on the 13.8vdc input but too much for the original mains psu. Not a problem.

73

David M0YDH

G8GKQ
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Re: Success Stories

Post by G8GKQ » Mon Feb 05, 2018 2:24 pm

Hi David

Looking good!

If you mean the audio out of the RPi (from the RTL-SDR receiver), it comes out of the 3.5mm jack at line level (or a bit lower). I used a pair of computer speakers plugged in there. It is better if you have a 4-terminal jack as the video comes out there as well and it can cause audio buzz if it is shorted.

Dave

M0YDH
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Re: Success Stories

Post by M0YDH » Mon Feb 05, 2018 5:30 pm

Thanks Dave. Good answer. Luckily I made up the TRRS jack to BNC and two RCA audio sockets so I can try that out. I used the information on the Wiki and what I could remember of seeing your master Portsdown unit. Is that why there are two broadcast station frequencies in the menu? Ones that can be heard in the Solent area?

My actual question was related to testing the microphone and headphone lines via the USB. I've no functioning DATV stations in range just now for a simple on air test. Is there a menu option for testing these off air?

Thanks
David M0YDH

G8GKQ
Site Admin
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Re: Success Stories

Post by G8GKQ » Mon Feb 05, 2018 6:01 pm

Hi David

If you select "Video" as the transmit mode, not only will the camera video appear as CompVid on the 3.5mm jack, but (if selected - Mic) the audio input to the USB audio dongle should appear on the audio channels (with a slight delay). Haven't found a use for the USB audio output yet (there's no audio from the in-built DATV receiver), so no easy test.

The broadcast stations are Radio 4 and Sam FM!

Dave

M0YDH
Posts: 264
Joined: Sat Dec 31, 2016 5:59 pm

Re: Success Stories

Post by M0YDH » Wed Feb 14, 2018 9:03 pm

I like your little developer privileges Dave!

Back in the shack this weekend, I had some positive progress. Whole watts of output from the Mini-kits 70cm amp were a source of joy and relief!
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I had taken advice from Paul G8AQA and Ray M0DHP on the amp. My construction techniques were poor said Paul and the GM3SEK Blog article 14 ways not to make a 70cm transverter agreed! Packing the PCB up on washers when using a Mitsubishi module is number 11. Lots of leaky radiation points too. I was getting 10 to 20 W out using FT817ND on its 2 lowest power settings. My Attenuator board was doing good service. My M0HMO power meter stopped working so I can't give input power values. I tried with the Portsdown as pictured and it made 5W out at 0dB into the meter and dummy load and 6W without the attenuator. I guess patch lead cut into 2 isn't the best overall connection but it's the best I have to hand.

I've made a pcb box for the low pass filter so it can definitely give no trouble in the amp enclosure.

73

David

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M5TXJ
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Re: Success Stories

Post by M5TXJ » Thu Feb 15, 2018 3:25 pm

Just had a (mainly) successful test on 146.5MHz, received by Seamus G7ITT at a whole 9.3miles DX. I've got a whine on audio, hence the mainly, but it's still a good step forwards. Constellations weren't good either but I think that will be cured when I install the attenuator.

73 Dave.
...are you sure I can't use a pair of 813's?... :shock:

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