Portsdown boxing/build thread

Discussion about this major DATV Project. See also https://wiki.batc.tv/The_Portsdown_Transmitter
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radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Portsdown boxing/build thread

Post by radiogareth » Wed Sep 19, 2018 1:26 pm

After seeing several installations at CAT18 I'm now progressing my own build. Thought it would be a good idea to start a build thread (mechanical) rather than electrical/electronic although its all intertwined somewhat ;-)

One very neat idea I saw was mounting the RF switch output SMAs on the back of their PC board, then mount this board on the inside back cover. Thus saving a lot of connectors and coax. Yes you can still screw on the connectors.

I have the PE4302 attenuator in and working, having tested it by using the Portsdown signal generator function. From what I've read this uses a different output from the DDS so needs its own cabling and socket on the back to provide a handy attenuated (by up to 31dB) test signal.

I've uncased my RTL dongle - they run hot anyway and that then allows direct plugin to the RPi USB without obstructing the port above. I'll probably do the same with the VideoDVR dongle for similar reasons.
I found these on eBay https://www.ebay.co.uk/itm/USB-2-0-Pane ... 2749.l2649 and these https://www.ebay.co.uk/itm/RJ45-Cat5e-M ... 2749.l2649 which will do a neat job of externalising RJ45 and a spare USB.

SInce it all runs off 5 volts I found a nice 5 volt 5 amp mains SMPSU in my big box of old SMPSUs. That will be load checked and tweaked up if required. A facility to provide 12 volts nominal from e.g. a car will be added, probably feeding a buck converter from ebay.

Finding a suitable box proved tricky, not sure how much I might ever end up adding etc etc but I settled on this one. https://www.ebay.co.uk/itm/ABS-Instrume ... 2749.l2649 Not cheap, but hopefully a tidy solution. Its roughly the size of an A4 sheet of paper.
Wondering how much the final 4 way electronic switch can handle - I can't find a figure for pass-through watts....correction, 16dBm = 40 mwatts? Is that right?
Finally, do I need a sound-card dongle for the RPi? The webcam has audio input, so does the Video capture device. I'm guessing YEs for the RPi camera which I also have hooked up. I've some 'Daffodil US01' USB sound adaptors that include volume buttons and a mute i/p &o/p button. ANyone used this?

Now to give some thought to front and rear panel layouts......

Gareth

G8GKQ
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Re: Portsdown boxing/build thread

Post by G8GKQ » Wed Sep 19, 2018 2:04 pm

Hi Gareth

Great to hear about what you are planning. A few comments:

There are 2 ways of using the PE4302: You can put it between the filter-modulator board and the 4-way switch, and this enables you to vary the drive level to your PAs; or you can use the other output from the ADF4351 and use the attenuator to generate a variable signal generator output. Your choice.

The eBay Panel connectors for USB and network look useful.

Watch the cleanliness and stability of the 5 volts that you supply to the Filter-modulator board. The reason that we recommend a linear regulator (the 7805) is that the F-M board likes a clean stable supply.

The 4-way switch can handle 40 mW (= +16 dBm), but it distorts a DATV signal at that level. I would not recommend more than 15 mW (+12 dBm) to keep your signal clean.

You only need a sound card for the RPi Camera, and even then you can switch the unit to use the EasyCap audio input and RPi camera video. Not sure about your sound adaptor. M0XTD had problems with a similar one - the software is fussy and was designed around the very cheap ones like this:
USB.JPG
USB.JPG (16.61 KiB) Viewed 905 times
Hope that helps

Dave

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Wed Sep 19, 2018 2:28 pm

Thanks Dave, yes, very helpful. Think I'll skip the sound-card then, can't see that it's going to be very helpful as my external bullet camera has sound included as does the C920.
The reason I asked about the switch was I'd seen a small amplifier used before it in one of the installs and wondered if it was up to the task. IIRC it was after a digilite board, not Portsdown so maybe OK. I might include some 'loop-around' facility on the output back panel where I can link the chosen band output through a small amp ready to drive the outboard linear etc.
Point taken about clean 5 volts. Missed that on the diagram :-( Reach for a boost converter :-)

Onward....

Quick question, when I calibrate the touchscreen it shows me the old and new. If I then re-calibrate it seems to still show the original (ie first time run) points, not the more recent set? Not that it matters ;-)

Gareth

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Re: Portsdown boxing/build thread

Post by G8GKQ » Wed Sep 19, 2018 2:36 pm

Hi Gareth

The touchscreen calibration always starts from new. It ignores that fact that you might have calibrated before.

Dave

radiogareth
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Re: Portsdown boxing/build thread

Post by radiogareth » Wed Sep 19, 2018 4:28 pm

Change of plan, it would be more logical to supply a nominal 12 volts into the box and have a downconverter for the RPi etc. A quick rummage in the China bin found these : https://www.ebay.co.uk/itm/391897110961 which since using the LM2596 can do an easy 2 amps with some heat-sinking as a sensible investment. The voltmeter can apparently be on, off and selected for in and out. Cheap too.
Now reaching for an old SMPSU from a flat screen as these are 12 Volts. I know I have one 'somewhere' :-)

Gareth

g8vpg
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Re: Portsdown boxing/build thread

Post by g8vpg » Wed Sep 19, 2018 4:54 pm

Gareth,
I have used the same PSU board in my Portsdown. It works well, but it generates a lot of rfi, which is a real problem on 144.750MHz when out portable, when the Portsdown is quite close to the aerial. I am now looking at ways to replace it with something quieter. I had the same trouble with a 12/28V step up board to power the relay on my 5.6GHz kit.
73 Shaun.

radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Wed Sep 19, 2018 6:08 pm

I'll see if it can't be either filtered better and/or shielded. Tis the curse of SMPSU's though, in the name of efficiency.
Gareth

M0YDH
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Re: Portsdown boxing/build thread

Post by M0YDH » Wed Sep 26, 2018 10:22 pm

Hello Gareth
Andy G3UEQ directed me to these boxes:-
https://www.ebay.co.uk/itm/Professional ... 0189692778
British shop belonging to HA5IA. If you buy three you pay for two. (I've bought four different ones - one at a time :cry: then found the bulk buy offer). They're very good - as long as you like grey and cream colour scheme.

I've added the inductor and capacitor shown as optional ripple filter in fig 23 of Texas Instruments datasheet on the LM2756-ADJ
LM2756 circuit with ripple filter.JPG
LM2756 circuit with ripple filter.JPG (25.71 KiB) Viewed 754 times
to all the Chinese DC-DC converters in my DATV system. I assume something similar can be seen in the G4KLB Portsdown pictures on the Wiki. I don't know if this is sufficient from an RFI point of view. I hope it's good practice.

73
David M0YDH

g0mjw
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Re: Portsdown boxing/build thread

Post by g0mjw » Thu Sep 27, 2018 8:07 am

radiogareth wrote:
Wed Sep 19, 2018 6:08 pm
I'll see if it can't be either filtered better and/or shielded. Tis the curse of SMPSU's though, in the name of efficiency.
Gareth
Switching regulator noise is an issue, even more so on the lower bands. We don't need to use switching regulators. The portsdown requires only 4A and assuming efficiency is not a primary requirement (it might be but if you are in a car less so) a linear regulator based on one of the 5A devices, perhaps with a series resistor, would be an RF quiet alternative. Handy for warming your hands on in the winter too. Another option for portable is to use LiPo cells in series and a linear regulator.

Mike

radiogareth
Posts: 155
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Mon Oct 29, 2018 8:30 pm

Now 'most' of the bits and pieces have arrived I'm starting to mock up some internal layouts. As I'll have 2 spare USB sockets I bought some panel mount sockets on 500mm leads with a USB plug. This leave quite a lot of spare so I'm thinking of cutting the plug off and hardwiring the leads to the relevant pins on the RPI PCB. Anyone see an issue with doing this? Is there some filtering inside a USB socket I wonder?

Also have an RJ45 panel mount that I'm going to shorten and recrimp, all in the name of 'tidy'.

I've also uncased the RTL and video grabber PCBs to aid their cooling (RTL in particular runs hot) which also makes them easier to fit in.

Thoughts??

Gareth

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