Portsdown 4 build ideas

[M0YDH]

Hello all
As I may have trashed the Pi 3B in my Portsdown 2020, my thoughts turn to the next great thing - Portsdown 4. I've a Pluto that I haven't yet altered, a 40MHz Leo Bodnar reference for it (the 25MHz side of which stabilises my LNB) and a working Lime Mini plus all the elements of the old Portsdown 2020. The SmartiPi2 case is rather good and I've used the 4 as a receiver at home. I do hope for a Pi camera rotation option in the software so I don't have to hack the case like Colin's article a couple of CQ-TV editions ago. I know that there's a -rot 90 term in the raspivid command that does the trick.

I had thought that hard disk drive ribbon cable would make a fair connection between the Pi 4 computer and the GPIO breakout card housed in the companion box. The example from the loft is 39 pin. There’s a blank socket in the connector for foolproofing. Drat. I guess there are 40 pin ribbon cables to buy.
I did get a 3.5mm 4 way jack to red, yellow and white RCA sockets from Pi Hut for composite video out. It's a bit too long but very tidy compared to my last efforts.

https://wiki.batc.org.uk/2-Way_RF_Switch - how well will this switch work as a means of choosing Pluto or Lime SDRs? Wouldn't that make a great does everything transmitter with Langstone software in the same box? With narrow band receive for the e.g. Pluto.

Could I insert a SP5189Z amp card after the switch and before the programmable attenuator? And connect it to the TX line in band select? Probably bad for the 8 way switch?

I would like to do a better job of filtering the buck converter. The February 2017 edition of Radcom has Andy G4JNT devising filtering for the boost converter to make 28V across the G4BAO 23cm amp. I've Jim's G7NTG's revival of the kit to build so this has a direct application there. The buck converter that I use in the 2020 has a ripple on the output and nasty frequency transients coming from its input. Did any member adapt Andy's article for a buck converter application?

In a DATV fantasy, I'm using Mike G0MJW's superb RF path estimation software with ASTER data on the Pi 4 rather than the mini-PC, like I was yesterday. The mini-PC is redundant and the 1GB of NASA images for the data are e.g. mounted on a usb memory stick.

What do you think?

73

David M0YDH

[G8GKQ]

Too many questions at once!

Do remember that the Pi 4 won't drive a filter-modulator board or 3.5 inch display, or work with composite video output. But there again, the Pi 3b won't drive a Pluto... I use one of each (well maybe 2 Pi 3s and one Pi 4....).

No need for GPS stabilisation of the Pluto if you are just transmitting TV.

No imminent prospect of the 90 degree rotation for H264 encoding - it's a bespoke application, and it can only mirror (vertically or hozontally), not rotate. Hack the case.

40-way ribbon cables: https://shop.pimoroni.com/?q=40-pin+ribbon

The 2-way switch should work well between Lime and Pluto. Just remember that it will limit the upper transmit frequency on the Pluto.

I did not take any laptops/PCs with me for my portable operations yesterday. All done on 3 Raspberry Pis (but no path-plotting software - only range and bearing on the Portsdown).

Dave

[radiogareth]

As I'm building the 'combo' unit (Ports-Stone??) I'm not convinced that having both a Lime and a Pluto are a requirement for me. I was going to 'build in' a Pluto, giving external access to RX & TX ports. Most (actually, all) my amp solutions can be fully driven with the Pluto. (4m to 5.8Ghz).
As the Plutos integration with Portsdown continues (I hope) and I have a LimeUSB (not a mini) it will make me a neater solution for me. I will have external USB ports for other occasions, should the Lime prove indispensable.
'tis in vain to do with more, that which can be done with less'......unless I'm missing something here.....
Gareth

[keng8vdp]

Lots of questions. But good ones.

Re powering stuff, I have to stick my opinion in as I have 2 Portsdowns.

No1 is the filter modulator board original, Currently out on loan. Its built using several Buck converters to run of 12vDC.
No2 is/was for shack use only so I built it with a 5v switch mode power supply inside the case. Its tweaked up a little to 5.1v (trimmer on the board)
eBay item number: 254252328250

Turns out that it works great off my 12v / 150w mains inverter in my car.
You can buy on ebay for less than £20 ... + some have 5v usb ports too ... mines doesnt its just a single mains socket.

This means I can easily move the whole thing from shack to car ... go /M as its running from car battery.
Just take it out of car and back into shack

I never have low voltage warnings as im powering onto GPIO pins. Runs PI, 7" screen + 1 buck converter 5v in 12v out to side of case.
I run C920, Easycap, Lime-MIni all direct from PI USB's ( works great NO voltage issues )

I built a LM386 amplifier into case with volume control. + yellow phono video out + hdmi interface for Pi cam. 5V out on side of case too.

Both the 5V out & 12v Buck out, are on side of case for powering those little Chinese amps. or BAO 23cm & 70cm.

My case is Reversable ( invert screen ) as its a sloping desktop type , it can lay FLAT or be stood upright (which I prefer).
No 2 portsdown in photos, is a plastic case which means the PI works great on my wifi.
No1 portsdown is a metal case and it struggles a little with wifi.

Case off ebay is item 19188831511 £14.50 + post of course , as of today

1st photo is of it laid in "laid down mode"
2nd photo shows interface sockets on side
3rd photo shows it stood up "on its back edge"
4th photo shows access to the tricky little thingy SD card.
5th photo shows speaker and vol control.

Ken G8VDP

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[keng8vdp]

My Portsdown Pi4 build

It similar to the one I posted further up (black case with a Pi3B+ .
This one with Pi4 is Same case but in grey. I added stereo amplifier this time and x 2 speakers
The 2 buttons just under screen turn on 12v and 5v outputs to side of case for powering external small amplifiers
The C920 webcam sits nicely on top.