Portsdown boxing/build thread

Discussion about this major DATV Project. See also https://wiki.batc.tv/The_Portsdown_Transmitter
G8PEF
Posts: 90
Joined: Mon Oct 30, 2017 6:42 pm

Re: Portsdown boxing/build thread

Post by G8PEF » Thu Nov 15, 2018 10:25 pm

G4uvz wrote:
Thu Nov 15, 2018 10:15 am
I have on loan at the moment a 23cm Tonna yagi ...and I was considering a copy if it were possible to replicate the 'stand off' mounts for the elements which are mounted on a standard square section aluminium mast.
The only difficult bit would be guessing what is in the folded dipole mount without resorting to an Xray!
How have you found the Tonna? Have you tried it in a variety of weather conditions?
The reason I ask is that I used to have the 35ele, which I used for the 23cm UKACs - I found that it worked well in dry weather, but in rain, or damp air (condensation on elements and standoffs), performance was much poorer. The first time I experienced the problem, I thought that I had a receiver problem... As I said, in the dry it was fine, and I could regularly work F8BRK at a distance of about 520k from my perch on Winter Hill with my 8W of SSB, but with condensation, I was lucky to get QSOs into the Midlands. Others I know who have had Tonnas of the same design, have reported similar degradation. I now use a Wimo, which seems to be a much better all-round performer.
I'd be interested in hearing how you got on with the Tonna, particularly for ATV.

John

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Fri Nov 16, 2018 9:58 am

I've never used it in anger John, it came from a junk sale and I kept it for 'one day'. That day is looming as my Portsdown nears completion.
Gareth

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Sun Nov 18, 2018 7:17 pm

As usual a good morning out at the annual CATS bazaar where I picked up a nice looking amp that might do me good service on 2M DATV. The vendor 'thought' it was to do with paging or comms and it was marked as GUYS (hospital) on the back. Certianly loos like VHF and its TUNABLE. The company that made it (in 2002) is still in business so I've emailed them for circuit info etc. A sweep of the input shows a good match at 146 and at 156 MHz (unpowered). The device itself is a MRF275G-MOT Transistor, RF MOSFET, 150W, 500MHz, 28V, Motorola. The board includes a pre-driver and a VSWR output via an Analog Devices log detector chip. I hope they let me have at least operational info.....
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Looking forward to feeding it some DC and then RF :-) A pair for £15, with fanned heatsinks :-)

I also picked up what looks like a PA for something mobile phone based (??), with an identical pair of Ericsson 20247 (PTB20247) 150 Watts, 470-860 MHz UHF TV Power Transistor, this was all of 50p :-)
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Got a Dolphin PA for 70cms so no rush to do anything with the latter, but 50p? I wasn't laving that behind!
Gareth

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Mon Nov 19, 2018 11:20 am

Well this gets mainly better and better.... although the makers say they don't support this product anymore (16 years old) I have had a good look at the circuitry. The input is a mere BF988 (200 mW max dissipation) so I was wondering what the planned output was likely to be. However, there is a little black box hiding under the PCB and it turns out to be one of these: https://www.rfmw.com/datasheets/p1db/CA2832C.PDF

A 35dB gain block for VHF? That'll do nicely. I can see that the powerfet pair MRF275 can be made to earn their keep, although needing 28 volts to do it. Once my Portsdown if finished I'll move on to this beast and see if I can persuade it to amplify as required.
I love surplus finds, such a 'potential' bargain.
Gareth

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Fri Nov 23, 2018 8:51 pm

Big wire-up of everything this morning and it ALL STILL WORKS :-)
I'm amazed how much has been crammed into the software and I can see the inclusion of the RTL dongle a great asset.
Just a few more different shape clips to design and print, audio level pot to be included and I'll show it the camera.
Like a top-spec car, this little transmitter can genuinely be described as 'fully loaded' - all the options :-)
Audio level is excellent from the streams, a bit quiet from the RTL FM broadcast but a little more gain will help that I hope. Currently fed from the RPi audio pins via a pairing arrangement of 1K resistors.
Gareth

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Sat Nov 24, 2018 6:55 pm

And its finished.....(minor fault in the 4 band filter switch/amp) but everything else works :-)
A huge thank-you to everyone who has contributed to make 'Portsdown' possible. Its capabilities continue to amaze me. Quite how many hours its absorbed I have no idea, but its one of the many projects I've been waiting to do. Its a tight fit, but serviceable. Front panel has touch-screen and pen holder (vital;-)), Voltmeter for RPi/battery/off, shielded shut-down button and LED, video and audio in to Easycap, band indicators and TX light. Rear has the four band outputs, composite video out from the RPI, Audio on/off/volume , speaker under hood on lid, 15 way D has the 4 band amp control, tx control and 'DC input' out. Two spare USB sockets, RJ45, heatsink for linear 5 amp regulator and a HD waterproof screw-secured DC in 2.5mm.
Thanks again to those who drove, and are still driving this project.
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Last edited by radiogareth on Sat Nov 24, 2018 7:06 pm, edited 1 time in total.

g8gtz
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Joined: Wed Apr 07, 2010 6:26 pm

Re: Portsdown boxing/build thread

Post by g8gtz » Sat Nov 24, 2018 6:59 pm

That looks great and it's clear a lot of thought and work went in to it - I'd be worried if I was thinking of entering the Portsdown construction competition - which I'm not (and there isn't one)!

Looking forward to the first QSO report :-)

73 Noel

G4uvz
Posts: 91
Joined: Sat Dec 09, 2017 10:30 am

Re: Portsdown boxing/build thread

Post by G4uvz » Sun Nov 25, 2018 11:05 am

Just looking at the pictures of the build ...It 'appears' that the Filter board is in cct After the Modulator???
Mine has been running successfully for 12 months with it in position after the LO and before the modulator board?
It is difficult to se on the picture may be it is belt and braces with two filter boards??

Just interested to know?

Adrian

radiogareth
Posts: 158
Joined: Wed Jan 06, 2016 9:46 am

Re: Portsdown boxing/build thread

Post by radiogareth » Sun Nov 25, 2018 12:41 pm

Whoops! Well spotted, not sure how THAT slipped through!! Pretty damm clear on the block diagram I have printed out here too. Some quick cable re-routing I think!!
Gareth

G4uvz
Posts: 91
Joined: Sat Dec 09, 2017 10:30 am

Re: Portsdown boxing/build thread

Post by G4uvz » Sun Nov 25, 2018 3:09 pm

Glad to be of assistance!!!

A

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