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Saturday, 20 April 2019

A Portsdown Conundrum


As part of my Es'hail-2 experiments, I am now preparing a DATV TX system for the satellite. I've ordered a Spectrian linear amplifier which seems to be the way to go, it looks like this but isnt here yet:

But in the mean time, I have been playing with an eBay sourced "wi-fi booster":

I have modified this to be permanently in TX by shorting pins of the op-amp as per many published explanations:

and simply connected this between the 23cm output port on the Portsdown and the Wi-Fi antenna that came with the amplifier.

Firstly, to test all is well with the setup, I have set the Portsdown to:

  • Frequency 146.5MHz
  • Modulation: DVB-S
  • Encoder: MPEG-2
  • Output to: Lime Mini
  • Source: TestCard
  • SR 1000
  • FEC 7/8
  • Lime Gain 88
This feeds from the 2M output port of the Portsdown to the linear I made back here and then to the 2M beam on the mast.

I have connected a "white stick" antenna thats on the house somewhere to the input of the MiniTiouner from here and these are the results:


Now, I change the Portsdown TX frequency to be 2407.75 MHz, change the antenna on the MiniTiouner to be a 2.4GHz patch on the bench:

and this is the result:

With a suitable piece of wire shoved into the front input socket on the spectrum analyser I can see the 2.4GHz signal I am transmitting:

So I am really not sure why I can't decode the TV signal on the MiniTiouner - any ideas anyone?

** UPDATE **

So, thanks to the BATC forum and mainly G8GKQ, we concluded this was a phase noise issue.

I did some experiments starting at 23cm (1296 MHz) and slowly increased the TX frequency until it failed; I found this to be at 2150 MHz. It turns out the problem is ripple in the PSU for the MiniTiouner - so this is an RX issue not a TX issue as I suspected.

The MiniTiouner includes a buck converter to take the DC input and drop it down to 4V to feed the on-board regulators. I was feeding this with either 12V or 18V and also routing this input voltage up the coax to the LNB. It seems that the higher the voltage, the more the ripple.

I've modified my MiniTiouner now to run the internal RX electronics from the USB power (I have it connected to a USB 3.0 PCI card with an internal PSU connection)  and only now use the external switchable 12/18V for the LNB power.

Not sure I fully understand the reason for the problem, but it is now fixed.

Local conditions.

Saturday, 6 April 2019

70cm DATV - Portsdown again!


You may remember a while ago I built a Portsdown 2019, well today I've been thinking about how to get that on the air on 70cm (437MHz).

John, G4BAO does a nice driver amp kit for this frequency, and I have built one here today:

I've built and tested it as per his instructions, and then built a fairly simple circuit to switch the bias line which needs +12V on PTT. The schematic below is built on the veroboard you can see in the image above and takes a ground on TX line from the Portsdown and uses that to switch the VCC to the amp, turn on an LED and also provide a ground on TX line out (to go to the PA perhaps).

I've done some very initial tests and the spectrum analyser image below is created with a 30dB attenuator in line:

Without the driver amp in line, the output was measured at -29dBm (so about +1dBm without the attenuator) and then -6.59dBm with the driver amp in line. I make that a gain of about 23dB which seems bang on the money.

The driver amp is now completed in the box you see atop the Portsdown.

Good, egh?

Monday, 1 April 2019

Digital TV - really? QO-100 again!


Over the weekend I have been playing with the software KG-STV.

This is a kind of digital TV; its slow scan TV that's digitised on TX.

It took me a while to get the software to key the radio - eventually I figured out it doesnt seem to work if the selected COM port is > 9. Hey ho, as my PC Is COM port city, I had to shuffle some stuff about.

Here's two instances of the software running at the same time; the top one is my TX signal going up on 13cm and the bottom is my RX of the signal on 3cm.

And here is the same image as received by CT1BYM, Miguel:

and here some more images Migual has been kind enough to share. This is his RX setup:

How cool is that?

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Friday, 22 March 2019

SSTV - though a Satellite?


Been playing some more with my Es'Hail-2 setup.

I noticed yesterday some SSTV signals on the band from Mauritius; I've not used SSTV before so I installed MMSSTV and have since had some QSOs.

I've annotated some images and created some templates in the software to enable reports and the like to be exchanged:

It's really quite fun!

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Sunday, 17 March 2019

ADSB Receiver - Really?


For some time I've run an ADSB receiver here called PiAware - It's by flightaware, runs on a Raspberry Pi and uses an RTL dongle and a short bit of wire wedged in the shack window as an antenna - not the best.

Today I've been making a better antenna, a masthead amplifier and checking for improved reception. I recorded my musings as a video:

Fun, egh?

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Sunday, 10 March 2019

es'hail-2 dish feed


Very much inspired by the fun back here, I figured it would be great to try and make a better single feed for the dish for both bands.

This seemed to be just the ticket.

Not this needs to be plumbing, not electronics!

I paid a visit to fellow ham and insane constructor Ian, G4EVK; who has some amazing model making equipment and a good plumbers blowtorch!

Here's some photos of the build:

I'm waiting for a "rocket" LNB that I hope will fit on the end of the waveguide (read 22mm pipe) using a compression fitting, I have also used the trick from here to check the 2.4GHz return loss - after a little bit of bending it's now looking spot on.

Yesterday I very nearly mowed the lawns, today we woke up to this:

Let it snow.....

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** UPDATE **

I have used the lens from a "rocket" LNB on the front of the feed and removed the feedhorn from an Octagon LNB (with a hacksaw) and connected it all together with a 22mm compression pipe connector and some waterproofing with some silicone. I have also modified the LNB to take an external 25MHz signal (as above):

I've used the same trick I used back here to measure the return loss on 2.4 GHz and its around 20dB; I have also lashed up the receiver on the 10GHz downlink and that is working just fine.

Now, how on earth can I weather proof this?

Miss Maggie and Miss Pepper Cat seem to be economising by using the same bed? Bonkers.

Local conditions....

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Sunday, 24 February 2019

Portsdown - again?


I've been building myself another Portsdown DATV transmitter.

This is the Portsdown 2019 - instead of the Filter Modulator board in the last version, this uses a LimeSDR Mini.

I'm rather pleased with this new build, it's a lot neater than the 2018 version I made:

You can see the LimeSDR in the picture above, its in a 3D printed case - that's now got a 20mm square fan fitted.

The front panel is a lot better than the last build, if I had got the holes for the LEDs upright it would have been even better.

I wanted this second Portsdown so I can take it portable without destroying the shack to remove the 2018 version.

I'm rather pleased with this.