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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.


  1. Have you tested the RF output level of the WiFi amplifier?

    1. Yes, its well below spec but OK for about 2W clean signal.