MER and D for es'Hail beacon ?

[G4WIM]

HI guys,

been fiddling around with my dish, Inverto LNB, MJW feed and lens trying to optimise my rx on the beacon.

With my technomate LNB by itself and my 1.2M Channel master dish I would normally get an MER of 9 to 9.5 and a D6 using Minitiouner V0.9

Having switched to a dual feed I now get an MER of 8dB and a D4 / 5.

Same back end and same wx - sunny and clear with clear view of the sky.

I thought it maybe useful to compare results with others taking into account dish size, feed, LNB etc.

So let's start a list / thread on results.

That said looking at the Goonhilly feed it maybe that the beacon is a dB weaker than in the past which may explain things ?

Regards Tim

[g8gtz]

Hi Tim,

I did think your 9 was unusual on a 1.2mt dish - there's a table at the bottom of this wiki page which seems pretty consisent with what people are seeing: https://wiki.batc.org.uk/Receiving_Osca ... TV_signals

MER.jpg (19.57 KiB) Viewed 5215 times

Also we think the GH dish has moved and is down by a couple of dB but also Phil can adjust the gain remotely to try and keep it looking about right. 500 mile round trip to tweak the dish is planned at the end of May

And for the record on my 1.2mt Channel Master I used to get 7.5 > 8 with an unmodified dual octagon through an MJW patch. With the modified dish arms I now get a consistent 8.5dB.

73

Noel

[G4WIM]

Thanks Noel,

I wonder what sort of lens you'e using ?

I'm using the lens which came off the AB LNB which is made by Inverto.
I may experiment with other types of lens to see if that helps.

I suspect I'm not seeing the same 1dB improvement as my reference point was made using a Rimant C band mount which enabled me to get the feed more or less where it needed to be in the first place.

Thus the longer arms only provided an incremental improvement.

I also notice if there's a lot of strong traffic that can suppress the beacon by 0.5dB or so - as you might expect.

Regards Tim

[radiogareth]

Interesting, I'm getting 8-8.5 & D5 with a single stock Octagon on a 1.1x1.0 Triax. It needed a LOT of tiny tweaking to get that though, done live on site with a laptop. Very short feeder 8M to a passive 4 way splitter.
Gareth G4XAT

Eshail.PNG (121.03 KiB) Viewed 5199 times

[g0mjw]

I am afraid I only get MER 8 with a 2.4m dish but there are trees and I don't think it is quite at the focus. You also have to take into account phase noise, if you have locked your LNB it might be limited by the phase noise if not all is well with the PLL.

Mike

[G4WIM]

Hi Gareth,

wonder what sort of feed you have ? Just the LNB or a dual feed ?

I've just upgraded to Minitiouner V0.9beta8_9 and it displays MER to 0.1dB and I'm seeing 8.2dB with just the beacon on air.
May try and tweak the dish a bit more now that I can see 0.1dB increments.

I don't have my LNB phase locked at the moment, but know from past experience it impacts by about a dB so likely will not phase lock for WB operation.

Wish I had a 2.4M dish - could hide it at the bottom of the garden behind the shed

73 Tim

[g4hiz]

Hi all,

test results receiving beacon. Dish, old, unknown 1.2m offset (f/D 0.5 ?) well constructed with webbed back, mounted on heavy tripod. Feed arm arrangement home-brew, with MJW patch, AB lens and modified Octagon (26MHz xtal). Receiver Mintiouner Mk 1 (Sharp) running 0.8. Built as a transportable system, it goes in and out with the weather, hence every time is a new setup.

Yesterday early evening, MER 9dB consistent, flicking occasional 10dB - yes, I couldn't believe it myself. Wx light to heavy rain, which stopped tests.

Today afternoon, MER 9dB consistent with v0.8. Changed to v0.9 beta 7, displayed MER 9.0. Wx gusty, rainy with occasional sleet. Stopped in when the latter started.

Line-up was using an analyser on the beacon signal its self, which was clearly shifted into the L-band due to the LO change on the Octagon (now 9389MHz). This change also results in the IF not losing about 20dB of gain on the Octagon, which will influence the effect of the Rx noise figure and any cable losses on the system noise figure. For an unmodifed LNB, try a 25dB amp directly after the LNB.

For a comparison, I tried the AB LNB its self that I had taken the Lens from. The LO in this case was the standard 9750MHz. Required use of Minitiouner Mk 2 (Serit), MER 8dB/8.0dB (v0.8/v0.9). However, too many variables to form a safe conclusion on this MER wrt that previously.

Interestingly, initially I still had the Mk 1 Minitiouner connected, which indicated MER 6dB. It tuned to the input frequency of 742.5MHz, but with obvious degraded performance.

So plenty of things to play with, but getting the antenna geometry correct with feed at focus position most important. After that, pointing accurately !

73
Jen

[G4WIM]

Hi Jen,

thanks for the info - gives me encouragement that I may still find an extra dB or so because I'm using a 1.2M dish, them same mjw feed and the same AB lens.

Currently using the AB LNB as well, but will switch to an Octogan type tomorrow.

I had carefully aligned the tip of the AB lens at the focal point, just like mentioned but found moving it +/- 10mm had little effect.

Regards Tim

[G4uvz]

When I set up my 1.2M dish I used the NB lower beacon into an SDR to maximise the signal ..Latterly I have also used the same beacon but with 18 volts selected and twisted the LNB to MINIMISE the received signal...Not sur if this is a valid way to ensure that the polarisation is spot on for the WB signals?

Second question...I am familiar with MER ...but what is D all about ?

A

[G4WIM]

I use the same method to set polarisation accurately - ie null the NB signals with 18V applied to the LNB.

The D numbers are generated by the latest version of Minitiouner and are calculated by comparing the rx'd MER to the required minimum C/N for a given encoding scheme.

More tweaking today but no improvement stuck at beacon 8dB MER (with no other signals) - so going to leave it alone for now.

Regards Tim