Monday, 13 April 2015

144EME tests

Whilst I continue to refurbish my 2.3m EME dish I have taken the opportunity to temporarily attach one of my 9 element 144MHz YU7EF yagis on my Spid Ras AZ EL mount, using an improvised pole arrangement.
According to VK3UM EMEcalc I should be able to measure 3.2dB cold sky to sun noise at the present solar flux intensity, using my terrestrial 0.7dB PGA144MHz masthead preamplifier into my Anglian 2m transverter. The measurements were made using Spectravue in Continuum mode on my SDR-IQ at 28MHz.
I am measuring just on 3dB sun/CS with this system. I think this is pretty good for a single yagi and shows that the claimed gain of the 9 element YU7EF (13.97dBi) is probably pretty close. Of course I cannot be sure of the actual 'cold sky' temperature at this location and this can affect the measured value quite quite strongly. In the non-cold directions sky noise is about 0.5dB higher. It is gratifying that the numbers seem to work out!

  




Tuesday, 17 March 2015

EME dish drive again

Ignoring the big aurora allegedly in progress, I worked on my EME dish mount this afternoon. Auroras come and go, but good weather is rarer!!!
It never ceases to amaze me how much you can forget after just two years out of service. However, the Spid RAS motors and encoders have been wired up and seem to be doing all the right things. 
I did a rough calibration of AZ and EL, using the sun's known position ( from VK3UM EME planner) and then eventually remembered how the controller was connected, and to which COM port, on the shack desktop. With this I can use Moonsked to track various celestial noise sources, the strongest of which is the sun, of course.
Right now the dish mounting hub ( no dish in place yet) is following the sun and I can see which trees are going to require a severe pruning in the next few days!
My 'Lidl' digital inclinometer is reading out the actual elevation since the +/-1 degree resolution of the Spid encoder system is inadequate for tracking the moon with my 2.3m diameter dish at anything higher than 13cm.  Above 13cm it becomes practical, with this size dish and a decent LNA, to track on moon noise.
Altogether, I am pleased with today's progress.
Sam


Saturday, 7 March 2015

Ostermeyer Trophy

I am delighted to say that the RSGB Technical Committee has seen fit to award me the Ostermeyer Trophy for the most meritorious description of a piece of home-constructed or electronic equipment published in RadCom. I am sure there were more deserving articles in Radcom, but I am so pleased that the article on SMT for HF was so well received. I understand the kits have sold well, showing that the simplicity of the project together with the availability of all the SMD parts has persuaded so many to have a go at SMD construction.
I will be at the RSGB AGM in April to receive the trophy.
Thanks RSGB


Wednesday, 4 March 2015

EME mount

It was warm enough today (10C) that I could move the pallet mount to its new position in the middle of the lawn.
This is the same mount I was using several years ago for 23 through 6cm EME. 

After considerable discussion with G3WDG I have decided to go with linear polarisation on 3cm, so I can use my Chaparral feed, which is well suited to my KTI prime focus dish. It is easy to change from vertical to horizontal polarisation with the way I have arranged the focus box in the cage.

I have been promised a potent SSPA but I'm still waiting for the DL/PA0 LNA.  In the meantime I will probably try my Octagon LNB-based LNA in front of the frequency-locked DB6NT G3 transverter.

The biggest challenge is still going to be tracking and I'm going to try a simple system used by both G3WDG and G3LTF. This system combines moon noise tracking with a tweakable auto tracking arrangement. The Spid RAS tracking system will be uncoupled and used only for approximate position indicating when on 3cm.

A remote digital inclinometer gives absolute moon elevation as a back up and confidence booster.

I hope to re-install the 23 and 13cm system on the dish in due course.



The moon can be seen in the eastern sky to the right of the Spid RAS positioned.




Monday, 2 March 2015

Beacon update

The 1Ghz low noise PLL clock has been assembled into a surplus HS400 case with a 1GHz distribution amplifier featuring 4 outputs for future beacon expansion.
The Toslink NMEA drive to the DDS unit is being prepared, ready to connect to the indoor unit.
Today it was found possible to retrieve the G3RUH GPSDO from the BT Martlesham tower. It has proven rather difficult to liberate the GPSDO so that it can be interfaced, but at least it has been done!
More info on the 3cm beacon progress in the near future.


Friday, 6 February 2015

Beacons

After the Martlesham 23 and 3cm beacons failed a few weeks ago my thoughts turned to upgrading the 3cm beacon, once again.
The 23cm beacon, GB3MHZ, was quickly returned to service, no fault found (FNF), but the 3cm beacon was taken completely out of service.
Two faults were found.
One was that the driver output was down and that could explain the reports of poor signals levels for the last year or so.
The other fault was more serious. The RDDS had failed. The result was that the beacon was no longer locked but had defaulted to the bottom end of the VCXO range, giving an output around 10368.780MHz
At this point it was decided that the beacon should have a complete rebuild and incorporate MGM ( digital modes) at last. For the last few years the beacon has been running frequency locked but with FSK keying and plain carrier only.
The other big change was that the group decided that we should adopt the Danish Next Generation Beacon (NGB) platform. This is well developed and supported in Europe. In addition to running the Danish developed PI4 digital mode, it is easy to change the mode to one of several others as conditions and  bands dictate.
A DDS board and a 1GHz clock board were quickly ordered and have arrived. The clock board generates the required clean DDS clock and can be shared amongst all the other bands, if required. The clock board is driven by our G3RUH 10MHz GPSDO. NMEA output from the GPS time locks the digital mode sequence.
Each new band will require a new DDS board. We are thinking about 13cm next. 
The photo shows the DDS board in its screened box.








Friday, 23 January 2015

Moon bounce muses

I was last on EME ( apart from some listening on 2m)  2 1/2 years ago when I made my last 23cm EME QSO.  I did operate briefly on 6cm EME in July/August 2012, just before EME2012. I wanted to work the TM8PB Plumier Bodeau set up, which I did ; and several more besides. Since then, zilch. Nada.

I had to remove my dish when my neighbours erected a large extension along our property line, well down the garden, and effectively cutting off anything beyond SSE from the dish.
Not good and not much I could do about it. At least it made a good location for a lean-to greenhouse!

Since then I have agonised over where in the garden (lawn) I could get away with re-erecting the dish and mount. I believe I have located a good position ( and my neighbours can still get the full benefit of looking at it).

I am waiting for the weather to warm up before I start to prepare the ground for the pallet mount. I also need to dig a trench for the cable duct. Right now the ground is still a bit hard.

Having got the dish back in operation the question is which band(s) to activate?  Long term I really want to try 3cm and to that end I have already started to collect parts. Realistically, I suspect that my operation will be using JT4F as I will be power-limited to around 14W, using a surplus SSPA and the 2.3m dish.
I have one of the new DL3BLC ( I hope I have Ron's callsign correct....) 0.65dB LNAs on order and a back up under construction. Similarly I have a new feed under construction.

I suspect I will opt to bring the 23cm EME system back on line first. Since I was last QRV on 23cm EME there has been a noticeable increase in activity on the band (I know, because of the number of VLNA23 preamps I have sold to potential 23cm EME ops!).

I am also tempted to resurrect my 13cm system as my dish really worked well on that band and I would like to try 2300MHz since I was one of the team that pushed for its inclusion in the recent OFCOM changes to 13cm and 9cm....

And of course I have a complete system for 9cm EME that has never been tried, other than on receive, so that ought to be given an airing. 

So, there is lots to do and few excuses other than laziness to stop me getting on with EME,  now my interest has been piqued again.

Last week's visit to Dwingaloo has a lot to answer for. 

Let's see how this all pans out.......

Sam