Friday, 6 February 2015


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.......


Saturday, 3 January 2015

Moved the shack indoors

Now that it has become increasingly difficult to keep the garage shack warm enough to be comfortable, I have moved the main rig back indoors and using the coax cables between the two shacks to allow me to keep the transverters and PAs in the outside shack. The six wire control cable is used for PTT and for bringing remote meter readings back to the indoor shack.
One innovation this year has been to combine the K3 28Mhz IF transmit and receive with an MCL BNC combiner in the indoor shack, at the back of the K3. In the outdoor shack I've put another (SMA) MCL splitter inside the Anglian transverter to split the 28Mhz IF back to transmit and receive, again. This way I use just one cable, at 28MHz, for the RF path between the shacks.
The second, lower loss, coax can be used for another IF! e.g. for the 23, 13 and 3cm bands using the K3 or another rig.
Rotator control uses my ERC controlled Yaesu G1000DXC, over the home WiFi network and outside shack PC.


Wednesday, 17 December 2014

PGA144 follow-up

My initial measurements now show
NF 0.6dB (usual caveats apply)
Gain 2.5 to 20.5dB ( adjustable)
Input third order intercept >+8dBm!
Input return loss ~9.5dB
Notch at 98MHz, -43dB wrt 145MHz at full gain
Unconditionally stable

All subject to further tests, of course.

+8 to +16v working.
110mA current consumption
Can be optionally powered over the coax

Mechanically mounted in a screened tinplate box.
Connectors-  SMA female.

The PCB can be used without the box, if you want to mount the preamp inside another rig. Provision is made for two separate types of SMA connector on input and output to facilitate this. You could even use miniature coax cable direct to the input trace.




The new 144MHz preamplifier. The picture shows the prototype kit, built up for tests. A couple more are under construction.


Monday, 8 December 2014

Debugging transverters

I spent several hours today, fault finding on a couple of Anglian transverters assembled by customers.
A few dry joints were found on the reflow-soldered PCBs. 
A thorough visual inspectio, after assembling the board into the box, would probably have found the problems.
I was always taught and in turn, when a telecoms instructor, that visual inspection is he first thing you do when looking for faults. Power supplies are second!
In the case of Anglian transverters a visual inspection is also essential after the board is seam soldered into the case. It is quite easy to disturb parts if care is not taken during this part of the assembly.
Yes, both units are now working correctly!


Monday, 17 November 2014


ISCAT-A beacon signals successfully decoded from G4JNT's personal beacon on 2300.350 this afternoon. Once Andy turned the beacon antennas roughly towards me decodes started quite regularly. As London Heathrow is pretty much on this path I assume it was principally aircraft into and out of the airport that were responsible.))))))
I am very impressed by ISCAT-A for aircraft reflection compared to JT65C at 2300MHz.
Generally, if you hear the reflection burst, you can expect to have a decode. When ISCAT-A reports below about -20dB decodes are less reliable, although more testing is required. In a large number of decoded frames the number of erroneous decodes was seen to be less than a dozen or so over a three hour period.

I am now turning my attention to enabling the PA switching to work with the preamplifier box so I can try a two-way QSO on the new band. You need to be very careful with sequencing when switching 250W at 2.3GHz on a single coaxial cable with connection to a very low noise preamp!