Posts by David G0MRF

Testing of the low level upconverter is now complete.

Gain was lower than expected. It seems the insertion loss of the 2 band pass filters increases near 2400MHz.

Also, the ERA-2 output stage needed better earthing before it was unconditionally stable.

Eventually, I swapped the ERA 2 for a slightly higher gain MMIC, A VNA-25 from Mini Circuits.

Now, linearity is very good and 10dBm on the input at 70cm produces 10dBm output at 2400MHz.

Now I just need to wire up the 12V PSU to the drive, Spectrian amplifier and the fan.

In 'other news' A Venton LNB arrived this morning. - Thanks Mike and Heiner. Not spent long looking at it, but how do you remove the dielectric lens?

73 David

Upconverter: First test.

LO and upconverter board mounted in enclosure.

Input at 432.510 MHz at 0dBm

Output apx at 2400.0091 into frequency counter.

So far so good. Testing output power / conversion gain / linearity in the morning

73 David

Hi Thomas.

This is the last press release I can find from ESA Education office. Dated May 23rd.

"After having started its in orbit commissioning, since a few weeks the ESEO mission has been experiencing an anomaly. The educational path of the ESEO students however continues.

The ESEO AMSAT-UK radio payload was successfully activated in the morning of 12 April 2019, and it started transmitting its payload telemetry. These data were received by many radio amateurs around the globe.

Unfortunately, a few hours after the AMSAT-UK activation, ESEO suddenly started to behave anomalously, repeatedly sending the same notification message to ground, which normally should have been sent only once. The continuous use of the radio transmitter to send these notifications, in combination with the AMSAT-UK activation, led to a temporary discharge of the battery when the spacecraft was in eclipse. This under-voltage then triggered the protections to automatically shut-down the AMSAT-UK payload.

A clear reason for the anomaly has not been identified yet, but the most accredited hypothesis is a possible radiation effect on a memory cell, which in principle could be recovered through an automatic reboot of the on-board computer (data handling system), that cannot however be anticipated.

In the meanwhile, until this malfunction is resolved, ESEO cannot receive tele-commands and its in-orbit commissioning cannot continue."

End quote.

Current status: On 31st August the OBDH system reset following a low battery watchdog. This stopped the continuous transmissions and put the satellite back into safe mode. At present, telemetry is being received on 70cm and the attitude control system is being investigated. Commands are being successfully sent to ESEO and temperatures and battery voltages are back to nominal values.

Speculation: After the platform checks have been completed it would be reasonable to assume the S band ( 2.1 + 2.2GHz commercial spectrum) system will be checked so that the science data from the student payloads can be gathered and downloaded via TU Munich.

Thanks

David

Looks neat so far with upconverter PCB using 120mA at 12V now final ERA2 has been installed 'dead bug style'.
Oscillator operates from 5V regulator on back wall of enclosure. Not sure it will look so good after all the wiring is added.

Water bottles these days have a new meaning, but this 'old school' version provided an easy method of assessing the performance of my "high stability 10MHz source" bought at a radio rally a couple of years ago.

For a 25 to 60 degree temeprature change this Murata oscillator drifted 6 kHz at 1967.5 MHz. Probably no more than a big crystal and a TTL inverter housed in a large metal can. Buyer beware !!

Oh well, the ECS TCXO may have digital jumps, but it does compensate very well and stays within 200Hz .......Another couple of bits in its A to D converter and it would be much better.

So with 10 days to go before setting up the demo station, it's time to get these parts into a box and wired up to the Spectrian PA.

Perhaps a test by this weekend?

In the words of Homer Simpson.....Dooh !
Yes, of course, how can 393.5 be an integer. There are so many settings I just selected INT-N and didn't check the rest.

OK, I will find the PICKit and try again.

I've already found a rather ancient ovened 10MHz oscillator module, But at 40mm cubed I just hope it does not draw more power than my PA. (hi)

Thanks, adjusted for +2dBm and done...... David

And the not so good:
The local oscillator is operating, but looking at the signal on a FUNcube dongle shows a couple of issues which need to be improved.

Firstly, the TCXO is manufactured by ECS and is available from Mouser. While it holds the frequency stable over a period of time it has internal correction that uses a D to A converter. This produces frequency corrections as 130Hz jumps in frequency every time it drifts outside a preset limit. Not too bad when warmed up, but not pleasent when starting from cold or if mounted in the same box as a power amplifier. If anyone can suggest a 7 x 5mm 10MHz TCXO that is not 'digital', please let me know. The spectrum of the LO is shown below on an image from SDR#. The signal on the left is the ADF4351 with the TCXO 'jump'. The signal on the right is a reference signal from a signal generator on 1967.5kHz.

The second, lesser problem, is spectral purity. I have used integer N operation to minimise spurs and hopefully improve noise performance.

Unfortunately, the carrier appears to have odd bursts of 'phase noise' or interference that extends +/- 90Hz from the carrier. Beyond 90Hz the signal is very clean, so I'm not sure what this can be. I have copied the register settings from the Analog Devices software below. If anyone has a better performing set, please let me know. This is not visible on this SDR sharp image, so it may be an intermittent issue that will go away with proper shielding and supply line decoupling.

73 David (Yes...I know. I wouldn't get frequency jumps with GPS locking ! )

More steps forward and some steps back. - Here is the 'good'.

I managed to programme the 12F629 with the code from G7DOE adapted for 1967.500MHz using interger N as suggested by Remco.

The Chinese pickit-3 put up a small struggle, but I finally got the 'build successful' and 'verify' responses from the free MPLab-X software telling me that the software had been loaded into the processor.
It took some time before I managed to get the synth board to lock as, for some reason, the data is not transferred successfully when power is applied. What is needed is that after power has been applied the MCLR pin near R11 on my board needs to be momentarily connected to ground. After the voltage comes back up, all is well and the 'lock' LED on the synth board is illuminated.

Frequency is good (see later) power output is also good at 0dBm. The programmed level was +2 dBm but I've assumed this is measured as the total from both outputs rather than just the one that I'm using. Finally I replaced the drifting 25MHz crystal with a 10MHz TXCO. So what could go wrong?..........

73 David

The upconverter board is 90% complete and only one minor issue has been found so far, - a missing coupling capacitor.

The board uses 2 bandpass filters, I thought I would use different types to evaluate performance.

Filter A in the image below is the popular SF2124E. It has 6 connections: Input, output and 4 ground pads. Importantly, there is no DC connection from input to output, or from input or output to ground. This means you do not need coupling capacitors and I have a direct connection from the filter to the input of the ERA2 that follows it.

The second filter (B) is a TDK DEA252450BT. It has 4 connections including grounds that take up the entire length along the sides of the device, making it easy to fit to the board with a regular soldering iron. Unfortunately this device has a DC connection between all of the pins. This property means I need to add a coupling capacitor between the output of the ERA2 and the filter input. I think I have some 100pF 0402 caps somewhere. There is just about enough room to squeeze one in if I remove about 1mm of copper track.

Next task. Programme the PIC12F629 and attach the Local Oscillator module. Then some measurements and fitting the the final ERA2.

73 David

Thank you Nice project

How is duplex operation achieved so you can monitor your signal on the transponder?

Unfortunately I do not believe Leila will work in this situation even if the signal had been within the 2 beacons.

Leila appears to transmit a signal on top of someone operating with excessive power. This just makes the situation worse as now you have 2 high power signals. However, I was under the impression that the NB transponder had AGC and the WB transponder does not.

Is it not possible to set the AGC threshold to limit the total output power below the maximum limit....and way below any level that will trigger alarms in Qatar?

73 David

Looking at the board layout, you should be able to scrape some soldermask off the track and then add a small 0603 inductor in series.

Repositioning the 10pF looks to be OK.

Need a microscope though.

David

Hi Mike.

Didn't the rocket LNB become 'unobtainium' several months ago. Even the LNB suggested by Heiner seems to be 18 Euros ish on e-bay.co.uk. If the performance is 'poor' in comparison to the LNB in front of a small Sky dish, I'll chase this update after the upconverter has made some progress. Not sure Nylon 60 is totally suitable for 10G.

David

SP3OSJ This point does not seem to be in the signal path. Instead it looks to be a supply line, so the inductor is nice....but probably not necessary.

When I tested this board, I did not check the gain mid band. I wonder if the amplifier is just working too close to the band edge? Can you measure this and let us know? Perhaps it could be tuned a little.

Thanks for the info 73 David

The upconverter PCBs have been here for a couple of weeks but finally it's time to see if they work and find out if I have made any errors in my rather rushed layout.

The design uses a PIC12F629 to control an external PLL source that is based around the Analog Devices ADF4351. The same board used in the RSGB Easy-100 project.

The 1967.5MHz local oscillator is amplified with an ERA1 which feeds +7 to +10dBm to a RMS30 mixer.

Input to the mixer is at 70cms and the mixer output is 2400MHz.

The board has 2 bandpass filters to remove any local oscillator leakage and the image frequency around 1535MHz.

The wanted signal is normally amplified by an ERA2 then a RFPA5208 from Qorvo up to a level of 500mW.

In this particular build I only need 10mW to drive the Spectrian amplifier to 25W, so the Qorvo PA will be replaced by a second ERA2

Pictured below is the blank 43 x 41mm PCB with a matching BGA heatsink.

DD0KP Hello Heiner.

I have not glued the lens in position, so it can easily be replaced. With my 0.5m RX dish I can see the transponder noise and I hoped that the extra loss in the Nylon POTY lens would not be very noticable as I have extra gain from 0.8m.
However, your MER going from 2.9 to 5.2 suggests otherwise. I'll move the focal point and measure the change. If there is a significant difference, perhaps I can arrange to buy the lens from you. Does it fit 22mm tube without much machining?

73 David

TIme for a little work on the antenna system. POTY feed kit / Octagon OTLSO with TCXO / Mix Digital 0.8m dish and finally a nice tripod designed to hold a loudspeaker with a max weight of 50kg. ( Care needed, probably Chinese kilos)
The POTY kit went together very easily. Only the dielectric lens needed a little sanding before it would fit into the 22mm Copper waveguide.

The Mix Digital dish came with a LNB holder designed for a standard 40mm diameter LNB. However, it now needed to hold the 22mm pipe. There are many ways of making a suitable spacer....40mm diameter with a 22mm hole in the middle, but finding a short length of 40mm nylon or other waterproof material was difficult. Even 40mm diameter wood used for handrails came in 1.8m lengths, but I only needed 50mm or so.

Eventually I found a craft supplier on e-bay selling 40mm diameter hardwood, each piece 40mm long. A few Euro bought a pack of 4 pieces with free delivery.
A friend drilled a 22mm hole and then carefully cut vertically along one side with a band saw. The small amount of material removed with the saw allowed the LNB holder to clamp the wood to the pipe....perfect. A couple of coats of varnish and I was ready to go.

A demo at the Cray Valley Radio Club gave me the opportunity to test the feed. What a pleasure to not have to align two separate dishes. Signals with 3W were not as good as my home system, but good enough for a QSO to impress the 28 members. Looking at the feed, I'm probably a couple of centimetres off the correct focal point. Time to optimise that later. Next step :- The upconverter boards have arrived..........

My guess would be cost. Making an LNB for 10 Euros can't be easy. So the 2 waveguide probes set at 90 degrees are very cheap to implement. Just 2 bits of wire soldered to the board. Not sure what the equivalent would be for LHCP + RHCP in an LNB. ??

Hi Mike.

I had a similar reply on Twitter from M1SJE. He recommended a piece foil on the output line as it turns 90 degrees along the edge of the enclosure. I think there is a photo of that in one of the other topics on the forum. I had better check that NEC transistor and find out what the maximum limits are before I start exceeding them.

So, I'll cut a couple of rectangles of foil and glue them to the end of a cotton bud, then I can prod it onto the output lines and see if I can make an improvement or two.............

Well, the tuning aid worked. After checking all the way from the PA drain coupling capacitor to the isolator, the best place is as suggested by M1SJE and others on this forum. A fairly large piece of foil is needed at the 90 degree turn near the edge of the enclosure.

Without foil......14.5W with foil 22W. There is an increase in PA current as well, but overall I'm saving a little over 1 Amp for the same power output. I suspect if I changed the PA voltage from 12.2 to 13V it would be close to 25 - 30W at 10A supply.

However, I will keep it at just over 20W.....leaving a little in hand for the odd mistake.

Tuning aid with foil glued in place pictured left. Added Copper foil right. - Note PA bias pot is very sensitive. Now set to 5.5A