10m Is At It Again.

After a low in solar activity it is now up again. Solar flux 121 that last two days is quite a bit, and a daily sunspot number of over 100.

10 has seriously woken up this week end.

From East Asia in the morning and almost until noon, Australia morning/noon, and fro the first time I have seen it in Cycle 25. my receiver spotted New Zealand. 

Around noon the 4X6TU was through, and in the mid afternoon the South Americans were there, lots of them.

Then, still mid afternoon I heard the 4U1UN beacon in New York was there while I was elsewhere in the house. Checking the PSK-reporter, yes, sure enough there were several spots from the East Coast of  the US. 

Then a bit quiet in the early evening, and suddenly spots from near the West Coast of the US, around 9PM local time here. This looks very much like trans-polar propagation, not unheard of at this time of the year.

Definitely an interesting day on 10m.

Rough Layout for a 2.4GHz Transverter - "LEGO-Style".

After yesterday's test I found a shielded box with dividing walls that should be usable for starting the build of a 2.4GHz transverter and/or QO-100 up-converter. 

2 amplifiers are added to the design, one for receiving and one for transmitting, and a further filter for transmitting. The extra TX filter might be better placed in an amplifier box, we shall see. This might provide a better balance in the filter/amplifier gain/attenuation, maybe even a better LO and image rejection. 

What I did is simply putting the "LEGO" modules in their approximate places. Of course, the modules will be mounted parallel to the surfaces of the box, but the picture below gives an idea of what the layout should be. 

The mixer, filters and the hybrid will be placed at the bottom of the box, the two amplifiers at the sides inside the box.

The image gives a rough idea of the layout. The bigger casing next to the module box is the LO,  a non modified 2009MHz oscillator, at this moment. Initial tests, like the test yesterday, will be with my signal generator at 391MHz, and with a receiver capable of 391MHz.

Modifications of the LO will come later It needs to generate a 1968MHz signal for converting between 2400 and 432MHz.

I would expect the TX output of this to be around -10dBm (100uW), and the RX sensitivity not too good. With the modified LO, however, it could be used for a short range experiment on 2400MHz.

Now for some mechanical work, and that takes me longer, then some tests of the set-up.

For the record: The idea is not my own, I first heard about it from OZ2OE, Ole. The mechanical set-up is my own, though ;) .

Quick Experiment With the LO Module and Some Chinese Modules. 2.4GHz signal achieved.

 Today I got a quick set-up to see how some of the modules I have could be used as a transverter or up-converter from 432MHz to 2400MHz.

Here are the parts:

- the 2009MHz oscillator module I tested a few days ago

- a mixer PCB module, IF DC-1.5GHz, RF/LO 1.5-4.5GHz

- a 2.4GHz filter PCB module using "hairpin" resonators

- a Wilkinson combiner/divider hybrid PCB module

All this was just lying loose on the lab desk, connected with SMA cables with the first port to the 35-4400MHz spectrum analyzer and the second port of the hybrid terminated with a 50 Ohm load. The second port is intended for use in 2.4GHZ reception

For the test I set my signal generator to a 391MHz IF, mixing with 2009MHz to get 2400MHz out.

The raw signal out of the mixer was as expected, a bit of 2009MHz LO feed through with LO +/- IF signals about 30dB stronger

Adding the filter (and the hybrid) provided a solid signal on 2400MHz. The LO signal was about 45dB down, and the image frequency was about 55dB down.

The results are encouraging. I would expect the stray LO and image signals would be better attenuated when the mixer/filter/hybrid  modules are mounted in a shielded casing, but for the transmitter path I intend to mount a second filter between some of the amplifier stages, in a second shielded casing.

For a receive path in a transverter A second filter is probably also a good idea, but at present it may not be necessary. In principle this is a very low powered and very insensitive 391/2400MHz transverter.

What comes next (in no particular order)?

- modifying the LO module to generate 1968MHz, so a 432MHz  can be used as the IF.

- building an amplifier chain, so I can get a minimum of about 500-800mW output.

- building the modules into shielded casings Except the LO, it is already in an excellent shielded box.

- Start mounting this arrangement into a sufficiently large casing

- adding circuitry for supplying and controlling the LNB used for QO100 reception. Right now the QO100 set-up has separate transmitter and receiver.

- adding receive amplification/filtering for 2.4GHz.

- adding control circuits, such as T/R switching, band switching etc.

- adding a second down converter, so the LNB's IF signal can be received on 144 or 139MHz

- maybe a bit more when I can think of it.

Results of the Solar Panel Relocation.

After relocation the illumination of the panel is clearly improved. Last year, at this time of the year, the battery got too discharged, as it was supplying the charge controller.

This year, after relocating, and making sure that snow was removed from the panel, the voltage has been kept above 12V, often around 13V. A considerable improvement over last year's performance.

In the spring I should get more set up, along with a lot of maintenance of my antenna system.

It looks like next year will have much more outdoor activities for me.

Testing A 2GHz Brick Oscillator, And My Microwave Testing Limitations.

Some time ago I purchased a few surplus 2GHz oscillator modules fro RF-Microwaves in Italy, designated SU-03. They are now sold out, but I finally got to start testing a few of them.

Those are synthesized modules operating on 2009MHz, with a reference crystal of 8MHz. From the description it is indicated that with a modified reference frequency the unit could be modified to operate in the 1960 - 2035MHz band.

The SU-03 requires a dual power supply of +/- 12V. For the test I used my standard variable lab PS with 12V, and a set of 3 Li Ion cells to provide the negative voltage. The negative voltage is needed, as the unit has 2 GaAsFETs that need a negative gate bias.

Power output is specified to 10dBm (10mW), so to be sure not to over-load (and destroy) the probe of my old HP432 I connected a 10dB attenuator at the SU-03 output. That was good, as the measured output turned out to be +15dBm (30mW, well above the spec of the thermistor probe). Better safe than sorry. I now have 3 units tested and in-spec for the +10dBm output. This should be quite sufficient for use with a passive (diode) mixer. 

Next step: Look at the spectrum coming out of the SU-03. Here is where I think that the limitations of the low cost Chinese spectrum analyzer, covering 35 - 4400MHz comes in. This is a device costing less than $100, so how can we expect miracles? Well, we can't.

First of all, the maximum scan bandwidth of the spec-an is 350MHz with a 500kHz "IF" bandwidth, so in order to "see" the full spectrum I need to look at 300MHz at a time, then switching to the next segment, etc. It takes some time, and it is tedious, but it can be done. 

Second limitation I see is, as I suspect, the local oscillator - I guess an ADF4351 (or a clone) - has a square wave output, so subharmonics of the original input frequency show up on the display (1GHz, 666MHz, 500MHz) quite strongly. Well, knowing the limitation is half of getting more reliable results. 

Between 2GHz and 4GHz I see no spurious coming out of the oscillator, at least they are about 60dB or more down from the wanted signal. Also, between 1 and 2 GHz I see no spurious signals. This indicates that the output from the oscillator is rather spurious free.

When looking at a more narrow frequency span, the limitations of the low cost spectrum analyzer really shows. The curve is no longer a curve, but has steps of about 5dB in the in the spectrum, and further it is possible to see the effect of the direct conversion design in the analyzer, in that the center null is somewhat visible. 

When looking at a moderate bandwidth,  some asymmetric sideband noise is visible. I can not se if this comes from the oscillator block or the local oscillator in the spectrum analyzer, but I suspect it comes from the low cost local oscillator in the analyzer.

Clearly, the low cost solution, while not useless, is not very efficient, but for now it will have to do, as I do not have a (more expensive) analyzer covering up to 2GHz or above. What I do have is a rather old (analog) model covering up to 1.5GHz. With that I can test for spurious output(s) below 1.5GHz, that's all.

Next test of the oscillator will be a frequency test. While I do have a frequency counter covering up to 2.4GHz it is not locked to a frequency standard, neither does it have an input for doing so. So high precision frequency measurements are not possible.

The frequency counter that does have such an input just covers up to 1.3GHz. What will be necessary to use my GPS controlled 10MHz source is a divide-by-10 (counter), because this particular counter requires a 1MHz external reference frequency. Some soldering work needed.

There is, however, the possibility of adding a pre-scaler to it so all is not lost. It looks like I should get the soldering iron going again, so I can get a divide-by-4 pre-scaler up and running, with that one I should be able to measure frequencies up to 3.5GHz (with the use of an added calculator) with good precision. .More soldering work. Also, this would be my first (fully) microwave construction, not just using modules or adding modulators or doing small modifications. Now it gets interesting (hopefully not in the Chinese sense of the word ;) )

What is this (modified) oscillator brick useful for? Let me see, with modifications:

- 1968MHz is within the range of operation of the VCO, so a local oscillator for a 432 < - > 2400MHz transverter (or QO100 up converter) is possible

- possibly a base oscillator for a 10GHz transverter (followed by a x5 frequency multiplier, e.g. 1987.2 x5 -> 9936MHz - LO for a 10368/432MHz conversion)

- a precise 2000MHz oscillator for down conversion of 2400MHz to frequencies that a better spectrum analyzer or frequency counter. Possibly with a divider to 1GHz and/or a frequency multiplier for higher frequencies. We shall see. what I do

Small update: 

I tested the oscillator with the old spectrum analyzer (up to 1500MHz) No subharmonic signals could be seen. The oscillator is free of spurious signals from 0 - 1.5GHz on this one. Nothing could be seen from 1-2GHz and 2-4GHz. My conclusion is that this oscillator module is very clean, at least with regard to spurious signals. I cannot measure phase noise, but I can probably get that done at a ham radio friend with better instruments. 

This looks like an excellent candidate for 2.4 and 10GHz transverters with 432MHz IF. It is fair to say that a ham radio friend recommended this at a small ham meeting, so I mostly expected this.

The interesting part comes when I try a modification for an external reference frequency signal, how much it depends on the purity of the reference signal.

More on that later.