Tuesday, October 28, 2014

Playing with the ELCOM Ceragon DFS-1201

The easiest way to get a descent local oscillator for the microwave bands is purchasing the synthesizer fabricated by the Elcom technologies Inc. Most of mine units are purchased through the E-bay from well know Israeli vendor. To be honest, I was not so lucky with that as most of the units are not working or not working properly. It is well written that the vendor does not guaranty that the units are working properly, so it is on us to decide to buy or to skip... From time to time there are some new units available, sealed, followed with the documentation. This is the way to go. True, the price is almost double but buying four units and having one descent is even more expensive :-)

Let say you get lucky and you have your unit in order, you will need the controller to run this brick. Most of the guys are using Dave - WW2R design. What yo need to know is that you have to multiply the required output synthesizer frequency by 3 and edit the ASM code just using the first 4 digits, compile the HEX and program the PIC 12F675. Plug the power and the lock LED should blink once and lighted. BINGO.
This happens if all is going by the book.

The first sign that something is going wrong may be a LED not locking the ON state. The first thing is to check if the math was ok. Let say you want to program the 11800 MHz frequency. 11800 x 3 = 35400
So you need to program the ASM two lines with the 3540. Of course, the Dave HW is supporting two frequencies, so program another convenient one.
Still not working?
Well, do not expect to have the units working out of the indicated range. Many guys are looking to have the DFS-1201 running on 12.023.333 MHz (for the 24GHz beacon) but mine experience is that the units can lock from 11.250-11.860 MHz, so even narrower than declared.

Surgery - getting a screwdriver (better a battery one :-)
You can always open the brick. If you are lazy to unscrew all those screws, check the picture:

Simple as beans soup :-) The VCO is running on 2.8-3.0 GHz. There is a buffer right after followed by the resistor splitter for the PLL and MMIC doubler 5.6-6 GHz. There is a high pass filter and another 6Ghz MMIC amplifier to provide enough power to drive the x2 multiplier diode. A long 12GHz filter then is followed by 2 stage FET amplifier. The total multiplication factor is 4. Clear ?

Guys owing the Alcatel White box 23GHz equipment needs the oscillator running on 5.9GHz. This is not so common surplus e-bay unit. DFS-1201 can do that ! All you need to do is to run the 6GHz signal from the amplifier just before the diode doubler to the output SMA connector with a peace of semirigid coax placed where the diode multiplier, 12GHz filter and 2 stage amplifier sits. All this multipliers and amplifiers (except tha last 12Ghz stage) are Sirenza S1 and S2 (ERA-1 and ERA-2 mmics) so you will have more than enough power for your White box 24Ghz transverter.

I did not play around the PLL side so much, but briefly, the reference oscillator is running on 100 MHz and heated as per above picture. The signal is then multiplied by x9 and filtered with two ceramic filters. Another mmic multiplier by x3 using INA10386 mmic followed by 2.7Ghz hairpin filter. This signal is then going to the mixer on one side and the signal from the VCO from the other side and we have the mixer output of 100-300 Mhz going to the lowpass filter and then after to the PLL. The complete picture of the digital part is here.

Most common problem is that the frequency is odd. Of course, aging of the crystal with the constant temperature is resulting to have the output frequency shifted (in my case 23khz @ 12Ghz). Just above the crystal there is a small part looking as the trimmer capacitor, so this may be re-tuned, I think so.

I had some other problem, when cold, the unit lock properly, but after some time when heated, if the unit is switched on/off I can not get the lock state and no output at all. This remain to be investigated.

On some DFS-1301 unit I can not get the lock state at all, even when cold. Checked the VCO control voltage from the charge pump and the 6V measured. It should be 5V. After playing around VCO transistor (marked 420) i manage to get the lock, VCO control voltage drop to 5V. After restarting the same problem.
This should be also investigated. And yes, to run the DFS-1301 from the Dave board, the output frequency should be multiplied by 2 or divided by 5. Funny math, you get the same first for digits :-) to program the ASM code.

So that's all for now, at least my DFS-1295 is working properly if nothing else :-)

Thursday, October 9, 2014

Eyal Gal - 24GHz transverter

Coming back
For some time there was no new post from me, but here is the one that can be handy and interesting. I will try to bring your attention on this peace oh the "aluminum brick" called Eyal Gal transceiver. If you have one or if you are planing to buy one then you already have the G8CUB paper about it and the basics about building the 24GHz transverter.

Word of discouragement
Buying the Eyal Gal transceiver unit is just a half way to a working transverter, maybe not even a half way, let say 40%. I learn that on my unit, so be prepared to some extra sacrifices :-) and hiding the money from your wife :-) I will try not to repeat the good Roger Ray G8CUB article about this unit. Instead of that I will try to present my itinerary and the way how I made this thing to transmit.

First thing - shopping (Eyal Gal and ELCOM Ceragon)
I obtain my unit (two units) from the "24GHz microwave store" owned by a really BIG gentleman Ernie -HG5ED. It was a big gift from a big guy like he is. He knew that this is just a half of the story, so he included the local oscillator to drive this wild machine. Yes, you need the external local oscillator too, so start saving the money.... The local oscillator should work on the half frequency and what is required is the high side injection. As I choose the 70cm IF, the local oscillator should run on 12240MHz. This can be done using the various techniques, from the endless multipliers chain to the expensive low phase noise oscillators. My local oscillator is the CDFS-1295, ELCOM-Ceragon unit that can be found from time to time on the E-bay. More likely you will find the DFS1201 Ceragon unit that can operate from 11-12Ghz which is not good for this radio, we need the 1295  model running from 12-13Ghz. Whatever, you need the 10dBm @ 12240MHz signal. If you plan to use the Ceragon LO's then you need also the controller to run this unit. The controller can be found around the web together with the software for the PIC.

Second thing - more shoping (power supply)
OK, so you have the transceiver, the local oscillator and now you need the descent power supply for the Eyal Gal unit. As you already know, +8V, +12V and -12V  are required for this unit. I start to make the first test with the old PC power supply where +/-12V is available and +8V was produced with a single 7808 voltage regulator. This can work, but if you plan to run your transverter portable on the car battery then the PC power supply is not a good option.The tricky part is obtaining -12V and 120mA. For that purpose I use the DC/DC converter (thanks to Ernie) where I have the +/-12V and 250mA output which should be more than enough for the negative supply. The positive 12V is obtained from the 12V rail external power supply or the battery. 
Another tricky part may be the +8V where the consumption may reach over 1A in TX. This can be solved with the switching units. To make things simple, I use two 7808 regulators in parallel with the diode on the output. All the voltage regulators are fixed to the good heatsink.

Finally some soldering (IF switching unit)
So beside the L.O. delivering 10dbm you need a IF radio delivering -21dbm for the proper mixing. Of course, the attenuators are used. Take care, if you ran the IF radio with 2w of output you need 54dB of attenuation on 70cm which is not a trivial. If you used the relay for switching, it should be a good one, with the good isolation. Instead of that, I use the old fashioned switching with the PIN diodes. It is true that also on the RX side I have something about 5db of attenuation, I cure the problem with an extra MMIC amplifier in the RX side of IF switching unit. Of course, I was faced then with the extra gain and s-meter showing S-2. Then extra attenuator was introduced, which is not bad idea as the mmic see the nice 50ohms on input/output.

All those PINS (Eyal Gal transceiver)
The Eyal-Gal unit is a transceiver and not so much to switch around it. To make a story short, you need to key only PIN 1 and all the rest of the pins you can leave n/c. 

But who want to know more:
Pin 1 is described as TX inhibit pin. It mean that you need to ground this pin when on RX and lift up when on TX. This will result better reception and less current consumption that leads to less heating of the Eyal-Gal at the end. So do not forget, PIN 1 to GND when on RX.
Pins 2 and 3 are n/c ( I love when the pins are n/c :-)
Pin 4 is 0V ( I left my n/c as I have enough ground through the housing )
Pin 5 is AGC To be correct, you can reduce the TX conversion gain by applying 0-5V dc. Leaving this port n/c :-) you will have the maximum gain (and the output power)
Pin 6 is a output power detector, where you can see by the DC voltage if you have the output power. I measure a bit more than 3V DC on that pin when on TX. Do not expect the voltage following the modulation! You will have constant (more or less) DC voltage as there is the 2xLO signal and both mixing products measured. This is why you need a filter on the TX output side !
Pin 7 is the RX AGC control. Well it works the same way like the pin 5, if n/c you will have the highest RX gain, if 0-5V dc applied you can reduce the RX gain.

Filtering (spending more money)
The output filter on the TX side is a MUST. Do not operate the transceiver without it because you may interfere with some cell tower links. You do not want to do that. You will have to look for a experience microwave guy help here or buy the tuned filter for the desired frequency.

Antenna switching
You probably heard the stories that antenna relay for the 24GHz operation should be a waveguide switch and nothing else... So why there are SMA coaxial relays on the market rated to operate up to 26.5GHz ? The E-bay is good source of such relays with a fair prices. More over the latching relay type can be purchased really cheap. Using the SMA relay will save you a troubles bending the waveguides, using the flexible waveguide and at the end the waveguide switch is really expensive. So the SMA coaxial relay is not only a cheaper but occupy less space and the box can be smaller, which also reduce the final cost of the transverter.
I did not measure the difference and the losses, but messing with the waveguide switch comparing to the SMA relay is not worth money and time.

First tests
Even the desk measurements on the instrumens were OK, the real test was performed listening the live signal on the band. Observe the frequency stability of the Eyal Gal transverter and the Mini beacon running some 4km away. The mini beacon will be explained in the next article. Note: none of the units were conected to the GPSDO reference.

Finally results :-)
At the end, what can be done with the 24GHz transverter described, so far I made the 236km QSO in a not so good conditions, means humidity 60%, temp 17 degC and pressure 1016hPa. The antenna used was a "footer" 32cm dish. The qso was a SSB with a solid copy both sides. Well, do not forget to switch the LSB on your radio when operating USB due to high side mixing. The drawback is that the tuning the frequency is opposite, but this should not be a problem for a experienced microwave operator.
Have fun.....