I was searching for some simple LNA for microwave reception and found a very cheap board from China. For less than 10 Euro i ordered a LNA board that is specified to work from 50MHz to 6GHz. The gain should be about 20dB at 50MHz and still >10dB at 6GHz. Even if it does not work like that the PCB with shield and SMA jacks is still a good deal. You can find some measurement results below. The original condition makes clear that the gain on the upper frequencies is not good. Touching the bias network with the finger showed slight improvements. So it was clear that there is some problem with the components feeding the MMIC. Exchanging the ferrite bead by a 68nH RF coil gives much better results up to 4.5GHz but still has problems on the highest frequencies. So i tried a 2.7nH i series directly connected to the RF trace in order to avoid the stub that was there before. Now 6GHz is good but there is a resonance at about 3.5GHz. My last attempt was an additional 120nF to ground between the two coils. Thats pretty promising for the microwave bands but below 800MHz the LNA is not usable anymore. So the network still has room for improvement but it is at least clear that the board is usable.
Chinese LNA with german finger ;)
measurement results for different bias networks
Just before the May DUR competition i got my new 6cm Transverter working. Before I faced some problems with the multiplier chain.
Murphy made that saturday afternoon i burned the control circuitry of the SMA bistable relay – poff. So i had to exchange it with my own sequencer circuitry that needs some highside FET switch to do that job.
I used a dual-band ring feed i made for tests and connected it to a old 60cm dish. The result you can see on the photo below. Very beta version ;) The PA is still missing and therefore i had only about 250mW.
I also wanted to take 3cm with me. In order to limit the amount of equipment i decided to minimize effort for 23cm. 13cm is out of order at the moment anyway. That means only using the former Wimax patch antenna for 9cm.
The following result i can claim:
23cm 12QSO 772P
9cm 4QSO 481P
6cm 2QSO 351P (x2)
3cm 4QSO 489P
Next steps for 6cm will be adding driver (ordered from China) and the PA (10W, already here) as well as creating some better feed suitable for the mesh dish.
My goal is to operate 23/13/9/6 with one mesh dish.
This time i had a neighbour in JO61XA. DM4SWL was operating few meters away on 23cm FM only. Thanks for taking the foto !
after May 2017 DUR test
Attiny2313 + Uln2003 + highside FET switch for PA + lowside FET switch for RX-TX relais and a few bipolar Low Power stages on a two-layer board. The PTT input can be either high-side or low-side active. It also has lock input to connect several transverter to one antenna system. Via the driver IC a pulse relais and a fan can be controlled. There is also a Tx inhibit output that can be used with Yaesu tranceivers.
Attiny Sequencer Rev2 schematic
The circuit has two PTT inputs and two Error inputs (decoupled by diodes). A active high PTT input is available as well. There is a highside FET switch that can be used to drive a PA and a lowside FET switch that can be used for an RX/TX relais. The TX inhibit signal is available to drive the inhibit input of Yaesu transceivers. The active out is used to signal a sequencer in TX mode. This can be used to lock other sequencers via the error input. The ULN2003 driver is currently configured for another RX/TX relais, a fan which is running until 30s after releasing the PTT, another low active signal parallel to TX-inhibit (as PTT for TRX without TX inhibit) and output signals for a pulse relais (bi-stable RF relais). The serial interface (also used for ISP) is unused in the application. It might be possible to connect a temperature sensor for example.
The missing connection from Q4 to R7 is a print error.
The design was done with KiCad which is a open source PCB layout system. The code for the microcontroller was written in C. The 2k program memory are almost full now but one might be able to optimize. If you are interested in the design data let me know. I also have some spare PCB left over.
I wonder what else could be implemented with this PCB with the small program memory size. Feel free to give some ideas.
2nd version of the PCB i designed over 2 years ago. Hopefully without bad errors i hope ;) Lets see when the shipment will arrive…
I corrected the package of the microcontroller and swapped a few signal pins in order to gain some flexibility with the software.
Sequencer version 2 PCB
Currently i assemble a 6cm transverter kit that was already in the shelf for quite some time. The PCB is mounted to the enclosure now and the filter cups are soldered as well.
6cm transverter kit
I was not qrv from JO61XA for a long time. Now there was the chance to take all the equipment to Triebenberg again. During the last months i tried to repair some things here and there. The 9cm transverter got a new alignment and is working now. Saturday morning i collected all the stuff and partly assembled it. I wanted to go for 23/13/9cm and 3cm eventually. This time i used the 1m dish that i bought last year in order to save some time during the mast construction. In the end i was qrv 1 hour after beginning of the activity. So what… The goal is to test the hardware. First observations were not that promising: 1) bad connection of the DC supply for the mast transverters 2) control unit for the rotator was not working.
The later one was really bad. Later at home i noticed that i partly disconnected the cable for the display / keypad unit when fixing some loose screws few weeks ago.
For 3cm i picked a second IF transceiver. Unfortunately the wrong one. The IF is 432MHz but i took the FT-290 instead the 790R2 ;) RX/TX switching via the mimic for the 2m based transverters from the FT-817 was not working but it took me almost until end of the test to find out what was going on. So only 1 QSO there.
Also 23cm seemed to have some oscillation in the RX LNA. I got some very strange sounds from time to time when releasing the PTT. Maybe some feedback from the 13/9cm transverters because of the PTT mimic i use (i switch all chains to TX but only transfer the IF to the one i want to use. Decoupling is only 50dB which might be an issue. I need to investigate there).
Finally, when deconstructing the mast, i was a bit optimistic on the way to remove the ropes and had a very robust takedown of the antenna and transverters. The main impulse was taken bei the box of the 13cm transverter. Fortunately only the plastic box splitted into several segments. The transverters are still working fine… lucky operator ;) I anyway want to put it into a common box with the 6cm i am going to build and the new 9cm i have flying around as components here.
Hope to hear you again next time.
damaged 13cm transverter box
Since some time i own a DF9NP GPSDO. Currently i only use it to lock my signal generator but i also want to use it for my microwave transverter OCXOs. When connecting a SMIQ signal generator and checking the signal output at 6GHz i noticed some +-50Hz jitter under the poor reception conditions at thelocation of this signal generator. So i want to look a bit closer into that topic. In China i ordered a Neo-M8N module that can be configured to provide a 10MHz clock at its timepulse output. I tried to compare it with the GPSDO and the OCXO of my SMY-02 signal generator.
Of cause the digital clock has significant jitter because it is generated by a CPU (specified with +-10ns).
Neo-M8N clock output at 10MHz
The picture of the timepulse at 10MHz shows, that it seems that comparing the clock to a stable oscillator over a relatively short period could be sufficient for adjusting the frequency of this oscillator to the GPS.
GPSDO, M8N, OCXO
The screenshot shows the oscilloscope triggered to the GPSDO (green). The output of the M8N module (yellow) shows the jitter and the adjustment range within 60 seconds (yellow shadow). The third (blue) trace comes from my SMY-02 which was locked to the GPSDO. The SMY signal shows some slight jitter compared to the reference. To me it is not clear if the cause is the reference or the locking in the generator. The clock from the M8N module shows significant adjustment of the clock frequency within the 60 seconds shown compared to the GPSDO which has a TCXO that is slowly compensated by the GPS inside the reference.
Looking to the signal in frequency domain shows this picture:
Neo M8N spectrum
There are rather close sidebands that require narrow band adjustment of a oscillator eventually locked to this GPS clock. Wideband the spectrum is noisy as well.
M8N phasenoise at 10MHz
Finally i took a short video showing the the scope triggered to the 10MHz OCXO reference of the SMY and comparing the GPSDO and the M8N output. The OCXO is slightly off 10MHz and therefore the picture is moving all the time. You can also see that the M8N is slowly adjusting compared to the GPSDO output.
The above shows my 9cm transverter. It gives about 5W in 3400MHz. The boxes are rather old but still work fine after adjustment of all currents. The PA has 46dB gain which makes a attenuator necessary.
transverter component side
This photo shows the assembly side with the RF transistors. The other side carries the filter cups aß Well as some other larger components.
transverter top side
The small box ist the oscillator/multiplier and the other one the transverter.
G8ACE OCXO at 103.5MHz
103.5MHz oscillator briefly measured with R&S FSP30..
PN Plot G8ACE OCXO
I think above 1kHz the PN figure is determined by the FSP oscillator.
Does someone have a better measurement of such an oscillator, especially above 1kHz up to 200kHz ? Unfortunately i do not have a better PN testset.
The following picture shows the cold-start behavior of the OCXO from room temperature to 60 degree celcius. The X-axis shows time in seconds and the y-axis frequency in Hz.
G8ACE OCXO Startup