10GHz Transverter, Continued.

 In the autumn/fall last year I was out making a receive test of a 10GHz transverter briefly described a few days ago in the previous post. 

When I should have had a signal from the OZ7IGY beacon about 25km away, there was ... nothing.

I started the fault finding with a measurement of the LO module, and it did look pretty good. So Now the down converter should be tested.

I located a signal generator (low cost Chinese circuit with the ADF 5351 synthesizer. As the signal generator has a fixed output, I made a small loop for 10GHz, soldered to a low cost (chassis) SMA connector. Measure on the spectrum analyzer (with built-in frequency counter the signal generator seemed to stay within a few 100 Hz, with a fixed offset of about 10kHz. Good enough for a first test.

Power up the transverter with 12.5V, the IF connected to a Malahit DSP2 SDR set to 144MHz, and let the system warm up a bit. The 12.5V was about what the battery delivered at the test. 
It sounded absolutely dirty, with some irregular jumps in frequency.

Where was the instability? I tried connecting the FT-290 and it was the same. Apparently I could eliminat the possibilty of the Malahit going faulty. Now remains the LO of the transverter or the signal generator.

Next test was, let us see what happens if the supply voltage is increased.

Bingo. at 13.5V the LO apparently jumped to the correct frequency (well, about 3kHz low) and stayed there, the tone sounds good, all the dirt gone from the audio, and the sensitivity looked much better. You may laugh, I don't mind, because I foind the fault.

Connecting back to the Malahit SDR, and it looked good.

The Chinese signal generator, though has a rather noise output. Good enough to test the system, but the phase noise is atrocious, only about 10-20dB below the carrier. I heard that a ham not too far away has made some modifications, and I will look into that.

So what to do when I do go out into the field? I need 13.5V and the battery delivers only 12.5V. Too low for a good function.

I think I will try first with a different battery and a DC/DC converter. I know that the DC needs extra filtering, but it should be usable for the first field tests. Next step: check the TX function.

Fault Finding in an Old 10GHz Transverter.

In the autumn I made a first test of a home-made 10GHz transverter I got my hands on, and started testing.

The initial test was a simple connection to an older FT-290 transceiver, and going out to spme place a bit higher than where my house is located.

I was listening for the beacon OZ7IGY at a distance of about 25km. Nothing in the garden. If I placed an satellite TV LNB about 4m above ground I could hear the beacon, very weak, because it is behind some hills about 30m higher than where I am.

I tried to go to a place somewhat higher with the FT-290/transverter setup on a tripod, and tested. Absolutely nothing heard. tuning about 30kHz to either side of the beacon frequency.

So now I got started fault finding.

The first suspicion after talking to a local ham was the 2556MHz local oscillator module. Testing on a spectrum analyzer showed a nice signal with an offset of less than 600Hz. Not bad, this would give an offset of less than 3kHz. The output (to the Qualcomm up/down conversion module) is close to 5dBm, so that looks quite good. I can safely say that the LO module works nicely.

Now more tests are necessary.

 I do need a small 10GHz signal source, and I have thought of using one of the following:

- a low power (0.5W) 70cm FM transceiver with an attenuator and a single diode as multiplier

- a synthesizer PCB with a AD 4350 or 4351 chip, just using the 3rd harmonic. 

At least I can test those with the spectrum analyzer, so I know if there is a strong enough 10GHz signal.

I think the simplest of the two is the attenuator/diode multiplier, so I think I should start there.

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.

Microwave Parts and Modules Part 2: Surplus PCBs and Modules.

Some weeks ago I went to a small ham gathering at the site of a  local repeater.

I had a talk with local hams about uplink equipment to the QO100 satellite. Many people are planning getting active on the satellite, so equipment for the 2400MHz band is in higher demand.
I had been planning to use some cheap Chinese modules for the local oscillator, but one suggested to find some better modules with Franco, alias RF-Microwaves.

Looking at the site I found that they have a lot of interesting stuff, especially in their surplus dept. Here are a few examples:
- A local oscillator module running at 2009MHz with the standard 8MHz crystal
- Some LNB modules without feed horn, but with input connectors
- PCBs with 4 HEMT FETs, where the PCB is arranged, so that it is possible to cut out two low noise amplifiers
- WLAN PCBs with several good components, including some 2.4GHz band pass filters
- 15GHz oscillator modules with several 10s of mW output.

I ordered a few of each, and some microwave absorbing foam. The service from Franco is excellent, I ordered one afternoon, and 2 days later, in the morning, the goods were delivered. The exception would if he is at a ham gathering, such as the Friedrichshafen Ham Meeting, probably the biggest in Europe.

Now for the goods, some of which are the last few left.

The 2GHz local oscillator module (about €20):
This is a complete module with casing and mounted with vibration absorption. Looks really good. On the website there is some modification information. The VCO can be used from about 1960 - 2040MHz, and the modification consists of making an external reference oscillator, replacing the internal 8MHz crystal oscillator. The external reference can be made with a well filtered DDS module.
For the IF of 432MHz the LO frequency should be 1968MHz, which is in the VCO range

As s second use of the LO module, it should be feasible to add a multiplier x5, for a local oscillator for a linear 10GHz transverter/converter.

A brief description of the LO module is on Franco's website.

LNB module (about €3):
This is a DRO controlled down converter module for satellite TV, with the mixer/oscillator in a single chip.
F6CXO has proposed the use of this module as a down converter for a (lower frequency) spectrum analyzer. The modification involves removing the 11/12GHz amplifiers and the filter. This cannot remove the image frequencies, so one needs to be aware of the frequencies that can be generated by the circuit you are testing. For amateur use, it does present a possibility to see what is going on in the 10GHz band, without having a more expensive spectrum analyzer. Mine covers up to 1.7GHz, so with a LO tuned to 11GHz the frequency range of 9.3 - 12.7GHz can be monitored.
Max RF input for the converter is about 0dBm (1mW). The RF input connector should be changed to a SMA, for the original ones it is probably very expensive or difficult to find a source for them.
The modification, if done carefully and with antistatic precautions, should provide you with 3 working GaasFETs, apart from the intended converter. I would probably make 2 converters, the second one using the lower LO frequency of about 9.7GHz, thus covering 8.0 - 12.7GHz with my analyzer.
A description of this modification is posted at Franco's website.
I would propose a few uses for the module, apart from sourcing components:
- Using the converter as it is, as a WBFM down converter to the 600 - 800MHz range.
- Adding a connector to the output of the 10/12GHz  preamplifier (before or after the (modified) band pass filter, providing a simple 10GHz amplifier with a gain of 15 - 20dB, likely with 20-30mW output.
- It might be possible to add injection locking to one of the DROs, if so the converter could be used as a simple narrow band down converter for 10GHz.
- Using the LNB as it is, for rather unstable down converter for wideband FM.
- Using the casing (moulded aluminium?) as it is for other modules I should build
I am sure other uses, apart from being a source of components, will turn up ...
Not bad for a €3 module.

PCBs with 4 HEMT FET amplifiers:
There is a document on this PCB, too, on Franco's website.
Here are some uses the document suggests:
- A low noise 10GHz LNA from a cut-out piece of the PCB. Each PCB could provide two of those in a relatively easy way, also salvaging two HEMT FETs. Yes, the board has 4 amplifiers, it looks like it has come from a dual head LNB. A negative supply for the gate of the FETs is necessary to add to the simple amplifier.
- Using a piece of the 50ohm stripline as a piece of test equipment, e.g. a component tester or for a bias-tee. The PCB material is good for up to 20GHz.
- Making 1 12/24GHZ doubler.
- The FETs are useable on 24GHz with up to +13dBm output and a gain of about 7dB.
This looks like an excellent source for building microwave stuff.
Like with the "connector-LNB", you get a lot for €3.

The WLAN PCB looks like a good source of components for building some 2.4GHz transverters/converters.
I was buying them, mostly for the 2.4GHz filters, but there is a PLL IC, a prescaler, and other good components there.

The last one, the LO PCB:
This contains two LO chains for around 14/15GHz:
- A straightforward receiver LO, starting on around 2.5GHz, adding multipliers. A tripler for 7.5GHz and a doubler for 15GHz
- A TX LO which also includes a modulator, meaning that it looks useable as a (WB)FM modulated transmitter, with a suitable PLL oscillator modification of the 2.5GHz part.
The output transistors, (two) coupled with a hybrid, are supposed to be capable of delivering about 100mW on 14GHz. I am now wondering if the hybrid is broadbanded enough to cover 10GHz, but that is something that needs to be tested. Also the 14/15GHz filters should probably be bypassed and replaced with some 5 and 10GHz filtering. I am hoping to be able to use a modified version of this PCB as a 10GHz power amplifier with 100mW output, if the hybrids have sufficient bandwidth. It may, however be necessary to design a separate PCB or set of PCBs, using the output FETs. With that, I will have to ask someone with **much** more experience than I have. I know, my general knowledge will probably not be sufficient for such a design ... yet.
- Also, an excellent source of components, FETs, MMICs etc.

Oh, well, so many ideas to try out, and lots of other activities. It will take time, and learning some new skills, but, as a start, I have a few of those modules

One 10m Antenna With Multiple Receivers.

Some time ago I made a modification to my IC-703. It was a RX antenna adapter, originally made for the IC-7300.
It was possible to fit it into the IC-703, albeit with a bit of extra work: I had to file a bit of the adapter's plates an a bit in the radio casing, but it looks acceptable to me.
For a while I only had it connected to loop back the receiver signal, but this week I connected a signal splitter, so it is possible to connect more receivers in a way that does not destroy the receivers when I transmit with the radio.
Yes, when I transmit, I cannot receive anything on the 10m antenna, but I consider that an acceptable compromise. Further, it is possible to use a more complex system, so a transverter could be connected to the transceiver, too.
A TX power amplifier I have, I can connect it to the RX part/common connector, so I can transmit up to 200-250W with that combination

This is how the system looks right now:

10m vertical --- IC-703 ---                               !--- IC-703 RX input
                                         !                             !
                                         !                             !--- RX monitoring 28.074 (FT8)
                                         --- Signal Splitter --
                                                                       !
                                                                       !--- RX monitoring the international beacon project
                                                                             on 28.200

The splitter has more outputs
At the moment the signal splitter is just hanging next to the TRX, but it is the intention to build a casing for the system, so a preamplifier (attenuation in the splitter is too high for some of my receivers) and a switch for transverter or separate RX antenna can be added. For now, the system just has to work as it is, as well as possible. Improvements can come later, after other projects have been done, at least in part.

I would like to have a similar system for the higher bands (6-4-2m and 70cm), but that will have to wait.

Idea Box: 10GHZ TX Mixer from the cheap HB100 Module ?

I may have mentioned it before, but I intend to use this blog, not just for telling you about ideas etc, but also for me to be able to find old ideas I have had.

Looked through 10GHz websites. Found a teardown of the HB100 Doppler radar module. It turns out that, apart from the expected DRO (oscillator) is a passive balanced diode mixer, much like seen in older LNBs. It looks like a simple modification of the HB100 module - removing the DRO (or maybe just the power for it) - and entering another LO signal, the mixer could be used the other way, too, i.e. a TX mixer.
The modification should involve adding a few SMA connectors (two for RF/LO and another one (maybe SMA, too) for the IF port, and likely cutting a PCB line from the original oscillator.

The idea could be tested by using the module as it is, just entering a low frequency (IF) drive signal and see what comes out on the RX port.

The HB100 module is an interesting device, even for modification or salvaging the very few microwave components it has, the price of the module off eBay is less than $5.