2019-02-20

Old Post About MMDS Converters, From When I Received Them.

A few words from the old blog post, describing the MMDS converters I purchased several years ago :

About two weeks ago I decided that my setup for S-band reception needed to be upgraded seriously.


So I looked into possibilities for improvements. I found the filters necessary for the AR8200 receiver to work, and looked around to see if I could find some converters that were (relatively) easily modifiable.

I think I found it . MMDS converters cover the bands around 2150 MHz and around 2600 MHz, and it should be possible to modify the filters

TranSystem Inc makes some MMDS converters, I found some on ebay, TranSystem Model EIDC 3033 Down Converter, apparently with the following spec :

RF bands :
2150 - 2162 MHz and
2500 - 2682 MHz,
Intermediate frequencies :
116 - 128 MHz and
222 - 408 MHz

This is possible with a LO frequency of 2278 MHz. Since I want to use the converter for the 2200 - 2300 MHz band, some modifications are necessary :

RF filters - one pair at the input and one pair between the RF amplifier and the mixer - must be modified to cover 2200 - 2300 MHz

The Local Oscillator (LO) needs to be moved away from the wanted passband, preferably for a low side LO.

I took a look at the inner workings of the converter, and the RF frequency filters are stripline filters made of copper with air insulation (not microstrip etched on the PCB), so they are expected to be fairly high Q filters. For satellite S-band I think the best strategy will be to shorten the 2150 MHz strips (careful - we do not want to get too high in frequency), then disconnect the higher frequency filter (hmmm - that may not even be necessary).

The other modification concerns moving the LO down. The LO is a PLL with a frequency divider (256x) 2278MHz down to 8.898438 MHz. (Xtal in the reference oscillator).

It would be nice to have the oscillator running on a "rounded" frequency like 2000 or 2100 MHz, but that would require new Xtals to be made. Since I would like to be able to lock the LO frequency to a stable source that complicates things.

The other option will be to use a 8 MHz crystal oscillator, then lock that to a 10MHz TCXO or other standard. This will provide the converter with a LO frequency of 2048MHz. not exactly very "rounded", but still with a full MHZ, so the readout of the converted frequency should not be all too confusing (that remains to be seen). After all, a computer can do wonders in calculating the correct frequencies and control the receiver(s).

Time is a bit tight this week end, but I hope to be looking into it after all.

Local Oscillator for the 2.4 GHz transmit(/receive) Converter.

It appears that I already have a ADF4350 PLL board. The chip on the board can produce 137MHz to 4.4GHz signals, so 2256MHz (for 144MHz IF) or 1968MHz (for 432MHz IF) is within the range.
I also have an Arduino board, so now it is a matter of software.
I found that someone had made a piece of software for programming the (later ?) 4351 chip (same, except the lower frequency possible is about 37MHz). I will have to find out if the software will program the 4350 chip as well.

Unfinished business ;)

Yes, I know.
I have a ton of project ideas. Not many of them will come to fruition. However, I intend to use this blog as a notebook to myself about ideas for building amateur radio projects.
Maybe someone else can use some of the ideas.

Today's project ideas are all about using low cost TV LNBs and older MMDS (yes, I have a few of those, too) converters for different ham projects. For example :
-LNBs for narrow band reception. Yes, the satellite downlink is one of those, but with a relatively stabilized LNB I should try to receive a terrestrial beacon located about 30 - 40km from my location.
First test should be with the LNB on its own, i.e. without a dish. I do not expect to be able to hear it, but it is worth a try.
-Simple 2400MHz converter with the MMDS converter. I should probably "adjust" the filter and the local oscillator in the converter, i.e. shorten the resonators in one of the internal filters.
-Using the filter and the amplifier in the MMDS converter as part of the 2400 MHz transmit converter. Same applies with respect to the "adjustment" of the filter.
-Using the MMDS close to its intended receive ranges, monitoring solar noise around 2700 - 2800 MHz. Since solar noise is broadband, there is no need to adjust the PLL in the converter

More than enough to try, just in this frequency range, and that is just a few ideas. The above ideas could take quite some time, anyway. As I said above, too many ideas, not enough time...

Update : The MMDS converters have "disappeared" in the mess of a large removal, it may be a while before I find them.

2019-02-18

Tropo and a Bit of PA Trouble

Last Friday there was a bit of tropo propagation on 2m. With FT8 I worked stations at up to about 800km distance.

Further, there is a report of someone not too far from me in Denmark (I did not get the call) heard the 10GHz beacon from the Faroe Islands (OY6BEC), at about 1200km. This is, as far as I know the first time this has happened. The beacon uses a horn antenna directed to Denmark, but this was still a surprise.

One of the fans in my Gemini PA seems to have developed a fault, making a rattling sound. It sounds as if a piece of wire, or a cable strip is too close to the fan. Time to contact the dealer, to see if he has problems with me looking into it. It is still under warranty.

Oh, yes - the ups and downs of amateur radio.

Loop antennas.

Quick update on the loop antennas:

Since the excitement about the Es'hail satellite has resulted in spending some time preparing equipment, and some research on the internet, there has been only a little activity.

The shielded loops have been painted in green and brown colours, for blending in with trees and bushes. Also an unshielded single turn loop has been created. Some experiments with the single loop will be underway.

Es'hail 2 Sattellite, aka Qatar OSCAR 100

The Es'hail 2 satellite has been launched and has entered geostationary orbit. This satellite has TV transponders, and something new for radio amateurs : a 2400MHz to 10GHz transponder in geostationary orbit.
The coverage should be all of Europe and Africa, to the East into India, and to the West a tiny bit of Brazil. Even Antarctica should be within range, if some of the research stations are within the footprint of the satellite I assume that some testing will be going on before the transponders go online, but this is an exciting time for radio amateurs interested in satellite communication.

First update:
The sat is in orbit and the amateur radio transponders are now operational.
They work very well. An SSB uplink with 60cm dish antenna and linear polarization produces a readable signal, a around 10-20 dB above the noise, as I have heard on the WebSDR.
On the spectrum of the WebSDR it is even possible to see the effect of running too much uplink power. This creates dark bands on the waterfall spectrum, and sometimes audible attenuation of received signals.
Frequency stability is the main problem with the uplink and downlink, for obvious reasons.
As a first attempt at working through the satellite I was thinking of purchasing a relatively low cost up converter from SG-Labs in Bulgaria for the uplink. This has about 500mW output, and with a 1W power amplifier at the feed point it should be possible to be heard via the transponder with SSB, and certainly with CW.
A fun experiment would be trying FT8 or JT65 with a much lower ERP.
Receiver side will be with a low noise satellite PLL LNB, possibly with a later modification of the reference oscillator.
I have decided to take time to attempt a simple up converter made of Chinese modules available on eBay.

Second update :
10GHz reception converter (arriving shortly) for downlink:
LNB suitable for OSCAR 100 reception has arrived. Octagon OSLO (PLL controlled Local oscillator.
Initial test will be done with the unmodified LNB.
It will need a modification for better suitability: External reference oscillator, preferably a TCXO, at a stable temperature, fed through the cable (disconnect the internal XO, info on the Internet).
Alternatively, for even better stability, a GPS locked oscillator could be used.

2.4GHz uplink:
Modules from China have been ordered :
1) Synthesizer : ADF4350, covers 137MHz - 4.4GHz Needs to be programmed. There seems to be a library for the Arduino microcontroller. Price per unit about 10 GBP
It turns out, looking through my stock that I have a single AD4350 and an Arduino UNO, so it is possible to start the process of building the local oscillator for the transmit converter. Now for learning some Arduino (variant of C) coding.I ordered a few mor ADF4350s as spares in case I have an accident of destroying the one I have.
Learning the coding could easily take the time needed for the stuff from China to arrive, unless I find a suitable program that just needs a simple modification. No need to invent everything all over again.
2) Passive up (and down) converter modules (also to have some spares). Price per unit about 8 GBP
3) 1W amplifier modules. Price about 10 GBP
I ordered a few, because I have a long run of cable, and would like to have one as output for the indoor unit, and one at the antenna feed point.
The official uplink power for the satellite is regarded to be about 10W into a 60 - 90cm dish. However, an output of 1W appears to be sufficient to make SSB contacts via the satellite, as I have heard several stations with similar set-ups via the WebSDR.
4) Double balanced RF mixer (down conversion) Price about 5 GBP.
Why a down converter ? Well, it is a simple addition adding receive functionality, creating not just a satellite uplink transmit converter, but getting a 2400MHz transverter, making simple two-way contacts possible on that band, albeit with low power. It will most likely be possible to make some local contacts, and possibly a bit more during tropo conditions.

I already have some amplifiers capable of an output of about 100mW on the band, more than sufficient drive for the 1W amplifier mentioned above. Those were priced about 5 GBP.
One more thing is needed for this to work without making interference. A band pass filter.
I need to look into the best solution for that.

If (when) I succeed in getting a signal through the satellite, the adventure begins. Optimization of all aspects of reception and transmission, and experiments with very low power. I was told by OZ2OE that he had heard a Dutch station running a 75mW CW signal into a 1m dish, and it was audible at 539.
Also, running 1W into a much smaller antenna is an idea I want to play with. I have a tiny Wifi yagi, 40cm boom length and 17 elements. That will be an interesting comparison with the 80cm dish I have, and a good comparison. Constant gain from the yagi, and seeing the different improvements to the dish and feed.

I see quite a bit of experiments and lots of optimization in my future.

2019-01-19

Winter VHF Day in Ringsted, Denmark.

Today, for the second year, I went o an annual VHF (etc) Day.
The gathering of (mostly) VHF-UHF and microwave amateurs is held about 45 minutes drive from my home.
There are a few presentations, but I mostly stayed in the hall and had chats with some old friends.
There is a small flea market, but not much was found there this year. Last year was pretty good, so maybe next year there will be more interesting stuff.
All in all a good day spent with ham radio friends from all over the country.