Receiving OSCAR 100, Stage 2: External Reference.

A few days ago I made the simplest possible modification for external reference of a LNB. The LNB was a Twin type with two independent outputs. It was purchased with a local low cost dealer, and turned out to be a PLL type, suitable for modification. They also have a single PLL LNB, of which I purchased a few, just for experimentation (I said they were cheap).
The 2 port LNB modification is done by sacrificing one of the outputs for use as a reference frequency input. This eliminates some SMD soldering. Here is the process:
1) The crystal was removed after looking with an oscilloscope which side was the reference input for the PLL IC.
2) The port nearest the input was disconnected from the output circuits by cutting the PCB tracks
3) The input of the PLL IC had a connection to ground with a capacitor. PCB track to that one was cut, too.
4) A relatively large (1006) SMD capacitor of 220pF or so was soldered directly from the (now) input terminal to the soldering pad for the crystal. Not very pretty, but it works nicely.

That's it ! (pictures will follow.)

Testing this with a signal generator from a transceiver test set failed miserably. I could not find the signal in SSB mode, so initially I thought I had destroyed the LNB.

Testing the signal generator with a SSB receiver on 25MHZ revealed the problem: The 25MHz signal had audible small frequency variations, sounding like something between a warble and a rumble. Multiplied by about 400 this made the SSB signal extremely hard to find, but with the receiver in wideband FM mode, I found it. The LNB was OK.

Now for building, in the simplest possible way, a 25MHz oscillator stable enough to receive signals. I found in my drawers a canned crystal oscillator marked 25.000 00 MHz, and soldered the circuit, including a 7805 voltage regulator and some decoupling capacitors (ceramic and electrolytic), all mouned in an old (used) die cast box with BNC connector and a feed-through capacitor, used for reference frequency output and supply voltage, respectively.

Everything connected, and voila! Test signal received.

Getting the LNB out to the dish, and - here we go. After settling in for a few hours, the OSCAR 100 beacon was about 15 kHz high on my receiver, corresponding to the 25MHz oscillator being about 40Hz too low, but with a clear tone, if drifting a bit. It settled quite nicely in the evening. What a relief having a more stable reception. Stable SSB signals were readable without re-tuning for longer than 5 minutes.

The result is quite satisfying, and should be quite useable for normal SSB/CW contacts via the satellite.

Opening the window next morning got the reference drifting down 5-10Hz, moving the LNB output signals a few kHz upwards.

I decided that it was foam insulation time. I found a piece with a cut-out almost fitting the die cast box I use. I had to make a small cut-out of a 1cm wall and for the cables (power ans 25MHz out), and a piece of flat foam to make contact. Simply taped them together with - yes, you probably guessed - duct tape. The frequency slowly settling, interesting to see where it ends up. 

The oscillator frequency was slowly drifting upwards, even with the window open, bringing the reference closer to the wanted frequency of 25 000.000kHz.

There seems to be just a bit of heat generated in the box, and I hope it would stabilize.

I will wait a few hours to see how it settles.

The LO seemed to settle around 8 - 9kHz too low on 10GHz.

This morning the offset had increased a bit, to just above 9kHz. Opening the window appears to increase that to about 10kHz. Much better than without the insulation.

I think I will try with some resistive heating inside the box, to see if I can bring the frequency closer to the wanted one. A bit of experimentation is probably necessary.

Very usable, but I will probably try to mount a, say 220ohm, heating resistor to see if I can get closer to the wanted LO.

Could be fun to get within 1 - 2kHz of the wanted frequency most of the time.

Long term I will have to make a better reference frequency generator (probably GPS disciplined or a Rubidium standard), but this will have to do for now.

Time to think about up-link transmit capability. Probably from 432/439MHz, because it is easier to filter out the image frequency. I have some of the stuff, and more is on the way from China.

Receiving Es'hail QO 100 With Own Equipment, Stage One.

The Octagon PLL LNB has arrived and the set-up is beginning.
Today I got my initial setup for receiving OSCAR 100 up and running :
This is how I did it:

Assembling 60cm dish
Mounting dish on the"main" mast
Cable from shack to LNB
Feeding DC from the sat receiver through a two "output" signal splitter, so the next RX can be safely connected.
Trial and error alignment to maximize signal from Hotbird at 13deg E
Setting azimuth for Astra1 at 19deg E
Optimizing elevation for Astra, and adjust the elevation a tiny bit down.
IC-R7100 would not start up, so got the older AOR8200 down from the upper "shack".
S meter showed full, so inserted an attenuator.
LO deviation from standard frequency was unknown, so initially tried to tune RX +/- 50kHz. It turned out to need 200kHz, meaning that the reference XO was about  500Hz too low.
Optimized azimuth for OSCAR 100, the transponder noise is audible and the beacon (and other signals) quite strong. Maybe more attenuation needed.
Frequency stability is sufficient to be able to make a QSO, but too much for comfortable operation. Frequency was seen to vary about 20kHz with the current, relatively stable weather.
Not bad for a day's work.

Better frequency stabilization is needed. For the moment I will not modify the only LNB of mine that I know is a PLL type. Two new low cost ones are on the way from a "low cost" shop, known to be PLL types.

One day later :

I went to the shop, anyway, could not wait for the cheap LNBs to arrive :
Purchased cheap LNBs at Harald Nyborg, a low price shopping chain nearby.
The price for a single LNB was DKK 58, a TwinLNB was 139, and the Quad was 199.
Tested those and others I have purchased lately.
All single LNBs were PLL types Octagon OSLO and the locally purchased - branded Maximum ST-11, as expected, because others have tested them. All were relatively stable and with a clean tone reception from Es'hail, albeit at different down converted frequencies.
A cheap Twin LNB branded "Goobay" was stable, but the tone of the received/down converted signal was not clean. Phase jitter, maybe.

The other Twin LNB, Maximum ST-12 sounded clean.

The quad LNB from Maximum turned out to be a DRO controlled model, though not extremely unstable, and not suitable for narrow band operation.
Same is the case (as expected) for an octo LNB from Octagon.

The quad LNB from Maximum and the Twin LNB from Goobay are hereby relegated to use for satellite TV only.
Two more Maximum single LNBs and one Twin LNB are on the way, still, so I decided to start taking the Twin version apart. The sealing of the shielded box turned out to require  quite a bit of work, so not finished yet.

Finally finished disassembly of the Twin LNB, and things look good for a simple modification.
This simple modifications sacrifices one of the IF outputs for use to connect the external reference in the simplest possible way, and requires two cables to be connected to the LNB for just one down conversion. The "reference input" will be completely disconnected from the IF output/DC input, cutting the PCB tracks to the F connector. Ole, OZ2OE mentioned that the DC input circuitry may be the source of attenuation of the reference signal in the single LNB versions, where it is connected to the DC regulator through a low pass filter with a cut-off frequency suitable for the IF, and not to the reference frequency.

For the experimentation I needed a sufficiently stable signal source for approximately 10GHz. The initially useable solution turned out to be a cheap Baofeng transceiver transmitting on 432.000MHz. This provides a decent, if drifting, drifting signal, enough to check if the LNB is locked to the reference.

A better 10GHz signal source is planned, and probably involves a relatively stable crystal oscillator, or possibly a stabilized DDS generator with a simple multiplier made with a Schottky diode. The housing and antenna could be a now discarded LNB - it had lost its protective sealed cover for the horn, and is useless anyway, and the horn antenna has not rusted or anything, so after a bit of cleaning the feed horn should work nicely, at least for indoor work.

Stage 2 will involve doing the modification for using an external reference, and making that reference source. I still have to decide how to proceed, exactly. When it is done I should make a description of the modification I use.

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. And small update.

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.

Update :
I have some 2500-2700MHz and 2150-2162MHz MMDS down converter units lying around, and may order a version that has only 2500-2700 MHz range.
If the  RX mixer in those units are passive devices it might be possible to modify the unit for use as a very low power transmitter converter.

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.

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.