Contents :

A collection of thoughts, and my notes about experiments and ideas, technical or otherwise, connected to Amateur Radio, Satellite working and monitoring and other electronics.

Wednesday, July 22, 2009

Too close for comfort - poof !

Looks like I blew my sband LNA.

I noticed that I could not hear the "beacon" sat signal on 2242.488, so checked. changed the LNA to another one, and signals came back - probably with a slightly higher Noise Figure (L-band LNA).

so - I opened the LNA and what did I find ? it is not a GaAs Fet amplifier as such, but a GaAs MMIC. Not really a problem, I have a replacement with the same pinout - only snag - it is SMD, so I hope my soldering and vision will up to the challenge.

LNA Spiritus Basta !

Why did this happen ? I transmitted on 2m with an antenna too close to the sband antenna. Oops !

Tuesday, July 21, 2009

half hour antenna for satellite reception

I was growing tired of having poor reception of the transmissions from ISS on 145.800/825 and 143.625 MHz, so decided for a quick ground plane antenna. What to do for a quick antenna ?

Here we go :

1) use a piece of coax, strip about 53 cm of the shield off
2) connect 2 pieces of (insulated) wire about the same length to the shield connection
3) insulate with duct tape for a quick weather protection (will not hold long, but this is a temporary setup)
4) string the thing up between the clothesline and the balcony railing
5) pull the cable through the wall/door/window
6) add connector indoors to the radio and connect to radio
7) done

Results receiving ISS were better than using mu uhf-satcom log periodic array (no real surprise there)

I still need a better antenna/antenna position (poor reception when the ISS signal has to go through the buildin), and since I have some noise, so more to do.

Probably a 2m antenna with preamp (cable length) in the dormer.

Saturday, July 18, 2009

A bit of slow progress for S-band

In order to test the filter I got via ebay, I just connected it outdoors, not really the best thing to do.

Today I went to the local "elektronica-boer" and got some connector adapters making it possible to move the filter indoors. I had to retain the filter before the extra indoor amplifier in order to avoid IMD problems, so a bit of extra adapters were necessary.

One day I will have to make a web page describing the whole thing, but that is for later.

Busy day tomorrow with non-radio stuff, so hope to get a bit more done today.

Friday, July 17, 2009

Another alternative for S-Band

I just found yet another alternative for "watching" satellites on S-band.

I have an Icom R3 receiver, covering up to 2.5 GHz, albeit only for FM and ATV. However, I found a rather simple modification for an IF output at the site of G6LVB where he describes the mod.

I think I will do that one and see how it works, even before I start modifying the converter. Only problem seems to be frequency stability.

The IF in question is 26.05 MHZ, but I have one of the Elektor programmable SDR's covering up to 30 MHz, so that looks like a useable, if not ideal solution.

This could, of course also be used with a HF receiver for receiving SSB or CW on the 13 cm amateur band

So many ideas, so little time.

Thursday, July 16, 2009

MMDS converters have arrived

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.

Wednesday, July 15, 2009

LRO without GSM

This morning I woke up early and saw the moon was out. Tested the reception of the LRO, and it was not loud but clearly there, even audible in the speaker, more details later.

Saturday, July 11, 2009

GSM interference not quite gone .... well - it was, really

It looks like I spoke too soon.

The interference from the GSM has re-appeared, tough not as strong as it was. After setting up some 260MHz antenna and preamp again, it came back. I may have to use a different preamplifier (tuned) for that system.

More work to do ....

*****Update : It was *not* the dreaded return of the GSM interference ....

Apparently , by adding the second amplifier (and a second receiver) in the system, I inadvertently made a loop creating humm in the system.

with less "MIC boost" at the pc sound card input the problem disappeared (only the base 50Hz and the 3rd overtone 150 Hz are visible on the spectrogram now), and I am now back to a quiet S-Band reception.

Phew !

S-Band filters have arrived

I picked up the S-band filters on the post office today, and it turns out that there are indeed two different filters

1) Centre frequency 2125 MHz, Bandwidth 295 MHz (I assume 3 dB B/W)
2) Centre frequency 2375 MHz, Bandwidth 295 MHz

I tried both filters and it looks like the lower freqeuncy filter does not - to a sufficient amount - attenuate the unwanted signals, so I will use the second one .

The GSM sidebands have completely disappeared, much to my relief. (Not a trace of them in the spectrogram). I need a bit more amplification, but that is easily arranged using a second satellite TV in/line amplifier.

It looks like my theory of insufficient image rejection in the receiver is correct.

Now for some S-Band satellite signal hunting - and of course the LRO on S-Band.

Monday, July 6, 2009

S-Band Filters

I found someone selling some filters on eBay. The description said centre frequency 2125MHz and bandwidth 295MHz

However, when looking at the photo it looks like there are two different filters :
2125/295MHz and

If that is correct I will have two very useful filtersone covering approx 1975 - 2275MHz (useable for most of the satellite S-band downlinks (2200 - 2300MHZ), and one covering 2225 - 2525MHz also useable for a good part of the Satellite S-Band downlink band , as well as the Amateur radio *and ISM) band from 2320 - 2450MHz.

Both filters are indeed usable for reception of the LRO on 2271.200MHz

If the two filters in the photo are indeed what I will receive.

When I receive the filters, I will be able to test whether my theory of poor image rejection in the receiver is correct, or if the problem is caused by IMD outside my RX system.

In any case this is going to be interesting.

Thursday, July 2, 2009

Lunar Reconnaissance Orbiter

The last week or two I have made an attempt to receive signals from the Lunar Reconnaissance Orbiter (LRO).

The LRO is currently in a polar orbit about 50km above the surface of the Moon, and has a transmitter on 2271.200MHz. It is possible to receive on Earth, as several people have done, already in it early days.

I decided to see if I could do this using "off the shelf" equipment with the antenna on a balcony.

I started my efforts using a handheld scanner , the AOR 8200 Mk3 which covers this frequency in SSB mode. Since I know that the sensitivity is insufficient on that frequency I started out using a LNA2227 (LNA), having a Noise Figure of less than 1.5 dB and finally a logarithmic-Periodic antenna (LPDA). no luck, but got a grid of "carriers" spaced about 215 Hz .... hmmm ... sounds like GSM.

After a few days I found myself digging out a WiFi grid dish with linear polarisation. still no results, and still GSM carriers.

Testing if this was Intermodulation Distortion (IMD) in my receiving system was done with a 10 dB attenuator ... the interference duly reduced by 10 dB, eliminating the suspicion of IMD in my system. I suspect two possibilities : Either IMD created somewhere outside my RX system or poor Image Rejection of the receiver. Most likely is the Image Rejection problem, since the GSM sidebands are strongest in the direction of a nearby base station.

Testing the connection between LNA and receiver revealed that the LNA had insufficient gain to overcome the high noise figure of the receiver, so what to do now ?

A quick test was set up using a satellite TV in-line amplifier, powered by a satellite receiver (off-the-shelf, remember). Still no success, but the noise performance was clearly better, as witnessed by other satellite signals in the 2.2 GHz band. Well, the moon was hidden by a tree at the moment of testing, making it difficult to point the antenna in the right direction. Still no signal from the LRO. I was beginning to doubt the usability of my system, but not yet giving up.

Finally, yesterday evening, the Moon was clearly visible, the antenna was pointed to the Moon, and bingo .... there was the signal ! A slanting line on the spectrogram showing a downwards change in Doppler shift.

Preliminary image 1 :

I followed the signal till the LRO disappeared berhind the Moon, with the Doppler change getting much lower.

Preliminary image 2 :

So - after a week of experimentation, finally success.

The receiving system need much more work, the first test will be making a filter that should (ideally) get rid of the GSM interference.