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 !

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.

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.

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.

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.

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
2375/295MHz.

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.