COMPARISON OF 2 VERY SIMILAR 1090 Mhz SAW FILTER CHIPS

Some measurements. Look at the db scale on the left. The FA filter removes stuff around 820Mhz but the SAW filter removes both 820Mhz and 950Mhz

  1. No filters
    https://img2.brain4.photobox.com/000345718828cc4f6595b893863a6bcac5e03d97aa534b980ba152a8a9bb4290294e06e5.jpg

  2. With FA filter
    https://img2.brain4.photobox.com/9163425981eee2b08a4d4830405173dd59ce94fbc377a4d6bd568e7d81bce8ca890298a6.jpg

  3. with SAW filter
    https://img2.brain4.photobox.com/72844502b51796fec603e55b71fecfb32d05de8f396c6c41de9ffe6e9c5b459fa533ced1.jpg

Some hints on how to make the job easier–

You still need good hands and good eyes, but an illuminated magnifier helps
A temperature controlled soldering iron with a good, clean, small tip is a must
30 gauge solid wire (such as wire-wrap wire), available pre-stripped
a small sharp blade such a hobby knife (I use a #11 scalpel, replaceable blades)
double-sided tape and a scrap of pcb material

The input and output connections are seemingly the hardest, but there’s a trick to make it easier (well, a little easier)

Secure the SAW upside down to the pcb material using double-sided tape

take a 1 - 2 inch piece of bare 30 gauge wire and solder it across the input and output pins, leaving at least half an inch hanging off the side of the chip.

A way to make this easier, and to insure you work quickly is to use about a 3 inch piece of wire. Hold it down to the pcb in place across the SAW with two fingers of one hand, say your index and middle fingers. Place a small amount of solder on the soldering iron tip and tack the wire to the SAW. It won’t hurt that much.

When both input and output are soldered (work quickly, please), use the hobby knife to cut the part of the wire shorting input and output

Do the same thing to solder a piece of bare wire across the ground pins on either side of the input and output wires

Now that you’ve got your wires attached to the SAW, you can use the tip of the hobby knife to peel it from the pcb, and then place it on your target board.

Solder the ground wires first. Keep the length of the wire between the chip and the board short, but don’t get overly concerned about a fraction of a mm.

Solder the input and output wires last, putting the edge of the hobby knife across the wire at the SAW to keep it in place in case the solder decides to flow.

bob k6rtm

Thanks Bob, some useful hints for when I do my next one.

Does the SAW filter work both ways round? I’ve tried it with the antenna connected to both the input and the output but can’t see any difference in signal. As I explained above, I have no idea which is pin1 so don’t know the orientation of the chip.

The drawings and diagrams show that the input side is the middle pad on the side with the long ground pad.

Bob’s directions are the most sane. Really, without a rework station and fine tip adjustable iron, working with these components is very difficult if not nearly impossible to do successfully.

I would add at minimum a set of Helping Hands of your choice, these seem OK amzn.com/B008VO7H9E

and a head magnifier like this amzn.com/B003UCODIA

Then you’re gonna need one of these amzn.com/B008OC0E5M

Unfortunately, working with SMD components for a one-off project is not very cost effective in this case unless you plan to do mass production of filter mods.

That said, once you get the hang of it, using Bob’s method, you could probably knock out several of these once you get the hang of it, especially if you can figure out how to make a sort of jig to hold the thing in place for the initial tacking.

It looks like those notches might be your friends if you are creative with tweezers and the Helping Hands.

http://i65.tinypic.com/2isjx2d.jpg

I’ve made a second one of these following Bob’s instructions. Much easier the second time, thanks Bob :smiley:

I use http://www.rtl-sdr.com/new-rtl-sdr-panoramic-spectrum-analyzer/ as a spectrum analyser. The filter takes out 850Mhz and 930Mhz as above. This one does pass 1090Mhz unlike the first one I made. I use http://www.hdsdr.de/

Putting the filter in line, the messages/sec and aircraft numbers drop by 20 - 30%.

Anyone else put one of these in their system?

[Edit] Is it necessary to connect all 4 Grounds? Would make life easier to just do one.

Connect all the grounds, and connect them with short wires! The RF performance relies on all the ground pins being ground.

From your description, you popped your first SAW, and the second one is performing nominally.

These SAWs have an insertion loss of around 2.4 - 2.8 dB, which can be quite noticeable. If you don’t have your SDR gain maxed out, crank it up a bit!

bob k6rtm

Second day of testing so far so good.
This filter worked for me.
I also used the “dead bug” design.
With some(little) experience it is easy enough to solder all these pins.
The RF environment is more or less quiet in my location but I wanted to get rid of my own HAM radio transmission RFI as it dropped significantly message rate.

Now I should say filter did the trick - no message drop when my station is on air.

The filter did introduce some insertion losses, so I had to increase gain to max (-10 vs 49).

But I have a home made SPF5043Z LNA in the attic around 13db gain (ANT is 1/4 wave spider).
So, filter is behind the LNA…

I think without LNA the insertion losses effects would have been more noticeable though.

73 Igor AK4T

Thanks Bob, I do have my gain turned down a bit. I’ll crank it up to max.

@igorvyaz, good to know someone else has tried one of these. Any chance of a picture?

2 triggers - you know I liked your design you posted a few messages before. I guess this is close to optimal design soldering this SMD unit by hands.
Mine is more a proof of concept. Just wanted to see how it looks right after receiving the package from China. I am still thinking to add post amplifier using the same SPF5043Z MMIC which I would recommend as LNA - they are cheap and have decent IP3. Minimum parts are required to build an LNA.

ok. I am trying to upload the picture. not sure if you can see anything. Update - silly question: how do I upload an image ?

Just for clarification my setup is 1/4 spider on attic followed by SPF5043Z → 10 meters of RG-178 coax and now this SAW filter feeding Nooelec SDR.
By the way I am not using an RPI but a MK806 IV TV stick it has 4 core ARM and 2 G of RAM and also WIFI. Runs very nicely :slight_smile:

Thanks,
Igor AK4T

I upped the gain to max but the noise jumped too much. I’ve trimmed it back to around 45db and it is working fine.

I’ve made a third one and it is working exactly the same as my second one. The first one is in the bin :open_mouth:

I’ll let it run for 24 hours and post some stats.

https://www.dropbox.com/s/0fchtzi03n5gt8b/saw_filter_standalone.jpg?dl=0
Here is my experimental stand alone saw filter. It helped to get rid of RF interference and improved message rate by 10…15%.
But due to insertion losses I had to set max gain which means too much noise.

Now getting much better results with version of saw filter coupled with SPF LNA. It helped to reduce RTL gain - now trying between 41 and 45.
Preliminary results: usually I would get around 210 to 250 K of daily reports. This “version 2 saw filter” gave me well above 400K reports today :slight_smile:

https://www.dropbox.com/s/85n94oi73q71t4a/saw_spf_initial.jpg?dl=0
This is how I was putting initial components: the filter followed by LNA chip. Will try to make a better image of the complete device.

As promised here are my stats from the last 24 hours.

https://img2.brain4.photobox.com/017057385515f50f16e4b5390364f75ae61bb25cf707b90c1bae2834faa05d270d3ca7fc.jpg

https://img2.brain4.photobox.com/705656040ccf84bfb6997dd2c52dd2c747da4cf7a20a646d656a133732dc7d88bdd4a692.jpg

https://img2.brain3.photobox.com/803141123876d4f062008ddf062e45b60d7a1aa01960f7134f463ef1c9f1d176e17720fc.jpg

The dip on June 16th was due to lightning taking out my router :open_mouth:

I previously had a satellite diplexer in the chain which worked as a high band pass filter. I now only have the SAW filter in line. The number of planes/hits & distance hasn’t moved very much but as it has only been a couple of days it is a bit early to tell. I do get a lot of variation on a daily basis as I’m about 25km from Heathrow. Friday’s are usually very busy.

For you experts out there, how do my graphs look? Do I need to wind the gain down a bit more?

@igorvyaz Thanks for posting pictures of your SAW filter. Difficult soldering isn’t it?

triggers.
How you generate the MRTG graphs???

@spatieman

The graphing is included with the setup scripts in this post by jprochazka.

http://discussions.flightaware.com/ads-b-flight-tracking-f21/ads-b-receiver-project-setup-scripts-t36532.html

The graphs are produced by collectd https://collectd.org/

triggers,
SAW filter alone was not too difficult.
Second version coupled with LNA amplifier was a bit more tough.
I used this schematic from dl2kq.de web site:
https://www.dropbox.com/s/e70tmvbszaq4dzn/spf5043z.gif?dl=0

And simply added SAW filter in front of C1 capacitor.
The final device looks rather ugly in the picture:
https://www.dropbox.com/s/o88w48xa2lnr1yf/saw_lna_complete.jpg?dl=0

But it does work :slight_smile:

@igorvyaz
Great job. It does’t matter what it looks like as long as it works. It’s not a beauty contest :wink:

When I will do it, it will be worst.
Waiting for Chinese sail boat to arrive and bring my 5 pieces of TAI-SAW filters. May be I will shove these in my spare parts drawer, instead of trying my soldering incompetence.

thnxs!!!