@datastream
I’m also in the UK and would like to get a second RTL-SDR triple filter. Where did you see one for sale as everywhere I’ve looked is out of stock.
It may be worth posting a link to this thread in the ADS-B Flight Tracking section. I seem to remember someone there posting about a 1100MHz signal.
OK found it Do I Need A Filter? - #718 by pretoescuro
The southern end of your “splat” points to my back garden!
that was off my little copper man made antenna before this all kicked off! haha!
maybe I could change the title of this one too (Do I need a filter part 2) on the end…
DON’T FORGET YOU NEED Bias Tee
@datastream
I have Bias Tee thanks for the reminder.
I’m in 2 minds whether to get the triple filter or a cavity filter 1090 MHz cavity filter for Mode-S / ADS-B | cf1090-kt30 This one looks like it might knock your 1100MHz on the head
hmmm…! not sure…
I even had a look to see if 1100mhz is listed…(well my mate told me about this site in the U.K)
by the way, why do you want/need one mate?
Not really, it is only about 4dB down at 1100MHz.
Thanks for that, your wiring confuses me, the “biasT” I thought that was 3 - 5 volts 500mA. input but yours looks as though it’s then outputting to another board with 1 x SMA output into the filter?
Can’t make it out…lol
Thanks
I think you can make it out now 
NOTE: There are two independent DC power supplies. one PSU feeds RF Noise Generator, other PSU feeds Bias-T.
aha! that makes sense, I was like how the hell is he feeding this, so! that RF noise generator, is that just to pump a shed load of “noise” down the filter for testing? I’ve never seen them before.
And also, the 5V DC for LNA, I thought that would go after RF out (so after the noise generator but before the filter) and then to the filter, but it’s after the filter with the 5V going into the filter via it’s output?
Thanks again.
what does that mean? (sorry just a n00b here trying to learn)
10dB rejection reduces the signal to 1/10th of its original power.
As dBs are logarithmic 20dB is 1/100th of the original power (10x10)
30dB is 1/1000th (10x10x10)
So you can see, 30dB is a LOT better than 10dB
I was backing up what @wmccouch said about signals at 1100MHz not being rejected as strongly as signals farther away. The curve on the display is how much signal gets through as a function of frequency. At 1090MHz, the attenuation is 2.7db - it cuts the signal about in half. But as @Humpfrey points out, the 10db attenuation at 1100MHz means about 1/10 of whatever that is still gets through. Every 3db is dividing by 2. 10db is dividing by about 10. (Edit - but the attenuation at 1100MHz is only about 3db - per @LawrenceHill)
I didn’t have markers at 1100MHz or 978MHz (for UAT) but using the legend for the markers that are there you can kind of approximate. I can sweep it again with markers at those locations if anyone cares.
This thread is of real interest to me since I tried to swap a light blue filter that is still letting in some cell booster signal that is swamping my receiver, for a dark blue filter. My range went to less than 50 miles and plane counts fell way off just for a filter swap with no other changes. This was on a blue dongle which already has the 1090 SAW filter in it. I was just expecting better noise rejection.
The blue dongle made a huge improvement from the orange dongle (that doesn’t have a SAW filter) with the light blue filter in line. For some odd reason, the dark blue filter really messed things up for me too which is why I scanned it. But it matches the scans the FA team posted in the original dark blue filter announcement. I don’t see a problem. It’s a puzzle.
Thanks fort that, I’m kinda getting to grips with it. I admit I have a lot of learning to do.
I’m running 2 scans that will be completed tomorrow, both 24 hours, one with and one with out the “filter”
When you say “markers” at 1100mhz, what does this mean, what would be the purpose of it?
When you say you tried to swap the filter? who was that with, Flight Aware?
I have another SDR in the back of the PC that’s attached to a “eurostick dx 25-2000mhz” I used to have that plugged into a scanner, but when I went to buy the scanner at a guys house it was awesome, he was tuned into all sorts, I gets it home and could really only pick up a shopping mall and a hospital
Even now all of my SDR software I can only pick up repeaters, the odd digital channel, and the standard FM radio channels.
What frequency would I be looking at on the radio so I could get a look at what’s transmitting on 1100mhz?
Thanks again for the patience in explaining it to me.
Markers are the little triangles shown on the screen on SFRobert’s reply above.
When set to frequencies of 1100MHz and 1090MHz, the VNA will give a reading on the display as to the difference in level in dBs., hence the rejection between the wanted and unwanted frequency.
I only make it about 3dB.
Despite what it says about the 1090MHz centre frequency 1100MHz is actually the centre line.
100MHz per division and 1200MHz is the marker on the next line to the right. The 1090MHz marker you can see is 10MHz to the left of the 1100MHz centre.
so in layman’s terms, what does it say about the filter? that it’s allowing so much of frequency’s that are close to 1090mhz into the stream/feed…?
It is designed to reject frequencies much further away from 1090MHz.
This is what I use.
@LawrenceHill - good eye! I’m just getting used to this critter and misread the scale. In this measurement I put markers at 980MHz (for UAT - down 19db) and at 1100MHz - down just 2.8db (while 1090Mhz is down 2.7db).
It was a direct replacement. I halted and powered down the station, unscrewed the light blue filter, screwed in the dark blue filter, and powered up. I had already swapped (last week) to the blue dongle from the orange which was performing much better. I am wondering if it’s just a flaky connector issue but haven’t had a chance yet to look deeper into it. Once I saw how bad my range was, I swapped back to the light blue filter and range went back to normal.
With an SDR you could just tune to 1100MHz and see if you could sort out what it was but if it’s digital you might only be able to know it’s digital depending on what it actually is. The waterfall plots you already posted are great for seeing signals. That’s maybe the best way to see what other signals are causing problems.
But basically, unless I’m missing something, as @LawrenceHill pointed out, 1100MHz is very close to 1090 and not attenuated by the blue filter much at all. I’m kind of confused just yet why when you or I put that 1090 dark blue filter in line, both of our stations perform much worse than the 2.7 db insertion loss (that can be mostly compensated for by LNA gain in the dongle).
