Filter for ADS-B

Pape · Jan 24, 2015

Hi guys,

I currently use a RTL dongle to feed my VSR server. I decided to upgrade my antenna and add a LNA4ALL. Doing this will probably give me poor result if I do not add a pass band filter, specially in my crowded city.

After research I came down to 2 models and wonder witch one is the better:

MiniCicuits VBFZ-1065+ This dongle was used by other peoples in the same situation as me with good result

Or

MiniCircuits ZX75BP-1100+ that I found to be more appropriate lower cut off.

Thanks

prcguy · Jan 24, 2015

You might check Ebay for filters, I bought a very nice 1100MHz tunable filter (five or seven section, I forget) with impressive skirts for something like $15.
prcguy

Pape · Jan 24, 2015

Can be a option but I will need to also buy a noise generator / source so I can tune the filter properly.

prcguy · Jan 24, 2015

That's also cheap on Ebay and you can probably use your RTL dongle as the analyzer for tuning, see: Noise Source Simple Spectrum External Tracking Source | eBay

I have one of these although I usually use a spectrum analyzer with tracking generator to tune filters.
prcguy

Pape said:
Can be a option but I will need to also buy a noise generator / source so I can tune the filter properly.

Pape · Jan 25, 2015

I did take a look on ebay and did not find anything to my interest in a nice price range or did I miss something ?
guess I go back to my original idea

prcguy · Jan 25, 2015

The link was for a noise source that works from 50KHz to 1.5GHz and would allow you to tune filters using your RTL dongle. The noise source was priced under $20 with shipping. If that's out of your price range then I'm afraid I can't help you.
prcguy

Pape said:
I did take a look on ebay and did not find anything to my interest in a nice price range or did I miss something ?
guess I go back to my original idea

Pape · Jan 25, 2015

sorry, I was referring to the filter.
source price is well acceptable.

ericcarlson · Feb 1, 2015

I started using the VBFZ-1065+ filter and saw a 10x increase in frames per second. I am in a high RF urban environment. Your results may vary.

vagrant · Feb 1, 2015

Look at the insertion loss difference between those two MiniCircuits filters. Perhaps spend the money on the right one now. Everyone's RFI is different and I default to a filter before amplification. Insertion loss is a factor and that's when a clean signal boost may help. Unfortunately, one "may" need to then address the noise coming over from the AC power if not using a battery.

Please follow-up on this thread and let us know what you went with and how it is working out for you.

Pape · Feb 1, 2015

I ordered the 1100+ as I prefer to have the entire 900 block.
I was aware of a lot of RF pollution around here but after testing the new antenna: it really bad and I do not have the LNA in yet.

I was more planning to put the LNA at the antenna and the filter at the receiver so I can amplify the weak signal, overcome the lost in coax / device and remove everything not needed signal wise at the receiver by using the filter.

What are the pro and con of doing filter than LNA ?

Thanks

Thunderknight · Feb 1, 2015

Putting the filter before the LNA reduces the chance of overloading the amp or creating intermod products in the amp.
The downside is any insertion loss in the filter is plain lost.

prcguy · Feb 1, 2015

The whole purpose of using a filter is to prevent overload from out of band interference and an LNA can be very susceptible to overload. The filter should always go in front of the LNA and hopefully the filter will have negligible insertion loss like .5dB or less. Even with 2dB of filter loss in front of an LNA you will probably receive things that were not possible without the filter and LNA combination.
prcguy

Pape · Mar 10, 2015

Here are some comparison of filter and no filter.
Both where compared using the same antenna and signal.

the Setup

this is the graph with the filter
9:00: 27 914 messages & 942 positions
10:00: 38 750 messages & 1 989 positions
11:00: 20 658 messages & 930 positions

this is without the filter
9:00: 22 639 messages & 707 positions
10:00: 32 719 messages & 1 603 positions
11:00: 18 548 messages & 874 positions

So this is my quick test, I wish I have less lost in my wiring and adaptors but this is what it is.

This is a combined map

More to come.

SCPD · Mar 10, 2015

Pape said:
Here are some comparison of filter and no filter.

One thing that you don't have is the R820T2 RTLSDR. That is also a benefit for me... it's quite a bit better than the R820T.

NooElec - NooElec NESDR Mini 2 SDR & DVB-T USB Stick (RTL2832 + R820T2) w/ Antenna and Remote Control - NESDR RTL-SDR Receivers - SDR Receivers - Software Defined Radio

Pape · Mar 10, 2015

I have one on order and will do the comparison

Filter for ADS-B

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