Do I Need A Filter?

[cptr2022]

Hi abcd, I bought recently this type of filter from the same seller and it works fine. Out of curiosity I checked its response with a nanovna and I got a similar curve and attenuation like the one you posted.

I live at the last floor in an apartament building and my antenna is placed in a window, with direct view to several gsm antennas, less than 150m. The filter is connected between antenna and a LNA and without it I get almost no planes. With the filter I receive more than 1000 planes/day with a max range of more than 220nm.

So from my point of view the filter is fine and worth buying.

[abcd567]

@cptr2022

So from my point of view the filter is fine and worth buying.

Thanks for feed-back.
Actually I dont need a filter as I already have all the filters I need. It caught my attention because of it’s low price. I ordered it just out of curiosity to find how it performs. Your experience, and other purchaser’s comment on seller’s site show that it is worth buying.

[abcd567]

Has anyone used this ?

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[Jonseyt23]

Hello, been following this tread with interest. I recently just set up my Pi FA in the last week and have been looking to try and improve things if I can, I am reaching out to 200nm in some directions, but do think trees may be an issue that are about 100-125 meters away

My set up is as follows

Homemade 8 leg spider mounted 26ft above ground (2.5ft clear of my house roof, piped into the loft with 8 meters of PF100 Sat cable connected to the RTL-SDR V3 USB dongle.

I have took a frequency reading and can see some interference in the 810/820 & 920/960 range with 1090 being very faint, see below images

I read the above as possibly needing a filter, so I have orderd the Air Nav SAW 1090 filter which should be here tomorrow from Amazon.

Do you think I have any possible chance of increasing the range, the max I have seen on mysky page is 203nm. The red line on the Position & Aircraft is when I moved the antenna to a roof mast

[abcd567]

The transmission of 1090 MHz Radio Waves is in straight lines like rays of light. The maximum distance your antenna can see the aircraft is limited by curvature of earth and terrain around antenna (hilly or level ground).

First of all check what maximum range you can get from your location

What is the Maximum Range I can Get?

 

[Jonseyt23]

Yeah I have done that and added the rings to my skyaware map also, their looking about right for what I’m currently seeing tbh. Just the frequency on 1090 looking faint in the graphs, so hoping the filter might help to an extent, but will look at a LNA in the near future also, to see if I can pick up more or not.

[Jonseyt23]

Well filter did diddly squat apart from reduce the msgs and aircraft it picks up, tried every gain setting available. Think I’m at the limit of what I can receive with what I already have. Without filter 97 aircraft - 946msgs. With filter best I got was 45 aircraft - 542msgs worst with filter 18 aircraft - 7.9msgs

[abcd567]

@Jonseyt23

Think I’m at the limit of what I can receive with what I already have.

You will get a noticeable improvement if you replace DIY Spider antenna by a higher gain commercial antenna such as Flightaware antenna or Jetvision antenna.

Please note that high gain antennas not only receive the 1090 Mhz signals better, but also recieve other interfering frequencies better.

Depending on RF noise at location of antenna,
the high gain commercial antennas may have a poor reception without a filter. The need for filter is totally location dependent, and final confirmatory test is to compare performance with and without filter.

[wiedehopf]

@Jonseyt23

8 meters of PF100 Sat cable connected to the RTL-SDR V3 USB dongle.

If you’d have lower coax loss and an LNA, the spider would do much better.
And LNA after 3m of coax for example would be a strong improvement.
Improving any part of the system will probably give you an improvement.

[Jonseyt23]

I will try an LNA first see what that does, am looking at the uputronics one and from reading reviews looks to be a good amp. Would this one be a good buy to try and gain some improvement on my current set up.

I will look at aerials and coax but which coax would be best as replacement though?

Also this is my feeder site,

Dave Jones ADS-B Feeder Statistics - FlightAware

Am I just chasing unachievable gains or do you think my stats are good for a DIY antenna?

[jaymot]

@Jonseyt23

I will look at aerials and coax but which coax would be best as replacement though?

Look at the specifications sheet or data sheet for each type of coax that’s available where you live, and look at the attenuation loss per 100 meters at higher frequencies in the 900-1200MHz range. The less loss the better, though there are other factors such as weight, thickness, cost that may make you decide to compromise and get one with slightly higher but still acceptable loss. While looking at the specifications also look at the outside diameter and weight.

That’s a beautifully built spider antenna, by the way.

[geckoVN]

@Jonseyt23

8 meters of PF100 Sat cable connected to the RTL-SDR V3 USB dongle.

The RTL-SDR V3 is an excellent general purpose dongle, but is not overly sensitive. It greatly benefits from a filter / amp at most locations.

As ABC says, the 1/4 wave antenna is functional, but not a high performance device. It’s more of a ‘wet sunday afternoon’ project rather than a max. range antenna.
Your site showed an improvement when you got your antenna up higher suggesting there are gains to be had.

[fishymamba]

I’ve used that buck converter in a couple if projects. It works alright, but it definitely cannot supply 3 amps continuously. It gets hot enough to burn my finger. Worked alright at currents below 2 amps, but still got very hot.

Like most of the other buck converters I’ve bought from AliExpress, the output isn’t very clean, especially when under a significant load. I recommend getting one rated for higher load currents and with some heatsinking.

[CathalFerris]

It may be worth spending the time and effort and very low cost of materials to make up a coax colinear antenna and try that in place of the 1/4 wave vertical currently in use.

My best-performing ADS-B antenna is one I self-built from scrap 75-ohm satellite feed coax.
I followed these instructions https://www.balarad.net/ and I actually made three very slightly different 8-element antennas. This was because at the time I did not have any way to measure the velicoty factor, so I made some best-guesses. I built them without any balance resistors or 1/4 lambda stubs, and I continued to use the one that performed the best. I don’t see the point in the balancing resistor, as I’ll explain later on.

I’ve the coax colinear inside a PVC tube to keep it mechanically protected. I did think about a higher number of elements, but as it is I am hearing all of the planes overhead at the same time as hearing the quiet signals at the horizon. If I were using an RTL-SDR blog SDR instead of the Airspy Mini I’m currently using, then I’d build a longer colinear to better compress the dynamic range available, as the AirSpy does have more than enough dynamic range for the current scenario.

Side by side with a Radarbox.com commercial antenna, I’m getting a few dB higher signals with my colinear than the commercial antenna, and I’m getting signals down to my radio horizon. The Radarbox was overloading overhead and not giving me nice levels at the horizon. Pretty much every signal that can make it to the colinear antenna I am able to process. Because I’m using the RTL-SDR Blog ADS-B sawtooth LNA filter/amp device at the antenna, my receivers are well able to hear the noise floor of my antenna - even when the SWR is nowhere near 1.

For a receive-only antenna, SWR is of absolutely no relevance once it’s seen that the nosie floor at the receiver increases when the antenna is attached. (if the noise floor does not increase, then by all means try to match the impedance to raise the signal+noise_floor, or add a low noise amp).

I do see a significant improvement with my message rate using the 1090 LNA+filter compared to an LNA alone, so I’ve put the LNA+filter in place and left well enough alone, and the results are pretty good, maxing out over the past week with a relocation of antenna of ~1400 messages/sec.

[PA1NT]

@Jonseyt23

I will look at aerials…

Vinnant builds aerials with a great price/performance ratio, i.e. COL1090/5-S.
Be aware that they’re built in batches, so limited stock/availability.

My feeder (Pi4, Airspy mini, RTL-SDR Tripple Filter LNA, Cavity filter) is connected to a COL1090/7.5-P. Here are my stats:

PA1NT ADS-B Feeder Statistics - FlightAware

[abcd567]

@abcd567

Has anyone used this low-cost SAW filter?

Received the 1090 Mhz SAW filter from Aliexpress seller. The SAW chip is different from that advertised.

Advertised

 

 

Supplied

 

[rugomol]

New Original TA0970A 970 SAW Filter 1090 MHz

Model Number: TA0970

SAW Filter 1090 MHz

[abcd567]

@rugomol

Thanks for finding that the 970TA is a 1090 MHz filter. I thought it is 970 MHz filter.

I now found the Datasheet link, if anyone is interested to brows or download it:

https://www.rfmw.com/datasheets/taisaw/ta0970a%20_rev.3.0_.pdf

 

[abcd567]

 

SOURCE: https://www.everythingrf.com/community/what-is-a-saw-filter

What is a SAW Filter?

Surface Acoustic Wave Filters or SAW Filters are compact, low-cost RF filters that can be used in a wide range of applications up to 3 GHz. SAW filters operate by converting electrical energy into acoustic or mechanical energy on a piezoelectric material. To do so these filters uses interdigital transducers (IDTs). The IDTs have interleaved metal electrodes on either end of the device which converts an electrical signal into an acoustic wave and then back to an electrical signal.

Once the electrical energy is converted into acoustic waves, the waves travel across the surface of an elastic, piezoelectric material with an amplitude decaying into the substrate material, such as quartz, lithium tantalite (LiTaO3) or lithium niobate (LiNbO3). This decay is what causes the insertion loss in SAW Filters.

Surface Acoustic Wave (SAW) filters are best suited for applications up to 3 GHz. The filter selectivity starts to decline above 1.5 GHz, and at about 3 GHz their use is limited to applications that have modest performance requirements.

The center frequency of a SAW filter is impacted considerably by temperature variations. Except for the Quartz substrate, the center frequency of a filter will shift upwards at lower temperatures and downwards at higher temperatures in a linear fashion. To compensate for these shifts in frequency, temperature shift components are often added to SAW filters. Another option would be to use TC-SAW Filters i.e. Temperature Compensated SAW Filters.

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SOURCE: https://www.everythingrf.com/community/what-is-tc-saw

What is TC-SAW?

What is Temperature Compensated SAW technology?

Schematic view of a typical TC-SAW stack

TC-SAW or Temperature Compensated Surface Acoustic Wave filter, as the name suggests, is SAW filter with improved thermal performance. The center frequency of a SAW filter is impacted considerably by variations in temperature. TC-SAW aims to provide higher performance in crowded RF spectrum by minimizing variations in the center frequency of the filter over temperature.

Standard SAW filters show a temperature-dependent frequency drift anywhere from -20 ppm/K up to -40 ppm/K, which makes them unsuitable for high-frequency applications and narrowband RF communication where the temperature can vary.

Frequency drift of a SAW filter as a function of temperature for non-compensated SAW filter and TC-SAW filter using silicon dioxide

In TC-SAW filters, a thin film of Silicon Dioxide (SiO2) is used to obtain good temperature coefficient of frequency (TCF). The application of silicon dioxide for temperature compensation reduces the temperature-dependent filter frequency drift and no significant drift is observed. It is worth noting that the filter performance strongly depends on the quality of the deposited SiO2 as it contributes to the acoustic wave propagation. For narrow band applications, the SiO2 thickness must be increased to achieve good TCF characteristics.

 

 

[jaymot]

@abcd567

Thanks for finding that the 970TA is a 1090 MHz filter. I thought it is 970 MHz filter.

If you were thinking it was a UAT filter that’s 978MHz.