Have i got optimum or can i improve range

[wiedehopf]

@M0UPU

I like to think of the (with all due respect) the RTL is more a sledgehammer with all that filtering and high gain compared to our more “surgical” lower NF less insertion loss unit.

People with cavity filters in front of the LNA have reported very very slightly better results with the uputronics.

But you are correct, the diminishing returns are quite apparent!
Only so much information in the ether

[g4jnw]

Sods law bought mine 10 days ago.

[keithma]

@M0UPU

How strange I would not have expected that given the pretty flat out of band attenuation (Yellow = ceramic, purple = SAW)

If I can pull the details out of the graphs, I can show what I mean.

@M0UPU

When we have the new unit ready I’ll get a sample out to you.

That would be great, thanks. It’d get tested on my loft receiver but I’ll know straight away whether it’s worked.

[nicolasguiral]

Hi M0UPU

I have tested and compared the RTL-SDR LNA and your Ceramic Filter LNA.
The Ceramic filter works better for me, I have wider coverage (+20 NM), but I neded to use it with a cavity filter, otherwise the slightest carrier on 145Mhz for example, and the signal drops drastically, until nothing more is received !

Hope that your new Filter LNA won’t have that worries.

[hellhound604]

The purple trace tells me there is some leakage past the filter… maybe a track running between input and output, or some layout-related issue. I have seen the same in some (very cheap) filtered GPS patch-antennas, and when I looked at the PCB layouts, it was always layout.

[hellhound604]

When you talk about a cavity filter, is it a bandpass or notch-filter? From what I can see, in the sdr-blog ADS-B amp, the path is Amp-filter-amp-filter. If you need a cavity filter before the LNA, it means you have very strong signals overloading the first amp. Thing is, in general, some approaches works best, HPF- amp-SAW filter-amp SAWfilter(best for noise figure, i.e. sensitivity), but not always (if you have a pesky RADAR/GCA, etc). Even in the old days, when receiver had a narrowish filter before the first RF amp, it could be a problem. That is what makes RF systems hard, what works best for most, is not to say it works everytime. That is why a peak spectrum wideband scan of just the antenna in your position always works the best before starting to purchase amps/filters, etc…

[M0UPU]

@hellhound604

The purple trace tells me there is some leakage past the filter… maybe a track running between input and output, or some layout-related issue. I have seen the same in some (very cheap) filtered GPS patch-antennas, and when I looked at the PCB layouts, it was always layout.

Which bit ? the TA1090EC SAW we use is only about 30dB max out of band attenuation. The purple trace is the filter with this SAW in it.

[hellhound604]

Ouch… Couldnt remember the colledge filters were THAT bad… Always used TDK filters in pairs. In anycase,
Low gain LNA->filter->LNA->filter should give you optimum, but no point if strong signal overloads the first amp, or 1st SAW filter. Can remember endless problems with some of my crap when a client had a 10kW transmitter whose antenna were right next to my antennas at less than 10% difference in frequency.