For those living in Europe I would prefer Ultraflex 10 over LMR400: conductor, foil and braid are 100% copper instead of copper coated aluminium leading to a much higher shielding effectiveness of 105dB compared to the >90dB of LMR400.
Perhaps better described as âcopper braid over copper foilâ as opposed to " tin plated copper braid over aluminum foil" for LMR400
How does the price compare?
The Ecoflex 10 has about the same spec as LMR400, so I guess retailers would stock one or the other.
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Irrelevant for low power applications. We are not building transmitters.
Yes, they are. But that doesnât change the fact that inside the tuner chip the matching impedance is a 75 ohm resistor.
Those dongles were build initially for TV applications, so they were build with 75ohm intent and matching RG59/RG6 cable.
Of course some of the LNA that are added on some of the dongles (or external) are made for 50 ohm (cell tower application) but the impedance miss-adaptation in our specific case of decoding digital ADS-B signals is negligible.
If there is a terminating resistor inside the R820T, itâs not shown on the simplified block diagram
Either way, (as above) the PCB traces are not impedance matched, so a significant discontinuity will exist.
Does it matter (for this purpose)? As you say, probably not.
I donât know exactly what is inside the Rafael chip, just that it was build for TV antennas. Hence 75 ohm specification.
Inside of those âblocksâ are real parts that are not shown. A classic RF input for CMOS technology has a resistor on the silicon, matching the desired impedance of the input, similar with this pic.
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True. Thatâs why âsimplifiedâ appears twice above
The resistor on the input is designated Rb - Iâd suggest its function is to provide a load on the base of the FET (M1) to prevent it oscillating.
But itâs not!
If you read the datasheet, the R820T chis is not specified 75Ω
The measurements are referenced to 75Ω
eg. 
but that is not the same thing.
Sorry, but I have to disagree.
Iâve just put a Fluke onto the input pin (P24) and it reads infinite resistance. There is no resistor or pad on the input of an R820T
Agreed, the Messi and Paoloni cables are very good and decent value. When I move my aerial, Iâm going to need a short run of coax, probably 4m or so and Iâm going to use either Ultraflex or Hyperflex 10. I actually use EcoFlex 15 on my 144/432MHz vertical but itâs a) not long enough to go to the top of the mast and b) not really flexible enough to go around the rotator anyway.
Regards 50 or 75 ohm cable - I know what I prefer but Iâve given up raising it on this forum. Lifeâs too short 
From that page
However, the RG-series designations were so common for generations that they are still used, although critical users should be aware that since the handbook is withdrawn there is no standard to guarantee the electrical and physical characteristics of a cable described as âRG-# typeâ. The RG designators are mostly used to identify compatible connectors that fit the inner conductor, dielectric, and jacket dimensions of the old RG-series cables.
Also noted is the attenuation for standard RG6 is different for the Belden cable you selected in your next post.
What exactly are you trying to tell us?
S.
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Because is internal, on the Silicon, connected to exterior via an internal series capacitor capacitor to block the DC
Thatâs why the chip doesnât start to work from 0 Hz, but from 42MHz and up. That capacitor impedance is zero at 1GHz. Zero in series with 75 makes 75.
The Rb is the bias resistor for the gate of the MOS transistor, it can be any value they want - 50 or 75 ohm or even 1Mohm. But lower values minimize the HF noise.
The chip was designed as TV tuner. All the TV antennas and cables are 75 ohm. And thatâs allâŠ
These are TV dongles for North America.
No 50Ω SMA connector.
Only 75Ω F-connector or PAL-connector for RG6 or
https://www.amazon.com/dp/B015IL0FIW/
https://www.amazon.com/dp/B07K58THHX/
https://www.amazon.com/dp/B06WGL96C4/
These are DVB-T for Europe
75Ω PAL connector
The DC blocking capacitors are external (C2, C13 on the ref. design). Typically the necessary capacitance is physically too large to put on the silicone. Putting the cap internal would also severally limit PCB design options.
The R820T is Specâd 42 to 1002MHz, but as we know, will work outside that range. The actual limitation is the range the PLL will lock.
I misread the cct - Rb1 is as you say, provides a biasing voltage to the FETs base. It is not a terminator.
Is that circuit only representative or is it from a particular device?
With only a partial (and preliminary) datasheet available (and no specification for the input), I think weâve squeezed as much blood from this stone as is available.
Thatâs a circular argument
Itâs a TV tuner so it has a 75Ω connector so it is a TV tuner so it has a 75Ω connector âŠ
The three devices youâve listed - can any of them be used as an SDR? (piaware, sdr#)
Yes, if someone breaks their digital decoding system, like hobbyist broke the decoding system of DVB-T over a decade ago. Since then the RTL DVB-T is being used both as DVB-T (Digital Video Broadcast, Terrestrial) for which it was originally designed and manufactured, as well as an SDR.
And by âyesâ you mean ânoâ.
The RTL (even when used as a TV tuner), IS an SDR receiver.
The RTL chip passes raw ânoiseâ down the USB cable and the demodulation is done in the PC, Pi etc.
If there is any demodulation performed within the dongle, then you canât demodulate it a second time to find something you filtered out on the first pass.
Think of of it like trying to construct a video starting with only the audio track.
Once the data has been filtered out, no amount of post-processing will put it back.
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The info where the demodulation takes place is not made public by dongle manufacturer. Infact no details of hardware & software are made public. Someone expert in electronics has to analyse these dongleâs circuitry and chipset to determin this.
Well⊠no. The 2832 has a demodulator for DVB-T in silicon and, in DVB-T mode, does the demodulation there and passes just the mpeg stream over USB.
The SDR mode which we use for ADS-B et al is really just there for DAB decoding, and bypasses the DVB-T demodulator entirely. It doesnât provide enough bandwidth in that mode to do DVB-T decoding on the host.
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Ok, I didnât realise the 2832 has two modes, but that doesnât contradict what I said above.
If the 2832 did not have an SDR mode, it would not be useful to us.
Right. Certainly DVB-T support on non-2832 chips doesnât indicate that theyâve got any sort of SDR support; doing DVB-T demodulation on the host would be pretty unusual. For digital audio a SDR approach is more plausible but I donât know how widespread that is. Youâd probably have to spy on the USB traffic while running their digital radio software to see what theyâre doing (thatâs how the 2832 SDR mode was first discovered AFAIK)
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History and Discovery of RTLSDR
A $40 Software-Defined Radio By Stephen Cass, Posted 25 Jun 2013
Antti Palosaariâs Linux web page
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I would prefer Ultraflex 10 over LMR400
I would prefer/recommend Hyperflex 10 over Ultraflex 10, because it has better figures on SHF and the price is about the same (~âŹ2,-/m). Plus it is more flexible, too, so suitable for rotors.
Another option is the Airborne 10, which is the best performing .400 cable, but it is a sturdy cable because it has a solid core, so not suitable for all installs.
Attenuation/100m @ 1296MHz:
Ultraflex 10 : 16,4dB
LMR400 : 15,7dB
Hyperflex 10 : 15,4dB
Airborne 10 : 13,6dB
When using less than 5m, one would still be below 1 dB.
The M&P cables have better screening attenuation (shielding).
Better shielding means less background noise (pick up of unwanted signals).
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