Outdoor antenna works indoor only

This is my experience as discussed in a few other threads.

If the “built-in” filter isn’t the first component in the receiver chain (after esd protection of course) then the LNA can simply “give up” with a strong signal anywhere in it’s frequency range.

A little update here: after adding a standalone filter everything works like a charm. Thanks for all the replies!

I have yet to confirm, but someone from FlightAware should be able to easily chime in on whether or not this is correct:

I believe the FA Orange and FA Blue radio use the SKY67150-396LF for their amplification. Per spec @5v, this chip has a nice, high IP3 of +38dBm (In a nutshell, the higher the better for saturation purposes). Most alternative low(er) noise amps fall between +30-35dBm for comparison.

That said, I think they opted to feed the chip 3.3v to help keep the power consumption down (remember the USB port needs to power all this on top of the tuner). Unfortunately Skyworks doesn’t have 3.3v specs in their datasheet, but besides some positive effects (lower power consumption, lower noise factor), doing so also lowers the IP3. Comparative chips have measured 8-10dBm drops when being fed 3.3v vs. 5v.

So now we’re looking at an amplifier running with a lower linearity intercept making it much more predisposed to saturation. This is why both of these radios tend to perform better with some sort of upstream filter.

This is my theory and still need to take one of my metal cases apart to confirm (stuck mine in metal cases for cooling and shielding). I suppose anyone from FA could save me the trouble…

I suppose if this is the case, and some run their radios though powered hubs, there could be another thread on how to mod these things :yum:

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I solved it like this: used Generic Dongle with Triple-Filtered LNA + Bias-T + 5V dc power adaptor to power the LNA through Bias-T.

OK, then i apologize for not believing it.

Just experience the same issue after removing the FA filter, I’m using the Prostick Plus with the “refurbished” Jetvision antenna.
Probably my setup is very close to saturation.
Does anyone ever tried to install a variable attenuator before the RTL-SDR dongle?

Not continously variable, but stepped like this:
3 dB (attenuator #1)
6 dB (attenuator #2)
9 dB (attenuator #1 + #2)

https://discussions.flightaware.com/t/announcing-the-pro-stick-plus/19202/125

It showed that at my location, the RF interference is so bad that without an external filter, Pro Stick Plus’s front-end LNA gets saturated, and performance drops to near zero.

However if attenuaters are added, these dampen the interfering signals and performance shoots up even without an external filter.

 

It would be interesting to have a PE4302/PE4312 controlled by the Raspberry that would allow change the attenuation by SW.

I’ve tried it, but discovered my uW variable attenuator passes nothing below 2GHz.
They can be had cheap for TV if you still have an interest
image

An attenuator will “attenuate” the signals you want by exactly the same amount as the noise you don’t. By adding an attenuator, you’ll be trading long range (weak) signals for local.
An attenuator compliments a filter, but it does not replace it.

That goes without saying, and is obvious conclusion from the graph in my post which was linked. I am posting that graph here for ready reference.

I still have a rough time assimilating a single graph without a watermark to illustrate whether or not a change in setup is having an affect. Example:

ss (2020-09-24 at 08.41.52)

I’d be looking to take fish out of my diet and scratch my head over ham. In reality it’s the same untouched feeder dealing with air traffic.

That said, I can somewhat identify from the previous post that Pro Stick Plus seems to present an issue in that setup, but so does fish on mine. As constructive criticism, I think it would help to show a side-by-side against a watermark setup since air traffic and environment are so unpredictable.

I’m comparing apples to oranges, but that’s my whole point. Please don’t take this the wrong way, I mention this with full respect.

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If you want to compare two settings and switch back and forth let’s say 3 times then you could say it’s likley the change is not traffic :wink:

Same goes for really drastic message rate changes.
Also some people have less drastic changes in message rate during a typical day.

(1) The drop and rise is drastic and very steep, almost a vertical rise/fall, very distinct as compared to your ham & fish example.

(2) Removal & insertion of filter and attenuaters was repeated several times, and each time a steep change took place.

(3) That test was done 4 years ago image . I have done another test 2 months ago image with same steep drops & rise. You can see it here:

  1. Up to 21:20 EDT > Antenna connected to Pro Stick PLUS through FA Light Blue Filter
  2. From 21:20 to 21:50 EDT > Antenna connected to Pro Stick PLUS directly (Filter removed).
  3. From 21:50 to 22:00 EDT > Antenna connected to Pro Stick PLUS through FA Light Blue Filter
  4. From 22:00 to 22:25 EDT > Antenna connected to Pro Stick PLUS directly (Filter removed).
  5. From 22:25 EDT to end of graph > Antenna connected to Pro Stick PLUS through FA Light Blue Filter

NOTE:
Every time I removed and inserted the Filter, I made sure that all connectors are fully tightened, so the drastic drop is not due to loose connection.

image

I’m not dogging you amigo, just trying to help with an idea to make your tests that much better is all. I know you have gobs of equipment laying around, may as well put it to use. :+1:

I never took anything you mentioned as “dogging me”. I always take it as a constructive advice / criticism intended for help, correction & improvement, and I am thankful to you for it.

This test involves FA Antenna and ProStickPro (Blue).
Unfortunately I have only one FA antenna and one ProStick Plus (Blue), so I cannot do a true side-by-side test.

I dont have “gobs of equipment laying around”

My Dongles are:

  • 3 x Generic
  • 2 x Orange ProStick
  • 1 x Blue ProStickPlus
  • 1 x Green FlightStick (RB24)
  • 1 x Red FlightStick (RB24) for 978 Mhz

My Filters are:

  • 2 x FA Light Blue
  • 1 x RB Blue
  • 1 x Triple-filtered LNA (RTL-SDR Blog) + Bias-T

My Antennas are:

  • 1 x FA Antenna
  • 2 x Stock Mag mount whips of DVB-T
  • 2 x Coiled Mag mount whips of different dimensions $4 each
  • 2 x Magmount with V-Stub Whip
  • 1 x V-Stub QuickSpider (made of coax only, no SO239)
  • 1 x Cantenna
  • 1x PCB antenna (Cheapo $6 pcb dipole from ebay).

 

Not specific to you, but I’ve wondered about about this point. N-connectors are very tolerant of tightening because the mating surface isn’t the RF connection. SMA’s are quite a different design and can be a bit finicky.

For interest, how do you satisfy " fully tightened". (finger tight?, 12" shifter? …?)

Tightened by fingers, then rechecked.

Sorry, I don’t understand.
“rechecked” how?

Tightened carefully by fingers, ensuring no cross threads, and the nut turns smoothly and fully. Put it back.

After few seconds grabbed it again and tried to tighten by fingers to ensure it is already fully tightened.

The correct torque for a brass SMA is 6"-Lbs, 8"-Lbs for steel.
Their performance can be very poor when loose.

A torque wench is a useful tool and the only way you’ll get it “fully tightened”.

image

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