In my intermittent quest to put my antenna outside, I was able to tone out an unused cable TV coax cable that comes into the basement from an outside wall. The piece of coax is maybe 10 feet.
I can plug the piaware dongle directly into the coax (need a female-female adapter) and then run another piece of coax up to the antenna mounted at the roofline.
It’s a 3 story house with a peaked roof. So I’m guessing I’ll need about 12-15 meters of coax (not a straight shot due to gables, box gutters, etc).
Will this degrade the signal enough that it makes putting the antenna outside moot? My guess is that there will be little to no signal loss, but I wanted to check with the experts.
On a positive note, there is the house ground right where the coax comes out of the wall, so another problem is solved
Thanks. Maybe I’ll start with seeing if my area covered increases with the antenna outside the first floor first VA the location inside the basement. And we can go from there. Because maybe then the benefit of getting it up and over the roof will be taken away by the signal loss from all the coax.
Tv coax is usually 75 ohm in resistance. You might want to consider a 50 ohm cable to keep in tune with the dongle and antenna resistance.
LMR 200 or ideally LMR 400 cable can improve your signal a lot and you don’t need to break the bank for such an improvement
thanks. Also, one other possibly (dumb) question –
I know that cable TV coax uses an F-type connector. What is the type of connector that comes off the flight aware dongle? Not the bigger N type that screws onto the flight aware 5 db indoor/outdoor antenna. the smaller one (smaller than F?). I’d need an adapter for that. (or, two, one to patch into the coax running through the wall and another on the other side)±
If you’re going to go LM400 (highly recommended) definitely get the LM400UF (Ultra Flex) as it’s infinitely easier to bend and fit into your installation. And remember to get a 2-3 foot jumper to go from the cable to your dongle. N-connectors only!
Basically any cable you get you can look up the loss per ft or meter.
LMR400 is probably the best choice for a run like that. However be careful because LMR400 is ripped off by a lot of companies and is only officially sold by Times Microwave.
So at 100m @ 1090 MHz you are going to lose between 12.8 to 16.8 dB which is quite a lot, however much much much lower than a junky or standard cable.
At 25m @ 1090 Mhz you can assume 100m / 4 ~ 3.2 to 4.2 dB of loss which is still pretty good.
You can think that every connection you make you lose 3 dB which is the way that engineers think about adapters and other things as this is a good estimation.
So if you have the following
25m of cable → light blue FA cylinder filter → blue FA SDR you have the following
3.2 to 4.2 dB loss → 3 dB loss → SDR equal to ~6.2 to ~7.2 dB of loss on your setup.
Since these SDR’s dynamic range aka what they can see is 30 dB and they tend to hear at faintest -36dB a 6-7dB loss is more about 1/6th of -36dB to 0 or 36dB totalish.
Therefore
with no amplification you basically cut 1/5th to 1/6th of your setups ability to receive.
this is actually not that bad using LMR400 cable
if you had this same run with standard cable you would probably be cutting your ability to receive in half.
with 5-10 dB of amplification before the SDR you are adding noise but mostly recovering that loss.
you can get these levels of gain with the following:
antenna with gain of > 5dB
LNA before the SDR
any active or powered amplification will also amplify noise.
As an additional note coax for cable or satellite are normally RG6 type which is a 75ohm cable which will have substantial loss for a 25m run. Also since the SDR’s run at 50ohm impedance this will cause reflection loss that is greater than the calculated loss below (basically add another 3 dB loss because of the impedance difference from 50 to 75). After all this add your connector / split losses (add 3dB per) that gives you the total.
None of those matter in RX mode, if you have a LNA at the antenna that can push the signal higher, and compensate for cable loss.
The cable loss matter only on the TX side, where loses are indeed relevant, because… the TX amp is on the other end from the antenna. Not relevant for ADSB receiving.
I’m going to disagree with you here. Signal loss due to coax inefficiency goes both ways. If your LNB boosts the antenna’s signal to 5dB, and your coax has a loss of 2dB, your actual signal should be about 3dB at the rcvr.
The issue here is that when you inject power into a signal you increase both the noise floor and the signal. The noise floor is inherently larger as it is the grass and the signal is like a tree sticking up. So if you are increasing the size of the tree and the grass you now have more noise across the board. Also any amplifier is not perfect so it is also adding artifacts in there and depending where they are at (close to the tree) they can totally affect your receiver. Now we are talking about small stuff here that should be manageable in general.
However when you increase the noise floor from say -36 dB to -31 dB and all your average signals from -20 to -15 dB things are looking good.
You have decreased your range because your receiver probably overloads between -3dB and 0 dB so instead of 33 dB of range you now have 28 dB or range.
Also signals you used to be able to receive that were high power like > -10 dB or -10 to -3 dB become possibly to strong to receive now and will overload your receiver.
Therefore what an LNA does is increase the ability to receive low power signals but you also cut off your high level signals.
It is better to have a good antenna with a good cable than to use powered amplifiers if you can in the case of receiving, but as long as you know what your amplifier is doing and what you are trying to get a amplifier can totally be helpful.
Wrote this up in 5 minutes off top of my head hopefully it makes sense. A note I am an Electrical Engineer with my bachelors and masters and my specialty is in electromagnets / RF / antennas / signals and systems communication. That doesn’t mean I am always correct nor does it mean that theoretical is better than real world data. Also as an Engineer I tell all my JR Engineers that techs and people that work on the equipment always know more than you do.
Also signal loss on cables adds artifacts if you have a perfect sin wave with peaks at -10dB and you amplify it 10 dB so the peaks are just at 0 dB then you have 10 dB of loss on your connections and lines at the end the signal you see should be -10dB but it will no longer be perfect it will be jagged and have artifacts in it both from the amplifier and the loss on the connections and lines.
So the question comes down to which is better amplifying up the signal to keep the power levels or minimizing the loss and in my experience it has been to minimize the loss.
Reasons for this is power is not always 60 Hz and the waves are not always perfect therefore the converting to DC is no where near perfect and even if the power in was perfect it is impossible to create a perfectly flat DC voltage from AC. The small changes make changes.
Then the amplifiers need a lot of protection and clean up to make them work well and they don’t work linearly with any power level + whatever it says its amplifying example its like a bell curve. A 10 dB amplifier may amplify -36 dB to -26 dB but -20 dB to -12 dB or opposite it is all about how the amplifier was created. They also have maxes or overloads and you don’t want the top of your wave to be flat because it overloaded based on incoming signals.
Anywho this stuff is much more complicated than how I am explaining it and there are a lot of caveats I am leaving out but I don’t want to write a book.
The outside LNA has lower noise levels than the one of LNA integrated in receivers. The GaAs E-pHEMT is just better than plain Si CMOS.
R820T inside most receivers has a noise figure of 3.5 dB, while in an external LNA you have MGA-13116 has 0.51 dB, SPF5189Z has 0.60… and with better linearity.
So using that for gain is better than boosting the ACG inside the receiver.
Cable attenuation is better to start from high level, when signal level is far away from noise floor. That’s why LNA are better installed at the antenna, not inside the receiver.
