That was the implication 
I received my RTLSDRdotCOM dongle along with the filtered LNA today and have just set it up to test. I managed to get the bias-t enabled using rtl_biast and then ran dump1090. It has improved reception by quite a bit. I am getting coverage over a radius of around 100 miles, which is maybe 30 miles more than what I was getting previously without the LNA. This is a definite improvement and there are many more list entries for planes coming in. This is still quite short of the theoretical maximum range as estimated by heywatsthat, but perhaps still reasonable for the DIY antenna that I am using. The RTLSDR does seem to be running rather warm though.
While waiting I also experimented a bit and also managed to capture some ACARS messages on 131MHz using the existing dongle and a DIY bowtie antenna. I intend to use one of the standard dongles for that when they arrive. Anyone know of a resource that can help me decipher and better understand the content of the messages?
Getting the antenna outside is a major point no matter what the type of antenna is.
The coax between the antenna and the LNA also is quite important (short, good quality)
Also you need to think about if nearby buildings or trees reduce your view.
heywhatsthat canāt account for those factors.
These are all good points . Thank you.
I am concerned by the running temperature of this dongle. I expected it to get warm but this gets very warm indeed. It maintains a running temperature of about 28-29 deg C. This is with the bias-t enabled and LNA powered from it.
It is expected to get that warm? I am a bit worried about leaving it unattended in the loft.
That doesnāt seem that hot. Other dongles probably get hotter but donāt have the metal case which makes it feel hotter to the touch.
The case is thermally connected to the chips so the actual chip temperature shouldnāt be much higher than that of the case.
And 30 C for most chips isnāt hot at all.
You can always use a fan to give your setup some airflow, try running a cheap 12 V fan on the RPi 5V supply:
Glad to hear youāve improved you reception, but unless you are limited by terrain, you should be doing better than that. Your antenna location is probably your limiting factor.
A bowtie is a directional antenna and quite large for 131MHz (80cm x 50cm). If you have an interest in ACARS, an omni-directional antenna may be a better choice.
It that your measured temp or the temp above ambient?
The temperature was measured using a cheap IR thermometer pointing at several different parts of the metal casing. The readings varied and the ends seemed a little cooler at 26 deg C, one side seemed a bit warmer than the other, but the predominant temperature was around 28 deg C.
In that case, you donāt have a problem!
Iām entering the ācoolā time of year, so the Piās now have a ālowā overnight temp of 36C ambient.
This too is well within spec.
A J-Pole made of 300 Ohms Twinlead works great. I used one on 2M (144MHz):
For exact calculations, use the following:
https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/
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The travelers friend!
Hook it to the hotel curtain rail and a hand-held will hit every repeater in town.
You got it!
I used one in a basement apartment to access the local community college hamradio packet BBS for my emails. This was before home internet access became widely available, and affordable.
In addition to this antenna, a Kenwood TH-225A handheld, with a Tigertronics Baycom type packet modem were used.
Thatās reassuring regarding the temperature. I guess mine is within spec then. At least the metal case helps to dissipate the heat like a heatsink.
Dxista, I might give that J-Pole a try. It certainly seems more compact and practical then the bowtie. I had thought that the bowtie was omnidirectional, especially if one adds more elements, in which case it becomes more like a discone?
My twin lead has arrived so I would like to try building a J-pole. However, which of those two sites has the correct calculations for the 2M band?
Although the wb3gck page shows the measurements in inches and the m0ukd in centimeters, if you convert one to the other, the measurements appear to be considerably different? For example, on the page by wb3gcl, the overall length is shown as being 54 inches in length, which is 137.16 centimeters. However, the m0ukd calculator shows this as 149cm - a difference of nearly 12cm?
I know that I will need to run the calculation for 131MHz, but I want to be sure that what the m0ukd link is showing me is actually correct? I actually expected both pages to be in agreement on the measurement parameters.
The three antennas shown are subtly different.
The wb3gck J-pole is open at the top - but the āspareā conductor is present.
The m0ukd J-pole does not have the āspareā conductor.
The m0ukd slim-jim is shorted at the top.
Thanks for the explanation. I take it by spare conductor you mean the disconnected section above the 1/4 wave radiator? I hadnāt noticed the difference. I presume for the m0ukd version it just needs to be cut off then? Since it is disconnected I wouldnāt have thought that it would make much of a difference, but I guess it is still a piece of metal an fairly close proximity which n some has way impacts the inductance of the active parts of the antenna?
Since I donāt have the measurements for the wb3gck version I guess I will have to build the m0ukd version. Thanks.
Which ever antenna you choose, just build it as shown. Maybe the author has actually tried it!
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I built the WB3GCK version. It think itās better suited if using twinlead.
As for the calculations for other frequencies, Iām pretty sure itās online, I remember seeing it.
Its not that Iām questioning the authors instructions and I can use the calculator to determine the parameters for the m0ukd version. However the wb3gck is calculated the 2m and I canāt find any information on what the parameters would be for a 131MHz version.
In any case, I just realised that at over 1.6m length, either antenna would be too long to fit vertically in my loft. I have 1.4m headroom max, ideally less than 1.3m would be required.
Ah - gotchya!
I suspect itās a development antenna - that is, he said āballs to the theoryā and made an antenna through trial and error that worked rather than sticking doggedly to a predicted result (that often missed a contributing factor).
(just a thought)