RTL Dongles

[moonbounce]

I have two, an R820t and an R820t2. I bought the R820t2 hoping I would get better reception on the 118 to 136 Mhz air band, but I am sadly disappointed. Neither is any better than the other. The airport is a mere 10 Km away and the Dongles have a really hard time picking it up not to mention all the noise I have to listen to to get what I get. I don't use an outside antenna, just an inside telescopic antenna. I would think that for 10 Km away that that would be all I would need. Most other frequencies above 136 Mhz come in with no problem.
Just wondering if anyone else has deaf RTL dongles in the air band?

MB

 

[popnokick]

Both my 820t and 820t2 work very well in the air band and elsewhere. However, the first step is to use something other than the antenna that came with the dongle. You need a good external antenna in the attic or preferably on the roof. In my case, I use an Off Center Fed Dipole (OCFD) as shown here:
Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

 

[majoco]

I use a cut down TV antenna with the elements shortened to 24 inches/600mm mounted on a TV mast about 12 feet/3.6metres above the ground - my local airport is about 12km away and although I only hear the ground and approach frequencies weakly, I certainly get all the aircraft until they leave the upper control zones. Not too clear in this pic but you get the idea.
http://forums.radioreference.com/at...allation-complete-jamesdale-antenna-2-sml.jpg

 

[jay427]

As others have noted an outdoor antenna is the fix. You could buy a $3000 radio and it may improve a tad but $100 outdoor antenna will be night and day.

 

[K5MPH]

I'm with every one on this get you an outside antenna then you really be hearing things you never heard before I use a old j-pole up at about 25 feet for air craftworks jus fine......

 

[Voyager]

Also keep in mind that the airport puts out very low power, so 10 km may simply be too far to pick up any ground station signals.

 

[moonbounce]

Also keep in mind that the airport puts out very low power, so 10 km may simply be too far to pick up any ground station signals.

I should have mentioned that I do have some scanners, and I have no problems with them listening to the local airport and they also bring in planes intransit, and I don't use an outdoor antenna with them.
Also for comparison sake, I was listening to a local firedept. approx.. three times the distance as the airport, so I know they aren't completely deaf.


Moonbounce

 

[mm]

What type of telescoping antenna are you using and how is it connected to the dongle, by this I mean does it have a counterpoise or sufficient ground on it or is it just the telescoping whip alone connected to your SDR receiver?


I found that with my R820 and simple telescoping whip connected to the dongle thru several feet of RG-58 coax cable.

I then connected a clip on counterpoise wire, using approximately 20 inches length of test lead with an alligator clip on one end, .

This clip lead was connected directly to the ground/outer connection of my whip antenna which I then secured in a plastic insulated vise arrangement and then I wrapped my coax at the telescoping whip antenna end several turns thru a ferrite toroid core.

Then I moved the telescoping whip/vise attached antenna around and away from the dongle and also away from my tablet/PC all the time looking for a drop in the spectrum analyzer displays noise floor while looking for a peak in my signal.


A good test signal for me was to use a distant weather transmitter in the 162.4 to 162.55 MHz range.

Next I moved the counterpoise lead around until the noise floor as observed on the SDR software Spectrum screen dropped even further by a total of at least several db.

It wasn't until I made these changes after which I was able to pick up ATIS from a couple of airports several miles away and some 55+ mile VHF P25 dispatch repeaters along with distant weather transmitters.


I also went back and periodically double checked my antenna setup and counterpoise wire placement using my ham radio MFJ259 antenna analyzer to confirm that I had a <2:1 VSWR when adjusting the telescoping whips length.

A antenna analyzer is an excellent tool for setting up dongle antennas as long as it covers your desired frequency band, in my case < 175 MHz for the MFJ259B model.

Under these conditions of tuning my whips length from approximately 22.5 inches at 124 MHz for my ATIS to 18 inches at 156 MHz for the P25 repeater I was able to confirm that my antennas Z was really presenting a good VSWR to my dongle.

 

[DaveNF2G]

The t2 is supposed to be enhanced for HF (shortwave) reception, so there should be no material difference in the VHF air band anyway.

 

[Token]

The t2 is supposed to be enhanced for HF (shortwave) reception, so there should be no material difference in the VHF air band anyway.

The R820T2 advertised tuning range is the same as the previous version, or at least it appears to be from most online sources I can find. Per NooElec add for the R820T2 based units "uses a brand new tuner IC, the R820T2 made by Rafael Micro, to provide increased sensitivity and improved SNR".

The slightly improved HF performance, I think, is due to it working a bit better with the HF experimental driver and exploiting the wider filters, and not in any native increased tuning ranges. Some people have reported decent operation for both the original and the T2 down to 5 MHz and below, while other people report much higher low frequency fall off. I think there is a lot of unit to unit variation.

I do not have the T2 myself, but might have to grab one to see if there is really any improvement.

T!

 

[moonbounce]

So I have done many experiments with the r820t and the r820t2 and on the air band they both seem to be deaf. I have even gone to an outside antenna and no joy. I also had my little hand held scanner working with a rubber ducky antenna (inside) and it would pick up the airport frequency with no problem. I can see the signal on the SDR display and I get volume but very hard to hear. So my conclusion is that (my dongles) the dongles are deaf on the air band, no biggie.
On another note I did pick up some guy talking on 26.9855 Mhz so I am thinking it is just the air band that the dongles are deaf on.
I am still very happy with the two r820t dongles though, wouldn't trade them for the world ( not to mention the fabulous software that runs them dsd's and sdr and pwd of which I thank the authors to no end).

Moonbounce

 

[Voyager]

Have you:

1. Calibrated the frequency to a known source?

2. Adjusted the gain to allow for better sensitivity? (they come nearly deaf - I can often get away with maximum gain)

You should have as much sensitivity on the dongle as your scanners.

 

[moonbounce]

Have you:

1. Calibrated the frequency to a known source?

>>Done<<<

2. Adjusted the gain to allow for better sensitivity? (they come nearly deaf - I can often get away with maximum gain)

>>Done<<

You should have as much sensitivity on the dongle as your scanners.

>>It does just not on the air band.<<

I had both dongles locked on to a frequency that I was monitoring with my hand held. I did all of the adjustments starting with PPM and minimum signal strength agc and so on. All that it achieves is throwing everything else out of whack so I have to go back in and readjust for other bands I might want to monitor and I still get very poor air band hits?

MB

 

[Voyager]

>>It does just not on the air band.<<

I had both dongles locked on to a frequency that I was monitoring with my hand held. I did all of the adjustments starting with PPM and minimum signal strength agc and so on. All that it achieves is throwing everything else out of whack so I have to go back in and readjust for other bands I might want to monitor and I still get very poor air band hits?

MB

It should not "throw everything else out of whack". If it does, you're doing something wrong or your dongle is defective.

One other question, have you selected AM mode in your SW? I'm sure you have, but just wanted to confirm it.

 

[popnokick]

My first R820T dongle was near deaf.... but it was consistent and deaf everywhere... not just airband. Ordered a new one and problem solved. And since then I also now have an R820T2.... it also works well in the hairbands. Since you've ruled out antennas via comparison with your scanners, I've got to believe it's a setting in your software. The suggestion to ensure you are using AM for aircraft is a good one (even if a bit elementary).

 

[moonbounce]

It should not "throw everything else out of whack". If it does, you're doing something wrong or your dongle is defective.

One other question, have you selected AM mode in your SW? I'm sure you have, but just wanted to confirm it.

I have tried it in AM and FM mode from 24 mhz to 30 mhz. Right now I am hearing 1 guy communication on 27.5375 NFM coming in clear as a bell don't hear the other side of the conversation though. I get a lot of strong WFM stations coming through also.

Other thing is if I have to change the PPM for the air band I will have to change it back in the higher bands.

I have to have AGC off or there is too much noise.

I am listening to Pink Floyd on 26.2875 Mhz WFM which turns out to be 96 FM a commercial radio station.

 

[Voyager]

I have tried it in AM and FM mode from 24 mhz to 30 mhz. Right now I am hearing 1 guy communication on 27.5375 NFM coming in clear as a bell don't hear the other side of the conversation though. I get a lot of strong WFM stations coming through also.

Other thing is if I have to change the PPM for the air band I will have to change it back in the higher bands.

I have to have AGC off or there is too much noise.

I am listening to Pink Floyd on 26.2875 Mhz WFM which turns out to be 96 FM a commercial radio station.

First, are you certain you don't have the SHIFT enabled?

If you set the PPM, it should be set everywhere. Your PPM does not change in different bands. If that truly is happening, your dongle is bad. Once you calibrate the PPM, it's calibrated everywhere.

I checked my airband earlier, and I get lots of activity. I can't hear the ground stations (too far away), but lots of activity.

You say you want to hear the airband, but you say you're tuning from 24-30 MHz. The airband is 118-136 MHz.

 

[majoco]

Send us a screenshot of your settings.

 

[majoco]

Does it look like this....

..........if not I'll send you a list of my settings....

 

[Voyager]

How about a screenshot of the RADIO portion of the window (the part that is cut off on the upper side) as well as a screenshot of the CONFIG screen? your noise floot looks very low.

How are you connecting your antenna to the dongle? I use jumpers and had one (out of about a dozen or more) that was bad.

Also I doubt you will hear ATIS at 10 km. Are you sure you are hearing the GROUND stations on your scanner or just the aircraft?