Airband

General discussions
joaosalvador
Posts: 2
Joined: Tue Sep 20, 2016 12:54 pm

Airband

Postby joaosalvador » Tue Sep 20, 2016 12:59 pm

Sdrplay is really great.

The only not good band is the airband

Airband AM (118-137mhz) is working bad. Poor sensitivity
My simple funcube is working better.
Anybody have the same "problem"?
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JMG
Posts: 16
Joined: Thu Mar 26, 2015 9:58 pm

Re: Airband

Postby JMG » Tue Sep 20, 2016 8:31 pm

SDRplay shows excellent sensitivity at the airband!

John
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g8ixn
Posts: 14
Joined: Thu Aug 11, 2016 2:47 pm

Re: Airband

Postby g8ixn » Thu Sep 22, 2016 6:45 am

It does but not if there are FM broadcast transmitter nearby, have found a tuneable notch helps but a airband bandpass filter is the best option.
Mil Air has it own problems too with DAB breakthough around the 240 to 300 Mhz spectrum.Again bandpass filters do help.They need to have a sharp cutoff at 230 Mhz.
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g1hbe
Posts: 195
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Airband

Postby g1hbe » Thu Sep 22, 2016 8:27 am

The SDRPlay has good sensitivity across its coverage. Its weakness is image responses, usually in the form of unwanted FM broadcast and DAB appearing at unexpected places. It's due to the conversion regime. Try selecting a different conversion frequency from the advanced menu, this might clear it.
I expect the next model from SDRPlay to have comprehensive front end filters. For now, add-on filters or notches are the only answer.
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Andy

dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: Airband

Postby dsalomon » Thu Sep 22, 2016 2:06 pm

The issue with imaging is very well known amonst ALL inexpensive SDRs of this type that do not have bandpass or other filtering built in. More expensive SDRs have bandpass and/or lowpass filtering built in (lowpass for HF type SDRs). It's also well documented that you NEED to put one or more filters inline before the SDR in order to alleviate these problems. That, or just hope that the images don't fall on frequencies that have signals of interest (not really a good plan). You cannot expect miracles from a very low cost receiver with minimal component count (i.e. no filtering). In fact, look under the hood of ANY GOOD receiver, SDR or multiple conversion type, and you will find good filtering. Depending on the type of and how much filtering you put in line, you may also need an amp if your filtering reduces the signal too much.

I would suggest a low end multiple range bandpass filter to start with. They can usually be had for $75 - $100 USD and are definitely worth the investment. Look at SV1AFNs site or on eBay for some HF bandpass filter choices. For higher frequencies, it's going to be more expensive (because they're more rare). A better bet for higher frequencies is a FM broadcast band trap, which are readily available (I have this one from Stridesberg Engineering: http://www.stridsberg.com/prod02.htm, which works very well). You may or may not also need an AM broadcast band filter if you are plagued wit overload from AM stations. Overload from both AM and FM stations is common is you are close to their transmitters. You do not need to be right on top of them to get overload. Many AM and FM stations broadcast VERY powerful signals (10s of thousands or even 1000s of thousands of watts) and will overload receivers miles away from their antennas. I have several FM stations that have antennas 10 miles away and I STILL need FM trap filtering on my RSP.

BTW, not I'm trying to be an advertisement for Stridesberg (I don't work there or get any commission), but they make numerous excellent bandpass and bandtrap filters. They're not the cheapest, but they are good quality and work very well. I've tried cheaper filters, but ended up mostly using Stridesgerg filters because they work better. They also make excellent amps and signal splitters. If you have multiple SDRs from a single antenna, they produce great active signal splitters (splitters with excellent low noise amps on board to ensure the splitting does not reduce the signal). I've tried many different splitters and, as you'd expect, some work better than others. Stridesberg's are always to performers, but again, not the most inexpensive. With filters, amps and splitters my experience is that you usually get what you pay for. A good test for any of this type of equipment is to buy multiple different devices and do your own A/B testing to see what works best for you. Return the ones that fall short and keep the one (or ones) that are best at YOUR QTH.

Also BTW, it's not terrible difficult to build your own filter. A quick Google will turn up many web sites with easy to follow instructions on rolling your own. You can also find kits that will save you a few bucks over pre-built solutions.

Here's a list of a few options to look at. A starting point to help:

Pre-built:
Stridesberg: http://www.stridsberg.com/prod02.htm
Winradio: http://www.winradio.com/home/ubf-1800.htm (this little guy can be an AM band or FM band filter, or a 20dB attenuator - only one function works at a time via internal jumpers, NOT cheap at $150 USD but very good quality build and very good performance).

Instructions and/or kits:
Numerous filter kits: http://www.minikits.com.au/eme174filters.htm#hpf9-1m8

73 - David, AG4F
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joaosalvador
Posts: 2
Joined: Tue Sep 20, 2016 12:54 pm

Re: Airband

Postby joaosalvador » Wed Oct 05, 2016 3:46 pm

I have no images, but very low signal on airband.
Im using a Airband vertical antenna 5/8.
On my single RTL, the airband signal is great, bur on sdr-play is poor.
Last edited by joaosalvador on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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g1hbe
Posts: 195
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: Airband

Postby g1hbe » Wed Oct 05, 2016 10:25 pm

joaosalvador wrote:I have no images, but very low signal on airband.
Im using a Airband vertical antenna 5/8.
On my single RTL, the airband signal is great, bur on sdr-play is poor.


That's strange. I listen to airband occasionally and find the RSP just as good as my AR5001d receiver, in fact it can be better as I can adjust the IF passband just as I need it. Maybe your problem is a strong out-of-band signal (or wideband noise) that is on an image frequency? I can't think of anything else. Have you tried a different LO frequency, or perhaps turning on/off the LNA?

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Andy

NN4F
Posts: 128
Joined: Fri Apr 03, 2015 1:54 pm
Location: Ridgeville, SC
Contact:

Re: Airband

Postby NN4F » Thu Oct 20, 2016 4:04 pm

joaosalvador wrote:I have no images, but very low signal on airband.
Im using a Airband vertical antenna 5/8.
On my single RTL, the airband signal is great, bur on sdr-play is poor.


One thing to check is that your desired RX frequency is not also on the LO of the RX, as any DC/IQ compensation can affect the signal, I have pretty good air rx, same as my desktop scanners, if not better... Just can't scan yet, but that is in the works... With sdruno and sdr-console

Paul - NN4F

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Paul Jones - NN4F, Charleston SC
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