New CHEAP LNA

Want to post something that doesn't quite fit into the other forums? This is the place for that.
jonfear
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Re: New CHEAP LNA

Post by jonfear » Sun Apr 19, 2015 11:29 pm

Hi

It is fairly obvious. If you see less aircraft than before using the LNA then you have overload!

The best way is to use the LNA with a device that can "auto tune" it's gain like the RPi and Dump1090 set up. Use the "--gain -10" switch in the command line. This should restore calm to the system.

Hope this helps.

Jon
http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

MarkRennie
Posts: 28
Joined: Wed Apr 08, 2015 6:51 pm

Re: New CHEAP LNA

Post by MarkRennie » Tue Apr 21, 2015 10:09 am

so here I am again confused! :D

Which cheap LNA should I buy? That is plug and play as I am new to all of this :D
I saw in another post of your Jon, you said you had a "cheap satellite amplifier". I love being confused all the time with this new hobby :D

Cheers
Mark

bfsapuk
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Joined: Sun Apr 19, 2015 10:26 pm

Re: New CHEAP LNA

Post by bfsapuk » Tue Apr 21, 2015 12:38 pm

jonfear wrote:Hi

It is fairly obvious. If you see less aircraft than before using the LNA then you have overload!

The best way is to use the LNA with a device that can "auto tune" it's gain like the RPi and Dump1090 set up. Use the "--gain -10" switch in the command line. This should restore calm to the system.

Hope this helps.

Jon
Hi Jon

Thanks for the reply.

Is this overload from too many a/c, noise, interference or a combination?

The reason I'm asking is that I'm quite new to this ADSB thing and recently got one of the little Cosy Cave LNAs, which I'm using with an R820T2 dongle, and when I connect the LNA the number of a/c jumps up quite a lot ;-)

The odd thing though is that sometimes, maybe after a few hours (there's no apparent pattern) the number of a/c is noticeably lower, and disconnecting/bypassing the LNA sometimes results in more a/c appearing, and sometimes not, so I'm not sure if this is overload or something else. I'm talking about maybe an extra 30/40/50 a/c appearing when the LNA is disconnected. The dongle with LNA seems to cope with a lot more - the most I have had at any one time so far is 251 a/c, up to around 220 miles away.

I've played about with the gain settings on RTL1090 and haven't found a happy medium so have left them both On.

The results aren’t bad, but I was just wondering if they could be tweaked and am waiting for a new collinear antenna to arrive.

jonfear
Posts: 365
Joined: Sat Feb 09, 2013 12:15 pm
Location: Wick St Lawrence
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Re: New CHEAP LNA

Post by jonfear » Tue Apr 21, 2015 1:59 pm

@Mark
The Cosycave product is quite good. You may need to use the --gain -10 switch in your command line. It is not plug and pray!

@bfsapuk
Overload is caused by too much signal overloading the front end of the receiver. Basically too much information at the same time. The reason for seeing a drift in AC quantities maybe due to the fact that that either there are fewer AC within your area or maybe there are a lot more aircraft therefore more signals arriving which is causing the overload.

With dump1090 the answer is simple, use the --gain -10 switch which makes the system control how much gain is applied to the front end automatically.

This is a quite complex subject and I have grossly simplified it for normal consumption!

Maybe it is time for one of our radio amateur guys to write up a simple users guide to LNA's and antennas? Andrew can then make that post a sticky.
http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

MarkRennie
Posts: 28
Joined: Wed Apr 08, 2015 6:51 pm

Re: New CHEAP LNA

Post by MarkRennie » Tue Apr 21, 2015 2:39 pm

thanks as ever Jon!!

Me109
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Joined: Sat Nov 01, 2014 4:54 pm
Location: KORH

Re: New CHEAP LNA

Post by Me109 » Thu Apr 23, 2015 1:08 pm

T-EGJA1 wrote:That VBFZ-1065+ is a very neat looking filter, however at around £32, it's a little more than I'm prepared to spend for experimenting/testing ....... hence I'm planning to build a filter using the circuit and calculator on this site: http://www.raltron.com/cust/tools/band_pass_filters.asp

I'm currently using a 1/2 wave dipole (nominal impedance 73 ) and 75 ohm feeder; so I entered 75 for RL, 1090 for Frequency and 50 for Loaded Q, which (I think) should give a bandwidth of around 20 Mhz
The calculator then suggests 2x capacitors of 97.3 pF (near enough 100 pF) and one inductor of 1.1 µH (nearest available is 1µH) ... add a piece of Vero board, a small project box and a couple of Type-F chassis connectors and the whole thing should cost less than a fiver ..... whether it'll work or not is another matter ....... I'll let you know in due course
Terry -

What are you using for the 1/2 wave dipole antenna, is this homemade or off the shelf? I've been thinking of an off the shelf ADS-B dipole, but other than the cost (this is after all just a hobby), it's also a 50 ohm load. I'd like to diplex the television and ADS-B antennas into a common 75 ohm feedline with an LNA, but it seems most off the shelf ADS-B antennas are 50 ohm. My EE classes and antenna theory were awhile ago, so I can't recall the downside of mismatched loads in a receive path...

Thanks,
Bryan

MarkRennie
Posts: 28
Joined: Wed Apr 08, 2015 6:51 pm

Re: New CHEAP LNA

Post by MarkRennie » Thu Sep 10, 2015 1:26 pm

I finally got the cosycave one today and to my disappointment I cannot even test it as I don't have a cable to go from the ANT connector to my antenna. The connector on my antenna is a female BNC/male F-type into a Female F-Type connected to my antenna cable.

any idea what short cable or connector I would need to buy please? :S

Cheers
Mark

MarkRennie
Posts: 28
Joined: Wed Apr 08, 2015 6:51 pm

Re: New CHEAP LNA

Post by MarkRennie » Thu Sep 10, 2015 1:44 pm

ok I think I need a F Type Male Plug to SMA Female connector but I can only find them shipped from china/hong kong. Anyone know of a local uk place please?

jonfear
Posts: 365
Joined: Sat Feb 09, 2013 12:15 pm
Location: Wick St Lawrence
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Re: New CHEAP LNA

Post by jonfear » Thu Sep 10, 2015 4:19 pm

http://www.360radar.co.uk, the new name for MLAT Radar in the UK and Western Europe.

Former PP feeder Bm. No longer feeding. I do not have time to sort out imaginary problems with NTP
when it has been working fine for 2+ Years.

MarkRennie
Posts: 28
Joined: Wed Apr 08, 2015 6:51 pm

Re: New CHEAP LNA

Post by MarkRennie » Thu Sep 10, 2015 4:25 pm

Spot on Jon.. Thank you yet again!

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