Airspy + my existing rooftop antennas

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Airdorn

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Hi there.

I have a few different antennas on my roof that I use with my scanner and they work great... very clear signals, etc. I have a couple of omni mag mounts up there, a periodic that's aimed at a cluster of antennas elsewhere in the city I use for 760+ Mhz stuff, etc.


So I got this Airspy and tried it out with my antennas... it doesn't seem to work well at all.

When I attach the little telescoping antenna I ordered with the Airspy, the Airspy SDR works great! It picks up some things that my scanner and all my antenna mess up on the roof won't. And the little telescoping antenna is just sitting down here next to me in my office.

What's going on? Can someone explain?
 

mtindor

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Hi there.

I have a few different antennas on my roof that I use with my scanner and they work great... very clear signals, etc. I have a couple of omni mag mounts up there, a periodic that's aimed at a cluster of antennas elsewhere in the city I use for 760+ Mhz stuff, etc.


So I got this Airspy and tried it out with my antennas... it doesn't seem to work well at all.

When I attach the little telescoping antenna I ordered with the Airspy, the Airspy SDR works great! It picks up some things that my scanner and all my antenna mess up on the roof won't. And the little telescoping antenna is just sitting down here next to me in my office.

What's going on? Can someone explain?
I'd go with one of the following:

  1. You have bad antenna systems on your roof (antenna / coax / something).
  2. You have too much interference from local strong signals wiping out the front end on the Airspy

#2 isn't necessarily a fault of the Airspy. You first need to know/understand how to properly set up things on the Airspy so that it is the most selective / sensitive without suffering from front end overload / imaging / etc.

If you run the Airspy at 10 msps / 64 decimation, it should outperform any scanner you've ever used on receive. If it doesn't, I have to blame it on either the outside antenna system or strong local signals (paging transmitters, FM radio signals, TV station signals, or just very close transmitters that are always on -- like a DMR control channel a block away).

My personal recommendations:
- 10 msps
- 64 decimation
- gain no higher than 18
- choose linearity over sensitivity

Report back your findings / thoughts.

Mike
 

Airdorn

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I'd go with one of the following:

  1. You have bad antenna systems on your roof (antenna / coax / something).
  2. You have too much interference from local strong signals wiping out the front end on the Airspy

#2 isn't necessarily a fault of the Airspy. You first need to know/understand how to properly set up things on the Airspy so that it is the most selective / sensitive without suffering from front end overload / imaging / etc.

If you run the Airspy at 10 msps / 64 decimation, it should outperform any scanner you've ever used on receive. If it doesn't, I have to blame it on either the outside antenna system or strong local signals (paging transmitters, FM radio signals, TV station signals, or just very close transmitters that are always on -- like a DMR control channel a block away).

My personal recommendations:
- 10 msps
- 64 decimation
- gain no higher than 18
- choose linearity over sensitivity

Report back your findings / thoughts.

Mike
Thanks, Mike!

It's clear this Airspy is a superior product. It can pull signals superbly with it's own little antenna.

I'm mainly wondering what's wrong with my antennas that they work good with my scanner but kinda bad with the airspy.

I'll try your suggestions.

BTW, what does msps mean?

Sent from my SAMSUNG-SM-G890A using Tapatalk
 

mtindor

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Thanks, Mike!

It's clear this Airspy is a superior product. It can pull signals superbly with it's own little antenna.

I'm mainly wondering what's wrong with my antennas that they work good with my scanner but kinda bad with the airspy.

I'll try your suggestions.

BTW, what does msps mean?

Sent from my SAMSUNG-SM-G890A using Tapatalk
mega samples per second. Just look in Airspy under Radio and you'll see where you can set 10 / 2.5. If you dont need to view a wide swath of bandwidth at once, and if your USB can keep up, 10 MSPS / 64 DECIMATION will offer best performance.

But, we don't always want to look at only 156 khz of spectrum at a time. So, when you want to look at more spectru, set Decimation to something less than 64. Just be aware that the more bandspread you are monitoring, the less performance you will have because you will be pulling a lot of signals into the passband that you otherwise wouldn't when using 10 / 64.

If I'm targeting a specific frequency, I always use 10 / 64. If I want to see more spectrum (what is going on around a certain frequency) I set decimation lower than 64, adjusting for whatever amount of actual spectrum I want to be able to see at once.

BTW - at my old location, I had a local TV station on 191 mhz and a strong pager locally on 152 mhz. I had to use filters inline for both of those in order to be able to use a high gain outside antenna setup with my Airspy (and any other receiver, like an RTL dongle) simply because the strong signals were in such close proximity to me. That's why I suggested that this might be what is happening with you... or not.

Mike

Mike
 

Airdorn

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mega samples per second. Just look in Airspy under Radio and you'll see where you can set 10 / 2.5. If you dont need to view a wide swath of bandwidth at once, and if your USB can keep up, 10 MSPS / 64 DECIMATION will offer best performance.

But, we don't always want to look at only 156 khz of spectrum at a time. So, when you want to look at more spectru, set Decimation to something less than 64. Just be aware that the more bandspread you are monitoring, the less performance you will have because you will be pulling a lot of signals into the passband that you otherwise wouldn't when using 10 / 64.

If I'm targeting a specific frequency, I always use 10 / 64. If I want to see more spectrum (what is going on around a certain frequency) I set decimation lower than 64, adjusting for whatever amount of actual spectrum I want to be able to see at once.

BTW - at my old location, I had a local TV station on 191 mhz and a strong pager locally on 152 mhz. I had to use filters inline for both of those in order to be able to use a high gain outside antenna setup with my Airspy (and any other receiver, like an RTL dongle) simply because the strong signals were in such close proximity to me. That's why I suggested that this might be what is happening with you... or not.

Mike

Mike

Mike...

You're the best! I tried your setting and man this thing kicks even more major A** !

I had skipped over the 'decimation', setting. I'm now understanding that playing around with ALL the settings really does yield positive results!

There's still generally degraded results using my antennas. I wonder if the problem is with the fact I have several different connectors changing from coax types, etc. between the antenna and my radio? With my scanner it doesn't seem to matter much but the Airspy really doesn't like them.
 

mtindor

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There's still generally degraded results using my antennas. I wonder if the problem is with the fact I have several different connectors changing from coax types, etc. between the antenna and my radio? With my scanner it doesn't seem to matter much but the Airspy really doesn't like them.
The Airspy shouldn't mind it if your scanners don't. But, yes there is additional loss induced every time a connector / adapter is added in between the antenna and the receiving device. And it gets worse if the connection between connectors and coax / connectors and adapters are shabby. To add insult to injury, not all adapters are the same. There are cheaply made knockoffs, and there are the real mccoys.

Are you feeding your scanner and Airspy off of the same antenna system at the same time? If so, are you using a simple "splitter" or a real device [like a multicoupler] that is intended to split the signal with minimal/no loss / with a few db of gain ? Splitters are from the devil. People on here often suggest how well simple splitters work, but they do not realize that using splitters tremendously degrades the signal reaching each receiver.

If you don't run a splitter, and if your scanner seems to be doing fine on the same antenna system that your Airspy does poorly on, it's probably one of the adapters that you are using to get teh Airspy connected. In my case, my cables terminate in BNS, and I use a BNC to SMA (or is MCX - I dont remember), or a similar pigtail.

So look at the parts that you're using to get the signal into your airspy -- those parts that are different from what you use to get the signal into your scanner. Could be loose. could be intermittent. Or could simpy be junk. I've been down that road many times.

Glad you noticed an improvement with decimation though. Definitely, when you don't need access to the spectrum swath that the Airspy of capable of receiving, always use decimation.

Although I will say something else -- There are Airspy Host Tools that you can find on github. One of the executables in those tools allows you to test your USB to ensure it can reliably operate at a speed high enough to support the 10 msps setting. Not all USB will support it. And if yours doesn't, you'll notice some pretty strange stuff showing on the waterfall in SDR#.

Of course, you could also switch to 2.5 msps with some amount of decimation and see if things seem to improve for you. If they do improve by switching to 2.5 msps, you might have a USB throughput issue.

mike
 

Airdorn

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Hey.

Thanks for the additional info.

I have a panel mount BNC coupler. My antenna runs from the roof, into the attic,and down the wall into that BNC coupler. Then a 2-ft. RG-58 pigtail runs from it into my scanner. Scanner works great and picks up well with that configuration.

But if I unplug from the back of the scanner and instead plug it into another BNC pigtail that converts to an SMA, then screw that SMA into the Airspy, the Airspy seems pretty degraded.

But If I unscrew that SMA from the Airspy and then screw the little Airspy antenna into the AIspy, all is well and things are pretty darned clear.
 

mtindor

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Hey.

Thanks for the additional info.

I have a panel mount BNC coupler. My antenna runs from the roof, into the attic,and down the wall into that BNC coupler. Then a 2-ft. RG-58 pigtail runs from it into my scanner. Scanner works great and picks up well with that configuration.

But if I unplug from the back of the scanner and instead plug it into another BNC pigtail that converts to an SMA, then screw that SMA into the Airspy, the Airspy seems pretty degraded.

But If I unscrew that SMA from the Airspy and then screw the little Airspy antenna into the AIspy, all is well and things are pretty darned clear.
Hmm, I certainly can't say for sure, but if it were me I'd be wondering about the integrity of the BNC pigtail that converts to an SMA.

Are you / am I sure that the connector on the Airspy is SMA and not MCX? At any rate, whatever the connector is, be sure that one end is male (has a pin in the middle) and one is female (has a hole in the middle). I vaguely remember a discussion on these forums of one of those small connector forms having adapters that would screw into one another (making one think there is really a center pin connection) when in fact there isn't a center pin on either side.

So check the pigtail / replace another if you have one -- and for sure check and make sure that the connector plugging into the airspy is the opposite polarity as the connector on the airspy -- meaning if the Airspy doesn't have a center pin, then the connector going into it needs to have a center pin, or vice versa. Otherwise, as you can imagine, with no center pin connectivity you'll get extremely low / no signal.

Mike
 

Airdorn

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Mike,

Airspy has an SMC female for antenna connection. The antennas have SMC male. It's basically inpossible to get that screwed up.

Also, the reception withbmy rooftop antennas and my scanner is great, but not so great with the Airspy. But the Airspy loves it's little mag mount mini antenna.

Is this some kind of impedance mismatch issue?

Sent from my SAMSUNG-SM-G890A using Tapatalk
 
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