Date   

Re: Best Gain Settings for 137 mhz reception

doug
 

On 09/13/2017 03:47 PM, jdow wrote:


On 2017-09-13 10:35, doug wrote:

On 09/13/2017 06:40 AM, Ruben Navarro Huedo (EA5BZ) wrote:

Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2
From the display, it seems to be doing its job. The FM station is 32 dB below your desired signal. Since the filter is a notch, it should have almost no attenuation in the desired band, and thus you have it
where it will do the most good. --doug, WA2SAY
selective cuts above
If the LNA4ALL is not being overloaded and the problem is simply AIRSPY saturation moving the filter after the LNA will purchase a modest noise figure improvement. If the LNA4ALL is generating IMD then the filter must go up front.

As a side point if the filter works placed after the LNA4ALL he can probably place it at the AIRSPY end of the coax. This will make it easier to take the filter out of the chain if he starts working on frequencies the BCFM stations are not a problem for the R820T.

{^_^} Joanne
Joanne is correct, of course, and in my earlier posts, I suggested putting the filter after the preamp, for obvious technical reasons, but in this case, it seems that the purpose of receiving the signals
the OP wants to hear is fulfilled as he/she desires. I don't think we need to go into a discussion of cascaded noise figure and third-order intercept here. It really is sufficient to almost all users to
connect things in whatever order works, and to explain, as Joanne and I have tried to do, what will work, and what might not. To possibly simplify things, I remember one contributor to this discussion
saying, use as little preamp gain as necessary to reduce overload problems. Amen to that!

--doug, WA2SAY


Re: Airspy R2: Interferences with antenna disconnected

doug
 


On 09/13/2017 01:23 PM, Doug wrote:

On 09/13/2017 08:09 AM, Ruben Navarro Huedo (EA5BZ) wrote:
Hello Airspy friends :)

I am doing some more tests with my R2.
Here you have 2 screenshots. Both screenshots are with NO antenna and NO coax. (Only R2 connected to PC).
I am using 4 toroids on USB cable.

One screenshot with Gain 0 and another with Gain 10.

Why do i have these interferences?

Tnx a lot.
This is a series of harmonics of something that is oscillating at about 160 KHz, OR the product of two strong signals that are 160 KHz apart. I would connect a 50 Ohm termination across the input to
your SDR and see if it makes a difference. Since you have no connection to the input, it may be the radio itself that has something oscillating inside it. Or it's even possible that there is something
inside your computer that is feeding back thru the USB cable. Do you have another computer--preferably with a different main board and different video card? See if the signals go away or are at a
different spacing. If you put a few more toroids on the USB cable, does that help? Put them right close to the radio.  Also, what is that big signal about 138.34 MHz? Where is that coming from?
After you terminate the input, try wrapping some aluminum foil around the whole radio and connect it to the outside of the input connector. Make a good solid connection.

--doug, WA2SAY, retired RF engineer.

PS: My connection cannot seem to reproduce the illustrations. Other readers will have to look back at the pictures in your original post.


Re: Best Gain Settings for 137 mhz reception

Ruben Navarro Huedo (EA5BZ)
 

Thank's Joanne !


Re: Airspy R2: Interferences with antenna disconnected

Ruben Navarro Huedo (EA5BZ)
 

Using 10msps mode i don't have the problem.
Then the problem is 2.5 msps with my pc.


Re: Best Gain Settings for 137 mhz reception

jdow
 

On 2017-09-13 10:35, doug wrote:
On 09/13/2017 06:40 AM, Ruben Navarro Huedo (EA5BZ) wrote:
Hello friends:

Thank's again for ALL your posts.
I'm learning a lot with this thread.
Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2

This evening i will test with NOAA's and Meteor M2.

Thank's again.
From the display, it seems to be doing its job. The FM station is 32 dB below your desired signal. Since the filter is a notch, it should have almost no attenuation in the desired band, and thus you have it
where it will do the most good.  --doug, WA2SAY
If the LNA4ALL is not being overloaded and the problem is simply AIRSPY saturation moving the filter after the LNA will purchase a modest noise figure improvement. If the LNA4ALL is generating IMD then the filter must go up front.

As a side point if the filter works placed after the LNA4ALL he can probably place it at the AIRSPY end of the coax. This will make it easier to take the filter out of the chain if he starts working on frequencies the BCFM stations are not a problem for the R820T.

{^_^} Joanne


Re: Airspy R2: Interferences with antenna disconnected

doug
 

On 09/13/2017 08:09 AM, Ruben Navarro Huedo (EA5BZ) wrote:
Hello Airspy friends :)

I am doing some more tests with my R2.
Here you have 2 screenshots. Both screenshots are with NO antenna and NO coax. (Only R2 connected to PC).
I am using 4 toroids on USB cable.

One screenshot with Gain 0 and another with Gain 10.

Why do i have these interferences?

Tnx a lot.
This is a series of harmonics of something that is oscillating at about 160 KHz, OR the product of two strong signals that are 160 KHz apart. I would connect a 50 Ohm termination across the input to
your SDR and see if it makes a difference. Since you have no connection to the input, it may be the radio itself that has something oscillating inside it. Or it's even possible that there is something
inside your computer that is feeding back thru the USB cable. Do you have another computer--preferably with a different main board and different video card? See if the signals go away or are at a
different spacing. If you put a few more toroids on the USB cable, does that help? Put them right close to the radio. Also, what is that big signal about 138.34 MHz? Where is that coming from?
After you terminate the input, try wrapping some aluminum foil around the whole radio and connect it to the outside of the input connector. Make a good solid connection.

--doug, WA2SAY, retired RF engineer.

PS: My connection cannot seem to reproduce the illustrations. Other readers will have to look back at the pictures in your original post.


Re: Best Gain Settings for 137 mhz reception

doug
 


On 09/13/2017 06:40 AM, Ruben Navarro Huedo (EA5BZ) wrote:
Hello friends:

Thank's again for ALL your posts.
I'm learning a lot with this thread.
Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2

This evening i will test with NOAA's and Meteor M2.

Thank's again.

From the display, it seems to be doing its job. The FM station is 32 dB below your desired signal. Since the filter is a notch, it should have almost no attenuation in the desired band, and thus you have it
where it will do the most good.  --doug, WA2SAY




Re: Airspy R2: Interferences with antenna disconnected

Ruben Navarro Huedo (EA5BZ)
 

I think i have the answer:

http://airspy.com/quickstart/

--> In some PCs, the experimental 2.5MSPS mode is vulnerable to USB noise. This will be improved with further firmware updates. The recommended method to get lower sample rates is to use some decimation with the 10MSPS stream.


Airspy R2: Interferences with antenna disconnected

Ruben Navarro Huedo (EA5BZ)
 

Hello Airspy friends :)

I am doing some more tests with my R2.
Here you have 2 screenshots. Both screenshots are with NO antenna and NO coax. (Only R2 connected to PC).
I am using 4 toroids on USB cable.

One screenshot with Gain 0 and another with Gain 10.

Why do i have these interferences?

Tnx a lot.


Re: Best Gain Settings for 137 mhz reception

Ruben Navarro Huedo (EA5BZ)
 

A lot of thank's !
I will try after some test with this configuration :-)


Re: Best Gain Settings for 137 mhz reception

David J Taylor
 

Hello friends:

Thank's again for ALL your posts.
I'm learning a lot with this thread.
Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2

This evening i will test with NOAA's and Meteor M2.

Thanks again.
=========================================

Ruben,

Great to see that there is an improvement!

What you have is the best /if/ the LNA4ALL is being saturated by the broadcast FM. For best performance (lowest system noise factor), I suggest trying:

Antenna --> LNA4ALL --> BCFM Filter --> Coax --> Airspy R2

If this is not so good when receiving images, you can always revert to your first scheme.

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


.


Re: Best Gain Settings for 137 mhz reception

Ruben Navarro Huedo (EA5BZ)
 

Hello friends:

Thank's again for ALL your posts.
I'm learning a lot with this thread.
Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2

This evening i will test with NOAA's and Meteor M2.

Thank's again.



Re: Best Gain Settings for 137 mhz reception

jdow
 

Fascinating - That link goes right to the listing. But if I try to search for it nothing turns up. I wonder if this is a bug in E-Bay, some form of "feature", a really long ago expired listing, or something even stranger.

{^_^}

On 2017-09-11 10:15, Siegfried Jackstien wrote:

Which "boom" are you talking about?  (I never heard of conductive attenuators either.)
I wonder if you have yet implemented an SDR dongle? I have two, one of which is supposed to work down into 100KHz. (I hope it can go lower.) Not hooked up yet. I'm going to build a loop
out of copper tubing, and then probably a grounded gate fet preamp.Will try to get a Linux driver working. (I dislike Windows!!!) If you have done similar, please advise!
--doug, WA2say
there are catv attenuators available (3,6, 10, 12 and 20 db) with a dc pass ...
these are sometimes used in catv or sat applications
http://www.ebay.com/itm/F-Connector-Attenuator-Choose-from-3dB-6dB-10dB-12dB-20dB/282522946690?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D46087%26meid%3D79235d14114d4d45960513329bd1975a%26pid%3D100005%26rk%3D5%26rkt%3D6%26sd%3D330459599538&_trksid=p2047675.c100005.m1851 and i use them to test signals on ham tv ... i can put 60 db in line (3x20 db in a row) and still have a good receive from our tv repeater 40 km away!!! (but that is with a 6 feet dish on 9cm band)
lnb need 12 or 18v (polarisation switch) and so i am SURE these attenuators have a dc pass (otherwise no receive is possible)
greetz
sigi (ps i measured them and they are almost flat over the complete range!!!)


Re: Best Gain Settings for 137 mhz reception

Siegfried Jackstien
 

Which "boom" are you talking about?  (I never heard of conductive attenuators either.)
I wonder if you have yet implemented an SDR dongle? I have two, one of which is supposed to work down into 100KHz. (I hope it can go lower.) Not hooked up yet. I'm going to build a loop
out of copper tubing, and then probably a grounded gate fet preamp.Will try to get a Linux driver working. (I dislike Windows!!!)  If you have done similar, please advise!
--doug, WA2say
there are catv attenuators available (3,6, 10, 12 and 20 db) with a dc pass ...

these are sometimes used in catv or sat applications

http://www.ebay.com/itm/F-Connector-Attenuator-Choose-from-3dB-6dB-10dB-12dB-20dB/282522946690?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D46087%26meid%3D79235d14114d4d45960513329bd1975a%26pid%3D100005%26rk%3D5%26rkt%3D6%26sd%3D330459599538&_trksid=p2047675.c100005.m1851


and i use them to test signals on ham tv ... i can put 60 db in line (3x20 db in a row) and still have a good receive from our tv repeater 40 km away!!! (but that is with a 6 feet dish on 9cm band)

lnb need 12 or 18v (polarisation switch) and so i am SURE these attenuators have a dc pass (otherwise no receive is possible)

greetz

sigi (ps i measured them and they are almost flat over the complete range!!!)


Re: airspy hf+ with linux

prog
 

If you can build this on your Linux, you are probably all set.

https://github.com/airspy/airspyhf/


Re: airspy hf+ with linux

jdow
 

I suspect Leif supports it quite well in Linrad.

{^_^}

On 2017-09-10 21:09, Ian Board wrote:
I am very interested in the upcoming airspy hf+, but almost exclusively use linux. Up to now, I have been using gqrx, which has worked out ok for me.  I was wondering what linux software will work with the airspy hf+.
What are the best options for using it with linux?
- Ian


airspy hf+ with linux

Ian Board <ian.board@...>
 

I am very interested in the upcoming airspy hf+, but almost exclusively use linux. Up to now, I have been using gqrx, which has worked out ok for me.  I was wondering what linux software will work with the airspy hf+. 

What are the best options for using it with linux?

- Ian


Re: Best Gain Settings for 137 mhz reception

doug
 

On 09/10/2017 09:21 PM, jdow wrote:
I hope I don't get pushed into a discussion of how noise figure and dynamic range can interact when you have a given receiver and are trying to make it work better with a preamplifier. That's a long dissertation done right. As with everything else in life, it's a trade-off. And it has serious teeth.

{o.o} Joanne
Joanne is absolutely correct. It takes a real system analysis, including the effects of overloads all along the receive chain. This will require analysis of gains, compression points/third-order intercepts,
of all the components along the line, as well as signal strengths that come down the feedline including the feedline attenuation, preamp characteristics--not just noise figure and gain. There has been some
serious attention to these on the thread, and one should pay attention to that. There have also been some serious filter designs, which should be studied and implemented if necessary, if one is going to
try to listen to satellites in the 130~170 MHz region. Two-meter ham band should not normally be a problem, unless you are fairly close to a repeater or an active amateur. For noise figure calculations,
either Joanne or I can give you the equations, but the net results have already been published on the thread. I will add, however, that the contribution of urban or suburban noise should not be significant
if you have a gain antenna pointed at a satellite. One other consideration: If you have LED lighting in the vicinity of the antenna, try turning it off and see if it makes a difference. The pwser supplies for
LED lighting can be noisy, altho they shouldn't be.

--doug, WA2SAY


Re: Best Gain Settings for 137 mhz reception

jdow
 

I hope I don't get pushed into a discussion of how noise figure and dynamic range can interact when you have a given receiver and are trying to make it work better with a preamplifier. That's a long dissertation done right. As with everything else in life, it's a trade-off. And it has serious teeth.

{o.o} Joanne

On 2017-09-10 19:04, Greg Ella wrote:
And if you put the AirSpy right at the feed point of the antenna, you won't have any cable loss either.
Greg Ella
AD0JP
On Sun, Sep 10, 2017 at 9:29 AM, David J Taylor via Groups.Io <gm8arv=yahoo.co.uk@groups.io <mailto:gm8arv=yahoo.co.uk@groups.io>> wrote:
From: adam9a4qv via Groups.Io
Hi,
[]
I disagree with all the guys here that gave you advice to use the LNA with
lower gain, somebody say 5db or a FET LNA.
Or use the proper LNA with high gain, low NF, high OIP3 or do not use the
LNA at all.
Here is the example:
Airspy NF is 5-6db
Using the LNA with 24db gain and 0.7db NF will decrease the system NF to 0.74dB.
Using the LNA with 5dB gain and 0.7dB NF will decrease the system NF to 3.26db
Using the FET LNA with 12db gain and 1.5db NF will decrease system NF to 2dB.
As you can see, the LNA gain is very important, this is what the Friis says....
If you need a constant good 137Mhz reception a good 137Mhz filteris a must.
===================================
I also questioned the need for an LNA in this system.  Using an LNA with an
unnecessarily high gain may simply exaggerate the strong signal problems. Of
course, if the cable loss is high then more gain may be justified  to reduce
system NF.  System dependant.
73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk <mailto:david-taylor@blueyonder.co.uk>
Twitter: @gm8arv


Re: Best Gain Settings for 137 mhz reception

jdow
 

Baby boom in our terms. I just missed being a Boomer.

I have. And if I spoke C# more fluently I might have something more suitable for SDRSharp than what I have. It works with SDR Console, though. And it controls GPIO. I have a very small fix I've not posted yet. The fix makes sure the Bias-T GPIO bit is reset when it is closed. I figure that is something polite to do.

I rather converted my RTLSDR.dll into Visual Studio C++. And it uses some features of Windows that make it quicker to poll for active dongles. When you have 6 or more plugged in at any given time that's worth the effort. This feature works a treat with the way SDR Console works. Youssef took a different tack which is quicker to respond when the start button is pressed. But it has other shall we say operational problems. For instance if you have to "clear" a dongle by removing and reinserting it you also have to restart SDR Sharp to use it. With SDR Console you don't. It's a design decision. And both ways have their advantages.

If you speak C++ it should not be overly difficult to move it over to Linux. Changing it to pure C would be a small bit more of a challenge.

I've not implemented exotic antennas. I've just played with my Isopole and long chunks of wire. I'm old enough I don't climb ladders much anymore. (Even the C# ladder is more climb than I enjoy these days. MS likes it. I don't. I've found that multiple inheritance can make cleaner code when I am the coder.)

{^_^} Joanne

On 2017-09-10 16:13, doug wrote:
On 09/10/2017 03:39 PM, jdow wrote:
Thanks for the pointer to sources. It's ironic that I prattle about looking to CATV technology for some good high dynamic range work and didn't think to look there for attenuators. I am getting old. Damn! I guess I am pre-boom and doomed to get old even if they still think they won't. {^_-}

{^_^}
Hi ,Joanne--
Which "boom" are you talking about?  (I never heard of conductive attenuators either.)
I wonder if you have yet implemented an SDR dongle? I have two, one of which is supposed to work down into 100KHz. (I hope it can go lower.) Not hooked up yet. I'm going to build a loop
out of copper tubing, and then probably a grounded gate fet preamp.Will try to get a Linux driver working. (I dislike Windows!!!)  If you have done similar, please advise!
--doug, WA2say


On 2017-09-10 02:08, Siegfried Jackstien wrote:

Mumble mumble - where can I get a 10 dB attenuator that passes DC with no attenuation? That's a start....
hello joanne
i have some attenuators with "f" connectors that are 10 and 20 db with dc pass (notmally use for sat and cable tv apps) .... and the 20 db are measured by me with an analyzer and they are almost flat from a few megs up to 2.5 gig (i say almost cause the attenuation is slowly creeping up if you go higher ... but only a db or two) ... did not measure the 10 db version but i am guessing those are almost the same thing

so ... it is possible to find such an attenuator

or build one ... a few resistors ... bridged with a coil (to have the dc pass) ... easy :-)

dg9bfc sigi




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