Received my HF+ and testing with 2 elements 40m monoband


Ruben Navarro Huedo (EA5BZ)
 

Hello friends:
Today i have received my HF+
We have been testing it with a 2 elements monoband beam 30m over the ground.
We are suffering saturation from broadcasting on 7200 and UP.
We own other SDR and have tested also today and they don't have this problem.
What do you think?


prog
 

On Wed, Jan 10, 2018 at 02:29 pm, Ruben Navarro Huedo (EA5BZ) wrote:
Hello friends:
Today i have received my HF+
We have been testing it with a 2 elements monoband beam 30m over the ground.
We are suffering saturation from broadcasting on 7200 and UP.
We own other SDR and have tested also today and they don't have this problem.
What do you think?
What's the SNR of that signal in the other SDRs?


W0LEV
 

Outside of the garbage at the very left below 7.000 MHz, I don't see indications of saturation. 

​Possibly post a screen capture of both SDR receivers using the same SW and on the same antenna.  That could help us see the problem.  ​

Dave - WØLEV


Alan G4ZFQ
 

received my HF+
We have been testing it with a 2 elements monoband beam 30m over the ground.
We are suffering saturation from broadcasting on 7200 and UP.
We own other SDR and have tested also today and they don't have this problem.
What do you think?
Ruben,

Look at the noise level, 40dB or more attenuation should be used.

73 Alan G4ZFQ


Ruben Navarro Huedo (EA5BZ)
 
Edited

Our other software doesn't measure SNR directly but it is around the same.


Ruben Navarro Huedo (EA5BZ)
 

Alan....external attenuation?


Alan G4ZFQ
 

Alan....external attenuation?
Ruben,


"2 elements monoband beam 30m over the ground"
On 40m an attenuator can help with a low dipole. You have about 70dB of antenna noise, your screenshot shows you have less than 60dB headroom.

73 Alan G4ZFQ


adam9a4qv
 

Alan, we do not spend the $10k in antenna mast and antennas to put the 40db attenuator on the receiver!

Ruben, welcome to the club :-)..... you need a bandpass filter for each HF band you want to listen.

Adam


Simon Brown
 

Ruben,

 

Run the HF+ at 768 kHz bandwidth, look for an even stronger signal higher up in the 41m broadcast band. There is no way the signal at 7.210 is causing problems.

 

Simon Brown, G4ELI

 

www.dxgalaxy.com
www.sdr-radio.com
www.sdr-satellites.com

 

 

From: main@airspy.groups.io [mailto:main@airspy.groups.io] On Behalf Of Ruben Navarro Huedo (EA5BZ)
Sent: 10 January 2018 22:30
To: main@airspy.groups.io
Subject: [airspy] Received my HF+ and testing with 2 elements 40m monoband

 

Hello friends:
Today i have received my HF+
We have been testing it with a 2 elements monoband beam 30m over the ground.
We are suffering saturation from broadcasting on 7200 and UP.
We own other SDR and have tested also today and they don't have this problem.
What do you think?


Alan G4ZFQ
 

Alan, we do not spend the $10k in antenna mast and antennas to put the 40db attenuator on the receiver!
Adam,

I've never had the good fortune to use such an antenna.
But I thought the purpose was to put 40dB on the TX signal, not to overload the RX.
It looks to me that the visible station is at 0dBfs. A BPF will not help with strong signals close to the frequency in use.
Or, is there something I'm missing?

73 Alan G4ZFQ


Ruben Navarro Huedo (EA5BZ)
 

Simon: i will test this night with 768khz.


jdow
 

Oh yes you do. If you can connect the antenna and have the noise go up more than about 3dB you have room for attenuation. And any decent transmitting antenna will have room for as much as 20 dB attenuation at quiet locations on the Earth, not in buildings, caves, or congresscreature's brains.

{^_^}

On 2018-01-11 00:49, adam9a4qv via Groups.Io wrote:
Alan, we do not spend the $10k in antenna mast and antennas to put the 40db attenuator on the receiver!
Ruben, welcome to the club :-)..... you need a bandpass filter for each HF band you want to listen.
Adam


prog
 

On Wed, Jan 10, 2018 at 10:30 pm, Alan G4ZFQ wrote:
Ruben,

Look at the noise level, 40dB or more attenuation should be used.

73 Alan G4ZFQ
Remember, there's an AGC with enough range to cover up to +15 dBm without saturation.
Leave the decision to use the right amount of attenuation to the AGC.

The problems I see in that screenshot:
  1. The SNR of the strong BC station is ... rather low for the antenna you are using. This means your antenna is picking a lot of noise. Bad isolation from the PC?
  2. I can see the same signal on Simon's and Alex's servers with the same splatter. Different locations, different antennas.
  3. Update your SDR#


prog
 

On Thu, Jan 11, 2018 at 03:00 am, jdow wrote:
Oh yes you do. If you can connect the antenna and have the noise go up more than about 3dB you have room for attenuation. And any decent transmitting antenna will have room for as much as 20 dB attenuation at quiet locations on the Earth, not in buildings, caves, or congresscreature's brains.
Keyword: quiet


Carlos Cabezas
 

Why adding an external attenuator? Isn't that a job for the AGC? Or has he run out of AGC attenuation range?

Regards,
Carlos

El 11 ene. 2018 12:01 p. m., "jdow" <jdow@...> escribió:
Oh yes you do. If you can connect the antenna and have the noise go up more than about 3dB you have room for attenuation. And any decent transmitting antenna will have room for as much as 20 dB attenuation at quiet locations on the Earth, not in buildings, caves, or congresscreature's brains.

{^_^}

On 2018-01-11 00:49, adam9a4qv via Groups.Io wrote:
Alan, we do not spend the $10k in antenna mast and antennas to put the 40db attenuator on the receiver!

Ruben, welcome to the club :-)..... you need a bandpass filter for each HF band you want to listen.

Adam





paul
 
Edited

On Thu, Jan 11, 2018 at 12:49 am, adam9a4qv wrote:
Alan, we do not spend the $10k in antenna mast and antennas to put the 40db attenuator on the receiver!

If your noise floor is as high as -55dBm and a broadcaster is clearly hitting 0dBm, I think you should.
You are only using half the dynamic range of the receiver :-)


prog
 

On Thu, Jan 11, 2018 at 03:15 am, <pbij2001@...> wrote:
You are only using half the dynamic range of the receiver :-)
That would be true if there wan't any AGC involved. But we have this:


paul
 

In that case it should all be automagic...


jdow
 

There is that. Nonetheless, external attenuation tends to be more linear than most electronically variable attenuators. That's why I automatically reach for them first.
{^_^}

On 2018-01-11 03:13, Carlos Cabezas Prudencio wrote:
Why adding an external attenuator? Isn't that a job for the AGC? Or has he run out of AGC attenuation range?
Regards,
Carlos
El 11 ene. 2018 12:01 p. m., "jdow" <jdow@earthlink.net <mailto:jdow@earthlink.net>> escribió:
Oh yes you do. If you can connect the antenna and have the noise go up more
than about 3dB you have room for attenuation. And any decent transmitting
antenna will have room for as much as 20 dB attenuation at quiet locations
on the Earth, not in buildings, caves, or congresscreature's brains.
{^_^}
On 2018-01-11 00:49, adam9a4qv via Groups.Io wrote:
Alan, we do not spend the $10k in antenna mast and antennas to put the
40db attenuator on the receiver!
Ruben, welcome to the club :-)..... you need a bandpass filter for each
HF band you want to listen.
Adam


adam9a4qv
 

On Thu, Jan 11, 2018 at 01:21 am, Alan G4ZFQ wrote:
I've never had the good fortune to use such an antenna.
But I thought the purpose was to put 40dB on the TX signal, not to overload the RX.
It looks to me that the visible station is at 0dBfs. A BPF will not help with strong signals close to the frequency in use.
Or, is there something I'm missing?

73 Alan G4ZFQ
That is true, not many hobbyist can afford yourself 2el.quad on 40mtrs but once you try it you can feel the difference.
I was lucky that in our club we had 2el.quad but more like oblong shaped and a  vertical polarization for 40mtrs band.
I think that guys did use some old Rothamel antenna book design.
Oh boy, this antenna was a miracle...

Coming back to the topic, we can see from the screenshot that the problematic signals are not in the HAM band of the interest.
The hams can not produce such a strong signal on the HF to run this radio in saturation.
There is a video on my YT channel where I was scanning the crowded HAM bands during the last WW contest. The HF+ perform quite good without any extra filters.
Adding the filter to cut out the really strong BC HF stations we can give more room for the AGC in the frequency of interest.

On the other hand, 2el.quad can have 4-6db of the gain over a dipole so antenna is not the cause why the receiver is overloaded.
More over, directional antenna can help to reduce the unvanted signals from various directions depending on the radiating diagram.

Attenuator can be used, but this is not a permanent solution.
A solution is to filter the frequency of interest and have the benefit of the full dynamic range we can get from the radio.
Using a 40dB attenuator is more appropriate for the TV dongle with 50dB dynamic range and not a radio that can handle 90dB.

Adam