Date   

Re: Ideas for cheap and effective loop antennas

W0LEV
 

True, the loop, a real shorted (DC) loop, single or multiple turns, is sensitive to the magnetic portion of the EM wave.  As such, it's a lousy E-field antenna (capacitive or short prove) but a superb B-Field antenna (inductive or a small loop).  The transformer is highly efficient due to the loop as a current source at coupling RF energy onto the coax from the differential amplifier.  What's really needed is a trans-impedance amplifier which effectively converts current into a voltage. 

On Fri, Aug 4, 2017 at 5:54 PM, jdow <jdow@...> wrote:
Probably very low impedance to a higher impedance such as 50 ohms. A really low input impedance LNA can materially boost a small loop's performance.

{^_^}

On 2017-08-04 15:13, doug wrote:

On 08/04/2017 02:33 PM, prog wrote:
This one can be built with a piece of coax and a small transformer.
It's a balanced two turns loop.
Thoughts?

30 cM =11.8 inches. What kind of transformer is envisioned here? What frequency is it supposed to work at, and what is the turns ratio?








--
Dave - WØLEV
Just Let Darwin Work


Re: Astro Spy - Signal Level Range

W0LEV
 

OK.  I understand.  Using my spectrum analyzers, there are many times I employ the 5 dB per major division, and, on occasion, even the 1 dB per major div.

While we're at it, using either the radio astronomy application aimed at the H1 line or the spectrum analyzer (SpectrumSpy), it would be extremely helpful if we had something as small as 10 kHz span and choice of resolution bandwidths.  Of course, there is always something more that would be 'absolutely' needed......

Personally, I have recommended the AirSpy to many customers (EMC and RFI) who do not have the resources to buy or rent  a full-up spectrum analyzer.  For the purpose of reducing radiated emissions, the AirSpy is just what is needed!  It's a wonderful piece of test gear if you don't have a spectrum analyzer (which I do).  But, this is getting off the subject.

Dave - W0LEV   



On Sat, Aug 5, 2017 at 10:36 AM, prog <info@...> wrote:
I have the impression his problem is more about the flexibility of the display than the actual quality of the signal, which seems good since it's not the problem he's complaining about.




--
Dave - WØLEV
Just Let Darwin Work


Re: Ideas for cheap and effective loop antennas

joe@polcari.com <Joe@...>
 

Isn¹t the original also out of phase, input to output? Or is that part of
the design?

On 8/5/17, 1:06 PM, "Leif Asbrink" <airspy@groups.io on behalf of
leif@sm5bsz.com> wrote:

The new drawing is quite different. It shows a simple
two turn loop with its midpoint grounded.

The old image was NOT a loop, try follow the yellow line
from one side of the transformer to the other side.
Impossible. Some connection is missing.

The way the transformer is drawn is misleading. The primary
winding should have few turns and the secondary winding
many turns if you connect to a 50 ohm system.

Look again. The loop has two turns in series with a center tap.
The loops swap between the inner and outer condictors of the coax.
I simplified the diagram a bit:
It is clear now:-)

73

Leif




Re: Astro Spy - Signal Level Range

prog
 

The problem is that "bit" also affects SDR# and all the spectrum plugins, since it's based on the same reusable component.
The easiest trick is to increase/decrease the RF gain by 1 tick (3 dB) which will align your signal in the right region.


Re: Ideas for cheap and effective loop antennas

prog
 

I only removed the other side of the shielding from the same diagram.
Now this build technique ensures the currents induced by the E-fields will be canceled at the grounding point, which is a desirable property.


Re: Astro Spy - Signal Level Range

Jochen Richert
 

Hi Dave

Thanks for your answer and the description of your setup. "prog" explained it right, I have not a problem with the signal strength, I would like to have the possibility to scale the signal strength in smaller steps than only 10 dbFS.
In the moment, I can also see the 1.5 dBFS lowered noise floor, due to the coronal hole facing to us. This is also the reason, why the level drops below -70 dbFS. You may have a look to my animation on youtube  https://youtu.be/4FC_6LQjpHA where you see the signal level over 24 hours.
My Setup is a 2 Meter Dish, a HB9BBD LNA with 40 dB gain and 0.19 dB NF. Than through 5 Meter low loss Koax Cable CS29 into my Airspy Mini. I agree, I do need a bit more gain but the next days, I will replace the Bi Quad by a Linear Horn or Septum Horn Feed.

So I hope, the developers could easily switch a bit and all is working ;-)

vy 73's de HB9DRT, Jochen


Re: Ideas for cheap and effective loop antennas

Leif Asbrink
 

The new drawing is quite different. It shows a simple
two turn loop with its midpoint grounded.

The old image was NOT a loop, try follow the yellow line
from one side of the transformer to the other side.
Impossible. Some connection is missing.

The way the transformer is drawn is misleading. The primary
winding should have few turns and the secondary winding
many turns if you connect to a 50 ohm system.

Look again. The loop has two turns in series with a center tap.
The loops swap between the inner and outer condictors of the coax.
I simplified the diagram a bit:
It is clear now:-)

73

Leif


Re: Astro Spy - Signal Level Range

prog
 

I have the impression his problem is more about the flexibility of the display than the actual quality of the signal, which seems good since it's not the problem he's complaining about.


Re: Astro Spy - Signal Level Range

W0LEV
 

We had a 'somewhat' similar problem at LTO (Little Thompson Observatory:  <starkids.org>) in setting up our H1 receiver.  Our setup:
     1)  14-foot diameter off-center-fed dish
     2)  1 GHz HPF (to get rid of local RF noise)
     3)  LNA (nominal +22 dB gain, NF = 0.5 dB)
     4)  Bias tee
1 through 4 are at the feed which is a loop 1/4-wavelength in front of a splash plate.
     5)  75-feet 1/2-inch hardline
     6)  Another +20 dB LNA
     7)  bias tee
     8)  AirSpy
     9)  PC running Radio Sky Pipe (freeware at <http://radiosky.com/skypipeishere.html>)

We had to include the second LNA in the warm room (item 6) to have enough gain to get the 'signal' significantly out of the noise for RSP.  Suggest you add another gain stage in front of the AirSpy. 

Our system noise temp runs - measured - about 100 k.  We should do better, but the requirement of the 1 GHz HPF dictates that initial loss to get rid of RF dirt from a close-by cell tower. 

Dave - W0LEV
'

     8)  PC

On Sat, Aug 5, 2017 at 6:03 AM, Jochen Richert <jochen.richert@...> wrote:
Dear Astro Spy Developers

I am using Astr Spy with my Airspy Mini on a 2m Dish and homemade Biquad for receiving and logging 1420 MHz HI signals. To have a better readability, would it be possible to make the signal level also pre selectable in 1 dBFS steps and not only 10 dBFS?
I already tried to change it from -65 to -70 but it will only show in 10dBFS steps. I would really like to have this feature, because my signal level sometimes falls just below -70 and so I loose about 9 dbFS os scaling factor, because I have to use -60 to -80.


Many thanks and greetings from Switzerland
HB9DRT, Jochen




--
Dave - WØLEV
Just Let Darwin Work


Re: Airspy HF+ USB specs

Alberto I2PHD
 

On 8/5/2017 4:05 PM, prog wrote:

The user-mode driver is already available on github: https://github.com/airspy/airspyhf
It should compile fine with the RPi without problems.

Thanks. Will give a look at that package.

--
73 Alberto I2PHD
Credo Ut Intelligam



Re: Airspy HF+ USB specs

prog
 

The user-mode driver is already available on github: https://github.com/airspy/airspyhf
It should compile fine with the RPi without problems.


Airspy HF+ USB specs

Alberto I2PHD
 

Will the low-level USB specs of the new Airspy HF+ be available when the unit will be on the market ?
This would allow somebody (maybe myself, maybe somebody else) to write an application for the
Raspberry Pi 3B, using Raspbian and libusb, to control the Airspy HF+ and to filter and demodulate its
output.

--
73 Alberto I2PHD
Credo Ut Intelligam



Re: Astro Spy - Signal Level Range

prog
 

Are you aware you also have the actual RF gain to fit your signal within the desired range?


Astro Spy - Signal Level Range

Jochen Richert
 

Dear Astro Spy Developers

I am using Astr Spy with my Airspy Mini on a 2m Dish and homemade Biquad for receiving and logging 1420 MHz HI signals. To have a better readability, would it be possible to make the signal level also pre selectable in 1 dBFS steps and not only 10 dBFS?
I already tried to change it from -65 to -70 but it will only show in 10dBFS steps. I would really like to have this feature, because my signal level sometimes falls just below -70 and so I loose about 9 dbFS os scaling factor, because I have to use -60 to -80.


Many thanks and greetings from Switzerland
HB9DRT, Jochen


moderated Re: Looking for Airspy Mini on Europe

Roberto Zinelli
 

Do not care if new or used, important more people use and appreciate it.
If one see the performance and quality, they do not look at competition the next time they buy a radio. 


Inviato da OldPhone

Il giorno 05 ago 2017, alle ore 13:09, prog <info@...> ha scritto:

This is definitely not the right place for it.


Re: SpyVerter Routing

Roberto Zinelli
 

Correct! 
Better put the switch outside.

Inviato da OldPhone

Il giorno 05 ago 2017, alle ore 13:07, prog <info@...> ha scritto:

unfortunately

This is a design decision, and a very important one. If you don't want FM BC leaking to your front-end and/or IMD generated by silicon switches, then you need to filter the whole signal path properly.
Coaxial RF switches that can preserve the current performance on HF are not an option, unless you are willing to pay $300 for a converter.


moderated Re: Looking for Airspy Mini on Europe

prog
 

This is definitely not the right place for it.


Re: SpyVerter Routing

prog
 

unfortunately

This is a design decision, and a very important one. If you don't want FM BC leaking to your front-end and/or IMD generated by silicon switches, then you need to filter the whole signal path properly.
Coaxial RF switches that can preserve the current performance on HF are not an option, unless you are willing to pay $300 for a converter.


Re: SpyVerter Routing

jdow
 

It could make a serious difference.

Presuming this is a manual coax switch, routing 2 is likely to be more sensitive. But the downside is a potential for a blown Airspy or Airspy bias-T if the VHF antenna includes a DC short circuit. Even if there is merely a chance that the VHF antenna might short circuit some day you'd have trouble.

If the switch is driven by the bias-T voltage then routing 2 would be better.

{^_^}

On 2017-08-05 03:40, anders@oerts.dk wrote:
Does it matter which routing I choose?
Thanks and best regards
Anders Ørts


Re: SpyVerter Routing

Anders J. Ørts
 

One additional question: Should I untick the Spyverter checkbox in SDR# when I switch to the VHF antenna then? 

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