HF+ Discovery use for 2m satellite downlink receive use - experiences ? #airspydiscovery


Alex P
 

I am interested in the 2m satellite receive experiences of any users of the Airspy HF+ Discovery hardware.  Prior purchase inquiry.

My current 2m satellite receive system is a variety of available antennas: 5 element yagi, 2 el crosspolarized yagi,  2 el circular loop 'yagi',  eggbeater, discone/  helical filter / LNA / downconvertor /  RFSpace Cloud IQ  (-137 dBm) / Simon's SDR Console tracking software.   

I am considering the Airspy Discovery (-141 dBm) with the better sensitivity specs to enhance my current RX capability. 

Wondering if  and what experiences users of this hardware might share in my 2m application ??   EME usage ??    
TIA.


Hasan Schiers N0AN
 

Alex,
I'm using an Airspy HF+ dual port on 2m for satellite work. It does require a decent preamp in front of it. I am running an ARR GAsFET (0.5 dB NF) and it works very well.

My satellite station uses SDR Console v. 3.x

Interlaced Yagi: 5 EL on 2m, 8 EL on 70cm
Tx: TS-2000
Rx: HF+ with ARR preamp
Fed with 1/2" hardline
Fixed elevation 15 deg

No elevation rotor is needed for LEO birds. Linear polarization works fine, either vertical or horizontal. So I'm running fixed uptilt of 15 deg, vertical polarization (works with moderate gain antennas, do not use a really high gain antenna or it won't have a wide enough 3 dB beamwidth to make the fixed elevation trick work)

Pix and description on my QRZ page
73, N0AN
Hasan


On Tue, Dec 29, 2020 at 12:14 PM Alex P via groups.io <winston376=yahoo.com@groups.io> wrote:
I am interested in the 2m satellite receive experiences of any users of the Airspy HF+ Discovery hardware.  Prior purchase inquiry.

My current 2m satellite receive system is a variety of available antennas: 5 element yagi, 2 el crosspolarized yagi,  2 el circular loop 'yagi',  eggbeater, discone/  helical filter / LNA / downconvertor /  RFSpace Cloud IQ  (-137 dBm) / Simon's SDR Console tracking software.   

I am considering the Airspy Discovery (-141 dBm) with the better sensitivity specs to enhance my current RX capability. 

Wondering if  and what experiences users of this hardware might share in my 2m application ??   EME usage ??    
TIA.


Alex P
 

Thank you Hasan.  What you are doing is what I want to do....get away from rotors.     
Question:  What LEO RX levels are you experiencing...dBFS  ?  


Hasan Schiers N0AN
 

First of all, I did not say get away from rotor(s)....plural. I said get away from an elevation rotor, singular. You still need an azimuthal rotor. There is no omnidirectional antenna setup for either rx or tx that is going to rival a small yagi. (5 El or 10 dBi gain).

I have a pair of M2 Eggbeaters and they are fine for high elevations (way high > 60 deg), but not even remotely comparable to the 5 EL yagi for everything less than 60 deg.

On my setup with 10 dBi gain antenna on rx, I see the satellite passband noise. That is the goal, if you can't see the noise of the passband itself (that is the base noise that the satellite is transmitting with NO input signal from a station), your receive setup is not optimal. When you can see that consistently, you have a signal to noise ratio (SNR) of approximately 30 dB. That is the dynamic range limit of the satellite system itself. That is the goal. (this is for linear birds (ssb/cw), not FM birds.

As far as what I see:

Calibrated to -120 dBM for a 50 ohm resistor:

My noise floor with an antenna connected is -112 dBM

The CW beacon is -80 dBM. No signal should EVER exceed the strength of the CW beacon, because downlink power is shared and we have to have signals into the birds approximately the same strength to share the available downlink power equally.

Most signals I see are > 20 dB SNR and quite a few are nearly 30 dB SNR. You will not consistently achieve these rx levels without a steerable yagi, and a preamp, and low line losses,  period.

I am also running 1/2" hardline for my feedline, which most people do not. More reason to have yagi gain. Then there is noise, which can be reduced by the directionality of the yagi. The omni antennas pickup noise from every direction. Not great.

So, bottom line:

1. A light duty rotor, if you are going to turn the antenna by hand. or a rotor with a connection for computer control.

2. Yagis with not much more than 10 dBi gain on both rx and tx

3. Low feedline losses to the antenna. LMR-400 coax at the minimum (unless length is really short). DO NOT USE LMR-400 to go around the rotor, insert a more flexible coax to go around the rotor or you will snap the LMR-400 solid center conductor from metal fatigue.

4. A low noise preamp, in the shack is ok, if line losses are kept down, but a preamp is important. I have tested the Arispy HF+ dual port carefully, and it clearly needs the preamp.

How can I tell if I am receiving as well as I should?

1. Can you consistently see/hear pass band noise (a hump of noise above the noise floor,the width of the satellite passband, typically 20 kHz wide) If so, you can't get any better. If not, there is work to do, but if you see it 50% of the time or more, you are pretty good.

2. Do you see an increase in noise floor when you connect an antenna? Do this experiment:

a. Put a 50 ohm resistor on your rx setup in place of the antenna.
b. If no resistor, leave it open circuit
c. Look at the noise floor in dBm. Listen to the noise level with your ear.
d. Connect an antenna: Does the noise jump up. If it doesn't come up dramatically (at least 3 to 6 dB), then your rx system is not adequate.
e. If it jumps way up, then your local ambient noise is very high and you are going to have trouble hearing satellites no matter how good your preamp is. A better yagi will help, but by the time you get enough gain to sideline the noise, you may have defeated the "no elevation rotor" goal because your antenna pattern has become too low.

So, now you can test your system. 
1. Satellite sigs should be at least 20 dB above your noise floor much of the time and many should approach 30 dB SNR
2. How many dB of ambient noise does putting your antenna on produce.

Hope this helps. 73, N0AN
Hasan


On Wed, Dec 30, 2020 at 11:17 AM Alex P via groups.io <winston376=yahoo.com@groups.io> wrote:
Thank you Hasan.  What you are doing is what I want to do....get away from rotors.     
Question:  What LEO RX levels are you experiencing...dBFS  ?  


Alex P
 

Thanks for clarifying the rotor matter and the additional detailed info....appreciate it.

My set up includes an azimuth rotor and no elevation rotor...yagi fixed at about 20 degrees elevation  primarily due to trees, 65 ft powerlines etc. (low ground install). 

I am surrounded by a suburban and industrial area and the EMI is pretty bad here. Being in the LA area, the high power FM / TV broadcasters also adds challenges, hence the helical filter, which does help significantly.

As for  your calibration comment...I use the same method:  50 Ohm load and adjust the cal level on the CloudIQ and SDR-IQ.   

Question:   I did some research of the comments here regarding the HF+Discovery and the differing views of dBm  vs dBFS  etc.    Having done professional MIL-STD-461 / RF engineering and testing (etc.) I am very comfortable with dBm, dBW, dBuv, dBuA, dBuV/m,  etc.    Raw noise floor measurements are very important to me.    I was under the impression   that the Airspy Discovery hardware/software does not allow direct reading in dBm.  If I am mistaken, let me know, otherwise are you able to read dBm directly  ?  Is there a calibration section  ?  Otherwise, I'm postulating that are you doing math to determine the dBm values which are based on the dBFS reading ?

TIA


jdow
 

AirSpy HF+ (Discovery) does not have a gain adjustment per se. It is designed to work with its AGC on. So even the dBfs concept is not necessarily meaningful since the gain will vary. If you step backwards and turn off the AGC, you then get "0..48 dB Attenuation with 6 dB steps". (copied from the software API file.)

{^_^}

On 20201230 17:00:43, Alex P via groups.io wrote:
Thanks for clarifying the rotor matter and the additional detailed info....appreciate it.

My set up includes an azimuth rotor and no elevation rotor...yagi fixed at about 20 degrees elevation  primarily due to trees, 65 ft powerlines etc. (low ground install). 

I am surrounded by a suburban and industrial area and the EMI is pretty bad here. Being in the LA area, the high power FM / TV broadcasters also adds challenges, hence the helical filter, which does help significantly.

As for  your calibration comment...I use the same method:  50 Ohm load and adjust the cal level on the CloudIQ and SDR-IQ.   

Question:   I did some research of the comments here regarding the HF+Discovery and the differing views of dBm  vs dBFS  etc.    Having done professional MIL-STD-461 / RF engineering and testing (etc.) I am very comfortable with dBm, dBW, dBuv, dBuA, dBuV/m,  etc.    Raw noise floor measurements are very important to me.    I was under the impression   that the Airspy Discovery hardware/software does not allow direct reading in dBm.  If I am mistaken, let me know, otherwise are you able to read dBm directly  ?  Is there a calibration section  ?  Otherwise, I'm postulating that are you doing math to determine the dBm values which are based on the dBFS reading ?

TIA


Hasan Schiers N0AN
 

Hi Alex,
This is rule-of-thumb ham stuff, to help you get the Airspy HF+ to work well with satellites, not an RF engineering study. The results of what I have described are quite useful for what I thought was your initial request, 'how well does the HF+ work for satellites?' .  For some to  dismiss as meaningless, the procedure because of AGC interference, is throwing the baby out with the bathwater.  The procedure outlined does lack precision, but it does not lack meaning or usefulness.   The measurements are not remotely accurate in the absolute, nor did I intend to represent them as such, but they are perfectly adequate for relative purposes.  AGC or not, the measurements respond to real-world signal level changes in a realistic manner, which makes them both useful and meaningful.

Used with a decent piece of software like SDR Console v3.xx, once calibrated to an arbitrary level, it is not difficult to make relative measurements in dB and that's what counts. I cannot emphasize enough, if you are going to work satellites with an SDR, use SDR Console software. I have seen nothing else available that doesn't seem like a  toy compared to SDRC.

We have made hundreds of comparisons between the FunCube Pro + and the HF+, as well as the RTL and SDRPlay series. When similarly calibrated the results were well within the tolerance needed to make decisions about antennas, preamps, satellite shading, polarity changes and other things that affect the received signal level.. IOTW, if we changed antenna gain, we observed the expected change, within reason. If we changed power levels, we observed that kind of dB change expected, within reason.

There are tons of variables that affect the observed signal levels when using an SDR for satellite work.  What I have described will get you in the ballpark in terms of how well you will hear satellites, and what signal levels you might expect, and the effect of any changes you might make with your system, which I thought was the original question, 

My purpose, in this case, was to explain how to set up a 'no test equipment' procedure that would help you evaluate the effectiveness (for amateur purposes) of your satellite station. 

If that is not what you needed, then toss what I've written. If I had known you wanted engineering level detail and accuracy, I would not have replied to your request, as I have no RF Engineering qualifications. 

p.s., another thing you are going to need is a 2 port duplexer as a 2m rx filter. If you don't use a duplexer as a 2m filter, you are likely to experience terrible desense and intermod with the HF+

The Comet CFX 514J (triplexer in this case, with a 50 ohm load on the unused HF port), works nicely.

Good luck, have fun. Hope to see you on the birds, 73, N0AN

Hasan


On Wed, Dec 30, 2020 at 7:01 PM Alex P via groups.io <winston376=yahoo.com@groups.io> wrote:
Thanks for clarifying the rotor matter and the additional detailed info....appreciate it.

My set up includes an azimuth rotor and no elevation rotor...yagi fixed at about 20 degrees elevation  primarily due to trees, 65 ft powerlines etc. (low ground install). 

I am surrounded by a suburban and industrial area and the EMI is pretty bad here. Being in the LA area, the high power FM / TV broadcasters also adds challenges, hence the helical filter, which does help significantly.

As for  your calibration comment...I use the same method:  50 Ohm load and adjust the cal level on the CloudIQ and SDR-IQ.   

Question:   I did some research of the comments here regarding the HF+Discovery and the differing views of dBm  vs dBFS  etc.    Having done professional MIL-STD-461 / RF engineering and testing (etc.) I am very comfortable with dBm, dBW, dBuv, dBuA, dBuV/m,  etc.    Raw noise floor measurements are very important to me.    I was under the impression   that the Airspy Discovery hardware/software does not allow direct reading in dBm.  If I am mistaken, let me know, otherwise are you able to read dBm directly  ?  Is there a calibration section  ?  Otherwise, I'm postulating that are you doing math to determine the dBm values which are based on the dBFS reading ?

TIA


Alex P
 

Hi Hasan. 

  No worries here...also no criticisms either.  You have given me many 'Golden Nuggets' of info  and I greatly appreciate it.   

 My original questions were certainly in the sense of ham radio and I would be very foolish, if not deluded, to expect that the subject hardware would be equivalent or near equivalent to an  HP/Agilent/Keysight/Rhode  EMI receiver. 

 I agree, as you say in your prior post, we can make reasonable relative performance measurements of antennas etc., and that is the process I use as well.

    Your duplex suggestion for the HF+ is also another 'Golden Nugget'. 

Thanks! 
Alex