Re: SDRC and Airspy R2


jdow
 

If he runs the PA at full steam (which is likely to also give the best dynamic range) there is a serious LOT of room for splitters. An 8 way splitter would work adequately. That's 9 dB so there is a room for a 2 dB to 4 dBpad on each output so that you have slightly better isolation. For 4 way split you'd use higher attenuation.

Erm,. I remember the day I decided to look into what happened with AGC circuits on analog circuitry. Every one of them I looked at gave dynamic range issues when the AGC was providing a lot of attenuation. I overdosed on Taylor series expansions. That was one of the worst aw s*t moments of my life - in the same league as when I figured out I could not live with my ex anymore. We were too different. (And now I've figured out that a lot of it is me as an aspergers trying to live with a neuro-typical who totally misunderstood me.)

{^_^}   (Undecided with regards to using diodes as attenuators which was not a thing back then.)

On 20220709 14:49:06, Conrad, PA5Y wrote:

If you do add a splitter it is best to do a system noise analysis; there would be very little point in having a 4 way resistive splitter with a 9dB RX NF connected to it using the LNA example I gave.  Its not difficult to calculate and AppCAD is free. The idea of the attenuator is to set the optimum gain for the conditions/ required sensitivity.

 

It is not totally optimal in terms of SFDR, but it is flexible, and you won’t be far off.

 

Regards

 

Conrad PA5Y

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Siegfried Jackstien via groups.io
Sent: 09 July 2022 22:10
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

that 18 db gain may make a bit deaf receive shine :-) 

or dig out that rare dx signal

or give you enough oumph on the cable to use passive splitters for a handful of receivers without worry about losses (last would be my thinking)

if you only want to do fm dxing then an added filter may help to clean up the receive a bit (and also such a filter plus cabling adds loss)

 

just thinking ;-)

 

dg9bfc sigi

 

Am 09.07.2022 um 20:42 schrieb jdow:

The cheapest one would probably be good enough. The next one up might be slightly better because you get a nice noisy power supply and (possibly redundant) Bias-T tap for it. The most expensive one would only be needed if you have some exceptionally strong signals nearby.

 

18 dB gain may be a little high with only 2.5 dB of cable loss. Something like one of the old HP 1 dB step variable attenuators might be good on the receiver input. Adjust it for a suitable compromise for dynamic range and signal strength. I suspect you do not need this 10V version of the amplifier.

 

(Did I just save you a bunch of money?)

 

{^_^}

 

On 20220709 11:12:30, Simon Brown wrote:

Thanks,

 

I'll start saving and buy a masthead preamp (below). My income is way down now due to COVID and other cost of living issues. Not a great time to be relying on donations.

 

 

They have a bit of input filtering already, don't know if it's enough.


From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of Conrad, PA5Y via groups.io <g0ruz@...>
Sent: 09 July 2022 17:37
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

According to the user manual with the preamp and noise reduction on the MDS at 91.1MHz is -138dBm in 500Hz, which equates to -165dBm/Hz. This is a 9dB noise figure and is probably 3-6dB worse because the NR makes things appear better than they are. If you add 2.5dB to that noise figure you can see that an LNA will be of great benefit.

 

I suggest that a system noise figure of around 2-3dB is optimum for Band II DXing.

 

Regards

 

Conrad PA5Y

 

 

 

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Simon Brown via groups.io
Sent: 09 July 2022 17:29
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

Hi,

 

What's the S3 noise figure on Band II ? I have maybe 2dB loss in the 25m RG6, so am wondering what the total NF is.


From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of Conrad, PA5Y via groups.io <g0ruz@...>
Sent: 09 July 2022 16:06
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

BTW I put the BPF before the LNA to help protect it from 144MHz EME high power. I am not suggesting that a PGA103+ will saturate from normal Band II situations. However, it has a little bit too much gain, so a good filter and an attenuator does no harm. The S3 really is excellent. Just like you said 😊

 

73

 

Conrad PA5Y

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Conrad, PA5Y via groups.io
Sent: 09 July 2022 17:01
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

Hello Simon, I have done a noise analysis and you WILL benefit from an LNA. I have a PGA103+ preceded by a band pass filter and it seems to work very well. However, I am still waiting for a bigger antenna. I ordered an OPTDES which never arrived. So, I will ask a few of the local Band II DXers for an alternative.

 

73

 

Conrad PA5Y

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Simon Brown via groups.io
Sent: 09 July 2022 13:22
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

FWIW,

 

The ELAD S3 is the best Band II receiver I have. Am thinking about a preamp on the mast for those very weak stations - if I get close to receiving weak signals from across the pond (USA, Canada).


From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> on behalf of George Stein - NJ3H via groups.io <nj3h@...>
Sent: 09 July 2022 08:08
To: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
Subject: Re: [SDR-Radio] SDRC and Airspy R2

 

Simon and others,

 

I have attached 3 pictures all with Console running.

 

Elad S2,

Airspy R2

RSPdx

 

 

The RSPdx is the only on of these three that has a decent signal. Running uno is fine also.

 

It is the other two that are causing problems.  The native software yields the same lousy signals.  There is a lot of noise on these two receivers for the station in question. I have fiddles with the R2 slide controls in both Sharp and Console. The Elad appears not to have any RF gain capability.

 

The frequency I am using for this exercise is 98.9, 92 watts, 25 km away.  I am using the same antenna for all three radios.  The antenna is pictured in an attachment. Same feed line to all three radios. My HF+ Discovery works fine also.

 

As I said in a previous message, the Elad S2 is the one that really puzzles me.  I would have expected it to come out the best (based only on price, that is).

 

Anyway, please let me know if more information is needed.

 

Thanks for looking into this.

 

Regards,

George

 

 

 

On Friday, July 8, 2022 at 11:38:57 PM PDT, jdow <jdow@...> wrote:

 

 

Frequency?

{o.o}

On 20220708 14:47:30, George Stein - NJ3H via groups.io wrote:

92 watts not 25.

On Fri, Jul 8, 2022 at 2:24 PM, George Stein -  NJ3H via groups.io

<nj3h@...> wrote:

Further to my last message.  The station in question is 25 km away and running a mere 25 watts. 

Using SDR Console:

With the Elad S2 and and the Airspy R2, the reception was very noisy.

With the Airspy HF+ Discovery and the RSPdx, the signal was full quieting. With the edge going to the HF+ Discovery.

This was not a scientific test, just a casual observation. The only thing I am surprised about was the Elad S2 performance.

I then used the native software for each device and had the same results.

Regards and YMMV,
George


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