Re: Elad S3 versus Perseus and FDM Duo


jdow
 

What about the stages that follow? They are also stages that can limit dynamic range. (The most effective trick for the noise figure increase and dynamic range decrease was calculated years ago for CATV systems. It's a gain of "e", the transcendental number. That is not the best from an economic standpoint, though. My spare time ham hacks through the 70s involved a lot of playing with noise figure, dynamic range, and receiver design to maximize this. It, too, falls victim to, "There Ain't No Such Thing As A Free Lunch." Every stage you add reduces dynamic range for frequencies that manage to pass through the stage. That was a pain in the panties for the S3A sonobuoy receiver given its architecture. Fortunately their dynamic range requirement as not at science fiction levels.

And, yes, 6 meters is fairly noisy. By 60s and even 70s standards the noise figures we get by default were considered exotic and low. Pushing for tiny noise figures (<1dB) on 2 is sort of pushing reality a little bit, and can really cost you with dynamic range.

{^_^}

On 20220330 00:55:47, Conrad, PA5Y wrote:

I completely disagree.

 

If you have an LNA that will not overload and has sufficient headroom you can use a step attenuator after the LNA to ensure that the input levels to the subsequent stage are appropriate for the conditions. For EME you are concerned with sensitivity.  During a summer Es opening in Europe you will need to reduce sensitivity and accept a small noise figure hit. It is the best way to handle these enormous variation in signal levels. What I do not want is to take the hit in noise figure due to cable loss before the receiver.

 

This is not HF and the sensitivity is always the primary concern.

 

The dynamic range for VHF in EU means that dynamic range is certainly not optional. I put systems together based upon total system analysis which includes both noise figure and dynamic range. On 2m with a 1dB NF which is a little better than needed for terrestrial operation in my semi-rural location. The system dynamic range is 101dB on 2m when I use either my K3S or TS-890. I expect it will be 2-3dB worse with the Elad FDM-S3. However for 2m this is still very good.

 

On 6m the noise figure does not need to be that good even for EME due to sky temperature.

 

73

 

Conrad PA5Y

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of jdow via groups.io
Sent: 30 March 2022 09:18
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Elad S3 versus Perseus and FDM Duo

 

A step attenuator plus LNA is not much of a solution for anything as it guarantees you a loss of dynamic range even for the no net change in noise figure case. It must be nice to live where dynamic range is optional.

{o.o}

On 20220329 06:43:54, Conrad, PA5Y wrote:

OK Simon.

 

I’m convinced.

 

My only comment would be that I do not use MDS as a metric as I always use an external preamp to set the system noise figure. Even on 6m where I sometimes do EME. While the NF requirements are quite low on 6m using an LNA allows the use of splitters for my transceiver and SDRs and also finding a sweet spot for any situation. It is easy to make a very high IIP3 LNA for VHF these days, just add enough gain to overcome cable/splitter losses and the receiver noise figure. During big Es openings I typically add 6-12dB attenuation, but this covers all eventualities. A step attenuator in the RX path is an essential accessory, does not matter if it is internal or external to the radio.

 

I must admit that I trust Elad and the photos of the innards of the FDM-S3 look very well implemented.

 

So I will buy one. 😊

 

I just remembered that I have a spare transverter for 2m so the downconverter may not be necessary, I will wait and see what Elad offer.

 

Regards

 

Conrad PA5Y

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Simon Brown via groups.io
Sent: 29 March 2022 15:27
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Elad S3 versus Perseus and FDM Duo

 

Also,

 

I would just add that the S3 is a class product.

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Simon Brown
Sent: 29 March 2022 14:23
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] Elad S3 versus Perseus and FDM Duo

 

My 10 pence:

 

1.       I assume that you cannot overlap the VHF and HF ranges, you select one or the other?
Correct

2.       I see several VHF ranges in the manual, one of which is 108-147MHz under sampled at 98.304MHz, so for 2m I just need a good external band pass filter before the VHF input, correct? Of course I will need sufficient gain to make up for the relatively high noise figure, this is easy.
I think so but there’s a big downconverter coming – suffering from unobtainable parts atm.

3.       On HF how does it compare to the Perseus, especially with respect to dynamic range. I have always found the Perseus to be almost good enough, another 3dB would be enough
It’s excellent. Can’t give you any figures, but FWIW I think the Airspy Discovery has better MDS than Perseus. Perseus is good but we do have better now.

4.       How does the FDM-S3 compare to the FDM-DUO, I owned one and it was not as good as I expected based upon user feedback. However it would make a fine uwave transverter driver. I probably should have kept it.
NO comment really – I use the DUO on HF and to drive 4m / 2m / 70cms Q5 Signal transverters, BDR at least 110 dB. For microwave there’s always the Pluto with preamp etc.

5.       If I like it I may buy a second one,  to cover 50MHz and MUF duties simultaneously, it all boils down to dynamic range

 

 

Simon Brown, G4ELI

https://www.sdr-radio.com

 

From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io> On Behalf Of Conrad, PA5Y
Sent: 29 March 2022 12:58
To: main@SDR-Radio.groups.io
Subject: [SDR-Radio] Elad S3 versus Perseus and FDM Duo

 

I am seriously thinking of buying an Elad FSM S3. At first I was going to buy an ANAN-7000DLE but then I thought about it. The ANAN delays are variable and I don’t really need a transceiver. What I need are receivers.  I see the Elad being useful for tracking the MUF during the Es season and also creating multiple receivers connected to different instances of WSJT-X on 6m

 

A few questions to those who have them.

 

1.       I assume that you cannot overlap the VHF and HF ranges, you select one or the other?

2.       I see several VHF ranges in the manual, one of which is 108-147MHz undersampled at 98.304MHz, so for 2m I just need a good external band pass filter before the VHF input, correct? Of course I will need sufficient gain to make up for the relatively high noise figure, this is easy.

3.       On HF how does it compare to the Perseus, especially with respect to dynamic range. I have always found the Perseus to be almost good enough, another 3dB would be enough

4.       How does the FDM-S3 compare to the FDM-DUO, I owned one and it was not as good as I expected based upon user feedback. However it would make a fine uwave transverter driver. I probably should have kept it.

5.       If I like it I may buy a second one,  to cover 50MHz and MUF duties simultaneously, it all boils down to dynamic range

 

I assume that on 6m I can easily create what Flex call ‘slices’. For instance I use a 1536kHz sample rate and I can create multiple receivers, 2 attached to WSJT-X for FT8 and one for 50.110 for example.

 

73

 

Conrad PA5Y


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