Nooelec SAWBird H1 LNA and internal switch to 50 ohm resistor

[andrew....@googlemail.com]

I have just received this from Nooelec themselves – I did not realise there are two different barebones Nooelec SAWBird H1 LNAs.

Andy

 

Kayla (Nooelec)

Nov 3, 2025, 15:43 EST

Hello, Andrew. No, I'm sorry. We have the standard model barebones version, not the 50-ohm resistor model.

[Alex P]

A relay before the LNA creates a higher Noise Factor unit. . I see little value in the resistor.

[Marcus D. Leech]

On 2025-11-03 17:33, 'Alex P' via Society of Amateur Radio Astronomers wrote:

A relay before the LNA creates a higher Noise Factor unit. . I see little value in the resistor.

The GaAs switch they use is relatively low-loss, although, not as low as the manufacturer claimed at the time this unit was designed.

You have to balance the higher noise against the functional utility of being able to switch against an ambient-temp terminator.  This is how Dicke-switching
  works, for example.  

On Monday, November 3, 2025 at 4:40:58 PM UTC-5 andrew....@googlemail.com wrote:

I have just received this from Nooelec themselves – I did not realise there are two different barebones Nooelec SAWBird H1 LNAs.

Andy

 

Kayla (Nooelec)

Nov 3, 2025, 15:43 EST

Hello, Andrew. No, I'm sorry. We have the standard model barebones version, not the 50-ohm resistor model.

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[b alex pettit jr]

With temp gain coeffs in the -0.1 dB / 10 dgC for current LNAs,  small dish H Line systems have 'drift'

error sources much greater than this to deal with.

[Marcus D. Leech]

On 2025-11-03 17:51, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

With temp gain coeffs in the -0.1 dB / 10 dgC for current LNAs,  small dish H Line systems have 'drift'

error sources much greater than this to deal with.

You're not wrong.  I was just observing that a relay/solid-state switch in front of the LNA shouldn't be dismissed out-of-hand.  While many deployments of these
  bits of kit are for "smaller" dishes, some are on larger ones, like our 12.8m.  End-to-end instrument design sometimes involves trade-offs.

On Monday, November 3, 2025 at 05:41:16 PM EST, Marcus D. Leech <patchv...@gmail.com> wrote:

On 2025-11-03 17:33, 'Alex P' via Society of Amateur Radio Astronomers wrote:

A relay before the LNA creates a higher Noise Factor unit. . I see little value in the resistor.
The GaAs switch they use is relatively low-loss, although, not as low as the manufacturer claimed at the time this unit was designed.

You have to balance the higher noise against the functional utility of being able to switch against an ambient-temp terminator.  This is how Dicke-switching
  works, for example.  

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[b alex pettit jr]

End-to-end instrument design pretty much always involves trade-offs. 

  

[b alex pettit jr]

[Andrew Thornett]

Hi All,

Interesting discussion on the resistor in some barebones Nooelec's.

So.....after all the tooing and froing can I ask:

1. Does providing a reference sample taken from the antenna side of the coaxial cable and LNA give an improvement over one taken next to SDR?
2. If yes to above, then does the resistor switch in some Nooelec Barebones devices also give improvement over the use of reference sample 3MHz away from the signal frequency as used in ezRA, in spite of the device's limitations already discussed on this group?
3. How about using a coaxial relay switch on the antenna side of the LNA to switch in a 50 ohm dummy load? In the H-Line group meeting yesterday it was suggested this could increase noise? How does it do that? How bad is that? Is it a major problem? Does that increase in noise offset all the benefit of getting a reference signal from next to dish?
4. One other question that came up yesterday is - the SDRplay devices can provide bandwidth 8MHz. If we use that whole bandwidth, does that mean that a reference signal collected from an offset frequency has to be over 8MHz away from 1420MHz? Is 8MHz enough or does it need to be further than that?

Thanks in advance for any answers - and please use very small words for my shrivelled brain!

Andy

Sent from Outlook for Android

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Monday, November 3, 2025 11:30:46 PM
To: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Re: Nooelec SAWBird H1 LNA and internal switch to 50 ohm resistor

 

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[b alex pettit jr]

Why not consider  Post Processing   the data set to correct the drift/shift rather than consuming Time from the H Line Data Acquisition ?

                 Here's an idea that works  its called " Cold Sky Normalization "

=========================================================================================

[Eduard Mol]

My understanding is that the switch to the 50 ohm load is useful for total power/ continuum observation outside the hydrogen line, so if you are looking for broadband sources like Cassiopeia A or Taurus A for example. For those type of measurements having a switch to a 50 ohm load for comparison is very useful for distinguishing between real changes in received broadband radio noise and changes due to gain or temperature variations. I have one of those barebones HI LNAs with the switch option as well to build a Dicke radiometer at some point.

For hydrogen line there is indeed not much added benefit, because a small shift in the background noise level won’t affect your hydrogen measurements all that much and can be easily removed. 

Op di 4 nov 2025 om 11:34 schreef 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

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[b alex pettit jr]

Hello Eduard,

I agree that the technique is most applicable for total power broadband extra-galactic source measurements as You perform.

Small Dish HLine system drift shifts over 24 hrs may be of significantly greater amplitude than the data   ( and of course, Not primarily from  LNA gain changes )

( my data & two other amateur RAers )

Regards,

Alex

=====================================

[Lester Veenstra]

Yes, one  of the uncased units is the same SAW LNA that is in the cased version we usually supply.  

The other uncased version has a RF switch in the fron end that will switch the :LNA input between the antenna and a 50 ohm load (hot termination).  The disadvantage of the switch version is that the rf loss  means it has a higher noise figure.

 

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y W8YCM/6Y 6Y8LV (Reformed USNSG CTM1)

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[Andrew Thornett]

Not the LaNA, Adrian.

I was talking about the Nooelec SAWBird H1 LNA, which it turns out has 3 versions.

1. What Nooelec themselves call the "Retail Version" - the one in a black case.
2. A barebones version with an internal 50 ohm resistor that can be switched in place of the antenna by shorting two pins on the board.
3. Another barebones version WITHOUT said option to switch out antenna and in a resistor instead, which is apparently the only version they currently have in stock, and which can only be obtained by emailing them directly.

Worth saying that it is expected that the retail version will be back in stock soon.

Much of the discussion following my post was about whether (2) above is an old version of (3) and consequently no longer in production.....but Ted has one, so perhaps a cheeky offer to him might get hold of it, for anyone who is interested?

Andy

[Marcus D. Leech]

On 2025-11-04 03:27, 'Andrew Thornett' via Society of Amateur Radio Astronomers wrote:

Hi All,

Interesting discussion on the resistor in some barebones Nooelec's.

So.....after all the tooing and froing can I ask:

1. Does providing a reference sample taken from the antenna side of the coaxial cable and LNA give an improvement over one taken next to SDR?

Yes, quite a bit--FOR CONTINUUM MEASUREMENTS.   Since there are many contributions to gain instability between the antenna and your final
  samples, you want the reference source as close to the antenna as possible.  You want everything "inside the reference loop".

1. 
   
2. If yes to above, then does the resistor switch in some Nooelec Barebones devices also give improvement over the use of reference sample 3MHz away from the signal frequency as used in ezRA, in spite of the device's limitations already discussed on this group?

For spectral observations, Dicke-Switching type scenarios are of limited utility.  Frequency switching is helpful to establish a spectral baseline
  (by determining the baseline passband shape), but it assumes that the pass-band of the receiving setup is the same over a 3Mhz shift.  It sometimes
  isn't.

1. 
   
2. How about using a coaxial relay switch on the antenna side of the LNA to switch in a 50 ohm dummy load? In the H-Line group meeting yesterday it was suggested this could increase noise? How does it do that? How bad is that? Is it a major problem? Does that increase in noise offset all the benefit of getting a reference signal from next to dish?

Any loss IN FRONT of the LNA directly adds tot he overall system noise.   If that relay inserts 0.5dB loss, then there's an additional 0.5dB noise figure
  in the system.  See Friis for receiver noise-chain analysis.  The NooElec barebones with the switch was built with a GaAs switch with very very
  good specs from the manufacturer, but in practice the insertion loss was considerably higher, which is why the "barebones with a switch" doesn't
  offer nearly as good a noise figure as the "retail version".

1. 
   
2. One other question that came up yesterday is - the SDRplay devices can provide bandwidth 8MHz. If we use that whole bandwidth, does that mean that a reference signal collected from an offset frequency has to be over 8MHz away from 1420MHz? Is 8MHz enough or does it need to be further than that?

The idea behind frequency switching is to move away from the spectral lumpiness created by the sky signal--even in "quiet" regions of the sky.
   You only really need to move away far enough to avoid galactic emissions.  The extragalactic emissions (which are red/blue shifted by quite a bit),
  are quite weak, so a short-period integration a few Mhz away will provide a good estimate of the instrumental response, which is what you're
  trying to account for.

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[Andrew Thornett]

This is brilliant - thanks Marcus!

Andy

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[b alex pettit jr]

Andrew, see if this analogy helps :

Alex

====================================================================================================================

Yes, quite a bit--FOR CONTINUUM MEASUREMENTS.   Since there are many contributions to gain instability between the antenna and your final
  samples, you want the reference source as close to the antenna as possible.  You want everything "inside the reference loop".

For spectral observations, Dicke-Switching type scenarios are of limited utility.  Frequency switching is helpful to establish a spectral baseline
  (by determining the baseline passband shape), but it assumes that the pass-band of the receiving setup is the same over a 3Mhz shift.  It sometimes
  isn't.

Any loss IN FRONT of the LNA directly adds tot he overall system noise.   If that relay inserts 0.5dB loss, then there's an additional 0.5dB noise figure
  in the system.  See Friis for receiver noise-chain analysis.  The NooElec barebones with the switch was built with a GaAs switch with very very
  good specs from the manufacturer, but in practice the insertion loss was considerably higher, which is why the "barebones with a switch" doesn't
  offer nearly as good a noise figure as the "retail version".

[Andrew Thornett]

Looks very interesting, Alex. What do the 5 images represent from left to right?

Andy 

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From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

Sent: Wednesday, November 5, 2025 11:12:19 AM
To: sara...@googlegroups.com <sara...@googlegroups.com>

Subject: Re: [SARA] Re: Nooelec SAWBird H1 LNA and internal switch to 50 ohm resistor

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[b alex pettit jr]

The Top 3 Data/Drift Pair shows using an image shift to measure system or sky changes. ( aka the 1423 MHz freq shift 'Dicke-Switch'  technique )

The Bottom 6 Data samples shows that, if the same time duration is used for both Data and Drift frames, 

twice as much Data can be collected in the same time period if a portion of the Image ( Data Freq Spectrum ) is used for calculating corrections 

aka

======================================================================

On Wednesday, November 5, 2025 at 07:34:56 AM EST, 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Looks very interesting, Alex. What do the 5 images represent from left to right?

Andy 

 

[andrew....@googlemail.com]

Gosh – the difference is significant!

 

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: 05 November 2025 12:54
To: 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Re: Nooelec SAWBird H1 LNA and internal switch to 50 ohm resistor

 

 

The Top 3 Data/Drift Pair shows using an image shift to measure system or sky changes. ( aka the 1423 MHz freq shift 'Dicke-Switch'  technique )

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