Is it optimal - BPF closer to SDR than LNA & Antenna

[Anthony]

Hi SARA Members,

I know the LNA needs to be close to the antenna, is it optimal to have a cavity band pass filter (BPF) closer to the SDR, about 15.24 meters or 50 feet away from the LNA & antenna?

Trying to configure the system with less electrical components exposed to the environment. 

[Marcus D. Leech]

Assuming that your LNA has built-in filters (like the SawBird+ H1), you may not need any filtering after that.   But, yes, it's
  fine to have a secondary BPF right next to the receiver in that situation.   The critical part is having the LNA up-close-and-personal
  with the feed.

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[Anthony]

Hi Marcus!

The LNA is the Kuhne LNA 1350 - 1450 MHz. I'm only using one cavity BPF, that's the reason for my question. If the BPF needs to be placed next to the LNA. 

I did think about adding in a second BPF, but for now, after taking down the current BPF & LNA, the Western LNA assembly had some water inside the fishing tackle boxes. Maybe from condensation. 

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[Marcus D. Leech]

On 14/10/2023 19:19, Anthony wrote:

Hi Marcus!

The LNA is the Kuhne LNA 1350 - 1450 MHz. I'm only using one cavity BPF, that's the reason for my question. If the BPF needs to be placed next to the LNA.

Presumably you had the BPF on the *output* of the LNA, after plenty of gain, so it could easily be "in the shack".

I did think about adding in a second BPF, but for now, after taking down the current BPF & LNA, the Western LNA assembly had some water inside the fishing tackle boxes. Maybe from condensation.

Yeah, so, your plan to reduce the amount of electronics that is weather-exposed is a good one.

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[Anthony]

Yes, on the output of the LNA. 

If that is feasible, then the PVC pipe may work on each dish, instead of the fishing tackle boxes, which are bulky. 

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[Anthony]

I'll build something similar to your PVC setup Marcus. 

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[Alex P]

The key to all of this is the Noise Figure for Passive Components ..

Once you are on the output side of the first LNA, all effects of passive attenuation loss dB = additional Noise Figure dB

 are reduced by the gain of the LNA ..( and additional gain stages )

The noise factor contributions of each stage in a chain follow this equation:

Friis equation

https://www.microwaves101.com/encyclopedias/noise-figure

Alex

[bsn...@gmail.com]

Somewhat off-topic but not by much.

Between the SDR in the house and the LNA is about 20m of 6X coax. I've wondered about putting a broadband amplifier about mid-point on the coax. Any have any thoughts???

Anthony, I use plastic a storage box for the LNA right at the antenna but my 3-D corner reflector makes it easy. Aluminum tape on the outside keeps it cool...Winter temps are another problem. Two tiny "weep" holes keeps it dry.

....bill....

[Marcus D. Leech]

On 15/10/2023 11:00, bsn...@gmail.com wrote:
> Somewhat off-topic but not by much.
> Between the SDR in the house and the LNA is about 20m of 6X coax. I've
> wondered about putting a broadband amplifier about mid-point on the
> coax. Any have any thoughts???

Depends on the gain of the LNA.  At the CCERA observatory, we use
SawBird+ H1 LNAs, and with the ~40dB gain of the
  SawBird, we can drive 15m of coax without any issue, into our USRP
X310 + TwinRX  receiver setup.  Your receiver
  may/may-not need a bit more gain ahead of it.

For longer runs, like we had at our previous observatory site, I used
broad-band SatTV inline amplifiers half-way along the run.

[Anthony]

Thanks, Bill! 

I'm experimenting by submerging PVCs, containers in water to see which handles moisture the best, but of course there's condensation and as you mentioned the winter season. 

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[Marcus D. Leech]

On 15/10/2023 12:27, Anthony wrote:

Thanks, Bill! 

I'm experimenting by submerging PVCs, containers in water to see which handles moisture the best, but of course there's condensation and as you mentioned the winter season.

Yeah, usually when you find water inside a container that "gee, I thought I sealed it well" it's due to "cryo-pumping", drawing
  water vapor into the enclosure, where it condenses, and never leaves.  That's pretty-much what happened to the box-section
  on the azimuth yoke on our big dish.

The "fix" is usually to drill a couple of small holes in the enclosure that preclude the pressure-difference that encourages
  cryo-pumping.  Have the holes arranged so that they, on average, face the ground, and never face "up".

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[Anthony]

Marcus, 

With the use of broad-band SatTV inline amplifiers along the run, what about the SNR performance, wouldn't those low end inline amps cause possibly more input return loss, signal integrity and induce more noise in the system? 

Could you use a Cavity BPF to increase the Q-factor ( high-quality) of the signal and selectivity?

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[Anthony]

Appreciate that Marcus! 

I do remember other SARA members mentioning that as well. Maybe the reason for the Western dish LNA assembly had moisture, not enough holes perhaps. 

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[Marcus D. Leech]

On 15/10/2023 12:43, Anthony wrote:

Marcus, 

With the use of broad-band SatTV inline amplifiers along the run, what about the SNR performance, wouldn't those low end inline amps cause possibly more input return loss, signal integrity and induce more noise in the system? 

Could you use a Cavity BPF to increase the Q-factor ( high-quality) of the signal and selectivity?

Those broad-band line amplifiers are optimized for higher linearity, and not for low-noise.  But modest amounts of noise added
  *AFTER* a bunch of low-noise gain ahead doesn't contribute very much to overall Tsys (or, in the telecom world,
  SNR degradation).    Adding a BPF after an already filtered LNA might help with very-strong out-of-band signals being
  delivered to your radio.   But if they're that strong, they probably have also caused non-linearity at the very first gain stage.
  Won't do any harm.  But don't expect miracles if your LNA is already filtered.

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[Anthony]

Thanks, Alex,

Not to mention output of the LNA, introducing cables, the right BPFs to reduce low insertion. My reason for also looking at Cavity BPFs with low insertion to help maintain a high SNR. 

Unlike the Cavity BPF and LNAs I'm using today, there is a low SNR on the Western dish, not sure if the LNA may have gotten wet or fried from the sun.

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[Anthony]

As you said Marcus, the universe moves slowly, and I need to take my time designing my system.

Every component I'm looking at carefully, I even wish I had painted the two, 3-meter mesh dishes white to keep the heat from the sun down but I'm unsure if that would contribute to any thermal expansion and  cause the dish alignment shape to change. 

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[Marcus D. Leech]

On 15/10/2023 12:54, Anthony wrote:

As you said Marcus, the universe moves slowly, and I need to take my time designing my system.

Every component I'm looking at carefully, I even wish I had painted the two, 3-meter mesh dishes white to keep the heat from the sun down but I'm unsure if that would contribute to any thermal expansion and  cause the dish alignment shape to change.

If you were doing mm-wave experiments, that would be a concern.  But not at these wavelengths.

White has the added inconvenience that you get some IR reflected from the dish and presented at the feedpoint :( :(

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[Anthony]

Oh, I did not know about IR and painting the dish white. 

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[b alex pettit jr]

Two Options :

White : IR reflection but a  physical temp ~= air_temp

Black :  no IR reflection (?)  but a surface temp up to 30 dgC higher

??

[bsn...@gmail.com]

Thanks Marcus. I'm also using the SawBird LNA and can't imagine an extra 5m will make much of a difference. FYI, the nominal impedance of the 3D corner reflector is 72 ohms but modeling shows that a passive director element properly placed lowers it to about 50 ohms which matches the SawBird. May help a little bit.

Hi Anthony, winter condensation here in Maine is not that much of a problem :-) but keeping it warm is. So far a bit of loosely wrapped heavy black plastic seems to help.Fortunately, I don't get the temperatures Marcus does.

As always...thanks....bill...

[Marcus D. Leech]

Amusing(??) story.

When DRAO started working on their Next-Gen Solar Flux Monitor project several years ago, they got a 6M antenna,
  and painted it flat white with relatively-ordinary flat-white paint.

They built a lovely multi-wavelength feed assembly, electronics box, enclosure, all at the feedpoint.  On the first test,
  the enclosure melted.  They had to find a paint that did a better job of more-random scattering at IR wavelengths.
  Ended up with a paint that had very-small glass beads in it as I recall, with a light-grey paint colour.

Now, granted, in *their* application, they *track the sun for hours at a time*.   For us, that would be an only-incidental
  occurrence.

[Lester Veenstra]

Before you do that, when you turn the SDR antenna bias off and on (power to the LNA), how many dB does the noise floor change,  in the area of the H Line frequency?

 

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

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

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[Anthony]

On my solar telescope, I used high temperature paint, rated at 648.89 Celsius

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[Anthony]

That is an interesting story Marcus!

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[fasleitung3]

Hi Anthony,

with the Kuhne LNA you will have ~ 33 dB of gain with a nominal noise figure of 0.4 dB. Subsequent loss due to the cable and the filter will contribute to the overall noise figure only by a small amount as explained by Alex in his post. This is true unless your cable loss gets really large. It does not matter in which sequence the loss from cable and filter occurs, so you need not to have the filter right after the LNA. There may even be a potential advantage to have the filter at the end of the cable: Signals outside the passband of the cavity filter are reflected. So if there is a significant amount of out of band signal this will be reflected back to the LNA. If there is a cable between the LNA and the filter, this reflected signal will be attenuated by the cable and thus is less likely to have an impact on the LNA. I should point out though, that this scenario is only of concern if there is really lots of out of band signal.

We have set up a telescope for a university which uses exactly what you are planning: Kuhne LNA direct at the feedhorn, then cable and then a cavity filter in front of the SDR.

Best regards and good luck with your setup,

Wolfgang

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[Anthony]

Hi Dr. Wolfgang!

Thank you! 

I plan on setting the system up by month's end.

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[B & MR Randall]

Anthony and all,

I have seen a preamp that was unstable with a filter directly on its output.  This was  due to reflections from the filter at out of band frequencies.  A small cable loss between the preamp and filter made it stable.  This was a 144MHz preamp that would oscillate at 4GHz.  A meter or so of RG58 cable had negligible loss at 144MHz but enough to stabilize things at 4GHz.  Modern preamps are much more tolerant of odd load impedance off frequency.

 

Another advantage of the filter inside is that it is not exposed to weather or temperature changes.  The filters tuning and loss will change with temperature and possibly affect observations.  Put the filter inside.

 

Looking forward to your shared observations when all is together and working.

 

Bruce Randall

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[Anthony]

Hi Bruce! 

Thank you! 

That may have been one of the issue with my old setup. 

The BPF was connected directly to output on N-type connector of the LNA (no cable between). This may or may have caused issues but there was always oscillations from both LNAs and poor SNR, randomly from either dish sides. 

We'll  see what happens in the coming weeks.  Thank you again everyone for the tremendous support!!

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[Anthony]

Big thanks to Alex for tremendous support on walking me through  building the replacement feedhorn or cantenna's. 

Thanks again, Alex!!

There is still some clean up one to do.

Screen shot attached.

On Mon, Oct 16, 2023, 5:21 AM B & MR Randall <bran...@comporium.net> wrote:

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[Anthony]

The VNA results from one Cantenna.. attached.

On Mon, Oct 16, 2023, 5:21 AM B & MR Randall <bran...@comporium.net> wrote:

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[Marcus D. Leech]

On 16/10/2023 05:43, Anthony wrote:

Big thanks to Alex for tremendous support on walking me through  building the replacement feedhorn or cantenna's. 

Thanks again, Alex!!

There is still some clean up one to do.

Screen shot attached.

Not sure I fully understand how those things are made.  Aluminum inside, but with HVAC pieces as a kind of scaffold?
  What's the "hat" on top?

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[b alex pettit jr]

Slices from two 6" dia cake pans & two layers of al flashing.

On Monday, October 16, 2023 at 09:22:31 AM EDT, Marcus D. Leech <patchv...@gmail.com> wrote:

Not sure I fully understand how those things are made.  

Aluminum inside, but with HVAC pieces as a kind of scaffold?

  What's the "hat" on top?

.

[Marcus D. Leech]

On 16/10/2023 05:43, Anthony wrote:

Big thanks to Alex for tremendous support on walking me through  building the replacement feedhorn or cantenna's. 

Thanks again, Alex!!

There is still some clean up one to do.

Screen shot attached.

Curious what was used to slice the cake-pans so nicely.

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[Alex P]

In the process of identifying a more " finger friendly "  approach to slicing the cake pans.

[b alex pettit jr]

A Safer Way to Slice Cake Pans

Turn the lathe chuck slowly by hand ( lathe unpowered ) .  Take several shallow cuts

Use  spacers between the chuck jaws & pan so as to better grip the cake pan ,

distribute clamping load &  to keep a distance between the saw teeth & chuck jaws .

I used 2 plastic feet / jaw

Worst case : the motor on the Dremel Tool stops from overloading...

...  slower, but  " finger safe "

Alex

[Anthony]

Very nice Alex!

That looks way more safer. 

I've ordered two more cake pans, for a newly acquired 180 centimeter dish, I plan to motorize (AZ/EL) this dish, it's a solid dish. 

I'm going to try something different with these cake pans and the aluminum flashing I've purchased again. 

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[Marcus D. Leech]

On 17/10/2023 20:47, Anthony wrote:

Very nice Alex!

That looks way more safer. 

I've ordered two more cake pans, for a newly acquired 180 centimeter dish, I plan to motorize (AZ/EL) this dish, it's a solid dish. 

I'm going to try something different with these cake pans and the aluminum flashing I've purchased again. 

Nice!

My first RA dish at my farm, back in the day, was a stamped-steel one, just like your new toy.  Smaller, but same kind of thing.

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[Anthony]

Lol, you called it Marcus, my toy! Haha! 😀

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[Anthony]

Hopefully it will survive the strong wind at times in Roswell, GA... 

On Tue, Oct 17, 2023 at 9:07 PM Marcus D. Leech <patchv...@gmail.com> wrote:

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[Anthony]

In addition, I wasn't sure about my current Cavity BPFs and decided to replace those as well with the link you provided Alex, to Mini-Circuit. I've checked the data sheets and specs on these Cavity BPFs, they look promising, and decided to order them a few days ago.

Arrival is tomorrow.

• Low Insertion loss
• Input Return Loss
• VSWR
• 1415 - 1425 MHz - 50 Ohms 
• N-Type connector 

https://www.minicircuits.com/WebStore/dashboard.html?model=ZVBP-1420-N%2B

On Mon, Oct 16, 2023 at 12:21 PM 'Alex P' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

In the process of identifying a more " finger friendly "  approach to slicing the cake pans.

Curious what was used to slice the cake-pans so nicely.

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[b alex pettit jr]

Hello Anthony,

I am uncertain of the requirement for this expensive filter. 

With a  digital SDR System providing the 'selectivity', a Cavity Filter will only improve protection

from out of band, saturation,  blocking, cross modulation = SNR reduction effects within  the SDR ..

If the RFI problem is severe, the device(s) experiencing the real problems will be the linear amplification stages  LNA (s)

Preceding the filter.  

My guess: a reasonably  'good'  band-pass Filter with a Good SDR will  provide the best performance/dollar.

( don't buy a $700 Filter to help a $30 SDR )  

Instead of just guessing, Test  i.e.  try a system with no Cavity filter, then one, two and compare.

Alex

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

[b alex pettit jr]

Are you aware of this Cavity LNA system  ?

This is interesting in that has in integral Pre-LNA Cavity Filter 

http://www.hb9bbd.ch/article.php?key=34

Cavity LNA for 1296 MHz Amateur and 1420 MHz SETI

The LNA (low noise amplifier or 23cm preamp) has been designed 

for small signal applications, primarily EME and SETI.

Connectors are SUHNER SMA male or female. 

N connectors as well as SMA(male) are available on request.

The cost per unit without shipping is EURO 650.

  ..

Alex

[b alex pettit jr]

Alex

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[Anthony]

I've tried early on my system with vanilla BPF, lots of RFI surrounding me. I have multiple BPF sitting on my shelves. They all have been tested on each dish, as an interferometer or as a separate system.

As far as price, what, the Kuhne LNAs were just as expensive. 😉

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[Anthony]

Yes, did lots of reading on the different Cavity filters, materials etc..

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[Anthony]

I appreciate the information Alex! 

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[Anthony]

I'm not using the SAW Bird LNAs, I'm using KU LNA 142 AH... I thought you knew that?

Like I said, when testing my other BPF and using BAA_Seminar to to review the results, I always ended up going back to my current Cavity Filters, which also were not cheap, but of course not as close in price to the new Cavity BPFs from Mini-circuits. Again, I went through the data sheets, even checked out their environmental rating as well and, I'm pleased with that. 

Only putting the system back up and testing out everything will tell. 

I even purchased two, 50' LMR 400 coaxes along with new power lines as well, and a 10 amp (bumped up) new Linear power supply. Next is replacing one or both dishes feedhorn & LNA mounting rods. Not sure why they are rusting when they should be made of aluminum. 

This is a total system overhaul with the exception of the two, 3-meter satellite dishes, and I'm still contemplating on purchasing two, 2.4 meter, motorized (EL/AZ) dishes. 

The plan wasn't just to build an interferometer to only do drift scans, but to track objects as well or as much as possible based on my location. Which is not on a farm or in the middle of nowhere but in suburbia Roswell, GA. Funny thing, I can tell which of my neighbors are causing RFI, when they turn on their electronics at night or during the day when I'm able to do a survey of the RFI surrounding the dishes. I've mapped each one of my 11 WIFI perimeter security cameras as well. 

I'm still learning, RAS, the learning curve is exciting and long! Appreciate the help Alex. 😀

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[b alex pettit jr]

What is novel about This amplifier is that it Includes a Pre-Filtered  LNA 

Typically, That adds significantly to the NF, but evidently, the close coupling of the CavityFilter >  LNA works well.

Alex

[b alex pettit jr]

Hello Anthony,

What's your new idea ?

As a final  tuning adjustment test .. remove the screws from the rear cakepan section  and slide it backwards say 1/2 inch.

Connect the cantenna to the VNA and slowly tap the back section forward & see if you can get the 'double dips' to converge.

Alex

[Lester Veenstra]

WOW  $690

Someone please buy one and reverse engineer the mechanical drawing

Sounds like a job for the four axis CNC.

 

But Wolfgang had shown us a design already that they fabricated.

 

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

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

Jamaica cell:    +1-876-456-8898

 

From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Anthony
Sent: Tuesday, October 17, 2023 9:46 PM
To: sara...@googlegroups.com
Subject: Re: [SARA] Is it optimal - BPF closer to SDR than LNA & Antenna

 

In addition, I wasn't sure about my current Cavity BPFs and decided to replace those as well with the link you provided Alex, to Mini-Circuit. I've checked the data sheets and specs on these Cavity BPFs, they look promising, and decided to order them a few days ago.

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[Lester Veenstra]

Exactly what the ScopeInA Box needs HI

 

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

les...@veenstras.com

 

452 Stable Ln

Keyser WV 26726 USA

 

GPS: 39.336826 N  78.982287 W (Google)

GPS: 39.33682 N  78.9823741 W (GPSDO)

 

 

Telephones:

Home:            +1-304-289-6057

US cell          +1-304-790-9192

Jamaica cell:    +1-876-456-8898

 

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers [mailto:sara...@googlegroups.com]
Sent: Wednesday, October 18, 2023 5:44 AM
To: 'b alex pettit jr' via Society of Amateur Radio Astronomers
Subject: Re: [SARA] Is it optimal - BPF closer to SDR than LNA & Antenna

 

 

Alex

 

 

 

 

 

 

 

 

 

 

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[Marcus D. Leech]

On 18/10/2023 10:09, 'Lester Veenstra' via Society of Amateur Radio Astronomers wrote:

WOW  $690

Someone please buy one and reverse engineer the mechanical drawing

Sounds like a job for the four axis CNC.

 

But Wolfgang had shown us a design already that they fabricated.

One of the reasons you put a filter IN FRONT of the LNA is to reduce the probability that it will get driven into
  non-linearity by strong out-of-band signals.   This always comes at a cost in terms of noise figure, although
  the HB9BBD design somewhat side-steps the issue by making the filter part of the matching network that
  is inevitably required anyway.

But with more-modern integrated MMIC LNAs, with MUCH higher p1dB and OIP3, the need to "kill" out-of-band
  signals right at the input is somewhat reduced, which means that in many many cases, you can defer filtering
  until after the 1st stage.

I'll also repeat this again.  Having an eye-wateringly low-noise LNA in a typical amateur situation, where you're not
  located "in the middle of absolute nowhere" and you have smaller dishes, is perhaps not the best investment.
  We had one person at our observatory suggest that we should put in a cryo-cooled LNA stage.  I pointed out that
  would be foolish, since the radome itself offers up about 40K in Tsys contribution...

We put a filter in front of our LNAs at CCERA mostly because we had evidence that there were strong out-of-band
  signals occasionally causing us grief.  We may take them out the next time we go "up top" in order to reclaim a
  little bit of Tsys.

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[Anthony]

Thanks SARA for all the feed back and opinions!

I'm still looking forward to the delivery today!  😀 

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[Anthony]

Coming soon... 😉

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[Anthony]

They HAVE arrived! 😊

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[Marcus D. Leech]

On 18/10/2023 19:00, Anthony wrote:

They HAVE arrived! 😊

Lovely plumage, the Norwegian Blue....

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[Anthony]

💯

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[Anthony]

Completed the mounting of both new cantenna's today. Maybe if time permits I'll start on building the LNAs enclosures and wiring. 

Eastern dish

Western dish

[Mike Otte]

How are you going to adjust the feedhorns for focus?

Are the legs telescoping?

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Mike Otte W9YS

[Anthony]

Both cantenna's are set at both 3-meter dish focal point of 46"

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[b alex pettit jr]

From documentation & test, I found the focal distance was  2 cm into the cantenna.

[Anthony]

Yep, I've compensated for after reading SETI online doc and a book I have for antenna wave propagation. The cantenna's are both inside the 46" focal point. Testing will begin hopefully this week, depending on my horrendous work schedule. 

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[Anthony]

A great read! Lots of math, though but a good book on antenna designs....

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