hello - new member here wanting to test the statement that there are no dumb questions:

[Chuck Snell]

Hello,

My name is Chuck Snell. Just joined SARA yesterday. I have been a "lurker" watching the YouTube channel videos.

I really want to press forward and get some results.

What I currently have:

1) a RTL-SDR

2) a few runs of what I am told is very good HAM radio coax cable run to the outside of my house (ran it in the walls when we built the house)

3) a possible semi-radio quiet environment - rural community and i am up on a hill (i can cut off my WiFi if/when the fun-prevention-officer agrees)

4) a low-grade anxiety of messing up with the hands-on portions.

What I don't have:

1) an antenna of any flavor - I assume either Radio Jove or Milky Way Hydrogen detection are beginner level - looks like one sort of sets the antenna and forgets it

2) a laptop - I have a desktop in the area where the mentioned coax cables start (or end) in a bonus room

Questions:

Since I can order a "scope in the box" from the society and seems to be an entry-level approach let's assume I will begin with Hydrogen / Milky Way

1) when doing a drift scan do I have to be outside or rather does my computer have to be outside? (weather / we have a dumb dog that can't leave stuff alone) Can I use the coax cable that is run from my bonus room to the outside?

2) How do I know if my antenna if "aimed" / pointed correctly?

3) Am i correct EZRA captures the live / streaming data?

(as I was wrestling with submitting this I had 4 questions but now I cannot think of the last one)

Thanks

-Chuck

[Alex P]

Hello Chuck,

A few quick comments :

Satellite TV or Cable TV / Internet RG6 Coax will work.

'Ham Radio' RG58 coax will Not.

Optimally limit the total coax run  from LNA at the antenna to SDR near the PC at ~ 50 feet.

Ok to have PC inside - that is pretty much normal

I recommend against purchasing the current  'Scope in a Box'  

The nooelec H1 feed is poorly designed, and it seems to have frequent internal defects.

I suggest the Kraken Discovery Dish System

https://github.com/AP-HLine-3D/HLine3D/blob/main/21cm_Step1b_KrakenDiscoveryFeed_Eval_05.pdf

Antenna Positioning : use a

 Digital Level

and

 Stellarium 

https://stellarium.org/

AND THIS CHART

Regards,

Alex Pettit

Project HLine3D

https://github.com/AP-HLine-3D/HLine3

[Andrew Thornett]

Hi Chuck,

I thought I'd drop you a few suggestions on your questions. I chair the BAA hydrogen line group, although thst doesn't make me an expert - but it provides a forum where experts gather and happily give advice to those like me with less expertise - if you are interested in that let me know and I will put you on mailing list for links to meetings etc. My email is and...@thornett.net 

Regarding your particular questions re capitals below.

Andy

Dr Andrew Thornett

Lichfield Radio Observatory 

---

Hello,

My name is Chuck Snell. Just joined SARA yesterday. I have been a "lurker" watching the YouTube channel videos.

I really want to press forward and get some results.

What I currently have:

1) a RTL-SDR.

A PROVEN PIECE OF KIT AND A GOOD PLACE TO START FOR HYDROGEN. ALSO COVERS 20MHZ FOR RADIO JOVE BUT ISN'T THE USUAL RECOMMENDED 1ST CHOICE.

2) a few runs of what I am told is very good HAM radio coax cable run to the outside of my house (ran it in the walls when we built the house).

I WOULD TOTALLY AGREE WITH ALEX. PEOPLE OFTEN ASSUME HIGH QUALITY CABLE IS WHAT MATTERS. MORE IMPORTANT IS THAT THE CABLE NEEDS TO BE RATED FOR THE WAVELENGTH UNDER INVESTIGATION. CHEAP RG6 AS ISDD BY HOME SATELLITE TV COMPANIES YES, EVEN MILITARY GRADE RG58 NO. SO IT ENTIRELY DEPENDS WHAT THIS CABLE IS GOING AROUND YOUR HOUSE. OF COURSE I AM TALKING ABOUT LOWER MICROWAVE - HYDROGEN LINE - 1420 MHZ - HERE. RADIO JOVE IS 20 MHZ - A COMPLETELY DIFFERENT KETTLE OF FISH.

3) a possible semi-radio quiet environment - rural community and i am up on a hill (i can cut off my WiFi if/when the fun-prevention-officer agrees)

MAYBE IT IS MAYBE IT ISNT DEPENDS ON AIR SOURCE HEATERS, SOLAR PANEL CONVERTERS, MONITOR AND TV SCREENS, ETC., IN VICINITY, FOR H-LINE. JUPITER = MORE SENSITIVE IN MY EXPERIENCE TO GENERALLY RFI ENVIRONMENT. CONCLUSION: ALL DEPENDS......

4) a low-grade anxiety of messing up with the hands-on portions.

RADIO ASTRONOMY IS LIKE FISHING - YOU FAIL, YOU TRY AGAIN, YOU FAIL AGAIN, YOU TRY AGAIN AND AGAIN AND AGAIN UNTIL YOU WANT TO THROW EVERYTHING ACROS THE ROOM IN FRUSTRATION!

What I don't have:

1) an antenna of any flavor - I assume either Radio Jove or Milky Way Hydrogen detection are beginner level - looks like one sort of sets the antenna and forgets it.

NO PROBLEM -BUY ONE!

2) a laptop - I have a desktop in the area where the mentioned coax cables start (or end) in a bonus room.

EITHER PROJECT REQUIRES A COMPUTER THAT CAN BE LEFT ON 24/7. DOES NOT HAVE TO BE POWERFUL. WINDOWS OR LINIX NOT MAC. WINDOWS EASIEST TO START WITH.

Questions:

Since I can order a "scope in the box" from the society and seems to be an entry-level approach let's assume I will begin with Hydrogen / Milky Way.

I AM NOT SURE I WOULD CALL IT BEGINEER BUT CHEAP CLEVER KIT MAKES IT EASIER.

1) when doing a drift scan do I have to be outside or rather does my computer have to be outside? (weather / we have a dumb dog that can't leave stuff alone) Can I use the coax cable that is run from my bonus room to the outside?

YOU CAN HAVE PC IN OR OUT FOR H-LINE BUT IDEALLY PC ON FLOOR IN MIDDLE OF THE 2 DIPOLES FOR RADIO JOVE. WEATHER PROOF BOX AND THEN REMOTE INTO IT BY LAN CABLE OR WIFI. SO NEED OUTSIDE POWER.

2) How do I know if my antenna if "aimed" / pointed correctly?

IF USING EZRA POINT WHEREVER AND USE COMPASS AND DIGITAL INCLINOMETER.

3) Am i correct EZRA captures the live / streaming data?

YEA, OTHER ALTERNATIVES AVAILABLE.

(as I was wrestling with submitting this I had 4 questions but now I cannot think of the last one)

Thanks

-Chuck

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[Chuck Snell]

Thank you all - 

I will confirm the HAM radio lines are not for the 21cm - visually get the description / labeling when I am home but short of confirming I know it's wrong. I asked some HAM's for recommendation for good HAM radio antenna line and it was pricey - but will be for the radio ranges

I have not ordered anything regarding the antenna yet - will search and look at the Kraken recommendation

surely i will have more questions .......

Thanks again

-Chuck (KJ4AWK)

[b alex pettit jr]

Hello Chuck,

FYI here is my QRZ page

KK4VB Callsign Page

KK4VB Callsign Page KK4VB personal biography

Alex Pettit

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

[Andrew Thornett]

Alex recommends the Discovery dish and feed.

I am not as negative about the SARA Scope in the Box which I think provides an effective way to get into H-line.

However, I have four H-Line telescopes:

Ex-military 4 x 4 dipole array - works well, its main benefit is its robustness - due to being ex-military - it just works! But they as rare as hen's teeth.

Solar cooker petal dish - for some reason I could not get this working well - others have done so on this group. Best guess is that it is quite shallow and suffering from excessive ground noise as a result as quite a lot of trees and houses close by.

SETI Lesgue Horn of Plenty - easy to make in sense that it is quite relaxed about every dimension being super accurate etc. But does seem to pick up RFI quite a lot. I am able to map Milky Way and demonstrate dark matter with it in spite of this.

Lastly, and working most effectively (aside from ex-military equipment) is an 140cm communications dish. This is quite deep and I suspect (but don't know for sure) that this might be reducing ground noise. In addition, I am using it with a Discovery H-Line feed. Alex has tested these Discovery feeds and discussed them previously at SARA meetings and demonstrated how great they are. But also I have a 3D printed stalk to hold the feed which both makes it very easy to mount it on a dish not originally designed for it and even better allows the focus point tl be determined easily by the simple expedient of yanking the stalk in and out of the holder whilst looking at the trace on the laptop, so that perfect focus can be easily obtained- a REALLY important part of the process of getting a H-line system to work.

So, I would say the following are important, and I give credit not just to my experience, but to Alex Pettit's work analysing a wide variety of these systems, and the comments lf Rich/Ted/Adrian/Jason and many others on focusing etc.

1. Important to get perfect or near perfect focus on dishes.
2. Important to reduce ground noise as much as possible, deep dishes or extending dishes with mosquito dish (a la Alex's recommendations in previous SARA Drakes/RTOP meetings).
3. Vital to get the LNA/filter AS CLOSE TO the feed as possible in H-line systems. This is something I personally tested a great deal as for some idiotic reason I refused to do it at the beginning (in spite of Alex regularly giving me the same advice). I even used LMR400 coaxial cable (expensive++). Doesn't matter what you use- you just can't compensate for loss down cable if LNA several metres away.

Alex has criticised the Nooelec SAWBird H1 LNA/filter. I am not qualified enough to give an opinion on their limitations and I will leave that to Alex. However, there are some reasons why the SAWBird has been popular:

1. Cheap.
2. Cheap.
3. Cheap!
4. The SAWBird contains 2 cascades LNAs with filter between them - LNA 1 amplifies the signal sufficiently to compensate for loss in the filter, the filter helps remove strong out of band RFI eg from cell towers occupying close by frequencies, and LNA 2 amplifies signal to compensate for signal loss down coaxial cable. This combination is quite brilliant amd if you don't use a SAWBird that you need to use a combination of devices to achieve similar outcomes. The Discovery feed already has done this, and uses a different LNA/filter system to the SAWBird. Using a Nooelec SAWBird or a Discovery H-line feed means you don't need to think about these things.

I am giving a talk on first day of the Eastern Conference reviewing my experience of hydrogen line radio observing at Lichfield Radio Observatory,  UK. A video of all the talks at the conference should be available online in a few weeks.

Best wishes, 

Andy

Sent from Outlook for Android

---

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Thursday, 30 July 2026 15:41:51
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] hello - new member here wanting to test the statement that there are no dumb questions:

 

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[b alex pettit jr]

>>>  INCORRECT <<<

It is the nooelec     H1 Dipole Feed   that is flawed.

I have many nooelec SAWbird H1 LNAs

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

Alex has criticised the Nooelec SAWBird H1 LNA/filter. I am not qualified enough to give an opinion on their limitations and I will leave that to Alex. .

[Jeff Jones]

A little AI info…..  50 ohm coax works best according to this info.  

Neutral Hydrogen (H I) 1420.4058 MHz Coax Recommendations

Recommended System:

-------------------

Antenna/Feed

      │

      ├── 6-18" short 50Ω coax

      │

1420 MHz Bandpass Filter

      │

Low Noise Amplifier (LNA)

      │

LMR-400 or LMR-600

      │

Bias Tee (if powering LNA)

      │

Airspy R2 / SDRplay RSPdx-R2 / other SDR

Preferred Impedance:

--------------------

Use 50-ohm coax and components throughout the system.

Reasons:

- Most SDRs are 50Ω.

- Most 1420 MHz LNAs and filters are 50Ω.

- Most microwave antenna feeds are designed for 50Ω.

- Avoids unnecessary impedance mismatches.

Can 75Ω Coax Be Used?

---------------------

Yes.

A 75Ω cable between 50Ω devices introduces only about:

- VSWR: 1.5:1

- Mismatch loss: ~0.18 dB per transition

Good quality RG-6 will work for receive-only applications.

However:

- It has higher attenuation than LMR-400.

- Connectors are less convenient (F connectors).

- Filters and LNAs are designed for 50Ω.

Do NOT use a resistive 50-to-75Ω matching pad.

A proper matching pad loses approximately 5.7 dB, which is far worse than the small mismatch.

Recommended Cable Types:

------------------------

Runs under 25 feet:

- LMR-240 (acceptable)

- LMR-400 (preferred)

Runs 25-50 feet:

- LMR-400 (recommended)

Runs 50-100 feet:

- LMR-600 (recommended)

Permanent installations over 100 feet:

- 1/2" Heliax or similar hardline

Approximate Cable Loss @ 1.42 GHz

---------------------------------

LMR-600

  25 ft : ~0.8 dB

  50 ft : ~1.6 dB

 100 ft : ~3.3 dB

LMR-400

  25 ft : ~1.3 dB

  50 ft : ~2.5 dB

 100 ft : ~5.1 dB

Quality RG-6

  25 ft : ~2.0 dB

  50 ft : ~3.9 dB

 100 ft : ~7.8 dB

The Most Important Rule:

------------------------

Place the LNA at the antenna.

Signal Chain:

Feed

 ↓

Short coax (6-18")

 ↓

1420 MHz Filter

 ↓

Low Noise Amplifier

 ↓

Long coax run

 ↓

SDR

Any loss BEFORE the LNA directly increases the system noise figure.

Loss AFTER the LNA is much less significant because the signal has already been amplified.

Connector Recommendations:

--------------------------

Outdoor:

- N-Type connectors (preferred)

Receiver:

- Short N-to-SMA jumper if needed

Avoid:

- PL-259 (UHF connectors)

- Thin RG-174 jumpers

- RG-58 for long runs

- Cheap SMA extension cables

Recommended Final System:

-------------------------

• 50Ω throughout

• N connectors outdoors

• LMR-400 for most installations

• LMR-600 if cable exceeds ~75 feet

• LNA and 1420 MHz filter mounted directly behind the feed

• Weatherproof all outdoor connectors

Bottom Line:

------------

Best Performance:

    50Ω LMR-600 + antenna-mounted LNA

Best Value:

    50Ω LMR-400 + antenna-mounted LNA

Budget Option:

    Quality 75Ω RG-6 after an antenna-mounted LNA

For serious H I radio astronomy, use a complete 50Ω system with the LNA mounted at the feed whenever possible.

On Jul 30, 2026, at 10:25 AM, Chuck Snell <chuck.sn...@gmail.com> wrote:

Thank you all - 

To view this discussion visit https://groups.google.com/d/msgid/sara-list/8abc0912-15dd-45a3-8a7f-1d3f7075ffc2n%40googlegroups.com.

[b alex pettit jr]

Unless All Else Fails

Do Not Install a Filter prior to the first LNA gain stage

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

Signal Chain:

Feed

 ↓

Short coax (6-18")  Zero Length Preferred

[Stephen Arbogast]

Here is what I am using and it works well for me.....

Discovery Dish/Feed-LNA->AirSpy R2->SDRAngel (10 MegSamples/sec)->ezColAngel260514a.py->EzCon250711a.py

Stephen

[b alex pettit jr]

And this is the Kraken Feed/LNA on a 1m WiFi Dish

Alex Pettit

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

[Stephen Arbogast]

Alex  has very  nice  plots!     I  would  like a  larger parabolic  antenna  some day  but   more $$$ , more space   and more  maintenance.  I'm thinking  about it.

[b alex pettit jr]

                          This is the relative area of the dishes

Alex

[Stephen Arbogast]

What  nobody told me  in the  beginning........  Collecting  raw data (assuming  the  spectrum samples  are  averaged)  is  easy. The  real  work  begins when you must  remove outlier  Radio  Frequency Interference  (RFI)..  Then  filter  low and  high spectral bins.   You  then  apply  correction  for Velocity Relative  to  Local Standard of  Reference (VLSR)  then  you trim  outliers  again.    Finally  you  see  cool  results!!!

[b alex pettit jr]

I fortunately, have no RFI requiring removal, nor has filtering been applied .

( It is not VLSR corrected )

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

[Stephen Arbogast]

Yes, I started  with  the WiFi  dish  a  few   years ago  then  read/discovered it was meant  for  WiFi .  The  original feed  is  tuned  for   WiFi   but happens  to  work  for  21  cm HI line.   The  feed that  Alex mentions is tuned for 21  cm  HI.

I have learned that  precision is not required for  results   but  optimal  results  come  from optimal  hardware  and  software.  It is  the  journey  that is a fun learning experience.

Stephen

[Stephen Arbogast]

Alex,  

Today I moved  my  small   Discovery  Dish  around to various  locations  and no  difference  in  the one  RFI  spike   I am seeing with two  different   SDR's far away  from the antenna.  No  idea...   where it is coming  from.

Stephen

[b alex pettit jr]

Did you try rotating the antenna to see if you could null out the noise ?

[Stephen Arbogast]

Yes   I  did......  no luck..   

I think  I need a bigger  antenna..   Ellie   in  the  movie  CONTACT....   https://www.youtube.com/watch?v=K8SeB2EgBrE&t=167s

Stephen

[andrew....@googlemail.com]

Hi Alex,

Ahh! That makes  sense. The Nooelec H-line feed is wrong length, as you previously mentioned – I was surprised that you seemed to have gone off SAWBirds – so my mistake, sorry!

Andy

 

Sent from Outlook for Android

---

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Thursday, 30 July 2026 11:53:50
To: 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] hello - new member here wanting to test the statement that there are no dumb questions:

 

>>>  INCORRECT <<<

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[b alex pettit jr]

Continuing on with strange ideas :

Try building a lampshade shape of al foil or window screen to block the RFI ?

I tried this technique to reduce ground noise : No Change

Alex

[Adrian]

May I suggest this possible RFI  dish mitigation  architecture as it is being applied in the new Deep Synoptic Array project slated for construction by CalTech in Nevada..

     

Adrian

[Stephen Arbogast]

Alex,    

I am not worried about  this...   I can  selectively  remove   outliers    from my   spectral  samples.

Here  is  my    notes file  in which I recorded  how I  post processed my raw   data....

Stephen

[b alex pettit jr]

Okay. but that's tedious and does not accommodate changes in freq nor different RFI signals turning on/off during testing

    -ezConRawFreqBinHide 1881 \
    -ezConRawFreqBinHide 1882 \
    -ezConRawFreqBinHide 1883 \

Any strong signal source has the potential to saturate or block the LNA 1st stage and this cannot be post-corrected.

I can attest to that from my experience at UCF when I installed the 1.2m system I built for them only to find

nothing but huge signal level shifts where H Line should have been  :(

A cell  tower had been activated between the time I RFI surveyed the area in January  and the installation in August.

It is  preferred to remove the RFI before reception as its effect on the electronics is indeterminate  and  "Hiding a Bin"  is only cosmetic.

Alex Pettit

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

[b alex pettit jr]

FYI here is the Matlab code I wrote to develop and test the Median/Mean Filtering now available in HL3D

Dorig = dAta;
dAta = Mag1;
Dmedian= dAta;
Dmax= dAta;
Dmin= dAta;
Dsmooth= dAta;
Dmedian1= dAta;

Dap = 5;  % averaging parameter ( moving average of +- x values )
Dsmoth = 3; % smoothing parameter ( moving avg of +- y values 
Chs = length(dAta);

%  Median Filter

for indx = Dap+1: Chs-Dap  
   Dmedian1(indx ) = mean((dAta(indx-3 :indx+3 )));     
end


for indx = Dap+1: Chs-Dap  
   Dmedian(indx ) = median((dAta(indx-Dap :indx+Dap )));     
end

% Find Minimum value 
for indx = Dap+1: Chs-Dap     
      Dmin(indx ) = min((Dmedian(indx-Dap :indx+Dap )));              
end

% Find Maximum Value
 for indx = Dap+1: Chs-Dap    
     Dmax(indx ) = max((Dmin(indx-1*Dap :indx+1*Dap )));            
 end
% Dmax = Dmedian;


% Smooth Final Data 

for indx = Dsmoth+1: Chs-Dsmoth    
     Dsmooth(indx ) = mean((Dmedian(indx-Dsmoth:indx+Dsmoth)));
end

% clean up end beyond filter
% Dsmooth(Chs-2*Dpg:Chs) = Dsmooth(Chs-2*Dpg); 

%  PLOT
figure;
hold on ;  
set(gca,'color', [0.6 0.6 0.6]);
% title ( 'Median Min Max' );
%  plot(Dorig, 'y');
 % plot(Dmin,'c');
 % plot(Dmax, 'g' , 'LineWidth',2);
 % plot(dAta, 'r*');
   plot(dAta, 'r', 'LineWidth', .1 );
  plot(dAta, 'r', 'Marker' , 'o' ,  'LineWidth', 1);
%  plot(Mag8Array, 'g:','LineWidth',2);
  % plot(Mag7Array, 'g:','LineWidth',2);
% plot(Dmedian, 'b', 'LineWidth', .1 );
   plot(Dmedian, 'b', 'Marker' , 's' ,  'LineWidth', .2);
   plot(Dmedian, 'b', 'LineWidth', .5 );

%  hold off;
  axis([ 150 , 250 , 6.15e-5 , 6.7e-5]);
 %  axis( [ 1 1024 -60 -56])
 title( 'JavaCode Development ')
 grid
 

[Chuck Snell]

Hello All - 

feeling a little overwhelmed reading this thread but it is exciting

Here is where I am currently - I am about to order the Kraken Discovery Dish from Mouser - in stock

Then order the Hydrogen Line Module separately - but again from Mouser - it's not in stock (says they are expected 8/10). Thinking I may get the main dish and can put it together while waiting on the module

and order some LMR-400 from Digi_key - but goodness LMR-400 is pricey - regarding the connectors for the cable - any difference or recommendation for crimp on or solder?

after those 3 things (dish, Hydrogen module, coax cable) - what next - the LNA? anything else

again - I have a RTL-SDR and desktop PC (no laptop)

I won't commit to ordering until I check back in this thread for follow-up comments - but the shopping cart is ready to go

Thanks again

-Chuck

[b alex pettit jr]

Chuck,

How long is your cable run ?

LMR 240 or RG6 Will work for 50-70 feet.

LMR400 is heavy, stiff cable. It is designed for Type-N connectors, and any transition

from SMA to Type-N must be supported to as to not damage the smaller connector.

 I have used LMR400 but I can assure you it is Not Mandatory for that system. 

For LMR400, if you are installing your own connectors, you Must use a Proper Crimping Tool,

or the connections will be so poor, the advantage of the lower loss in the cable will be overwhelmed by improperly installed connectors !

The 50/70 ohm impedance mismatch between the Kraken feed and RG6 is of no Realistic significance.

( and at least Try  SDR# > IFavg > HL3D > Rinearn ? )

Alex Pettit

KK4VB

Proj HLine3D

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

[Chuck Snell]

Hey Alex (and all) - 

I will hold off buying the cable for a day or so. This weekend I will measure rough distances.

here is my situation and options:

when we built our house (years ago) like I mentioned I let some HAM Elmers recommend very good cable to run in the walls for a proper install. I was hoping I could use those - 

no dice and the length would be on issue. My hobby room / HAM shack is upstairs and I ran the cables down to the crawlspace.

so if I put my radio astronomy hobby in my hobby room - that will add cable length and some  real work with running the cable - from upstairs to the outside yard.

I also have an office which is downstairs - and 2 options with the office

1) just brute force out a window

2) when we bult I had an (two actually) empty electrical box installed in the wall(s) with a conduit from my office to the attic

I could use the box/conduit to get to the attic and from the attic to the soffit then down the wall to the radio telescope - seems like I am wasting cable length with an up and down the wall

My ceiling is 9' - so 18+ feet of no lateral direction

Going out a window seems a little rough if I am going to be running 24/7 - weather / bugs / heating and cooling ....

What are the common ways people get to the outside to their telescopes? (almost want to make another thread and ask this as a straw poll.)

Think I am good to place the order from Mouser for the Kraken?

Thanks

-Chuck

[b alex pettit jr]

Hi  Chuck,

Measure & give me some distances. 

It would not be unreasonable to put a 1/2" thick strip of wood under a window and temporarily run the coax that way for a 24 hr drift scan.

 One good 24 hr sweep is all that is required at any Declination.  ( that is what I do )

You may need to initially do eval your antenna location if RFI is an issue.  

SDR# w/ IFavg will allow you to see the peaks in real time, change things and eval the difference.

KMR240 == LMR240, and this is an example of what will work.

Other options are to remote the  SDR and connect it to the PC via a USB Extender pair ..

Regards,

Alex Pettit

FYI, here is my 'best' system & some data in  Engineering Units : dB relative to Cold_Sky background

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

On Friday, July 31, 2026 at 04:26:45 PM EDT, Chuck Snell <chuck.sn...@gmail.com> wrote:

Hey Alex (and all) - 

I will hold off buying the cable for a day or so. This weekend I will measure rough distances.  GOOD IDEA

[Stephen Arbogast]

Science  is  tedious....    I am  just   saying    we  do  the  best we  can...   Any   strong  broad band signals  are  a different  problem.  I have  a neighbor    with a  heat pump  .... wipes  out my reception..  but  when it is off   I am able to remove    the  one   single  spur....   Digital Signal Processing  is  wonderful.

Stephen

[b alex pettit jr]

Any strong signal source has the potential to saturate or block the LNA 1st stage and this cannot be post-corrected.

It is  preferred to remove/minimize the RFI before reception  i.e. in Hardware Modification/Location

Software is the fallback solution;  median/mean processing is quite effective without manually identifying each outlier freq.

https://github.com/AP-HLine-3D/HLine3D/blob/main/Info_HL3D_processing_RFI%20Eraser01.pdf

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

    1)  try changing the Hardware with Antenna shields to block RFI source(s) or moving the Antenna to a different location.

    2)  enhance the Software by adding adjustable mean/median filtering 

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

Alex Pettit

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

On Sunday, August 2, 2026 at 03:18:45 AM EDT, 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Science  is  tedious....    I am  just   saying    we  do  the  best we  can...   Any   strong  broad band signals  are  a different  problem.  I have  a neighbor    with a  heat pump  .... wipes  out my reception..  but  when it is off   I am able to remove    the  one   single  spur....   Digital Signal Processing  is  wonderful.

Stephen

On Friday, July 31, 2026 at 3:13:53 AM UTC-6 b alex pettit jr wrote:

Okay. but that's tedious and does not accommodate changes in freq nor different RFI signals turning on/off during testing

    -ezConRawFreqBinHide 1881 \
    -ezConRawFreqBinHide 1882 \
    -ezConRawFreqBinHide 1883 \

Any strong signal source has the potential to saturate or block the LNA 1st stage and this cannot be post-corrected.

I can attest to that from my experience at UCF when I installed the 1.2m system I built for them only to find

nothing but huge signal level shifts where H Line should have been  :(

A cell  tower had been activated between the time I RFI surveyed the area in January  and the installation in August.

It is  preferred to remove the RFI before reception.

Alex Pettit

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

On Friday, July 31, 2026 at 12:40:58 AM EDT, 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Alex,    

I am not worried about  this...   I can  selectively  remove   outliers    from my   spectral  samples.

Here  is  my    notes file  in which I recorded  how I  post processed my raw   data....

Stephen

-

[b alex pettit jr]

Stephen,

System Test

===========

I have a suggestion : use the broadband Sun RF to test your system :

Point your dish along your Meridian and ( currently ) at Declination + 17 Degrees

and perform an 8-12 hour drift scan of the Sun.

Plot the background level shift in dB.

The shift should be in the range of 2 - 3 dB and look something like this