Peltier cooling for LNA with Discovery Dish

[Stephen Arbogast]

Has  any one  tried this...   https://www.adafruit.com/product/1335?gad_source=1&gad_campaignid=21079227318&gclid=Cj0KCQjw3OjGBhDYARIsADd-uX47muzSk0Z8lQMMMhtRqA4FAgQRgDH0GXwJcdfZqsxEERrTmvInmK0aAox0EALw_wcB

Thoughts?

[Alex P]

The nooelec SAWbird H1 LNA has a thermal gain coefficient of only  -0.1 dB  per + 10 dgC change

There are typically other variations which greatly exceed this.

[Stephen Arbogast]

Thanks  Alex,

So  I checked  with  Kracken RF    and  my  Discovery Dish  uses this  IC  https://www.mouser.com/new/qorvo/qorvo-qpl9547-lna/

I   don't have  professional  expensive gear to make measurements     just a  Nano VNA  and a  tinySA...

I have  discovered that   the  SOAPY SDR     for AirSpy   in  GNU Radio has  problems     will  need  further    exploration.

[b alex pettit jr]

Just need a nanoVNA, some planning,  & a week of meticulous testing  See Attached

Alex

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

[Marko Cebokli]

Usually, cooling is not for higher gain, but for lower noise. Considering gain, you just want to stabilize the temperature, at whatever reasonable value, like 30C.  Cooling will reduce noise, but in an amateur setup, water condensation and frost are a quite unsurmountable problem. Also, if the antenna is at room temperature, the thermal conductivity of the cable between the antenna and the LNA will be a problem - low electrical loss and low thermal conductivity usually don't dance together.

Marko Cebokli 

2025-09-30 05:50, je 'b alex pettit jr' via Society of Amateur Radio Astronomers napisal

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[Andrew Thornett]

How do you set up cooling? Do you just cool the LNA or do you cool the waveguide too? So for example i use a cantenna for my waveguide - if I wanted to Peltier cool my system, would that mean that I need to somehow cover the entire cantenna and LNA and cool the lot or is just enclosing the LNA in a casing a cooling that sufficient? Then what temperature is ideal? When i am doing astrophotography, I use an Atik 16200M camera which cools to 45 degrees below ambient. I live in UK woth temperature usually in range 15-20 C but can vary 0 C to 30 C. So I cool to -10C which means I can get that temperature at almost any time and the stable single temperature allows me to use a single set of dark frames and flat frames. Does radio astronomy work the same way? Can we calibrate with a single calibration standard used all the time as long as we cool our LNA (or LNA plus waveguide depending on answer to my question above) to the same temperature each time?

Sorry for all the questions but this thread fascinates me as I would love to know how similar radio astronomy and astrophotography are in this regard.

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Marko Cebokli <s57...@hamradio.si>
Sent: Tuesday, September 30, 2025 1:31:54 PM
To: sara...@googlegroups.com <sara...@googlegroups.com>
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

To view this discussion visit https://groups.google.com/d/msgid/sara-list/a19843243c51d800331589e2c69c4022%40hamradio.si.

[Marcus D. Leech]

On 2025-09-30 09:59, 'Andrew Thornett' via Society of Amateur Radio Astronomers wrote:

How do you set up cooling? Do you just cool the LNA or do you cool the waveguide too? So for example i use a cantenna for my waveguide - if I wanted to Peltier cool my system, would that mean that I need to somehow cover the entire cantenna and LNA and cool the lot or is just enclosing the LNA in a casing a cooling that sufficient? Then what temperature is ideal? When i am doing astrophotography, I use an Atik 16200M camera which cools to 45 degrees below ambient. I live in UK woth temperature usually in range 15-20 C but can vary 0 C to 30 C. So I cool to -10C which means I can get that temperature at almost any time and the stable single temperature allows me to use a single set of dark frames and flat frames. Does radio astronomy work the same way? Can we calibrate with a single calibration standard used all the time as long as we cool our LNA (or LNA plus waveguide depending on answer to my question above) to the same temperature each time?

Sorry for all the questions but this thread fascinates me as I would love to know how similar radio astronomy and astrophotography are in this regard.

Andy

You generally need to cool just the LNA -- the problem is that the LNA usually is in a "thermal marriage" with other components, like the feed-horn.

To get appreciable reduction in noise in an LNA, you have to cool it a LOT.    The professionals cool with LN2 or liquid Helium.    Cooling it down to -10C isn't likely to improve
  noise figure very much, but WILL create condensation/frost management headaches.

The main advantage in any kind of active LNA thermal management is gain stabilization.   You can achieve that in the OTHER direction, using heaters with a PID controller.
  There will be a very small noise figure penalty.    Even doing something like bolting the LNA to a bloody great chunk of steel will help smooth out temperature variations.
  What you'd like is for the gain to be stable-enough over your observing period to get a good total-power measurement of the object of interest.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/FRWP194MB275282815CCB6E87ED6BEE5EFF1AA%40FRWP194MB2752.EURP194.PROD.OUTLOOK.COM.

[b alex pettit jr]

Microwaves101 | Noise Temperature

Microwaves101 | Noise Temperature Microwaves101 | Noise Temperature

#1 : Optimize the Feed vs Dish position and reduce 290K spillover before considering cooling the LNA

Optical Equivalent to focusing the image and not trying to use an open frame Dob in the middle of a bright parking lot

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

[Andrew Thornett]

Yes, not surprised you say those things, Alex, and im sure you are right. I personally wasn't intending to try cooling my setup - however for my interest and intellectual development what are the answers to my questions?

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: Tuesday, September 30, 2025 3:16:11 PM
To: 'Andrew Thornett' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

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[b alex pettit jr]

Ref  Marcus' comments for the answer

[Don Latham]

combine with:

eBay item number:335280036615

controller

---

From: "sara" <sara...@googlegroups.com>
To: "sara" <sara...@googlegroups.com>
Sent: Monday, September 29, 2025 5:03:12 PM
Subject: [SARA] Peltier cooling for LNA   with  Discovery Dish

Has  any one  tried this...   https://www.adafruit.com/product/1335?gad_source=1&gad_campaignid=21079227318&gclid=Cj0KCQjw3OjGBhDYARIsADd-uX47muzSk0Z8lQMMMhtRqA4FAgQRgDH0GXwJcdfZqsxEERrTmvInmK0aAox0EALw_wcB

Thoughts?

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PO Box 404,
Frenchtown, MT, 59846
406-626-4304

[Stephen Arbogast]

Well...       I have decided  to   not  purchase /try  the  Peltier  Cooler   from  Ada Fruit.   I   am using  a  Discovery Dish   with   Hydrogen   Line  feed.   Velcro   strapping  the   large  chunk of  metal   to  the plastic  case...   enclosing   the  dipole  would  block E&M  waves   and probably not help much  at  stabilizing temperature.. not  to mention  problems  with the  weather. 

I  still  have my  old WiFi dish...   so maybe I  will  set it up again  and try to rig  it with  lna  temp   stabilization..... which  is  weather protected.....

[Stephen Arbogast]

 I  also  use a  TinySA.. it has  a mode  where  it   can  be used as a signal  generator.....  I  find it  useful  for testing..........      https://www.tinysa.org/wiki/

[b alex pettit jr]

IF you ever want to remote the SDR , It has a More significant thermal issue, as do Environmental changes,  than the small -0.1 dB / 10 dgC of the LNA

FYI, you can't use switching power adjacent to the Feed ...

Prof P

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

On Wednesday, October 1, 2025 at 10:26:03 PM UTC-6 Stephen Arbogast wrote:

Well...       I have decided  to   not  purchase /try  the  Peltier  Cooler   from  Ada Fruit.   I   am using  a  Discovery Dish   with   Hydrogen   Line  feed.   Velcro   strapping  the   large  chunk of  metal   to  the plastic  case...   enclosing   the  dipole  would  block E&M  waves   and probably not help much  at  stabilizing temperature.. not  to mention  problems  with the  weather. 

I  still  have my  old WiFi dish...   so maybe I  will  set it up again  and try to rig  it with  lna  temp   stabilization..... which  is  weather protected.....

.

[Stephen Arbogast]

So  I have   the  phase  lock   working  on my   Airspy   R2.....  GPSDO   with  gnu   radio   software not  that  I have two   antennas  but  hoping to try   it..

[Stephen Arbogast]

I   am operating  my    sdr's  in side  my  house..  at constant temp  no problems.   I was curious     about  my lna's   outside  at the  feed point of my dishes..   I have   found  that my   Discovery   Dish  lna    gain  goes  down   with  increasing  temp   as  most  do.     I  am  not   trying  to measure  with   precision.....

[Andrew Thornett]

Hi Stephen

Would you like to have Teams or Zoom meeting about GNU Radio? I am keen to learn more about what you have achieved.

If so, then send me email.at andrew (at) thornett (dot) net and we can arrange a time.

If anyone else wants to take part too then please let me know as well and I'll include you.

Andy

Sent from Outlook for Android

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From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Thursday, October 2, 2025 8:14:35 AM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Peltier cooling for LNA with Discovery Dish

 

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[Lester Veenstra]

Just a point with respect to Noise Figure (Not amplifier gain) ;  I would suggest that in most of our cases the antenna system temperature is dominated by side lobe contributions and small changes in NF with temp will not be significant.

 

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: Tuesday, September 30, 2025 10:30 AM
To: 'Andrew Thornett' via Society of Amateur Radio Astronomers
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

Ref  Marcus' comments for the answer

 

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[Lester Veenstra]

Does anyone know what the front end IC chip is used?  I am asking as am too lazy to pry the shield off  and look with the scope.

 

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

 

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[b alex pettit jr]

Hello Lester :

10000% Agree

Alex

[b alex pettit jr]

nooelec SAWbird H1  ?

https://www.mouser.com/datasheet/2/412/TQP3M9037_Data_Sheet-1500717.pdf

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

[andrew....@googlemail.com]

Does that mean that the best way to reduce this noise figure is to extend the sides of the dish, in the same way that Alex has done with his dishes, to reduce signal coming off the ground?

Andy

 

From: 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: 03 October 2025 11:56
To: 'Lester Veenstra' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

Hello Lester :

 

10000% Agree

 

Alex

 

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[b alex pettit jr]

Si Senor !

[b alex pettit jr]

Consider you get 100 noise units from Earth Temp Spillover & 10 from the LNA . = 110 noise units

If you chill the LNA to absolute zero , you might improve your system to 109 noise units .. 

VS perhaps to 50 noise units if you just block the Spillover

Prof P

[b alex pettit jr]

Real Values

[kb3puw]

I regularly use this similar device:

https://www.amazon.com/dp/B0CFK73LY7?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_5

- but on my Nooelec SDR because it runs hot.  I do not cool my Nooelec LNA because it has been stated (e.g. by Alex) that the LNA is pretty temperature stable.  I have done my own testing and found that the SDR temperature does vary (ramps up to 100 deg F with a 72degF ambient temperature) and can affect gain somewhat - and - when I run with my SDR outside in Texas 100 deg F ambient temperatures there is real concern of having problems.

On Mon, Sep 29, 2025 at 6:03 PM 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Has  any one  tried this...   https://www.adafruit.com/product/1335?gad_source=1&gad_campaignid=21079227318&gclid=Cj0KCQjw3OjGBhDYARIsADd-uX47muzSk0Z8lQMMMhtRqA4FAgQRgDH0GXwJcdfZqsxEERrTmvInmK0aAox0EALw_wcB

Thoughts?

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[b alex pettit jr]

This might put everything in perspective   not precise, but it gives a general idea ...( and yes, there are overlaps )

Prof P

[Brad Thomas]

I needed to solve some electronic noise issues. Note: this was not
noise due to thermodynamics of semiconductor junctions and the device
thermal surroundings, which would require cryogenic temps to fix. This
was noise due to bad electronics in the LimeSDR Mini. I immersed the
device in dry (by 4A molecular sieves) mineral oil and cooled that to
about -10C using a conventional refrigeration coil. Noise improved
significantly. Could not go below -10C because the device, probably
the XTAL oscillator, stopped working (reversibly) at those lower
temps. Using a heat-exchange medium like mineral oil, or more exotic
halogenated ethers designed to be compatible with electronics, is not
new. Server farms for bitcoin and such have used such cooling
successfully for a long time now. I hope this might be useful info for
some.

--Brad Thomas

On Mon, Sep 29, 2025 at 6:55 PM 'Alex P' via Society of Amateur Radio
Astronomers <sara...@googlegroups.com> wrote:
>
> The nooelec SAWbird H1 LNA has a thermal gain coefficient of only -0.1 dB per + 10 dgC change
> There are typically other variations which greatly exceed this.
>

> On Monday, September 29, 2025 at 7:03:13 PM UTC-4 Stephen Arbogast wrote:
>>
>> Has any one tried this... https://www.adafruit.com/product/1335?gad_source=1&gad_campaignid=21079227318&gclid=Cj0KCQjw3OjGBhDYARIsADd-uX47muzSk0Z8lQMMMhtRqA4FAgQRgDH0GXwJcdfZqsxEERrTmvInmK0aAox0EALw_wcB
>>
>> Thoughts?
>>
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[Lester Veenstra]

Thanks  I see some standalone amps with this also

 

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

 

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[Lester Veenstra]

Any way to get the side log gain down with respect to main beam is effort well spenf.  The quick and dirty test to get a few square feet of echsorb foam or equicalent and put in front of dish for Hot Measurement, remove and measure the delta down to :cold Sky” temp of antenna.  With antenna pointed overhead. And improving antenna for better delta will tell you if you are in the right direction.  Now the question of where to get the absorging foam  No clue here.

 

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

 

To view this discussion visit https://groups.google.com/d/msgid/sara-list/003501dc345b%242feb72a0%248fc257e0%24%40googlemail.com.

[b alex pettit jr]

purchase from Amazon   you need 1" (  4  thicknesses ) simulate 290K

On Friday, October 3, 2025 at 12:31:37 PM EDT, 'Lester Veenstra' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Any way to get the side log gain down with respect to main beam is effort well spenf.  The quick and dirty test to get a few square feet of echsorb foam or equicalent and put in front of dish for Hot Measurement, remove and measure the delta down to :cold Sky” temp of antenna.  With antenna pointed overhead. And improving antenna for better delta will tell you if you are in the right direction.  Now the question of where to get the absorbing foam  No clue here.

 

[Stephen Arbogast]

Thanks all,  while  lowest possible  noise is  great my goal was temperature  stability in the lna.   I have a  few  other  lna's  that would  be  easier to attach a  Peltier cooler  to...   probably  will   buy  a  Peltier  device and make some measurements.

In the  mean time I have made adjustments  to   split_ratio  in Pierre Terrier's  software .. GnuRadio Spectro Radiometer,  turned off  internet access  and so far here  are some  results.   The  bump is  when the sun  crossed through my  very small  dish  beam (70 cm).  The  spikes are me  fooling around  with other  windows.     In  a future  post  I hope to  show  how  the  gain  of my lna  varies  with temperatures   as the sun rises higher in the  sky  and then sets in the evening.

[Stephen Arbogast]

Correction   ....    Pierre Terrier's  software  is a modification of  Marcus Leeche's   software presented  in a  BAA  seminar.

[Stephen Arbogast]

Here   is what   I am using  that  fits  in a  window   screen  shot...

[Stephen Arbogast]

Very cool both figuratively and  literally...     The  sun is setting  here in South West  Colorado   behind the  La Plata  Mountains.  The    temperature  has already  dropped about   10 F.   One  can se e my  lna  gain  increasing......   

[Stephen Arbogast]

Sorry,   my  country   still has not converted to Metric!!!

[Stephen Arbogast]

Good   results   ....    I am  starting  to  record raw  data  in  ezRA format   so that I can use  ezRA   to post  process...

Stephen

[Stephen Arbogast]

Very  cool.... the milky way  out  of my beam..... 

[Stephen Arbogast]

Very cool here is  a screen  capture..    I  cannot   emphasize   enough that we   should  be using  GNU Radio for   future  real time   data capture   ..    ezRA  can be  used  for  post  processing ......   GNU   Radio   has   built in   ring  buffers  and   thread  management  and  version  4 is  promising    improvements.....   

[b alex pettit jr]

How about capturing 6 hrs or so of drift scan to show the Passage of the Sun through the disco_dish  @ high noon .

I'd like to see that pattern in this power trace

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

[b alex pettit jr]

change that to +- 6 hrs = 12 hr drift scan through Noon

On Saturday, October 4, 2025 at 02:41:35 AM EDT, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

How about capturing 6 hrs or so of drift scan to show the Passage of the Sun through the disco_dish  @ high noon .

I'd like to see that pattern in this power trace

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

[Stephen Arbogast]

So  far  I  have captured this..       the  bump   to the  right   is high noon  for me....

[Stephen Arbogast]

We  must  be   careful  of  digital  signal  processing ..     As  Marcus   Leech  has explained      errors   can be  introduced  in the  single pole low  pass  IIR  filter  if  alpha is too  low.   I   have set my split_ratio  to  2000..  The  errors   come from  limits  in   fundamentals  of numerical  computation...

[b alex pettit jr]

Was the Dish positioned at the Meridian, and at the Declination ~ of the Sun ?  ( currently -5 deg Dec )

aka did the Sun pass through the center of the Beam ?  

From the plot below, the Sun created a power level increase of ~  0.06   (  dB ?? )

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

On Saturday, October 4, 2025 at 02:50:19 AM EDT, 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

So  far  I  have captured this..       the  bump   to the  right   is high noon  for me....

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

[Stephen Arbogast]

azimuth = 180

elevation = 52.8

so that declination   = 0.07

[b alex pettit jr]

Is that value scaled in "dB" ???

If So, that is a very small change for a Sun transit ..   granted, the Sun is only 1/2 dg diameter and that is averaged in with the rest of the sky, but ..

Measure Earth vs Cold Sky .. should be a few to several dB..

[b alex pettit jr]

Regardless of the 'Units', the signal looks less than expected ... could be hardware or software

[Lester Veenstra]

Interesting but why is a good rf absorbing foam not closer to ambient (nominal 290K)?  Is it possibly not filling the main beam?

 

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: Friday, October 3, 2025 12:41 PM
To: 'Lester Veenstra' via Society of Amateur Radio Astronomers
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

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[b alex pettit jr]

 2" of the Eccosorb works ...

[Lester Veenstra]

Any reason why 2 inch does not approximate room temp?

 

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 8, 2025 8:30 AM
To: 'Lester Veenstra' via Society of Amateur Radio Astronomers
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

 

 

 

 

 2" of the Eccosorb works ...

 

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[b alex pettit jr]

All samples covered the feed choke ring 100%    different conductivity  / density ..

The high density foam was crumbly due to its high carbon content, the others not so much.

[b alex pettit jr]

?? It Does.

[Lester Veenstra]

Am I miss reading this?

 

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: Friday, October 10, 2025 9:01 AM
To: 'Lester Veenstra' via Society of Amateur Radio Astronomers
Subject: Re: [SARA] Re: Peltier cooling for LNA with Discovery Dish

 

?? It Does.

 

On Friday, October 10, 2025 at 07:38:58 AM EDT, 'Lester Veenstra' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

 

 

Any reason why 2 inch does not approximate room temp?

 

 

 

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