An experiment: How small of an antenna can detect the 21cm hydrogen line?
2,334 views
Skip to first unread message
Jan Lustrup LA3EQ JO28XJ_79FX
Feb 1, 2012, 2:55:54 PM2/1/12
to sara...@googlegroups.com, Tor Sætre
Has anyone else done this or similar
experiment?
Feb 1-2012
I did an experiment today to see
just how small an antenna I could be use to detect the hydrogen line
at 21cm.
I used three antennas for this experiment
today.
A horn (0.98m x 0.77m mouth)....
a double quadloop with "cake box lid" reflector
and....
a simple dipole with a single wire
reflector.
The ULNA I used was from Radio
Astronomy Supply. ( 0.32dB NF), 25
meters long RG-213 coaxial cable (with N-type connectors) run to the
house, then first a 21cm bandpass filter to do away with cellphone
interference, a second low noise LNA, and then two MAR-6 MMIC's
to make up for filter/cable/connector loss and to get get a decent level to
feed my HP spectrumanalyzer (@ -60dBm).
The analyzer was set for 10kHz BW and video
filtering at max, scan time at lowest speed (aprx 2min/MHz)
it's YIG frequency oscillator is
"free running" so the scan frequency is not excactly centered at 1420.5MHz
, but one can clearly see the hydrogen line around the middle of
chart..
The spectrum scan plots were done with the
spectrum analyzer D.C. vertical log output going to a dual TL-082 op amp
for level offset seting and filtering ( 2,2M Ohm to 1uF cap)+ 10X
amplification, feeding my LabJack 12 bit A/D converter, then the data
output USB goes to my 3.4GHz tripplecoare PC running Radio Skypipe
chart recorder under 'Windows 7.
Scanplot: Each scanplot shows 100kHz
horizontal division starting frfom the left at 1420.0MHz and ending at the
right at 1421.0MHz. and vertical divisions are dB/volt.
All antennas were pointed straight up towards
zenith (+ 60 Dec at my latitude). The gain was adjusted so the background
noise level showed appx -60dBm +/- 0.1 dB @ 1420.0MHz before
each scan.
As a reference level (around -60dBm is displayed as
0 dB on radio Skypipe chart) I pointed each antenna
towards coldsky @ 1420.0MHz.
Below are the results:
Even a simple dipole could detect the hydrogen line, but the
signal was burried in the noise, so one needs to filter and average
whole lot.
Even though these simple antennas (except the horn
antenna) pick up alot of hydrogen spinn/flipp photons from a very large area of
the sky, it also picks up alot of ground noise from the ground, buildings, trees
etc.
The hydrogen profiles you are used to seeing are
now more or less smeered out over a wide bandwith, so much fine
detail is lost, and averaged out, so you tend to get a bellshape profile
centered around 1420.4MHz (bad news if you want to do a sky
survey). This is due to the extreme wide
main antenna lobe.
1) Horn: The
maximun peak of hydrogen line showed up as 2,1dB
signal above background noise.
2) 2X quadloop: The maximun peak of
hydrogen line showed up at 0.7dB above
background nosie.
3) Dipole with wire
reflector: The maximun peak of hydrogen
line showed up at 0.5dB above background
noise.
Jan Lustrup LA3EQ
Norway
To download my hydrogen line survey with the horn
antenna last year clikk here: http://www.qsl.net/la3eq/radioastronomy/profiles/profiling.doc
--------------------------------------------------------------------------------------------------------------------------------------
Don Latham
Feb 1, 2012, 3:12:16 PM2/1/12
to sara...@googlegroups.com
Lovely, Jan.
> I did an experiment today to see just how small an antenna I could be
> use to detect the hydrogen line at 21cm.
--
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com
Marcus D. Leech
Feb 1, 2012, 6:08:30 PM2/1/12
to sara...@googlegroups.com
On 01/02/12 02:55 PM, Jan Lustrup LA3EQ JO28XJ_79FX wrote:
Has anyone else done this or similar experiment?Feb 1-2012I did an experiment today to see just how small an antenna I could be use to detect the hydrogen line at 21cm.I used three antennas for this experiment today.A horn (0.98m x 0.77m mouth)....a double quadloop with "cake box lid" reflector and....a simple dipole with a single wire reflector.
I easily detected the 21cm line years ago with my 1.2M dish, and
recently Hugh Pett in Kelowna,BC, was able
to detect the hydrogen line with a helical antenna about 2M long, one of my LNAs, and an SDR receiver.
to detect the hydrogen line with a helical antenna about 2M long, one of my LNAs, and an SDR receiver.
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
-- Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
Jim Sky
Feb 1, 2012, 7:49:42 PM2/1/12
to sara...@googlegroups.com
I have used just the transition section of my celotex horn to see
the line. Homebrew 1 dB? LNA (not so good by todays standards) ,
swept Cable TV tuner, homebrew IF and old oscilloscope.
jim s
jim s
Reply all
Reply to author
Forward
0 new messages