Loop Yagi antenna for 1420 Mhz
Siddhartha Jain
Hoping to do my first experiment with radio astronomy, I had this plan
in mind.
First - The antenna
---------------------------
I did some research on the various antennas for 1420 Mhz and given the
limited space I have, I was wondering how well would a quad loop yagi
work? I saw this design in use here:
http://home.comcast.net/~prutchi/index_files/astronomy.htm
So to save space, would it work if I used four five-wavelength boom-
length in a 2x2 stack? Since no such loop yagis are commercially
available, I was thinking of building them using:
- For boom, wooden dowel cut to the required boom length
- 14 loops, each of one wavelength perimeter and one reflector loop of
a slightly larger perimeter using 12 AWG solid insulated copper wire
- Feed the driven loop element with RG59 coax directly
Connect the coax to a satellite dish signal strength meter, point the
antenna (single, not the array) towards the Sun and see if the needle
gets excited.
Does this sound like a reasonable experiment for a newbie?
Thanks,
- Siddhartha
kl7uw
I can tell you a little about the use of Loop Yagis since I am using
two 45-element loop yagis at 1296-MHz for satellite ham radio use.
These are manufacturered by Directive Systems as a kit of loops and a
small diameter boom that packs well for shipping by mail.
http://www.directivesystems.com/
They make a 14-element loop yagi (LY) so this will give you a
reference to compare with. The 14-element LY exhibits a gain of 15 dB
on a three-foot boom, so four of these would result in an array of 21
dBi gain. My 45-LY have a gain of 20 dB and array gain of 23-dBi.
They are 12-foot long and stack about 16-inches apart.
Now compare this with a 3m (10-foot) dish which is the standard
antenna in use for either 1296 eme (moonbounce) or 1420 radio
astronomy. This antenna has a gain of 30-dBi (more than 4 times what
my two and nearly ten times your proposed array). My point in telling
you this is that your antenna array will be significantly less
sensitive than the usual amateur radio astronomy antenna. How this
will affect your abitlity to detect celestial objects is hard to say.
You will be able to see the Sun and maybe the Moon.
You will need one more item to make this work. You need a good LNA
for 1420 MHz. The satellite finder is a broadband detector and
indicator, but you need low noise gain ahead of it. Probably at least
30-dB gain.
I do not know your financial situation, but one could make a decent
antenna of four 45 or 55 element LY at 1300 MHz (26-27 dBi array gain)
buying directly from Dirctive Systems. The antennas would cost $600
and a four-way combiner 33-4PD is $78. Or one could build a system at
1600 MHz with four 44-element yagis they make.
You could write them about making a custom antenna for 1420 MHz but
that may be expensive.
But using a ten foot dish would be easier and probably more effective
if you can get one. In the USA they are often available free from
home owners who have gone to using small ku-band TV dishes (if you
offer to remove the dish for them).
As a side note: I have acquired a commercial 4.9m (16-foot) aluminum
dish that was used for educational satellite TV in the Alaska School
System when that was delivered on C-band. Now everything has gone to
Ku-band. My dish cost me $200. I will have to make a feed which
probably will cost another $100 or more in materials, and a motorized
mount which will be $300 or more. I already have a 1420 LNA and
1420/144 and 144/28 MHz converters so that my 28 MHz SDR-IQ will be
used at 190-KHz bandwidth for continuum observations.
I hope this helps you.
Ed Cole, SARA Board Member
http://www.kl7uw.com/raseti.htm
Brian
design instructions in the "VHF-UHF Manual" by Evans and Jessop
(1977). They call this antenna a "quad-yagi". They have all of the
dimensions labeled in the book (in inches) for an antenna for
1.296GHz. I setup an Excel spreadsheet to scale this antenna to an
arbitrary frequency so I could build one for 2.4 GHz (802.11b
networking). If you would like a copy, please let me know and I'll
post it to my website.
Brian
Siddhartha Jain
useful from a newbie's perspective.
Costs aside (since most of my $$ are sunk in amateur radio gear), the
issue I face is space since I live in a rented apartment. I think that
says enough about my 3D constraints. I could've probably gotten away
with a quad loop yagi with each yagi about 3 feet but as I understand
from your posts and other material on the internet that will only be
good for solar observations. Anything bigger will run into local
zoning laws as I found out when I wanted to put up a vertical for HF.
Incidentally, I did find some designs for loop yagis in the ARRL
antenna handbook and some construction notes on the internet too.
Brian - On 2.4 Ghz antennas, I recently ordered a yagi for the same
purpose (connect to the Meraki wirelsss mesh network here in San
Francisco). I found a seller on ebay who had these "Enterasys
Roamabout 14dbi Yagi Antenna". I ordered one and there are four more
left so unless you want the satisfaction of having built one yourself,
this might be something worth looking at. They are $40 each including
shipping.
http://cgi.ebay.com/Enterasys-RoamAbout-14dBi-Yagi-Antenna-WiFi-802-11_W0QQitemZ290224945267QQihZ019QQcategoryZ61816QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Back to radioastro, I was wondering if there is any volunteer work
available for small projects? I was hoping that the SETI guys who work
from the same office as I do, here in Mountain View, would have some
kind of open house but they seem to have stopped the practice. I
checked with the reception and the only volunteer work they were
offering was help with sending out mailers (licking stamps and such).
I dabbled a little bit in meteor detection with a TV yagi anntena at
my previous location, Santa Clara. Santa Clara had some unused TV
channels that could be used for meteor scatter detection. Here in San
Francisco, all FM and TV channels are used, plus my proximity to Sutro
Tower gives me a lot of IF harmonic distortion.
Thanks,
- Siddhartha
WV6U
--
- Siddhartha
WV6U
Rodney Howe
If tight on space, and interested in looking at the sun this might be a
place to start:
http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html
Has anyone tried to modify a C band TRVO LNB to match the 2800MHz frequency
of the 10.7 cm line? Pehaps a dab of solder on the feed element would make
it 1/4 wavelength, but would there need to be modifications to the LNB
itself, and the waveguide (feedhorn)? This would be a neat project I think.
Can these old feehorns be re-tuned to look at the 10.7 cm line for
monitoring the Solar Index?
http://www.nwra-az.com/spawx/f10.html
http://en.wikipedia.org/wiki/Solar_cycle
For some history: Dominion Radio Astrophysical Observatory:
http://www.drao-ofr.hia-iha.nrc-cnrc.gc.ca/icarus/www/sol_home.shtml
Rodney
Brian
the design parameters I found in the "VHF-UHF Manual" (Evans, Jessop
1977 http://books.google.com/books?id=zTNUAAAACAAJ). I've posted the
worksheet on my server here at home:
http://projectdevel.homeip.net/files/quad-yagi/
Brian
kl7uw
Considering your apartment constraints it will be a challenge to make
a workable antenna for 1420 RA. Going up in frequency may be a
partial solution. Could you handle a 1-meter dish (39-inch)? At 10.7
cm that would have quite a bit more gain (around 26-28 dBi) than loop
yagis which are reaching marginal design limits at this frequency.
I have an 85cm dish (33-inch) that I use for 2.4 GHz satellite
reception. I has a very good LNA (NF=0.6 dB) and super gain of 41
dB. I would imagine it would work well with a satellite finder
detector/meter. Sun measurements with narrowband receivers indicated
about 5-6 dB of sun noise, and about 3-dB of cold sky/warm earth
differential. This was using a bandwidth of 2.2 KHz. You collect
much more noise energy as the bandwidth increases. The Sat-Finder
probably operates in several MHz of bandwidth. Noise increases
proportional with bandwidth Pn (dBm) => 20LogB (Hz), so an increase
from 2.2 KHz to 2.2 MHz is 2200/2.2 = 100 power ratio or 20 dB!
The biggest challenge to making a 10.7 cm RT would then be converting
a C-band sat-TV LNA or LNB from 3.7 to 2.8 GHz.
If you have access to a microwave signal generator and signal analyzer
that would help. A noise figure meter would also be helpful. Would
the SETI group allow you access to such equipment?
Baring that then a 2.4 GHz LNA might be usefull with a very good high
pass RF filter to elimate everything below 2.6 GHz.
There seems to be more equipent available for communications/ham
frequencies than RA. You need to avoid 2.4-2.6 GHz becuase this band
is loaded with wireless internet signals that would interefere with
RA.
Have you considered the 3cm Itty Bitty Radiotelescope Project?
Regards,
Ed
On Apr 26, 3:52 pm, "Rodney Howe" <ah...@frii.com> wrote:
> Siddhartha, SARA
>
> If tight on space, and interested in looking at the sun this might be a
> place to start:http://www.aoc.nrao.edu/epo/teachers/ittybitty/procedure.html
>
> Has anyone tried to modify a C band TRVO LNB to match the 2800MHz frequency
> of the 10.7 cm line? Pehaps a dab of solder on the feed element would make
> it 1/4 wavelength, but would there need to be modifications to the LNB
> itself, and the waveguide (feedhorn)? This would be a neat project I think.
> Can these old feehorns be re-tuned to look at the 10.7 cm line for
> > Back to radioastro, I was wondering if there is any volunteer work
> > available for small projects? I was hoping that the SETI guys who work
> > from the same office as I do, here in Mountain View, would have some
> > kind of open house but they seem to have stopped the practice. I
> > checked with the reception and the only volunteer work they were
> > offering was help with sending out mailers (licking stamps and such).
>
> > I dabbled a little bit in meteor detection with a TV yagi anntena at
> > my previous location, Santa Clara. Santa Clara had some unused TV
> > channels that could be used for meteor scatter detection. Here in San
> > Francisco, all FM and TV channels are used, plus my proximity to Sutro
> > Tower gives me a lot of IF harmonic distortion.
>
> > Thanks,
>
> > - Siddhartha
> > WV6U
>
>
> >> If you are interested in building the antenna from scratch, there are
> >> design instructions in the "VHF-UHF Manual" by Evans and Jessop
> >> (1977). They call this antenna a "quad-yagi". They have all of the
> >> dimensions labeled in the book (in inches) for an antenna for
> >> 1.296GHz. I setup an Excel spreadsheet to scale this antenna to an
> >> arbitrary frequency so I could build one for 2.4 GHz (802.11b
> >> networking). If you would like a copy, please let me know and I'll
> >> post it to my website.
>
> >> Brian
>
> > --
> > - Siddhartha
>
> - Show quoted text -
Siddhartha Jain
Yes, I think a 33"-39" dish should be ok. I was eyeing a 36" dish on
craigslist that is going for cheap. But I am more interested in
something beyond solar observations.
Q. I was reading more about going up on the frequency and came across
all these papers, mostly very scientific, about 12 Ghz methanol
masers. Can someone please throw more light on this in a little bit
watered down language :) The Saser project page only has some data
collected from 2002. Also, there are several projects that go further
up, 36 Ghz, 44 Ghz .... upto 96 Ghz. What does this mean for amateurs?
About getting any access to SETI's infrastructure or , I am not sure.
They haven't had an open house in the last year at least. Maybe I can
ask one the employees when I run into them in the hallways of the
building. I was hoping if any of them are on this list then maybe they
could let me know about any volunteer work available for an
intermediate computer / beginner amateur radio geek :)
- Siddhartha
--
- Siddhartha
WV6U
Randall family
John Roberts
On May 13, 2008, at 4:05 PM, Randall family wrote:
>
> See if this bounces?
>
It went through.