This is a short version, the final of the ARTICLE describing how to build the Weather satellite 137 MHz V-dipole antenna. Complete text article will be published soon in the PDF format that will include background and a bit of theory how I came to idea to design this simple to build antenna. I decide to build the horizontal V-dipole antenna and to use all advantages this antenna offer.
Horizontal V-dipole
Ones we know how the antenna should look like just a simple dipole antenna
calculations should be applied. Using the simple formula for the ½ wavelength
dipole we get the following:
L(m) = 147 / F(MHz)
L(m) = 147 / 137.5
L = 1.068 m = 106.8cm
Each leg = 53.4 cm
Important: The length of the
each leg should include the connecting wire's length up to the coaxial
connector or coax. Keep this length as short as possible but it will be difficult
to stay bellow 1.5 cm.
For a dipole legs I did use the 1/8“ (3.25mm) aluminum rods. Do not use a
ferromagnetic materials due to increased losses caused by the skin effect. The
center of the dipole is made of Choc block terminals where the aluminum rods
are secured on one side and the coax from the other side of the terminal. The
center hole on the Choc block is used to secure the Choc block to the /mast bracket so the
antenna can be easily mounted on the mast/pole. Run the 50 or 75 ohms coaxial
cable to your receiving equipment. Bend the dipole legs to create a 120 degrees
angle and point the antenna to the North-South direction. You are ready for the
NOAA WX sat reception.
Results
My location is not a perfect but still very good for the satellite
reception. I have a clear horizon to the North but hills and a high voltage
power lines to the South limiting my south elevation to 7 degrees. The antenna
is fixed on the roof antenna pole, 8 meters above the ground.
First test made was including the barefoot setup, usually used by the beginners
looking to have fun and quickly receive the weather sat pictures. Starting from
the antenna (V-dipole) there was 2 mtrs of RG-213 cable / N connector followed
by N/N adapter and 12 mtrs of H-2000 cable. Another N/N adapter followed by 10
mtrs of RG-214 cable with another N/PL259 adapter. Finally, there was 1mtr of
flexible but lossy RG-58 cable and BNC/SMA adapter to match the RTL.SDR dongle connector. All together, there was 25
mtrs of the mixed quality cables and 4 coaxial adapters. On the dongle side
there was also SMA/SMA DC block used to isolate the DC from the dongle bias-t.
I was really pleased with the received picture quality despite the
mentioned limitations. There is a noise in the picture present close to the
horizon due to obstacles in the South and a weaker signals on the North. These
are really remote parts of the World and the air masses from that areas are not
affecting the weather where I am living. I found out that the Signal to noise
ratio (S/n) required for the noise free picture is close to 22dB. Bellow that,
the picture start to be noisy, resulting a black strips across the received
picture.
First test conclusion, a simple DVB-T dongle and a 20 meters of the SAT-TV
grade coaxial cable using the horizontal V-dipole can deliver quality and good
enough picture. Here you can see the reception using a barefoot setup.
Second test was made using the advanced setup. V-dipole antenna and an
FM-notch filter with the LNA4ALL with a Bias-t and ESD protection modification
on the antenna. The same coaxial length and the RTL.SDR v.2 dongle. WXtoIMG was
setup for 0 to 0 degrees elevation reception to get the complete pass and
evaluate the location regarding the blind elevation spots. Performance and
received picture was much better, mainly towards the North direction where the
picture was received down to 0 degrees elevation. Towards the South, the
problem with the hill and the power line is still present but less visible than
using a barefoot setup. Another advantage is that the signal to noise is higher
and the degradation in the picture caused by strong airplane signals in 137Mhz
band is not visible as the S/n is still high, over 22dB to meet the
requirements for the noise free reception. The top-notch setup should include
the 137Mhz steep band-pass filter and the LNA on the antenna.
Presented V-dipole horizontal plane antenna is a simple DIY project that
will deliver good results in receiving the 137 MHz weather satellite transmissions.
All performed test delivered very good and excellent pictures despite using a
home depot cheap materials and hand tools. This can be a beginner antenna
project for all RTL dongle users where the success is guarantied.
Awesome what is the software setup?
ReplyDeleteMy kids will love this
Love to know
Hello Paul, used SW:
ReplyDeleteSDR#
WXtoIMG
Virtual Audio Cable
Adam
Hi Adam,
DeleteI am going to build the antenna but I have questions about VSWR of this antenna: Is it matching 50 ohm? Should I be worried about it?
Thank you,
Hooman
VE3HJZ
Adam, sure beats the QFH antenna and the 3db loss is nothing especially with your L A in line to boost the signal.
ReplyDeleteAdam, thanks for these instructions. I've been using a discone and RTL-SDR.com v3, which gets good enough pictures, but the SNR hovers around 23-24, and there are many fuzzy lines. With your design the SNR is 28-30, and I get super-clear pictures.
ReplyDeleteThank you!
-Gabe
Hello Gabe, thanks for the update. Glad to hear that you have improved your WX sat reception. Saying that the simplest things are the best is true in this case.
DeleteAny update on new working keys for wxtoimg? The ones listed on its homepage are no longer valid after mid February.
ReplyDeletesomeone shared their key on reddit since the owner of software cant be found and he provided free keys anyway
DeleteIf anyone is curious of the performance out in the field with an Airspy receiver.
ReplyDeletehttp://imgur.com/a/Crd8T
Thank you Adam!
I'm going to be using 1/4 in. aluminum rods. What would I need to change the length to for the elements and is there any other values I would also have to change?
ReplyDeleteYou can use the same length also for the 1/4 in rods. Antenna is quite broadband and this will not affect the performance.
DeleteWhat if I use copper tubing? Will I need to adjust anything? I ask because that's what I have on hand.
ReplyDeleteAlso, this design suggests using half wavelength, could I use full wavelength? Would that increase the reception?
DeleteIts OK but the lengths will have to be a little shorter.
DeleteHello i have built this antenna, and with sdr# i dont receive any signal, i use gpredict to track satellite, and wait until its above me, and sintonize the APT downlink but not signal receive,
ReplyDeletedoes de antenna have to be outside my bedroom? on the roof?
i want to receive noaa transmision, please help me
pd: i respect all the measures of the antenna
Basement
DeleteWhat did you say that other signal was? I couldn't find a decoder or anything
ReplyDeletehi
ReplyDeletethanks for all
how polarized antenna?
1) S >| N
or
2) S |< N
" > " symbol is antenna
like 1
Deletegday! im wondering if i point to the magnetic or geographic north.. any help?
ReplyDeleteHi Diogo,
DeleteI'm using this in the UK and as long as I keep it 'roughly' N/S it seems to pick up OK. Try tweaking direction it as you receive a signal.
Hope this helps.......
hii,
ReplyDeletesir i will submit your pdf as an supplymentary material in my research paper so any problem?
what amp rating are the choc blocks?
ReplyDeleteI've built this and it works great. Was getting Meteor images but not when it went overhead. Trying a dual v-dipole design and having all kinds of issues....lots of noise.
ReplyDeleteI found a dicone scanner ant works good
ReplyDeleteThank you for your excellent article. I feel good about your article.
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