I started about 5 years ago with receiving EME signals. I am a volteer at CAMRAS, the agency, which runs the former and restaurated radiotelescope of Dwingeloo. Now it is not in function of the professional ASTRON (still owner), but is managed by Camras. They use the telescope for all kind of purposes. Like radio astromical observation for students, public activities, mostly in summer for tourists and so on. Astronomy obsevations like detecting pulsars, hydrogyn line, continüm obeservations of starsystems of our galaxy.
But also we have an EME team, which uses the telescope of 25 meters for making radio connections in EME mode. Frequencies are 70 cm, 23 cm, 13 cm and maybe 3 cm. The callsign of the station is PI9RD, former PI9CAM. I often join these EME sessions too. The modes are CW, USB phone and Q65-60C WSJT-X mode.
Picture below the Dwingeloo radiotelescope. In the focul point, the weatherproof focusbox, containing the antennas and LNA’s. All LNA”s are made by G4DDK. The telescope has two electric motors for elevation and one electro motor for the azimut. At a control console inside the housing, you can align the telescope at any point in the sky and keep tracking it. Tracking because the object at the sky does not move, our earth does.
Picture below: the EME- crew at the DT during an EME contest. Jan, PA3FXB, Harry PE1 CHQ and his wife. At the back various panels, computers. In the mid the transceiver on the table, a Kenwood TS 2000 and a laptop with the program of HB9Q to communicate with other EME radioamateurs during the contest. The left computerscreen at the back is the controle console for focussing the telescope to the moon and tracking it constantly. So you have to focus only once to the moon in the control console and the telescope tracks the moon constantly. Tracking, because the position of the moon is changing constantly by the earth rotation. You only have to sit down in front of your transceiver and just make the EME contacts. With a second PC with HB9Q for communication with other EME stations. So in the picture.
So I wanted to try it out receiving EME signals of my own at home. The goal first was trying receiving PI9RD via the moon once. And that was very easy afterall. Afterwards even more was possible.
For receiving EME signals I use the following items:
A yagi antenna 67 elements. Azimut and elevation by hand by a compass rose.
A LNA, 37 db gain, noise figur of 0,23 db at 23 cm.
An homemade indigital bandpassfilter for 23 cm. To keep all kind of spurious signals, noise away. Especialy of telephone repeaters in the 900 Mhz band.
A second broadband LNA to overcome the cable loss between the antenna LNA and the bandpassfilter in the radioshack. although only 11 meters.
A SDR module, type RSP1A from SDRPLAY.
Software: SDR Console and WSJT-X in mode Q65-60C. Former was JT 65C.
Below my antenna for receiving EME signals on 23 cm in the back of my garden. It is a 67 elements yagi antenna. Connected directly, without cable or relay, at the dipole, the G4DDK LNA. At groundlevel a 12 volt battery for supplying 12 volt to the LNA. Also to be seen, the dish antenna and the dipole antenna for the Hf amateur bands.
Above an example of detected EME signals, A Japanese radioamateur JA6AHB. Signalstrength -20 to -22 db. Working with a Polish station, SP7EXY, -20 db.
Above the picture of the WSJT-X sceen, above the waterfall screen. Note that the signal in still JT65C is very weak, but still detected.
My antenna is a 67 elements yagi antenna, mostly just enough for receiving EME signals in WSJT-X JT65C, but at the moment using a new mode, WSJT-X Q65-30C. The lowest signal I can detect is -23 db. The strongest signal I detected was the station PI9CAM, now PI9RD at the Dwingeloo radiotelescope (25 meter parabole). Signal strengh is about – 3 db.
USB phone signals are very difficult. Often the signals are that weak, that I could not see them in the waterfall screen. Even WSJT-X signals. More difficulties are very high trees in front of my house, direction south and south-west. So high elevations are necessary. Elevation at summertime haave to be > 30 degrees. Also large path loss of nearly -2 db can give trouble. A pathloss of -1.6 db is still acceptable. The signal is detectable, but not to be seen in the waterfall screen.
And very important: the weather! To operate your antenna in a heavy rainshower is not such a pleasure, hi.
Very helpfull then, when seeing not the signals in the waterfall, is to use the site of HB9Q to see at what frequency stations are transmitting, and then tuning your receiver to that frequency. Plus and minus doppler frequency correction.
Better should be used a large parabole antenna. It has much more gain. But that is quit another construction. Now I change the azimut and elevation by hand by a compass rose. You have to change them mostly every 10 minutes. But it workes.
In all these years, I managed to detect in this way, about 35 stations all over the world.
So receiving EME signals with a yagi antenna is possible, but signals are mostly weak. The larger the parabole antenna of the EME transmitting station, the stronger the signal. See the picture below.
HB9Q is very helpful then.
So with simple things a lot is possible.
Picture below my latest scores of EME stations.
This new part below is under construction!
At 8 december 2024 I started a new experiment. Putting a new feed in my dish antenna of 1,5 meter. A feed for 23 cm.
Normally there was a feed for 21 cm. For observation of the Hydrogyn line. Now I wanted to use the dish antenna also for receiving 23 cm EME signals. An experiment. If there is an improvement using the dish antenna instead of the 67 elements yagi antenna.
About a half year ago I constructed this new feed already, but did not use it yet since that time. The feed is again a Cantenna feed. With a calculator program, I adjusted the sizes of this new feed. Off course the sizes became larger for 23 cm. The diameter size stayed the same. The reason is, that I did not want that the illumination of the dish would decrease by using a larger diameter. So the illumination had to be maximal. So the length became pretty large. With my 23 cm transmitter I adjusted it for a acceptable SWR, by adjusting the length of the radiator inside the feed. That was most critical.
But now I decided to put this new feed in my dish antenna, in order to use it for receiving EME signals on 23 cm. Just to look if there is an improvement of the reception.
The expectation was, this new antenna will be better then my 67 element yagi. Hopefully it is.
The facts below:
1 – My yagi: 67 elements, gain 19 dB, opening angle 13,7 degrees.
2 – My homemade dish antenna: gain 24 db, opening angle 10 degrees (hopely :)). To make a dish antenna of your own is most pleasant.
You can find on internet all kind of handy calculators for construction dish antennas and feeds. So no difficult formulas to deal with.
The gain is calculated from the following calculator:
So the calculated gain of my dish antenna is 24 dB.
What is the opening angle of my dish antenna:
Beamwidth = 70 * lambda /D, where
lambda is wavelength antenna in meters.
D is diameter dish in meters.
So the opening angle from my dish antenna is 70 *0,23/1,5 = 10 degrees.
So this is a large improvement, comparing it with the 67 elements yagi antenna.
For calculating the dimension of my feed (Cantenna feed) the following calculator:
I used a suitable tin can with a diameter of 15 cm. I bought this in a hardware store. This diameter I have to use in the calculator.
In the calculations, you can see that the lower- and upper cuttoff frequencies are very good. And that the length L is pretty large, also seen in the picture below. But that is not a problem, I think.
For the focuspoint of the antenna the following calculator is used. In this calculator is it the focal length F = 0,669 meter. That is the point, where the feed must be placed. The deph H , you can choose yourselves. But in such a way that you have a reasonable F/D ratio. The F/D ratio depends upon the focal length. The F/D ratio is then at a focal point length of 0.21 m , 0,6696/1,5 = 0,4464 meters. This value is reasonable.
If the f/D ratio is low, say 0.25 to 0.35 then the feed will be very close to the dish and needs to spread its power at a wide angle by your feed, to efficiently illuminate the dish. The feed therefore needs to be of small diameter. If the f/D is 0.25, the feed is level with the dish aperture, which may make it difficult to make a satisfactory feed.
If the f/D is large like 0.5 to 0.75 then the feed will be further away from the dish and needs to project its power into a narrower angle. The feed needs to be of larger diameter. But when the diameter gets larger, the illumination of the dish will decrease. The feed is like a shadow for the illumination.
But the swapping of both the feeds, 21 cm and 23 cm, has to be most easy. That is what I wanted. So a new construction had to be carried out for this. I just wanted keeping the antenna in use for both frequency bands, 21 cm and 23 cm.
Picture below an impression of the the new feed in my dish antenna. Watch the large length of the feed.
After having mounted the new feed, I tested the SWR. I was still very well.
Now I have to check the results, by receiving the EME signals. The LNA from G4DDK will be put between the Cantenna input and the cable. Now I have to wait for a good weather situation, it is wintertime now, and favorable moon view, less path loss.