Regarding lunar and terrestrial radio communication, this is a goal pursued by many amateur enthusiasts. The large spatial losses and low lunar reflection rates associated with direct frequency communication make it unattainable for most hams. I have collaborated with some domestic hams to form a group, which we call the "Weak Chicken Lunar Communication Team." After over a year of practical tests and communication experiments, we have summarized some practical techniques for terrestrial-lunar communication. We hope that these techniques will encourage more new hams to seriously consider lunar and terrestrial radio communication and build their confidence.
First, it's important to clarify that lunar-Earth reflection is a direct frequency communication. The losses involved stem from the spatial loss due to the distance between the Moon and Earth, the low reflectivity of the lunar surface, and the influence of the Earth-Moon distance. While the specific calculation process isn't detailed here, the practical communication summary can be summarized as:
For extremely large-scale antennas (HB9Q, NC1I, DL7APV), we only need to operate at the appropriate time with a minimum power of 25W and a 15-element UHF Yagi antenna to achieve the first successful Q65 mode communication. (This requires favorable conditions, including timing, location, and personnel; it is recommended to purchase a BG7XWF U17 low-noise Yagi to improve success rates.)
For a similarly sized mid-sized station, at UHF frequencies, a Yagi antenna with at least 22 dBi gain is required. With an output power of approximately 70W (IC-910H, IC-9700) in Q65 mode, it can perform echo testing.
So, with Uni-Link EME, let's start by outlining the minimum requirements: a 25W linear radio, such as the FT817 or IC705, paired with a linear amplifier (e.g., Wein), and a Foshan Yagi U15 antenna. It seems straightforward, and many domestic amateur radio operators who transmit to satellites using this setup actually meet these requirements. However, why aren't they successful? The biggest problem is the inherent noise level. For EME, we need to appreciate every 0.1 dB of signal strength. Many amateur radio operators have excessive background noise, making it impossible to detect signals and leading to a loss of confidence.
The frequencies used for EME (Earth-Moon-Earth) communication include 50 MHz, 144 MHz, 432 MHz, 1.2 GHz, 2.3 GHz, and 10 GHz. For new ham radio operators, a Yagi antenna with a gain of 18 dBi at VHF (with an 8-meter main boom) is too large. The availability of 1.2 GHz equipment is limited, making the initial EME communication on 432 MHz the easiest. We will provide an example of a practical demonstration of the first EME communication on 432 MHz in the UHF band.
Equipment: IC-705, Weinan amplifier, u15 Yagi antenna, tripod, 5m of 50-5 meter coaxial cable, tripod antenna mount, computer, large capacity battery (essential for weak stations needing extended operation), small mallet, etc.
Software: wsjt (desktop), Super Moon mini-app (mobile)
Before establishing formal communication, our primary preparation was to arrange an appointment with a key contact. Given that large-scale collaborations are not constant and the frequency is unpredictable, we needed to make arrangements in advance.
We also need to know some astronomical knowledge. The moon doesn't have a fixed rising and setting time; we can check the exact times for sunrise and sunset on WeChat Super Moon or other software. For HB9Q, when the moon sets, they are observing its rise, and there is an additional reflection gain (clearly visible) when the moon is near the horizon at UHF frequencies. Therefore, it's recommended to schedule the observation a few hours before sunset on that day.
EME, one of our frequently used forums, is at https://hb9q.ch/
After formally registering, access the forum and use the designated frequency area to post your CQ information. The lower section is for general chat.
For example:CQ 432.060, 1st Q65B-1500Hz-CFOM-H-POL* (At sunrise, first transmission, frequency 432.060 MHz, mode Q65B, center frequency set to 1500 Hz, Doppler CFOM mode (constant frequency), horizontal polarization)（H)）
The first time you contact HB9Q, you can either mention him in a forum post or email him through his QRZ page.
Once the agreed-upon time has arrived, go to an outdoor location or a rooftop, and find a place with very low ambient noise. The spherical space should be unobstructed.
Before formally connecting to the network, we need to configure the wxjt software.
The settings mentioned above should be adjusted according to your own radio; ensure that CAT and PPT are properly connected, and that audio works.
In the software, in the lower left corner, first select Q65 mode under "Mode". If the other party is using 1st, (transmit even frequencies), no need to check, transmit frequency should be based on the actual situation of the forum, to avoid collisions. (It is recommended not to transmit at the extreme edges, as this can easily cause frequency deviation and make it impossible for the other party to decode). The tolerance should be 100-200. A large tolerance will affect decoding. Accept frequency: 1500, T/R should be set to 60 seconds.
For CFOM, this is a Doppler issue. On the software interface, clicking on "Astronomy Data" in the lower left corner will display the Doppler tracking. The options on the right side show 6 modes, which are labeled from top to bottom as 1-2-3-4-5-6. The principle is: 1-5, 2-4, 3-3. For example, if CQ posts about CFOM in the forum, it's referring to the third mode (constant lunar frequency). You should also choose the third mode.
Regarding radio end settings, USB mode: it is recommended to disable AGC, set RF gain to maximum, and avoid enabling any other noise reduction functions.
Once the basic settings are complete, we can set up the equipment and visually observe the moon. Aim the antenna at the moon (don't worry about missing; even if you don't hit the moon directly, the beam will illuminate the entire lunar surface, not just a small area of it).
If the weather conditions are poor on that day, it is recommended to use a satellite tracking software to aim and calibrate (calibrate the compass to prevent excessive errors).
Next, you can examine the audio spectrum of the software. If you find that your audio spectrum is quite noisy, you don't need to select "Flat" or "Reference," and instead perform a spectrum normalization operation.
First, align the antenna with the top of the building to ensure that there are no transmission-related interference within the waterfall chart.
In WSJT-X, select "Tools" – "Measure Reference Spectrum".
Then, after waiting for one minute, click "Stop" on the main page, and you will be prompted with "Reference spectrum measured".
Then you select "Reference Specifications" in the Waterfall Chart options, which will result in a very flat waterfall chart.
Adjust the slider next to "Reference Specifications" to achieve optimal display of the signal.
The "Gain Slider" on the left (cumulative) can be changed to "(Q65_Sync)" (see image).
Regarding antenna polarization, if Europe is horizontal, from the perspective of space, it does not align with China's horizontal orientation. After all, the Earth is round. Therefore, for EME to successfully make QSOs (two-way communication), it still needs to wait for the Faraday effect in the ionosphere to rotate the signal polarization to a suitable angle. Don't rush; beginners are advised to start with horizontal polarization first, which can effectively avoid local interference signals.
Many new users are not initially aware of the Q65 audio spectrum feature, and may easily misinterpret it. The image below clearly shows the spectral characteristics.
It's clearly visible that the spectrum of Q65 consists of a collection of points, with a line-like structure on the left and a few scattered points on the right.
The next step involves patiently receiving signals and then transmitting a reply only after successfully receiving one.
It's important to note that wsjt may conflict with your manually adjusted frequency and potentially interfere with your signal, so pay close attention to this.
Here are a few suggestions if you're not receiving a signal:
Antenna polarization switching (Faraday cage rotation problem)
The background noise level should be low (ideally within 1 second).
Recommended: Pre-amplifier (e.g., BU435)
Use a larger antenna or array (recommended: BG7XWF's low-noise long-boom Yagi).
Check frequency, mode, and radio RF gain.
After a successful connection, be sure to transmit your LOTW log and exchange cards.
I hope everyone can successfully achieve their first EME communication.
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