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====== The G4KLX 23cms EME Setup ======

**Background**

I have long wanted to start doing moonbounce, known as Earth-Moon-Earth (EME), as I felt it represented one of the most challenging parts of the hobby. It's almost at the extreme sports end of it in fact, everything has to be bigger, better, and well engineered, compared to other parts of the hobby. Having worked DX on most bands from 10m up to 3cms in my time, I needed a new challenge.

I first operated on EME in 1992 on 2m from the shack of Dave G0LBK. It was done using CW, very narrow receive filters, very high powers and whopping great Yagis. I worked three stations, two being in the USA and one in Germany. Although very impressive, it was not the direction that I wanted to go. The advent of weak signal digital modes for EME in the early 2000s piqued my interest and made the barrier to entry into EME much lower than before. I contemplated a 23cms EME system using a few hundred Watts and a 3m dish. To this end I bought a suitable dish feed from OK1DFC but then real life got in the way, and the feed stayed in its box for the next twenty years!

The path length to the moon is approximately 250,000 kms each way, and the Moon is a rather poor reflector too. This means that the path loss, which is frequency dependent, is very high indeed and needs to be overcome to stand any chance of working people.

My location is very poor for most amateur radio activities. I'm in a valley, and hemmed in by houses. HF and 6m ionospheric propagation is pretty good but otherwise it is a very limited location, unfortunately this also applies to EME. Looking East and West, my minimum elevation angle is close to 45 degrees, and South it goes down to 25 degrees. This still gives plenty of opportunities for working EME but I miss out on some of the more extreme DX that may be available, and also lose many hours of operating time waiting for the moon to appear.

**2024 Arrives**

I bought at IC-905 towards the end of 2023 nominally for operation using microwaves on hill tops, it can operate anywhere from 2m to 3cms excluding 9cms. It has built-in GPS frequency stabilisation, and is a rather lovely piece of equipment, to be fair, for the price I would hope so. I would have used my IC-9700 with the Leo Bodnar GPS frequency stabilisation added, but I felt that the IC-905 offered more. They both provide 10 Watts on 23cms as standard. So the IC-905 was chosen as the prime mover for EME. From reading the EME FaceBook groups I found that a few others are also using that radio to good effect, particularly Dave KG0D.

I still needed more though. Including:

  * Dish
  * Dish feed
  * Power amplifier
  * Preamplifier
  * Dish rotator
  * Dish mount
  * Sequencer
  * Sundry bits and pieces
  * Software

**The Dish**

Although you can buy suitable dishes new, notably from [[https://www.rfhamdesign.com/products/parabolicdishkit/24meterdishkit/index.php|RF Ham Design]], they are expensive. My friend Dave G0LBK (see above) put me in contact with a G8 selling a 2.4m dish also made by RF Ham Design. The dish came with linear feeds for 23cms and 13cms and simple elevation control system. The dish was ideal and with some work could be adapted for EME operation. At 23cms the dish has a gain of approximately 27 dBi and a half power beamwidth of 5 degrees. The profile of the dish should be good to a few GHz and the mesh is very fine so would not be an issue up to almost 10 GHz but the dish profile probably would not be.

**The Dish Feed**

In the early 2000s, OK1DFC came out with the design of the [[https://kl6m.com/23cm/23CM-SEPTUM-FEED.pdf|Septum Feed]] for EME operation. This was notably simpler than previous designs and created the required circular polarisation for EME. The sense of the rotation being the opposite for transmit and receive. This is because for a typical EME path the wave is reflected three times, at my dish, at the moon, and at the far dish. With every reflection the sense of the circularity is reversed, so the received signal is always opposite from that transmitted.

The Septum Feed design did all this without the complexity of RF splitters and combiners as used by previous designs. Indeed the Septum Feed is almost completely ubiquitous on 23cms EME at this time.

Luckily I had bought one of these dish feeds already so I just needed to find it in my storage unit, which I managed to do.

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** The Power Amplifier **

I wanted to have at least 200 Watts for EME, but with the use of digital modes where the transmission time can be up to two minutes, I really needed a much larger amplifier that I could underrun to ensure that it would survive the long overs of continuous carrier.

Roger G4BEL was a well known operator in the Cambridge area, unfortunately he became a silent key in early 2024 and his equipment was disposed of. Amongst it was a 600 Watt DB6NT amplifier already built into a rack case with fans and all of the required DC switching. Just provide 28 Volts at lots of Amps and some RF and off you go. For full output about 18 Watts is required so my IC-905 at 10 Watts will never push it to full power. The amplifier was bought, along with some other bits and pieces.

** The Preamplifier **

I had hoped to buy a G4DDK preamplifier which are state of the art, but Sam has stopped making them. I therefore sourced a WD5AGO preamp which promised to have similar performance, typically a noise figure of between 0.2 and 0.3 dB and a nice high gain from a two stage design. I also bought an old DB6NT preamplifier from the G4BEL SK estate which has a noise figure of around 0.7 dB as a standby.

** The Dish Rotator **

There aren't too many options for actually pointing the dish. Many people use Slew Drives which are apparently very good, and some create completely homebrew systems and use some form of encoder to accurately measure the pointing angles. Since a 2.4m dish isn't particularly heavy, relatively speaking, and doesn't have a particularly narrow beamwidth, I went for an easy option. I bought a [[https://thedxshop.com/product/spid-ras-azimuth-elevation-rotator/|SPID RAS]] which does both azimuth and elevation control. The controller has a USB input which allows for easy software control of the positioning. There have been reports of losing alignment under normal operation, but I haven't seen that.

** The Dish Mount **

This was purpose designed by Dave G0LBK. It is similar in design to the ones used to hold a satellite dish on flat roofs and weighed down with slabs. This one was designed to be much heavier duty and is fabricated out of 50mm steel scaffold pole and angle iron, and weighed down by almost 360 kg of concrete slabs. It is very stable. My wife painted it in green Hammerite. The mount is designed to be "temporary" with no permanent mounting into the ground for move to a later location, and maybe to help with planning permission issues should they arise.

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The dish feed is hung in front of the dish on the end of two glass fibre square section poles, and with ropes holding the end for stability. The dish feed is held firmly by cut and carved (!!) wooden blocks and lengths of M6 threaded rod. All of these threaded rods have been kept away from being a multiple of a quarter wave in length to remove any interaction with RF. Therefore the only bits of metal in the view of the dish are the Septum Feed and the co-ax, and nothing else.

** The Sequencer **

This was my own design, and is in many ways the heart of the EME system. It's based on an Arduino Uno and the four relay Arduino shield, the [[https://github.com/g4klx/Sequencer|sketch]] is available from my GitHub. It has two transmit inputs and controls three relays, with timings of around 30ms between each.

Its job is to control the transmit and receive change over for the RF relays, the power amplifier, and the radio itself. The basis of the design is that the transceiver does not control the transmit/receive changeover, so that it is guaranteed that the rest of the system is changed over first. This means that the signal to change over comes from either a toggle switch on the front of the sequencer box or via a serial port from WSJT-X. The radio being the last to be switched. The serial port transmit control from WSJT-X goes via a [[https://radio.g4hsk.co.uk/2020/03/01/enhanced-usb-to-serial-ptt-interface/|G4HSK PTT opto-isolator]].

The sequencer lives in a 2U rack mount case alongside 12V and 24V power supply for the relays and pre-amplifiers, and a co-ax relay used to switch the IC-905 RF between transmit and receive.

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** Sundry Bits and Pieces **

Another 2U case holds the main amplifier power supply, 28V at up to 70A, and a 15V 10A power supply to power the SPID RAS mentioned above. All of the power supplies for the system, except for the IC-905, are from Meanwell.

Hyperflex 5 co-ax is used for most of the RF interlinks, including from the pre-amplifier back to the shack, and a length of Ecoflex 15 to carry the transmit RF from the shack to the dish feed. A Bird 43 Thruline using a 500E element is used for measuring RF output and checking that the return loss is acceptable.

At the dish feed end the pre-amplifier is mounted next to another co-ax relay which provides isolation on transmit to ensure that the pre-amplifier isn't damaged. A small dummy load is used to terminate the pre-amplifier in transmit mode. The equipment at the dish feed is protected by a supermarket carrier bag!

All RF relays are powered in receive mode to ensure that a loss of power puts everything into a safe mode and doesn't have any transmit RF going into the pre-amplifier for example.

Much of the hardware sits in a wheeled 16U rack mount case which is moved into position when needed. My shack is on the wrong side of the house for EME operation and so EME operation is done from a conservatory and apart from the rack mount, the rest of the equipment sits on a dining table when in operation.

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** The Software **

In this modern world, a PC or similar is required for operation in most parts of the hobby, and EME is included. Indeed it is the development of WSJT-X that has allowed many people to try EME who would not have been able to put out a useful signal before, or would have worked very few stations otherwise.

The rotator is controlled by [[https://www.pstrotator.com/|PstRotator]] which is commercial software, but at only $30 a go, is a good investment. It understands how to talk to the SPID RAS natively and does far more than moon positioning, unfortunately most of the rest of its functionality is unused in my application.

The heart of the operation is [[https://wsjt.sourceforge.io/wsjtx.html|WSJT-X]] and one of its sub-programs. WSJT-X connects to the IC-905 via a CAT USB cable which also transfers transmit and receive audio also. The only thing that isn't transferred over the CAT connection is the command to go into transmit which goes over a serial port (actually a USB to serial adapter) and controls the sequencer.

An extra program is also used for band monitoring named QMAP. It takes the output of an SDR and can monitor almost the whole of the EME section of the band for activity and lists all of the QSOs and CQs that it can detect. It is about 2dB less sensitive than the full WSJT-X program, but is an invaluable tool. I use an AirSpy SDR feeding into SDR Console and that feeds into QMAP, between the SDR and the pre-amplifier is a 3dB splitter and my old pre-amplifier being used as a rather over engineered gain block.

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Feedback on operation is done via the [[https://logger.hb9q.ch/|HB9Q EME Logger]]. Other EME software is available, most notably from [[https://www.vk5dj.com/doug.html|VK3UM]] (SK).

** The Results **

The results have been spectacular. I expected EME to be a struggle, and it sometimes is, but not a lot of the time. I started on my first evening running 150 Watts, the old pre-amplifier, and a linear dish feed. This latter item means that I started with a 3dB penalty immediately compared to most other operators. As was right, my first EME QSO was with Dave G0LBK, with no stress whatsoever. The sked was arranged via WhatsApp, but all information was exchanged via the moon. On that first night I worked 13 different stations!

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By the next night I had replaced the pre-amplifier with the lower noise one, and proceeded to work a total of 65 unique stations in my first week of operation with my compromised system. For the next period of operation I had replaced the dish feed with my Septum Feed and slowly increased my power to 300W or so. By March 2025 I had worked 133 unique stations off the moon (known as initials), in all continents, in 102 grids, and in 37 DXCC entities. I think I have worked 15 US states.

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WSJT-X incorporates an Echo mode which transmits short pulses and detects the echo, and I can usually see returns of around -19dB (in a 3kHz bandwidth) which is more than enough to be able to work myself, if that were possible. Indeed I have worked many people running systems similar or smaller than mine. The smallest station that I have worked is G0HIK with two 33 element yagis, OE3JPC who uses two 56 element yagis is also regularly worked when the path loss is low.

An invaluable resource for EME operations above 2m is the 432 and Above EME Newsletter. The [[https://eme.radio/|eme.radio]] site is more than just the home of this newsletter and its archives and is highly recommended.

** The Future **

I have numerous changes that I want to make to the station, all of which are to do with ease of use and not in improving capabilities. Of course I would like a larger dish, but it already dominates the garden and my wife, who has been very accommodating of my hobby, has said no to that idea. I don't want any more power, and I think that my receive side is about as good as it can be. I would like to make some changes to the mechanical side to make the mount for my dish feed a little more firm, and the dish/feed counterbalance currently uses a four litre container of car screen wash in addition to the counterweight to make the system more balanced.

A potential problem is the results of WRC-23 which may have a huge impact on EME operation on 23cms, but at this time no-one knows for sure what it may be. In the extreme case I, and many others, may have to pack up on 23cms and look at getting going onto 13cms. This wouldn't be the most difficult change, the IC-905 can easily accommodate it, and the sequencer and relays would operate on 13cms without modification, but it would be an unwelcome termination of activity on 23cms, a band I have been active on since 1985.

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