A search on here throws up a few mentions of using EME on a SOTA activation. Historically, it was considered you needed a lot of power and multiple, long Yagis to make it work. More recently QSOs have been completed with powers as low as 25W. These have been achieved by all the “heavy lifting” being done by one station in the QSO which can receive the weak station and transmit with sufficient power to be heard by the low power station.
So I thought I would give it a go today from my home QTH. Equipment was a Diamond 10 el 70cm Yagi, IC-705 and MS Surface Go 2 tablet.
The attempted QSO was coordinated on HB9Q’s EME logger site:
Frank thinks if I can up my power to 50W a QSO might be on the cards. I think I may look at a better antenna first, if only to put off the expense of an amp or new radio - I would love an IC-9700 but they are not cheap.
Today’s little experiment showed that with a SOTA portable rig it is at least possible to receive an EME signal. The challenge is replying!
There is a lot to learn, even if I do upgrade my equipment. The moon was quite high in the sky today at about 30° and EME is supposed to be better if it is nearer the horizon. There is also a thing called EME Degradation which takes into account, as I understand it, several factors including how noisy the sky is. For example if the moon is in front of the Milky Way it isn’t good due to radio noise from our galaxy. Conditions today for EME Deg were rated only as “Fair”.
So I haven’t cracked SOTA EME but I think it can be done, as @K7ATN and others described on this thread. The trick will be doing it with the minimum of equipment, 50W and a better antenna may just be enough.
Instead of upping the transmit power , you could increase the beam size, which would help a bit on receive too. I have a 17ele for 70cm that is eminently portable (for easy walk in summits). Perhaps someone in a local club has one that can be borrowed.
The issue would be balancing the mounting for elevation. If the moon were close to the horizon then this wouldn’t be a problem. Being on a summit would also mean that there would be less likely to be any obstructions between you and the moon, even if it were on the horizon.
I agree the first step is a better antenna. The Diamond 10 element I have works but it’s hard not to describe it as anything but a “cheapie”. They make a 15 element version which is less than £70 and I guess I could carry two of those up a summit.
That antenna is a very, very old design. Which is a polite way of saying very heavy and very low gain. You should be able to make something which will easily out perform it for not much effort that is the same size. Or make something bigger that seriously outperforms it. Then you wont need so much uplink power to complete your 1st EME QSO.
You should be able to make the parts with hand tools. A pillar drill is a big help. If you are talking 2m or 70cms then errors of mm don’t make that much difference. 23cms is more critical.
Or a very old idea - a rope-boom roll-up yagi. I think most of the published designs were for 2 mtrs, including a Brendan Trophy attempt between VO1 & EI, but no reason it could not be adapted to 70 cm.
Martin’s 28 Ohms designs are perfect for a common SOTA station - maximum forward gain on a short boom.
For EME you rather want a clean pattern, i.e. a low noise antenna. I’d recommend DG7YBN. His site is interesting to read and somewhat encouraging if you want to try low-power EME.
Thinking outside the box a little, I remember years ago a ham in, I think, New Zealand, having success using a rhombic antenna aimed at the part of the horizon where moonrise took place. A wire antenna would be inexpensive but needs space and the trade off is that the moon would be in the window for a limited time.
In the mid 70’s Alex GD6IA (alias GM(D)3UMW) - on a visit to his GD QTH (he had not long moved from GM and an ex Member of WoSARS) a farm cottage outside Peel, along with the usual stacked & bayed 2M yagi array, he had a phased 2el 2M rhombic in a field adjacent to his cottage (on supports about 2.5M off the ground). The rhombic took up the whole length of the field. The field I reckoned was about 4 acres? The rhombic was centred on GM.
Running a wee bit of ‘welly’ at each end, I had nightly skeds with him from my parents QTH in the East End of Glasgow. Likewise Graham GM8FFX in Aberdeen. The only problem I had was Graham was off the back of my array. Alex had to QSP - hi!
Brian,
Ray VK3ATN (SK) of Birchip had a 4 wire stacked Rhombic Array. I saw it in about 1970 a decade after his first EME QSOs. He used the legal limit of 150 W DC input, CW (of course). The band used was 2 m. The supporting towers were circa 50 ft high as the array crossed a public road and the council mandated a lot of clearance. He owned property on both sides of the road. It was as large as some HF Rhombics. Maybe 100 wavelength per side.
There is no way it could be made portable even with several trucks.
My 2022 SOTA EME Station consisted of a Cushcraft A719B 19 Element 70cm Yagi (15.5dBd 13.75 feet in three sections), a speaker tripod, 100W KLM amplifier, a FT-857d w/ TXCO, Signalink, and a ARR preamp and laptop. Power was provided by a 12Ah LiFePO4 battery for the transceiver, and a 32Ah LiFePO4 plus a voltage stabilizer to power the amplifier. Altogether it was about 32kg and quite unwieldy but I could carry it short distances.
I made the following SOTA activation QSOs with this station: K7ATN on W7W/LC-164 (Prune Hill), 06 Mar 2022
17:30 DL9KR 70cm CW EME: JO40-CN85
18:18 PA2V 70cm DATA EME: JO22-CN85
18:46 NC1I 70cm DATA EME: FN32-CN85 K7ATN on W7O/WV-099 (Cooper Mountain), 10 Feb 2022
22:02 NC1I 70cm DATA EME: FN32-CN85 K7ATN on W7O/NC-051 (Bald Peak), 14 Jan 2022
22:30 HB9Q 70cm DATA EME: JN47-CN85
22:51 NC1I 70cm DATA EME: FN32-CN85
23:34 PA5Y 70cm DATA EME: JO21-CN85
73, Etienne-K7ATN
In 2011 a team of Vk3KH, Vk3xpd, Vk4uh and Vk1da activated 2m eme from Norfolk Island using a 19 el yagi built by Vk7mo and a 300w amplifier by TE systems.
Signal levels were not high. A large array at the other end and 1kw+ made a signal that was about -15db s/n at our end.
In my view dreaming of doing eme using SOTA gear is just that - a dream.
