Earth Moon Earth communications- very draft
IntroductionJosh, a new call, VK4JNA, suggested doing EME. I quickly went from uncertain to keen as it is very similar to satellite tracking, a long term interest. This post is on EME thoughts, mainly as a record of what we have found; I have a bad memory. It will be updated as we proceed. There will be spin-off posts on things of particular interest.
Mast and rotatorsLocate the antenna at the club; keep partner and neighbours happy.
The club has a new tilt-mast for UHF/VHF. Needs to be erected, about $600 to drill hole and concrete. https://www.nbsantennas.com.au/ A priority to get foundation and mount done as the concrete takes a month to cure.
The club has a new G-5500 Yaesu EL/AZ rotator. It needs the AL and EZ rotators to be mounted separately to suit the carriage of the mast.
The club has a computer rotator controller. https://ea4tx.com/en/tienda/antenna-rotator-system/ars/
I also have the same mast, two of the EL/AZ rotators and a EA4TX controller. The mast base is in, but I need to erect the mast. I have the controller working with the rotators. I was building them for satellite tracking.
While EME and satellite tracking can be done at ground level, having them on a mast gets them above trees, buildings and other obstacles for a 360 degree view of the sky. A view to the horizon is quite important in EME as that is when most QSOs are done.
AntennaThe antenna depends on the bands used. For 70 cm, a Yagi array is the norm. At 23 cm a dish can be used. Could use dish on 70cm as there designs for antenna and feedhorns.
Yagi arrayWhen I first got back in radio, I researched building high-performance 2m and 70cm Yagi for satellite tracking. I have all of the components to build both, I was following the design in the ARRL handbook that uses insulated elements for low noise. The antenna uses 25mm square section boom, nylon top hat washers and push-nuts to secure the elements.
For satellite tracking, the Yagi can have have both vertical and horizontal polarisation on the same boom, with phasing to get circular polarisation. The small satellites tumble, so both polarisations are necessary.
I had two 2400mm fibreglass poles made locally at $80 each. They were to mount two dual polarisation Yagi for 2m and 70cm. The satellites are repeaters with different band for up and down. The poles simplify mounting as they are insulators and do not interfere with the antenna, allowing centre of gravity mounting. Such mounting reduces the load on the EL rotator.
For EME, the same poles could be used to create the H to mount four Yagi. The EME Yagi are usually single polarisation and easier to make, even though the returning signal has mixed polarisation. I may need to get some more antenna components, but they are not expensive, less than $100. Priority to make first Yagi.
http://www.qsl.net/dk7zb/70cm-longyagi/13-ele.htm Not sure why they don't have better reflectors to stop noise, but front to back ratio is 30 db. Apparently ground effect, but this seems odd if QSOs are near horizontal. Important for echo testing, with the moon viable during the day. Probably a first objective.
http://www.stauff.com.au/index.php?id=3911&L=1&MP=3897-5448 30mm above boom clamps
http://miningandhydraulics.com.au/contact-us clamps 1/4" $1.20 each + GST
http://www.company7.com/telrad/products/telrad.html Telrad- telescope aiming device
I have a 2m Yagi with insulated elements and a double T match. It is mechanically easy to make. http://www.pa0ply.nl/articles/Matching%20of%20432Mhz%20Yagi.pdf
Comments from Moon-Net email: re 12.5 Ohm Yagi
http://www.vhfdx.ru/apparatura/8x18elements_430mhz 50 Ohm insulated
200...300 OHm-technology (50...75 x 4= approx 200...300).
This is one of the correct solutions for 432 at the small stack:
This is the BG's solution:
Note that Jan, DL9KR works only by CW.
World record of Jan: more 1000 initials in CW mode only.
Also, DL7APV's solution with the open feed line technology:
Yagi stackingStacking and power divider design in coax or aluminium square section.
Coax/Heliax- less connectors
Square coaxial- ratio of outer and inner diameters. copper, brass or aluminium rod.
https://www.dxmaps.com/VE7BQH70.html- comparing 70cm Yagi
http://www.qsl.net/dk7zb/Stacking/stacking.htm coax and aluminium
http://home.teleport.com/~oldaker/power_dividers.htm QST article
Parabolic Dish antennaI used to play with satellite TV as I am into home theatre. Prime focus C band 2300mm dishes are cheap new, about $250, but are also available for about $100 used on Gumtree. New is probably easier as collecting used ones are a hassle.
The dishes use a polar mount and can track the geo-stationary TV satellites by rotating in one plane using a linear actuator. The actuators have a reed switch so a controller can follow the tracking.
For EME on 23cm, the dishes need full EL/AZ control. That might be possible with linear actuators and a small computer control, but I am not aware of one (but haven't looked either). It might be possible to use the EA4TX controller, although it uses a variable voltage for position; all rotators use this.
It may be possible to use a Yeasu EL/AZ rotator with the EA4TX controller. The dish would need to be mounted at ground level to reduce wind loads, but the weight of the dish itself is not high. That would simplify mounting and control.
There are designs for the 23cm feed horn and antenna around. They can be made from sheet copper, which I have. The feed horn is to reduce terrestrial noise.
Probably easier to do Yagi array first then try dish. Put dish mount pole in when mast foundation done- Priority
CablesWe have 1/4" Heliax, possibly other sizes may be available at the club. -2.7db/30m (1/2" -1.6db/30m). For phasing lines. http://www.rfiwireless.com.au/media/downloads/pdfs/andrew-corrugated.pdf
For main cable either coax or open line. Coax easier and after preamp(s) and cavity filter. Will check on open line (shielding?)
Coax cable is the greatest loss in the RX/TC system. 50 Ohm RG142 is commonly used. So is RG814. The club has two 100m roles of RG214. It is thick and suited to long runs. We may need to get some more RG142, although I have some. The main advantage of these cables is the shielding to keep extraneous noise out; their losses are similar to common RG213.
Another cheap alternative is 75 Ohm satellite TV coax. It is quad shielded and low loss as it is designed for the first IF of satellite RX from 1 to 2 GHz. It could be used for TX up to 100W pulsed, provided appropriate matching is used.
The alternative is to use separate RX and TX feed to the antenna. This is almost necessary anyway as there is a low noise amplifier at the antenna for RX.
The impedance of coax is different between RX and TX. 75 Ohm is best for RX. About 38 Ohm is ideal for TX. 50 Ohm is a compromise for both RX and TX.
LDF4-50A, HELIAX® Low Density Foam Coaxial Cable, corrugated copper, 1/2 in
Cavity filterI haven't seen a cavity filter used in EME, but few know about them. It could be quite desirable to have a pass band cavity filter very close to the antenna and before the broadband low noise amplifier. (Not all LNAs are broadband, some have filtering. Filter=losses?)
The LNAs are usually mounted at the antenna, but the loss of a couple of metres of coax (-0.3 db) to a cavity filter (-0.5 db) may be justified to give 30 db of out of band noise attenuation. This would greatly help in reducing overload of the LNA by such noise. With a filter it may/should be possible to use much more gain at the LNA. (and perhaps reducing the need for gain in the antenna?? but need antenna gain for TX!)
QSOs are usually done when the moon is near the horizon. As such, the antenna will receive a lot of terrestrial noise. The cavity filter will reduce some of such noise.
A high Q 70cm pass band filter is a little taller than a quarter wave length, 250mm, and up to 200mm diameter to give high selectivity. The same cavity can be tuned to its third harmonic to work on 23cm with high Q and selectivity.
It may be better to use a pass-reject filter as the sharpness is much higher than pass-band. The reject frequency is immaterial in this application. (No- tried it and pass-band better. Some LNA use small pass-band cavity)
The use of a cavity filter or two might be our contribution to EME practice. In a quick Google I found a discussion about using them but none on actually using them.
Many LNAs, especially high UHF have filters, stripline, sometimes discrete components.
LNA (Low noise amplifier)LNAs used to be a major problem and a significant cost, however with cell phones and satellite TV, the cost has reduced dramatically. LNAs with a noise figure of 0.5 db are available for about $20.
We need a good source for a LNA with a filter if possible. (Priority) Ordered- L432LNA Down East Microwave.
http://eme.dokidoki.ne.jp/photo/jh0wjf/preamp/index.html- clear photo for cavity LNA.
http://www.qsl.net/dl5lf/432_preamp.html - cavity LNA circuit
FHX35LG- as used in cavity LNA- ordered 5 for $10 obsolete
ATF-10136- lower noise- ordered 5 for $10 obsolete
ATF-35143- even lower noise but surface mount
RX/TX switchingI have some BNC RX/TX relays plus the club has some too.
TRXThe club has an IC-9100 with 23cm. I have a IC-7100 to 70cm. IC-9100- 70cm 75W, 23cm 10W. IC-7100- 70cm 35W. Power might be enough for IC-9100, but will need amplifier for 70cm.
I think interfaces are similar. Both probably need firmware upgrade.
Could use 70cm transverter with IC-7300.
I have ic-7300 and numerous SDR RX and TRX. LimeSDR TRX with SDRangel might be good.
I can put a panadaptor on the IC-9100 or the IC-7100. They can be done either at the IF or RF after bandpass filters. http://vk4zxi.blogspot.com.au/2013/11/sdrs-at-first-if-of-trx-as-panadator.html http://vk4zxi.blogspot.com.au/2014/02/new-trx-ic-7100-look-inside.html
WSJT-X. It is what I had in mind with the GPS RX DSP approach. The signal is sub-audible but can be dug out of the noise. It seems to have its own spectrum and waterfall, negating some of the benefit of the SDRs.
Getting WSJT-X to work on our TRX is a priority.
70cm or 23cm seem the easier to try first. 70cm is probably preferred as we have the most gear for it and the components are't too small.
TX amplifierThe TX output of the IC-9100 may be enough. 100 W of USB Data?
My DATV amplifier is on 70cm and can put out more than the legal limit, although I do need to finish building it. http://vk4zxi.blogspot.com.au/2017/01/commercial-dvb-t-amplifiers-and-filters.html
OperatingMoon tracking seems achievable. Probably best to get echo working first. I think it can be done with the moon in any visible position.
Then try listening for signals, then try for QSO. I think this requires the moon to be in a particular place.
Basicshttp://www.g4ztr.co.uk/app/download/13284489/RaCcom_Feb14+EME+part+1.pdf Intro to EME
Generalhttps://www.dxmaps.com/eme.html Links to all EME.
http://www.moonbouncers.org/ It has papers and links to other sources for EME.
http://www.ok1dfc.com/EME/432/it9cjc.htm Minimum configuration.
https://www.amsat.org/ mainly satellite but good.
http://www.rfhamdesign.com/ Ideas for dish mounts etc.
http://www.n4rfc.com/?p=1419 Quick Guide To WSJT-X On The Icom IC-7100