Lower limit for EME

The following discussion about the lower limit for EME took place in the Moon-Net reflector. I found the subject so interesting that I decided to put together all the messages in this page.

(See also the discussion on minimun antenna gain requirements)

On 7 October 2000 WB9UWA wrote:
Has anyone figured out the lower limit for 2m EME reception?

I have been adding and subtracting DB's, trying to figure out the minimum station I should be able to work with my new array and PA. IK0BZY does not think I would hear him, and I suspect that I might. It seems the whole formula would be affected by extra noise on the receive end of the smaller station. I suspect that with multiple skeds, two 17dbd stations with 1kw would be very near the lower limit. My antenna gain is now 18.5 dbd, but my temperature should be low enough to compare with a 19 dbd array. I suspect the ARRL EME contest will show me a lot about my station, but some skeds will have to be tried to really dig into the noise.

Is there a rule of thumb that suggest that a certain ERP can be heard by a certain RX antenna gain, or is RX noise conditions too much of a randomizing factor? Obviously the smaller yagis have a higher temperature, effectivly further reducing receive signal to noise ratio. If the small array is fixed on the horizon, this would further increase noise pickup and seemingly to a greater degree than a higher gain array with its smaller main lobe.

I would be interested in hearing from stations in the 18 to 21 dbd antenna gain range for this question. I already know what W5UN can hear and that information is too far removed from my little station.

On 8 October 2000 W1JR wrote:
I used to have a rule for 2-meters that if everyone used legal power and a reasonable preamplifier, that the required gain was about 40 dB total between the 2 stations. Hence, if two guys are each using identical 20 dBi arrays (typically 4 10-11 element Yagis on about a 2.5 wavelength boom), they could probably work if Faraday was correct and they were no other extra unknown factors.

Playing number games, a station with 25 dBi gain could work a station with 15 dBi gain. In a practical example, if the stations mentioned abovechanged from 4 Yagis (as mentioned above) to a single Yagi at one end and the other station changed to a 16 Yagi array (as above), they were in approximately the same relationship. Going the full tilt, a 30 dBi gain on 2-meters (I think this is the ball park of W5UN-I have to check so don't hold me on that), could theoretically work a station with 10 dBi of gain (about a 5-6 element Yagi on a 5 foot boom)

 From these simple examples above, other combinations can be determined by raising or lowering power and other tradeoffs accordingly. One half power means 3 dB more gain etc. I'm sure you get the point.

On 222 MHz., I think it's about 45 dBi total and on 432 I think the magic number is about 50 dBi total etc.

Remember, these are very rough rules of thumb but I think they are close enough to do some fast in the ball park number for planning.

On 8 October 2000 K0FF wrote:
Very thorough analysis Joe, that's a good explanation of how to figure the possibilities between two know stations. 

As far as someone wanting to set up a station and work SOMEONE on EME, let me add from a practical side for other Newbies (like me) that with 4 of the Cushcraft 17B2's I played around  with varying power levels, and found that I could hear my own CW echoes at 600 W, and once in a while my own SSB echoes at the same level. As I  learned later, hearing your echoes is not a requirement for making contacts, and often very easy QSOs are made when there is no sign of your own echo, and conversely, many times, yours is the ONLY echo to be copied.

With this antenna, I have consistently had good luck with stations with 4 Yagis and bigger, and occasionally with a 2 Yagi setup, all random contacts. With another antenna here using 2 x 17 el but no elevation, I can copy all the big boys on my horizon,  and can be heard with the (only) 150 Watts
available on that setup, but no complete QSOs have been achieved so far. These few  tests indicate that under favorable conditions, they could be.

During last year's ARRL EME contest, there were at least 72 stations that could work me with this simple setup. I would like to encourage others to get on and try. even with the typical 150W brick and single antenna. Someone out there has the ability to make up the difference.

This year the ARRL EME contest is on two weekends, Oct 21/22 and Nov 18/19. Every 2M op owes it to himself to at least HEAR a signal bounced off the moon, at least once in his HAM career, and this is a wonderful opportunity to do that, and maybe more.

On 9 October 2000 SM5BSZ wrote:
Joe, W1JR wrote:

>I used to have a rule for 2-meters that if everyone used legal power and a
>reasonable preamplifier, that the required gain was about 40 dB totalis
>between the 2 stations.

In the old days, when 500W input was the limitit - without use of ground gain?

If both sides use ground gain the limit is even much lower - but then making a qso is extremely difficult. (Knowing ground geometry well at both sides makes is relatively easy, but possible sked times become few and short)

There are many many stations having EME capable equipment without knowing it :-)

On 10 October 2000 W1JR wrote:
Leif,

My original example left out ground gain, scintillation etc. on purpose. They just complicate the matter for those not familiar with EME, the one's we're trying to encourage. I sent a further message to K0FF on that subject. I'll try to send you a copy of that message.

Yes, there are other factors but let's keep it simple for the new comers. My example was trying to give a good solid base to operate from when both stations used elevated antennas.

On 10 October 2000 SM5BSZ wrote:
Joe,

What I wanted to say was that your numbers are a bit pessimistic. This is from practical experience, no theory involved.

My previous antenna 4x14 elements had a gain of 21.4dBd or 23.5 dBi. This means that the weakest station I could work should have been 14.3 dBd  and 1 kW using your rule "if everyone used legal power and a reasonable preamplifier the required is about 40 dB total".

I have worked practically exclusively on random and I have worked a large number of stations well below this limit. They have answered my CQ during contests. Below is a list of random contacts:

K1FJM M2 5wl 14.8dBd 300W. About 4.5dB below limit.

SK4DM 15el Cue Dee 12.9dBd 300W.  About 6.5 dB below limit. Could be questioned because I could also hear the direct wave. BUT the moon echo was pretty good. I had no problem to copy from that  - and I am sure because it had the proper time delay. The frequency shift is not a good enough
indicator. Airplanes often give shifted echoes with similar offset.

SM0PYP/W6 20el/4.2wl (14.6dBd ?) 850W. At the limit. Paul had a good signal. A note on his QSL: "you heard my weak signal directly" (I answered on his first 1 minute call)

W7OE M2 8wl 350W
F8ZW 17B2 14.5dBd 600W
SP2JXN 17M2 14.8dBd single 4CX250B
DL2FDX 6.6wl G8MBI, 300W
PE1LWT 2x12M2 15.8dBd 350W
PA3BUT 2x12M2  15.8dBd 400W
DH7FB 2x9 DK7ZB 400W

KC4/K6MYC 4x9M2 120W Ground gain on Mikes side. Very good signal
and easy QSO. Listen and look at:
http://ham.te.hik.se/homepage/sm5bsz/emedemo/xx.htm
http://www.g7rau.freeserve.co.uk/g7rau/sm5bsz/emedemo/xx.htm

EL2RL 4x9Tonna 16.5dBd 80W. 9dB below limit with no ground gain at either end!!
Listen and look at:
http://ham.te.hik.se/homepage/sm5bsz/emedemo/el2rl.htm
http://www.g7rau.freeserve.co.uk/g7rau/sm5bsz/emedemo/el2rl.htm

4S7CCC 4x small yagi, 200W.

>> >I used to have a rule for 2-meters that if everyone used legal power and a
>> >reasonable preamplifier, that the required gain was about 40 dB total
>> >between the 2 stations. Hence, if two guys are each using identical 20 dBi
>> >arrays (typically 4 10-11 element Yagis on about a 2.5 wavelength boom),
>> >they could probably work if Faraday was correct and they were no other
>> >extra unknown factors.

From real practical experience I think one can say that 40dB should be replaced by 35dB. This is a really big difference!

The EL2RL example, 4dB further down is an exception. I think one has to use better than normal receivers to achieve that, but I am sure it is reproducible. With the X-yagi and electronically rotated polarisation I have no problems with farady rotation and EME signal levels are always very reproducible (except during major auroras). Without a X-yagi one has to use very much patience (and maybe well planned skeds).

With the list of contacts above I have tried to show that the 35dB rule is not something that works only on special occasions. It is something I regularly do random during contest. As a matter of fact I hear many many stations who work W5UN et al - but I can not make a QSO because they do not hear my CQ even though I have a QBL5/3500. The smaller stations do not call CQ themselves so it is impossible to catch them that way.

During the Italian contest I worked 50 stations using a single 2SA13X, 13 elements on a 4wl boom. The gain is 14.4dBd. Some 2 yagi and many 4 yagi stations. It is quite easy to hear many many EME stations with a single medium size yagi.

It is quite another thing that many EME stations are much weaker than they should be according to what they say about their equipment. There are also many many stations who do not hear well.  There may be many reasons for that - some easily avoidable.

Here are two practical examples:

Commercially available antenna with gamma match (Cue Dee) at SM3PWM. Adding a simple sleve balun allowed a power reduction of more than 1dB for the same field strength in the far field.

Overtones. Seen at many QTH's (discovered at my own). We usually use a diode to measure the voltage of the forward wave in the coax. The diode has a short time constant because we want it to average power on SSB, not to show the peak power. Still, there is a time constant in the rectification process and it means that if the wave contains a lot of the second harmonic, the diode will measure the peak voltage and not the RMS power. With equal power, the phase relation between harmonic and fundamental affects the reading.

Many 2m amplifiers produce a good signal at 288MHz. The 288 signal is often amplified by higher coupling to the diode because of the higher frequency - but more important:  The antenna is nearly infinite VSWR at 288MHz. This means that it is possible to tune the coax for a resonance at 288MHz causing very high levels of 288MHz at the diode.

Practically this means that if one uses a directional coupler with a filter that only allows 144MHz to reach the power meter (diode) one finds a different tuning than the one found with the conventional power meter!!!

We should of course use filters between amplifier and antenna - but most people do not. They easily loose 1dB by tuning for the 288 to be in phase with the 144 rather than for max amplitude at 144!!!

Then there is water, phasing errors, poor connections.....

Hope to work many of you in the ARRL contest with a single 14.4dBd yagi this year.

On 10 October 2000 DL4MEA wrote:
Hello Leif and others,

Although I am doing EME on 70cm and although I believe I have a well operating system now, I can still remember my times of beginning. All the numbers you are showing here are those for experienced EMEers, but not for beginnners. Lets keep those reserve of the 5dB for beginners. I also know numbers when to start EME from a few tables, but these all are only possible if all at the station is fine working, if path attenuation is low, if faraday is low, but always remember that especially those 2 or 1 antenna stations don't have everything in balance and for shure not the experience to cope with all the surroundings of EME.

Showing an example, since there are some: EA3DXU creates a reasonable signal with two antennas, IK5QLO does, OE3JPC formerly did, too (now with 4 ant). So everyone with two antennas would create the same signal? No, it isn't like that, and the difference is about those 5dB, and it is due to experience and station optimization.

Maybe we should setup two numbers: For beginners, for getting their first fun, the number of 40dB is ok, and finally an experience gain of around 5dB or so.

Another item: Today I read the QST where Dave introduced his array. But at another page I found some notes about "Ham Radio In Future". It made me freezing how many hams dream about automatic operation of their radio. That again raises the question who wants to be a radio amateur: the person or the computer he owns? Waaaahhh....

On 10 October 2000 OZ5IQ wrote:
In my opinion theres has been several statements abt. the level of "how to make EME".

For more than I learned / told that a total of 47 dB antenna gain was sufficient.

Today - where the use of  processing devices, low NF RX?s , I would state that the 40 dB rule not is wrong, the devices in general just (good for us) has been improved caused by the tech. progress.
So whatever Leifs, SM5BSZ s experience/knowledge  is great for all of us, its simple "rule of thumbs"
who is easy to understand / accecpt / remember.

In the years to come I would guess, the coming EME?ers is laughing og the signal level  nessary today !

On 10 October 2000 F/G8MBI wrote:
my 0.02 dollars worth...

At elevation....

1....32dbd  total +1 kw each + some polarity capability (simple ok, complex better) will yield qso's at sensible times (moon distance+tsky+local parameters) a good percentage of the time.

based on my echoes and rationalising when simple 'detection' stops and actual 'copyability' starts......and the plethora of 2y to 2y qso's that have/do take place...

2....30 dbd , or some other combination of power reduction, will yield QSO's 'sometimes'

based on the fact that I have done it......as have others with various combinations.

3....28dbd and 1k each is probably the lower limit to yield a QSO 'infrequently'

Based on a bunch of listener reports of "I copied you on my 17 tonna", or even "on my 11 element flexa".......

you can 'fiddle' around substituting ground gain in here and maybe get down to 22 to 24 dbd with both at rise or set (I say that because spatial offset will be small, for guys with no polarity flexibility. Trying with one at set
and one at rise may be harder to find spatial+faraday workable combinations)

you can then fiddle with 'offset' abilities and power levels to arrive at a conclusion that dave (un) can work a 1kw station with a dipole... given that he has worked 100w and say 9 to 10 dbd (with/without ground) a few times this conclusion looks about right.....

the biggest 'delta' in the equation is personal ability....

As leif observes more should try, it is interesting that people with say 12 to 14dbd and a 200w brick seem to conclude that "having a go" at working w5un is a good idea, but the hundreds of folks with 14dbd+ and 1kw rarely seem to conclude ...."let's see *how many* 4 yagi stations I can work".....

**How about shipping a single page 'EME primer' with each 17 Mike ??? **

On 10 October 2000 AL7EB wrote:
Guenter, Lief, Jim,...

I hear the concern about giving conservative numbers for beginners.  But the original question came from
Jim Shaffer WB9UWA  [4 x UWA12's 18.5 dbd 2xGU74b, mgf1302, Stereo RX]. Since Jim has designed and built what appears to be a successful antenna system, I would not consider him exactly in the "beginner" status.  So I have a feeling that maybe Jim was hoping for a little more detailed "formula" to evaluate success potential.  I suspect he is looking for a version of the "radar" link equation for the moon.

A few years ago Christoph Petermann, DF9CY, published a basic eme performance spreadsheet [PATHLOSS.XLS] on his webpage, which would provide some basic answers to Jim's question.  Christoph's formula did not take into account Faraday, scintillation, libration, atmospheric losses.  He used [I believe] moon at perigee and a 7% reflectivity model for the moon, but I found it a good model to use for making decisions for choosing eme designs.

I would say that it would probably come up with the 40 dB model, but my observation of what is being accomplished today would lead me more to a 35 dB model.  Certainly considerable "fine tuning" of a new eme system should be expected by the beginner to achieve this performance goal, but I don't think it is necessary to build in a "crutch" value.

I know there will be some who will optimistically try to achieve eme with less capability, but they will find the "big guns" and hopefully learn and upgrade [what finally convinced me to try 2m eme was hearing K5GW with a 9 element yagi in 1997].  My first inclination was not to even try 2m eme because of the large antenna size [I was going to go on 432].  Then I convinced myself to go for a 2x yagi array [for a great satellite antenna I told myself].  Then before buying antennas I was convinced to go to 4x antennas and H/V.

I am now working to get my array back in the air for the ARRL contest.  I may only have 125w.  If I am really industrious I might have the 8877 on with 600w [power supply limited].

On 10 October 2000 WB9UWA wrote:
Thank you for this great and imformative exchange on EME lower limits.
Joe's example used two stations that have a 20 dbi antenna each. This would be 18dbd each, so 36 dbd
total antenna gain (not so far off). I think his example is for the old legal limit of 1kw input or around 650 watts output, but he has not verified this.

Thank you Ed for your comments. I am actually trying to make sense out of the big improvement that I have seen when I only added 1.5 db antenna gain. Even when considering G/T, my improvement in echos should have been no more then 3.5db. I am seeing (conservatively) a 6 db improvement in echos with the new low temperature array.

The difference is much more then I had hoped for, so the question becomes, Is my old array that bad or is the new array that good?

I think as far as the difference in copy for a beginner EME station, the difference is more than what was mentioned here. When I started EME with my 4 x W1JR8 element yagis, I could not complete a sked with VE7BQH on the first try. I was using 200 hz bandwidth and was not yet used to signals that weak. Just before I upgraded my array, of course I would complete very quickly on random with him using my 30hz bandwidth
stereo RX and improved noise blanker.

Thinking back (not too far) on my own EME beginings, I would have found it useful to have available to me, more information on EME operation. In particular, perferred CW tones and filter bandwidth information. As well, if this were to be presented on a Web site, some .WAV files should be present for download. This would have given me some signals to practice on to hone my skills for real EME reception. When I would hear a signal too weak for me to copy and the Web designer says it is a good workable signal, then I would have been forced to find out why I wasn't copying the signal. If this exist, It should be posted on Moon-net from
time to time (and where else?). In this way we will have a shot at those stations that only thought they could work W5UN.

Leif and Grahm, thank you for your observations on lower limit EME. I will have to adjust and compare to my station and decide who I dare to set a sked with.

I do have the EME link calculator provided by N1BUG in his software, but bandwidth and noise is one of those fuzzy areas only answered by practical experience.

On 10 October 2000 Oene Spanjer wrote:
To this point I would like to react:

It's definitely true that pointing at the horizon will give noise pickup but on the other hand if you have a good location, groundgain may be added and that can be as high as 6dB and that's indeed a lot.

In last year ARRL contest I heard IK3MAC calling cq in the last hour of the contest. Moonrise at both qth's and I started calling IK3MAC The first time he responded with  . . - - . .   and my adrenaline level raised. After the second time the answer was  P . . - - . .    and I was thrilled. .

Why? because I had only 25 W output into a single 12 ele DK7ZBopt ( 14.3 dBd ) no preamplifier, no elevation and 1 dB cable loss. Then the moon rose and I was out of the main lobe but I had great fun
that a little part of my .5 kW erp was heard by IK3MAC.

I suggest that this could be realized because at both ends we  had some groundgain and the GOOD STATION AND EARS! at IK3MAC. So I indeed believe that there can be done more as we presumably realize and the last evidence was made by Leif and his 1 yagi system during the italian eme contest.

Have the big guns who are capable of more bands at the same time ever experimented with simultaneous qso's on 2 70 23 etc. to see how faraday and libriation effects are on the different bands at the same time?

On 10 October 2000 WA6PY wrote:
Three years ago ( SM0PYP/W6) using single yagi  old 19 el CC modified per VE7BQH design to be 4.05 WL 20 el and running 800 W at the shack --> 650 W at the antenna, I QSO'd two other single yagi stations: PA0JMV - easy QSO using ground gain and SM3AKW  during second sked without ground gain. I did
not use any DSP just my ears and modified  IC202 as transceiver. This was below threshold of any path link calculations.

I would like to encourage all QRP stations.

On 10 October 2000 W2RS wrote:
Thanks for all the interesting posts.  My two cents' worth is as follows:

The smallest station ever to make a 2m EME QSO was CO2KK, who worked KB8RQ and W5UN running only 22 W output to two 5-el Yagis with total forward gain of about 13 dBi.  Arne's approximate eirp was 450 W (26.5 dBW).  Yes, he was using ground gain, which should be added to these figures.

When I was active on 2m EME from my own QTH, I worked 37 initials with 150 W output to a single CC 32-19 (15 dBi) and ground gain. My eirp, excluding ground gain, was 5 kW (37 dBW).

Of those 37 initials, 10 were with 4-Yagi stations and 2 were with 2-Yagi stations.  The smallest 2-Yagi station I worked was WB2VVV, with 18 dBi forward gain.

Both 2-Yagi stations, and 7 of the 10 4-Yagi stations, were worked using mutual ground gain, i.e., path geometry that permitted both stations to use ground gain at the same time.  Three 4-Yagi stations, however, were worked using ground gain only at W2RS as their antennas were elevated.  Those were AA4FQ (22.9 dBi), W7VXW (22.7 dBi) and W7HAH (23.0 dBi).

So, as you can see, Joe's rule-of-thumb formula of 40 dBi total antenna gain plus 1 kW output would have been far too conservative.  As I recall, PA0JMV worked over 500 initials with just 2 Yagis, and many others have also done well with pretty small stations, by making the most of the many favorable propagation opportunities which 2m EME can give you if you know how to take advantage of them.  Let's not forget Graham's and Dave's 1-Yagi to 1-Yagi QSO either.

One further point: Of my 37 initials, 36 were on skeds and only one, VE3ONT, was on random.  In fact, I was able to work only 4 stations on random at all: VE3ONT, W5UN, KB8RQ and the smallest, DL8DAT, when Manfred was running 16 Yagis with 28.5 dBi.  As I have discussed in previous postings, random operation requires 6-8 dB more signal strength than prearranged skeds.

So, if you want to work random, you'll need that much more gain than is required for successful skeds.

Hope this helps.

On 12 October 2000 KV6J wrote:
     All this talk about minimum stations is good reading.  Just had to jump in with my 2 cents.

     Let's leave out the 16.35 db on my waterfall DSP,  the internet transmission (I'm sending R's now) and the one I like best,  will you send a blank QSL and I'll fill it out when I get the transmitter on.  Now we're back to the real world.

     There have been some long term experiments by Ray (RS) and Graham (MBI) that prove what is possible with a single yagi.  Then there's Dave. The MBA, his operating skills and availability give us a beacon that
answers.  Perfect for testing.

     With my limited experience during ten years I submit:

     A good operator with less than 10 kw EIRP and good timing will have Dave copy his call on the first transmission.  N6ZE's XYL did it, and her call wasn't even on the 'cheat sheet'.

     With patience, very good conditions and a contest, about 2 kw will get you a contact sometime that day.  Subtracting a few db for an very good operator and another few for ground gain and you soon find yourself in the realm of anything is possible.

     Even switchable circular polarization, perfect conditions, 1.5 kw and 42 dbi antennaes(combined), will not prevent virtual lockout for hours at a time.

     One so so operator with a kw, 20 dbi(or one very good yagi with very good ground gain)  can almost always copy echoes when conditions are forecast excellent.  Very close to what the gurus came up with more than 25 years ago.

    Matching the spatial polarity is a good start but, there is something more that is not yet understood.

On 12 October 2000 SM5BSZ wrote:
Bill, KV6J wrote:

>Even switchable circular polarization, perfect conditions, 1.5 kw and
>42 dbi antennaes(combined), will not prevent virtual lockout for hours at a
>time.

This is just not true!!! At times with wery slow libration fading the EME signals bay be gone for a few minutes, not more. (And if it happens the QSB peak that unavoidably follows will be very long and easy to use. The most extreme I ever experienced is in the order of 30 seconds.)

The average power over many qsb up and downs is very constant for the EME path on 144MHz. Only at rare occasions with extreme ionisation it is possible to loose signal due to ionospheric absorbtion.

In my experience the strongest qsb peak during any one minute interval is always very few dB away from the strongest qsb peak during any other 1 minute interval if degradation due to sky noise and distance are accounted for.

The strongest peak during a 2 minute period stays within 1dB from its normal value.

The above is with the moon high enough to eliminate ground reflections and with an antenna that always uses the correct polarisation.

On 13 October 2000 WB6IMC wrote:
I have been reading the mail and think that it is good to press the envelope and try to accomplish the impossible.  Or should I say  what appears to be impossible.
Name your poison.  There are so many ways to enhance your chances of making a minimum link budget EME QSO, perhaps the requirements of today will be changed tomorrow.

Me, I have been inactive for the last three years and am in the process of building a station for 144 and 432.  My station is modest as I will be running two 2M18XXXs on 144 and two 37 el K1FO design Yagis on 432.  In stead of spending the big bucks on the radiating system, I spent the big bucks on the QTH.  The QTH is at apex inside a canyon which has openings to the east and to the west.  A natural continuous parabola. I have been tracking the moon off and on for the last 40 days or so and have found it to be a natural wonder for the EME type.  I hope the QTH will be a great enhancement so I wont have to maintain a big array.

The bottom line is EME is sure a lot of fun and it is extremely thrilling to work someone via EME especially when running QRP.   MBI and UN made the path, too bad no one has repeated the feat.

On 13 October 2000 K6MYC wrote:
<< Bill, KV6J wrote:

 >>Even switchable circular polarization, perfect conditions, 1.5 kw and
 >>42 dbi antennaes(combined), will not prevent virtual lockout for hours at a
 >>time.

> This is just not true!!! At times with wery slow libration fading the EME
>signals
> bay be gone for a few minutes, not more. (And if it happens the QSB peak
> that unavoidably follows will be very long and easy to use. The most extreme
> I  ever experienced is in the order of 30 seconds.)  >>


Leif,
Bill's observations may not be a result of a traditional lockout but I can tell you that I have experienced the same thing with Bill. As you know I use polarity diversity and there have been times when Bill simply could not hear me. I coould hear my own echos and he could hear his but he could not here me. I could hear him and the station he was calling for a sked fine.  I called him to try to let him know the other station was making the sked but Bill could not hear any of us.  I would have to side with Bill on this one. I stll think there are other things that influence propagation to certain parts of the world. I have heard you argue these points before with the same
emphatic statements. As an older guy with lots of experience with unexplained phenomena on EME and other places,  I find I have to leave room for other possibilities.

On 13 October 2000 SV1BTR wrote:
I couldn't agree more with Mike, since i have ALSO observed that on 432MHz 2 years ago several times, even though using 4*32+32el. Cross BVO Yagis, H/V polarity switching....

There are issues we might not be able to grasp if we have not practically experienced them....and yet even if we did, as myself and Mike indicate, we can not necessarily explain... Many weard things happen here too, in the most southern part of Europe......

On 13 October 2000 SM5SZ wrote:
Mike,

What you describe is just not happening here:

>Bill's observations may not be a result of a traditional lockout but I can
>tell you that I have experienced the same thing with Bill. As you know I use
>polarity diversity and there have been times when Bill simply could not hear
>me. I coould hear my own echos and he could hear his but he could not here
>me. I could hear him and the station he was calling for a sked fine.  I
>called him to try to let him know the other station was making the sked but
>Bill could not hear any of us.  I would have to side with Bill on this one. I
>stll think there are other things that influence propagation to certain parts
>of the world.

Presumably you tried both polarisations and Bill heard neither of them. With a physicists background I find this hard to explain (except in trivial terms like mistakes on doppler shift).

Since you say thay both of you could hear your own echoes one can rule out ionospheric absorbtion with 100% certainty. (Even without that statement I would say absorbtion is extremely unlikely.

The possibillity of deflection of the waves due to refraction can also be ruled out. If the beam of one station did not hit the moon due to reflection/refraction in atmospheric layers, that station could absolutely not hear his own echoes.

Other phenomena, known and unknown ones, can all be described in terms of multipath propagation. This is the same as to say they cause signal strength variation but they leave the average power level unaffected. Only absorbtion and refraction can change the average power level.

It is just not possible that the qsb caused by all the multipath phenomena can cause a qsb down that lasts for hours. It must be something else. I bet the signal was there but Bill did not hear it for some trivial reason or another.

Not only very strong physical arguments talk against it. I have now many years of experience and my interest in radio is mainly technical/scientific. I can assure you I have spent very much time on this and what I say on this subject is based on solid experimental work. I have spent thousands of  hours developing the tools that make it possible to really know what happens  at my end of the EME path.

On 13 October 2000 WA6PY wrote:
I observed many times that EME signals will be almost always much weaker when I hear in San Diego FM stations on 100 MHz from Santa Barbara area 250 - 300 mils north of me.

Once I heard beacon from Hawaii on 144, very strong   - report  599++, usually I do not hear any trace. At that time I had a sched with VK3CY and NJ0M, I did not heard any of those stations. Using single yagi I was rotating polarisation listening to the signal with headphones.

Even on 1296 and 2304 conditions were for some reason dependent on propagation, although Faraday  is reduced in high degree by circular polarisation, and ionosphere should be almost transparent.

On 13 October 2000 OZ1RH wrote:
> I observed many times that EME signals will be almost always much weaker
> when I hear in San Diego FM stations on 100 MHz from Santa Barbara area
> 250 - 300 mils north of me.

> Even on 1296 and 2304 conditions were for some reason dependent on

May I suggest refraction/reflection (ducting) and/or more scattering in the troposphere to be responsible for this. What I mean is an 'aboration' (hope this is the english word) or bending in the troposphere. Refraction is
mentioned in http://www.qsl.net/oz1rh/gndgain/gndgain.htm#_Toc426196575 though in another context. If it is a 'tropo' thing the effect should be more frequent on the higher bands.

Refraction might be noticeable on 10 GHz: beaming for moon noise your dish will point to the direction from where the signal comes. This may not be precisely the geometrical direction calculated by the pc. However I assume most folks would assume inaccurate readout of the AZ-EL if the moon is found 1 degree off.

Inversion/ducting might reflect your TX signal back to earth and/or reflect the signal coming from the moon back into space. Ducting is forecasted on http://www.iprimus.ca/~hepburnw/tropo.html Perhaps 'unexplained non ionospheric QSB' on eme can be correlated with this map.

Ionospheric scintillation (fast QSB) is caused by irregularities in the ionization, see http://www.nwra-az.com/ionoscint/sp_main.html . Such irregularities produces focusing/defocusing effects giving more QSB on the lower than the higher frequencies.

BTW I think libration fading is in fact ionospheric scintillation. Libration fading has been described to me as caused by the moon rocking in the orbit, but I can't imagine the moon rocking much in 1-5 seconds. Any libration fading on 10 GHz?

Slow fading at elevation angles lower than the vertical beamwidth of the antenna is likely to be ground effects - positive or negative ground gain - at one end of the path.


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