DL7APV in JO62jr

 

Start EME

What did it need to run first 432 EME QSO ?

There are several stations qrv with 8-15m dishes and 16yagies and they are able to work very small stations in JT65 :

 

 

Only with a single yagi and 20W !

 

 

 

BUT: There are several things that have to be fulfilled like:

 

 

1.    Antenna and environment:

 

·       Minimum of 15elements (in rare cases 2el.!)

·       Elevation rotor would be fine, but no must. A fixed el. at 10° or 25° can help

·       If no separate preamp and PA is used, a low loss short cable to the antenna is a must (<2dB!!!)

·       free view to moon, special if no elevation is possible

·       no qrm from neighbors due to plasma TV and others sources

2.    Transceiver + PC

 

·       Low frequency drift of the transceiver (<10Hz per minute)

·       Sensitive RX (or better preamp at antenna)

·       >= 20W output

·       WSJT installed on your PC and connected with the radio

·       a preamp and PA close to the antenna would be fine

3.    How to check if the system will work ?

 

First possibility is just to go to N0UK Logger or HB9Q logger or Live-CQ and see if anyone is qrv on 432 EME. Someone is always qrv on weekends with positive declination (see moon-calendar)

4.    Nothing on screen, WHY?

            Doppler shift?

 

        If moon is up you see now the doppler shift (dop) of your own echoes if the box grid is empty.

        When the grid box is filled with the locator of the other station the doppler shift between DX and Home station is displayed.

        If a station spots CQ 432050 expect his signal + the shown dop.

On 432MHz doppler shift can be up to +/-1000Hz !!!

5.      Faraday and Spatial offset

 

 

 

 

 

 

 

 

 

2nd check will be the sun-noise:

Example :

With Solar flux = 70 (what we have now aprox. In 2018) see http://www.solen.info/solar/

 

        Most stations have a linear polarized system on 432 so if no signals detectable maybe faraday rotates the signal while passing through geomagnetic field of the earth. Try again later or ask a station with a dish to change polarization.

        Spatial offset is the geometrical polarization offset between two stations on earth when signals reflected from moon.

This will change during moon pass and declination.

        E.g. from EU to JA we have mostly around 90 deg (abt. –20dB) but the JAs using V-pol. antennas and EU hor.pol. antennas so no extra loss due spatial offset.

EU- north America west coast, both using mostly hor.pol. antennas and we have also mostly 90deg offset so that’s hard to work them with linear pol.

EU to Australia is easy as spatial offset is mostly  <30 (45deg are 3dB loss)

        Use VK3UMs EME planner to check spatial offset

If this will not show any results we have to look why.

Antenna

RX

Sun noise vs. cold spot

Sun noise is :

Big guns can be heard:

11el. 12 dBD
No elevation

2.0dB cable loss ant-TRX & 2.0dB NF, no preamp

0.0 dB

Nothing

Up to -20

19el. 15dBD
No elevation

2.0dB cable loss ant-TRX & 2.0dB NF, no preamp

1.0 dB

Hard to detect !

Up to -17

11el. 12 dBD +elevation
(measure cold sky)

2.0dB cable loss ant-TRX & 2.0dB NF, no preamp

0,9 dB

Hard to detect !

Up to -18

11el. 12dBD + elevation
(measure vs. cold sky)

Preamp at antenna
Cable loss and NF 0.5dB

2.5 dB

Light move on S-Meter

Up to -15

19el. 15 dBD +elevation
(measure vs. cold sky)

Preamp at antenna
Cable loss and NF 0.5dB

3.9 dB

Easy on S-Meter

Up to –12 !!!

AGAIN, that’s maximum possible values under optimal condx !!!

Add some extra loss due to drift of radio, faraday, spatial offset, maybe apogee, librations, and MAN MADE noise! (typically 2 to xdB)

        The S-Meter on the common Transceivers are nor accurate enough to check sun noise. To measure sun noise turn off the agc of the TRX (if possible) and use the measure mode in WSJT.

        Or use a switchable attenuator between preamp and TRX. Turn attenuator to 0dB, turn the antenna to the cold point in the sky, storage the S-Meter reading in your brain and turn the antenna to the sun. Now switch the attenuator until to get the stored s-Meter reading and you see the sun noise on the attenuator. This will work when the gain of the preamp is good enough, you hear increasing noise when connect to the radio.-

        Most SDRs have an accurate S-Meter and can be used direct.

If the sun noise is below the expected value it can have different reasons.

  1. Check the cable, water inside connector not properly mounted

  2. Receiver / preamp ok

  3. Antenna bad

..4. Mann made noise

While 1 and 2 can be checked on the workbench (maybe at the club or a friend), 3 and 4 are hard to check. 3 test the antenna with a local beacon, or carrier. There should be 2 side lobes at 10-20dB down at each side and all other lobes should be down by 20dB or more. The main lobe should have abt. 23 degree. This will give a feeling for the antenna. When there are some elements bent is not critical, bad contacts by corrosion is a bigger problem.

Man made noise is hard to find.

 

 

Home

 

 

 

 

 

 

 

 

After we learned about the conditions we will have a look to the station we will use for 432 EME.

 

We have 3 major things to observe:

Preamp & RX

2.1 sensitivity & gain of preamp

2.2 good IP3 & filter

2.3 high qrg stability for dig. modes

PA & Transmitter

3.1 Power

3.2 losses tx-ant

3.3 qrg & power stability for dig. modes

Antenna

1.1 Gain & SWR

1.2 Side lobes

Losses dipol-relay

Location

4. Simulation of your system      

 

Minum requirement for a qso in cw.  So far I know the smallest stations used so far were :

I5TDJ single long yagi 1K – EA3DXU 2x13wl &KW, both were using a good preamp and more than one attempt. 4 yagi to 4 yagi is always easy if pol. is cooperative. OK1TEH can work with a single 23el. & 600w G3LTF (6m dish) regular on random.

 

In JT it´s possible to work with 30w and a single medium yagi the bigger stations like 10 or 15m dish. Record so far is 2el. & 60W to 16y or 15m dish. See qrp.

Several 1Y-1Y qsos were made, like OK1TEH to Z21EME expedition -28/-25dB (PA2CHR). Chris had 38el M2 and good power.

I would like to hear what was the smallest station so far from little or medium sized stations. Tell me !

 

Most important is the antenna, but I will start with the preamps.

 

2.1 sensitivity & gain of preamp

Like we will see later on 432 we need sensitive preamps as close as possible to the antenna. I will not go to deep into the well known theory but the preamps have to fulfil following requests:

Low noise figure NF <0,5dB

Good Gain, G > 20dB depends on cable loss to RX

High IP3 >10dBm

Absolute stable K>1

Maybe a resonator in the input circuit to have a filter function

 

 

This issue we will have a closer look to the preamp needed for EME.

In all cases sensitivity is needed to hear well. This is more valid on 432 & up due to colder background in the sky. The best preamps I know are around 0,25dB. BUT when talking about absolute values of noise figures we have to remember that the measurement error is nearly in the same range!!! You need a good Noise figure meter and you have to know what you are doing. If no expensive noise figure meter is available there is only the chance to measure the performance in the antenna with sun noise or other galactic sources.

 

I will give some examples from the VK3UM simulation software with a single 21el. F9FT yagi. Sun flux =70, Tsky = 30K, gain preamp 20dB.

 

 

More info you find at:

 

http://ok1teh.nagano.cz/eme_gal432.htm

http://www.ok2kkw.com/00003016/lna_oz1pif/lna_oz1pif_en.htm

http://ok1teh.nagano.cz/how_connect_lna.png

http://www.ok2kkw.com/next/dj3jj_70cm2010.htm

http://ok1teh.nagano.cz/eme_432_vs_144.pdf

http://www.vk3um.com/G3WDG_libration%20paper%20revised.pdf

 

 

RX

Noise figure

Sun noise

Difference

Trx+ 10m RG213

3,5dB

1,9dB

0

Trx+5m Aircom

2,3dB

2,7dB

+0,8dB

Trx+preamp 1dB

1dB

4,1dB

+2,2dB

Trx+preamp 0,5dB

0,5dB

4,8dB

+2,9dB

Trx+preamp 0,25dB

0,25dB

5,3dB

+3,4dB

Trx+preamp 0,35dB

0,35dB

5,1dB

+3,2dB

Trx+preamp 0,45dB

0,45dB

4,9dB

+3,0dB

 

 

 

 

 

We can see that a low loss cable + preamp in front of an antenna can improve signal like doubling the antennas. If all other parts are optimal a tenth of a dB at the preamp makes not the big difference. But 10m RG213 will kill all possibilities of a EME qso where small signals expected.

 

Which preamp is best?? This question has no answer which will fit every case. It depends on location and your wallet. In an urban area you need all selection what is possible and IP3 must be good, NF is secondary. On a lonely island only NF is interesting. And if you are able to use a soldering iron it can cost 20.-Eur, but you can pay up to several hundred euros for a commercial one. The one I use today is from Hubert, DJ3FI a very fine cavity with <0,3dB NF. Bandwidth is small and IP3 fair. Better IP3 have for example the DB6NT preamps with ATF54.. series Transistors, but they have wideband input. OZ2OE published in Weinheim  some years ago a preamp with ATF54143 which will cost only <20Eu. He used only a serial C input to Gate and no tune. Simple and good, a bit difficult to handle self oscillation. The production charges of the ATF are not always the same, so depended on the individual transistor you have NF will be 0,3 to 0,5.

There are of course many other preamps available. Google for preamp 432 and there will be much info.

Or look here :

http://www.g0mrf.com/432LNA.htm

http://www.ssbusa.com/db6ntvhfuhf.html

http://www.qsl.net/dl5lf/432_preamp.html

http://www.downeastmicrowave.com/PDF/70ulna.PDF

http://www.rfham.com/ preamps

http://www.kuhne-electronic.de/de/shop/143_Vorverstaerker

 

Next important point is the matching from the antenna to the preamp. If you buy a preamp or the homebrew preamp is optimized at a noise figure meter the best NF at the antenna can achieved only if the antenna has the same impedance as the noise source, typical 50R. So not loose sensitivity the return loss of the antenna has to be 16dB or better (SWR <1,4).

 

Enough gain of the preamp is recommended. Based on the example before, we change gain and cable length.

The NF of the TRX 2dB, the gain of preamp is 20 dB, cable preamp-TRX has a loss of 1dB. Now we change the values and see that with a 1 dB cable loss the gain can be as low as 16dB to affect the noise figure.

 

 

 

 

 

 

RX Trx+preamp 0,25dB

Cable loss

/dB

Preamp Gain

/dB

Sun noise

/dB

Difference

/dB

 

1

20

5,3

0

 

1

15

5,2

-0,1

 

1

13

4,6

-0,7

 

1

10

4,4

-0,9

 

2,5

20

5,2

-0,1

 

3

20

4,8

-0,5

 

5

20

4,7

-0,6

 

10

20

4,1

-1,2

 

10

10

1,7

-3,6

 

 

 

 

 

Tuning. All OMs who have a noise figure meter I hope know how to use, but for all other I have a very simple trick from OE3JPC. All you need is your station with a FM RX an analogue ac-voltmeter and a very small signal in band. The Voltmeter is connected to the audio out of the transceiver. Use long wires that you can read the voltmeter while tuning the preamp at the antenna. Tune the RX on a very small signal. Turn the antenna into the “cold” sky and tune the preamp until the reading of the voltmeter is in minimum. (In German a better description is here:

http://www.qsl.net/oe3jpc/eme/UHFTECH3.pdf

It is very simple to optimize the preamp in the used antenna; all problems due to mismatch (bad SWR) are solved this way. The only disadvantage is, you optimize relatively, so no idea about the absolute noise figure. This can be solved by measuring the sun noise or other noise sources compared to the cold sky.

 

Checking absolute noise figure of the preamp with the sun. If there is no noise figure meter, we can use easily the antenna and TRX as measuring system. We need two things to measure, a good S-meter (or a chance to get the voltage from the S-Meter) and a step attenuator. The measure function of the JT65 WSJT 4 fits not, because the demodulators of the receivers are often not linear. The preamp must have enough gain so that the step attenuator does not decrease the system noise figure. As we can see in the table above we need more than 20dB gain when a 10dB attenuator is needed. (depends on estimated sun noise)

 

With the VK3UM EME planer (or other software) we can calculate where are the cold sources and the sun are at a given time.

Procedure is to point the antenna first to cold sky (Aquarius, Leo or Pictor) and read the S-meter (or better a voltmeter parallel to the s-meter). Then we point to the sun and now we switch the step attenuator to the position that we get the same s-meter reading as before. Now we see our sun noise on the step attenuator. Because of local noise and (at high sun activity) various flux values this should be repeated 3-5 times a day. With the mean value of these values we should get close to reality. 

 

The same procedure can be made with the ground noise, but there are several problems to solve. First is to have a dry non conductive ground in your garden. It took me 3 years to find out that my garden is wet and has a good conductivity. Good for 80m verticals, but gives not the estimated ground noise values. Second is manmade noise, modern plasma TVs switching power supplies make some more or less noise. So I found out, that my house wall is the best “ground noise” when all PC & TVs are off. So instead pointing to the sun the antenna is pointing into the ground or house wall with the full beam and we get the ground noise.

With this to values measured carefully and some more times to get a feeling for this we can calculate the RX parameters.

 

Getting own NF by two measures.

The VK3UM EMEcalc helps us to find out if the station is ready for EME. For our example we take a single 21el. yagi which is very popular in Europe.

 

 

 

 

 

 

Gain

18,2 dBi = 16dBD

Flux today

75

Cold sky

20K (Aquarius) or 25K (Leo)

Loss ant-preamp

0,2dB (2m aircom+2N-connectors)

Preamp NF

0,5dB (start value )

Preamp Gain

19dB

Loss preamp to RX

0,4dB (5m aircom+connectors)

NF of RX

3dB (I hope worst case)

sidelobes

15K

backlobes

5K

 

 

 

 

 

These values we put in the VK3UM calculator. The last two needed values are a bit difficult, spill over and feed thru. These names come from dishes and mean at yagi side lobes and back lobes. The lobes give some extra noise to the dipole and the system. We go into the datasheet of the antenna and see first side lobe is 13dB down and the front/back ratio is >20dB. So we have up to 15K from the side lobe and about 5K from the back. These values can be much higher in a noisy urban area!!!

 

Now we can calculate the noise figure and gain of the system. For a 0,5dB preamp we have to measure 5,6dB sun and 4,7dB ground.

If not  :

 

 

 

Sun

Gnd

what is wrong

4,6

3,2dB

preamp has 1dB NF

4,6

4,7

antenna gain is 1,5dB low

4,0

3,2

NF is 1dB & 1db low Gain

 

 

 

 

 

For the two measured values we can calculate exactly gain & NF of the system when all other parameters are fixed and known. So this way shows how to find out the own parameters. With one yagi the gain should be as it was taken from the datasheet, otherwise the antenna has a problem. At bigger groups as 4 or more yagi also the gain can be wrong by error in phasing lines. This should be found out also by the method above.

 

Simulation

 

This time I would show the possibilities of the simulation, so everyone can assume what is possible to work with his station or check if all works fine. A good tool is the VK3UM EMECalc. There are others of course, but I believe Doughs software is the most popular.

 

Important:

What we get from the simulation is the absolute BEST value we can achieve. In practical the achievements may reach the simulation only for a short time under best condx. Not calculated is librations, absorption from the atmosphere and polarization due to faraday. When used circ.pol. the polarization is not a big problem, but on 432 and 144 MHz where most of the Hams using linear pol. it’s a big problem. During low sun activities absorption is not seen for longer and also faraday is not rotating so much.

But in real world you have to subtract from the calculated values a few dB.

 

Like all other simulations we need exact values to get good results.

Following values are needed, beginning at the left upper side.

 

Tsky

That’s the background temperature of your cold sky. For 432 it is 20 or 25K depends on which cold spot is visible for measuring, Aquarius 20K or Leo with 25K. For EME contacts you have to put in the background temperature of the moon out of the lunar calendar or VK3UM EME planner software. If you have no elevation you have to put in your local outdoor temperature in Kelvin (K); 290K is the value for 17°C = 62F.

In this case the cold sky (C/S) to ground value is not valid and has to be zero.

 

 

RxBW

The RX bandwidth has to be set to 2500 Hz at JT65 and to 120-50Hz in CW. In CW it depends very on your ear-brain filter training, how small a CW signal can be to decode the signals. DL9KR can decode small CW signals down to 50Hz or better, while an untrained operator has 120Hz or more.

Physical theories are that the signal/noise ratio becomes better when the bandwidth becomes smaller. Easy to understand your signal goes through the filter, while the noise left and right of the filter is blocked. So sum of noise is less with smaller filters and the signal is constant and so the signal / noise ratio increases. When we hear small signals the ear-brain uses biologics filters to decode the CW. This can be trained and represented as bandwidth of your ear-brain.

 

Mesh Diam & Spacing

Only for dishes is Self-explanatory

 

LNA loss is the sum of the losses between dipol and preamp,  Baluns, connectors, dividers, cables and relays. (More than you expect !! )

 

LNA NF noise figure of the preamp, can be worse by bad SWR. Normally all preamps are tuned at a 50 Ohms system. So if SWR is not too good NF can be less then measured.

 

LNA gain Self-explanatory gain of the preamp in dB.

 

All the above values are zero if no preamp is used.

 

Coax loss

with preamp it’s Self-explanatory the loss between LNA and TRX

b) without preamp it’s the loss between Dipole and TRX

 

RxNf is the NF of the TRX (Transceiver)

 

Spill over& Feed through I explained last issue. Then TX power and loss of TX line has to be set and also the outdoor temperature and distance to the moon (apogee or perigee).

 

Yagi Array

The last value will be the antenna gain. There it is easy to choose from a menu well known types, but you can put in just a value from your own antenna. Important to know that this software calculates always 2,85dB for doubling antennas. This can be wrong when stacking distance is not the best. 

 

 

 

 

 

 

 

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Update feb 2018