What did it need to run first 432 EME QSO ?

There are several stations qrv with 8-15m dishes and 16yagies and they are abel 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 enviroment:

·     minimum of 15elements

·     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 neighbours due to plasma TV and others sources

2. Tranceiver + PC

·     Low frequency drift of the tranceiver (<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

 

·     How to check if the system will work ?

First possiblility 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).

·     Nothing on screen, WHY?

1.   Doppler shift

·     Don’t forget to set 432 in the Band drop down menue

·     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 !!!

2.   Faraday and Spatial offset

·     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 mon 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.

2nd check will be the sun-noise:

Example :

With Solar flux = 130 (what we have now aprox) see http://www.solen.info/solar/

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

0.7 dB

Hard to detect !

Up to -20

19el. 15dBD
No elevation

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

1.3dB

Hard to detect !

Up to -17

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

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

1,0 dB

Hard to detect !

Up to -18

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

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

1.8dB

Should be detectable

Up to -16

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

Preamp at antenna
Cable loss and NF 0.5dB

2.8dB

Light move on S-Meter

Up to -13

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

Preamp at antenna
Cable loss and NF 0.5dB

4.5 dB

Easy on S-Meter

up to –10 !!!

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

Add some extra loss due to drift of radio, faraday, spatial offset, maybe apogee, libration, and MAN MADE noise !

·     The S-Meter on the common Tranceivers 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 antenuator until to get the storged 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 propperly mounted
  2. Receiver / preamp ok
  3. Antenna bad
..4. Mann made noise

While 1 and 2 can be checkd 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 carrrier. There should be 2 sidelobes 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 moise is hard to find. If possible take the rig to a lonely place and try sun noise and/or watching some EME signals again.

 

More to come soon

Home