mandag den 18. september 2017

144 MHz EME: New 4x6H Array

I've tried different antennes for EME on 144 MHz without much success. The antenna gain was 11-12 dBd. Sometimes an antenna received few signals from the Moon, but most of the time it received nothing. That was quite frustrating! I tried a sked with a big station (HB9Q) in order to get my first QSO, but the sked failed. He could not hear me, and I could not hear him.

To solve the problem, I decided to build a new antenna array with 15 dBd gain. This gain is generally considered as minimum for reliable EME communication on 144 MHz. LA3EQ Jan has succesfully used this antenna type for several years.

4 x 6-element yagi at OZ1BXM
My new antenna is 4x6H which is 4 stacked 6-element yagi-antennas with horizontal polarization. Each yagi is PA144-6-2 from Dual (YU1CF). The stacking distance is 2.40 m horizontal and 2.20 m vertical. All four antennas are mounted on an H-frame made of 1½" galvanized steel tubes. The 4-way power splitter was fitted using a homemade clamp. The box below the rotator contains a 1 kW coax-relay. The other box contains a HA8ET Extra-2 preamp (NF 0.5 dB). The horizontal rotator is Yaesu G-600 and the elevation rotator is Kenpro KR-550.

With this array, I hope to get my first EME QSO soon. Stay tuned!

Vy 73 from OZ1BXM Lars

søndag den 30. juli 2017

144 MHz EME: Antenna problems

My elevation rotor KR-550 was repaired and remounted last month. So far, so good.

My next step was replacing the 2 x 6 vertical yagis with an 8-element horizontal yagi (Wimo WY208). The reason for this change: I wanted horizontal polarization. I heard only a few stations with the vertical yagis.

8-element yagi with elevation.
I had a sked with HB9Q yesterday. He called me, and I called him. But there was no QSO, not even a trace on the waterfall. I was disappointed, because HB9Q is probably the biggest station in Europe transmitting a very strong signal with his 15 m dish. I tried with another big station, and he shifted between horizontal and vertical polarization. No trace at all on my side.

Some time ago I received signals from the Moon using my 2 x 6 yagis. So there seems to be a problem with my 8-element yagi since nothing is received. I'll do some troubleshooting, and hope to find out what is wrong.

73 from OZ1BXM Lars

torsdag den 22. juni 2017

Repairing my Kenpro KR-550 elevation rotor

My Kenpro KR-550 rotator was "frozen" and could not move in any direction. I searched for advice (Google is your friend) and found instructions from PA1IVO on how to disassemble and repair the rotor.

Disassembly of the rotor cabinet was tricky! The 8 bolts holding the cabinet together were completely stuck. I had to apply a dismounting technique, which I learned from a Youtube video: Heat the bolt and apply candle vax to the thread. That surprisingly worked!

The bolt can be loosened after treating it with candle vax.
Next step was to spot the error. The motor and gearbox were in good condition, and they operated normally when power was applied. However, the big gear wheel, which is fitted on the boom shaft, had chunks of clotted grease between the teeth. This was the core problem, and it prevented the big gear wheel from rotating. I removed the chunks and cleaned all gear wheels.

Clotted grease was found in the gear wheel.

Finally, I replaced the 500 ohm potentiometer inside the rotor. The new potentiometer was purchased at UKW-Berichte in their webshop (item 01999-KR-Poti). The spare-part cost me 27 EUR plus shipping from Germany to Denmark.  

The new 500 ohm potentiometer.
Now it was time to assemble the rotor. The gasket between the two halves of the cabinet was renewed. I applied Loctite 243 to the 8 cabinet bolts. Loctite 243 prevents loosening due to vibration, and it permits disassembly with hand tools for servicing.

The elevation rotor is now back in operation. I am eager to resume my EME project, and I will report my progress here.

73 from OZ1BXM Lars

tirsdag den 16. maj 2017

My Elevation Rotor is "frozen"

Some weeks ago, my elevation rotor KR-550 "froze". It does not move, and the elevation is fixed at 45 degrees.

The elevation rotor is more than 10 years old, and this kind of problem seems to be "normal" with this rotor type. A search on the net showed that other hams have had the same problem, e.g. PA1IVO. I am now going to repair it following his advice.

My first EME QSO is unlikely to happen until the rotor is fixed.

Vy 73 from OZ1BXM Lars Petersen

fredag den 7. april 2017

144 MHz EME: CQ heard

Last evening, just before midnight, the Moon was high in the sky, and the Sun had set more than 1 hour ago. The degradation was about 2.0 which means good conditions. I watched out for EME-signals, and I used the EME-chat (N0UK) as a guideline for their frequency. The EME-chat is mandatory because you want to know where the different stations are calling. Below is a cropped screen-dump of the WSJT-X Wide Graph waterfall (times are in UTC):
OK1DIG calling CQ on 2m EME.
OK1DIG decoded by WSJT-X (JT65B). 
WSJT-X decoded the JT65B signal (sync tone at 1165 Hz) as OK1DIG calling CQ. His signal was pretty good and between -15 dB and -13 dB. His equipment: 4 x 17 yagi and 1 kW.

I could also see K1SCE answering the CQ (sync tone at 1389 Hz) He used 4 x 9 yagi and 1 kW, but he was not picked up by the other station. The signal from K1SCE was not strong (best -20 dB), but it was perfectly readable at my QTH.

If my SSPA was connected, I would have answered OK1DIG. My first priority is getting on the air - and flying to the Moon!

Best regards OZ1BXM Lars

lørdag den 1. april 2017

144 MHz EME: Graves radar 143.050 MHz heard

Today Friday 1st of April is my lucky day! I've heard the first radio signal off the Moon!

I listened for ham radio signals from the Moon after having erected my 2x6 vertical yagis. I listened most of the time on 144.120 MHz - but no stations were heard. I was disappointed. I had expected at least some stations be visible on the waterfall. The reason - probably - was lack of big gun stations.

The danish ham radio magazine OZ published "Experience EME using simple equipment" in their July 2015 issue. The message was clear: Use the French Graves VHF-radar signal as a beacon, and listen to its reflections off the Moon! The radar is located in 70140 Pesmes, France (locator JN27SI). It transmits a powerfull beam between 15 degrees and 40 degrees elevation. The azimuth angle is between 90 degrees East through South until 270 degrees West. The purpose is to track LEO satellites. As a side effect, the radar signal at 143.050 MHz will hit the Moon and bounce back to Earth.

The map below shows the location of the Graves radar. It is far away from my QTH.

OZ1BXM QTH and the Graves radar in France.
I used my EME station for receiving the Graves signal. My Yaesu FT-847 can easily tune to 143.050 MHz, and when I aimed the antennas towards the Moon, the radar signal (continous wave) was heard immediately and visible on the waterfall.

A screen-dump of the "Wide Graph" waterfall in WSJT-X is displayed below.

Wide Graph waterfall displaying the radar signal.
Kind regards from OZ1BXM Lars Petersen

fredag den 24. marts 2017

144 MHz EME - Antennas are up

Spring has arrived in Denmark, and now it's time for antenna work!

During winter I've spent much time preparing the new antenna set-up. The antenna mast was down resting on the lawn. I've mounted the following items onto the mast:
  • Two new 6-element antennas (Dual PA144-6-2) 
  • Elevation rotor (Kenpro KR-550)
  • Wooden cross-boom
  • Pre-amplifier
  • Power splitter
  • Coax-relay 1 kW
  • Coax cables for RF
  • Control cables
I decided to erect the antenna mast on a sunny day in March. I called a friend to assist me. Two persons can do a safer job than one. My friend was on the roof pulling a rope, which was fastened to the top of the mast. I was on the ground pushing the mast. After some minutes, the mast was erected and secured to the house wall.

144 MHz EME antennas.
Building an antenna system is fun, but it can also be cumbersome. I am very much looking forward to hearing my first EME signals, and I will report my results on this blog!

OZ1BXM on the roof (photo by XYL).
Regards from OZ1BXM Lars Petersen

onsdag den 18. januar 2017

144 MHz EME - HW and cables

The complete system for 144 MHz EME.
The sketch above shows the complete EME system. The TRX (Yaesu FT-847) is placed in the radio room, and it is connected to the antennas as shown above. Control cables carrying 12V to relays, PTT, preamp, etc. are not depicted.

The receive path.

The sketch above shows the RX path. Number 1a and 1b are antenna feed points. Both of them are connected to the power splitter (2) where the antenna signals are combined. From the power splitter, the signal moves on to a coax relay (3) and from here it is routed to the preamp (4). After amplification in the preamp, the signal is sent via another coax relay (5) to the transceiver in the radio room (6).

The transmit path.

The sketch above shows the TX path. Number 1 is the transceiver inside the radio room. From here, RF (about 20 W) goes to a coax relay (2) and then to the SSPA (3). The SSPA amplifies the RF signal and provides 1 kW output. The RF power then goes to another coax relay (5) and continues into the power splitter (4) which divides the RF power between the two antennas. Each of the antenna feed-points is supplied 500 W (6a and 6b).

You can get more info on hardware, cables, and antennas by visiting this page: EME station and antenna for 144 MHz

Regards from OZ1BXM Lars

lørdag den 14. januar 2017

144 MHz EME - PC and peripherals

My PC and peripherals are connected as shown in the sketch below. This set-up is for my EME project.

PC and peripherals at OZ1BXM
1: Interface from ZLP Electronics.
2: Asus USB sound card.
3: Interface from ZLP Electronics.
4: Rotor controller ERC-3D from Easy-Rotor-Control
5: USB-to-serial adapter (FTDI chipset)
6: HP Compaq PC (Intel dual-core processor @ 3 GHz; 4 Gbyte RAM)
7: WLAN adapter
8: Transceiver Yaesu FT-847 with crystal heater QH40A installed.

Regards from OZ1BXM Lars