CJU.pdf

THE ‘CJU’ ANTENNA

THE MAGIC ANTENNA

Scheme nº1: ‘CJU’ antenna scheme

I have published in the Unión de Radioaficionados Españoles monthly magazine

several articles about how to enjoy ham satellites, with an HT and a whip antenna or a

bit more complex with a fix station.

Pedro EB4DKA published in January 2.000 a marvellous article in which we

could learnt step to step how we can work LEO FM satellites with a simple portable

station, a full-duplex FM 5 Watts HT and a high gain whip antenna. He showed us how

to program the HT memories and what skills we must develop to change the frequency

while we are searching for the right polarization.

Later in January 2.004 I published an article by means of which I tried to

demonstrate that a 50 Watts satellite fix stations with a couple of little VHF and UHF

yaguis could make the same contacts that a HF fix station with a three-band yagui

without depending on the propagation. But somebody could say that a HF station is

simpler to work, I disagree with this opinion because if you have a PC which aims the

antennas at the moving satellite and changes the frequency, we only must talk, our

reliable friend (the PC) will do the hard work.

Photo nº1:

Photo nº2:

The necessary stuff to build the

The different parts ready to be assembled.

“CJU” antenna.

Pedro EB4DKA and I usually have long conversations and we always have the

same idea on the brain, to make the ham satellites easier to work so more people will be

able to work them. On this occasion we were thinking about how to improve our

portable station to make it more efficient.

Lately we have been working in a mixed way which we name mobile/portable,

well we stay in the driver’s seat with the driver window facing to the satellite pass

maximum elevation. On our left hand we handle our HT with a whip antenna changing

the orientation to get the best downlink signal and a pair of headphones, with our right

hand we handle the mobile station microphone whit a 1/4l whip antenna on the roof car

and 50 Watios to uplink. This way of working have given us a impressive outcome

even with SSB LEO satellites, but I will not speak about them to clarify the article.

We were analysing how to improve this mobile/portable station and we decided

that we must improve the reception because with the 1/4l whip antenna on the roof car

and 50 watts we did not have any problem to uplink, and if it was necessary we could

always increase the power out.

How all of us know the difficult thing is to receive the downlink because the

satellites usually transmit with power out between 50mWatts and 500mWatts with

changing polarization and up to 800Km far away. Somebody could think that it is

impossible to receive with an HT and a whip antenna, but it is possible. We can not

expect to hear it clearly, we will have to make an effort to pick the modulation up from

the noise and we must add that we have to change the polarization and the frequency to

face to the Doppler effect.

The LEO FM satellites usually work in V/U mode (we must transmit in the VHF

band and receive in the UHF band), so the Doppler effect in the downlink is up to +/-10

KHz in the worst case. On the other hand in the VHF band the Doppler effect is less

noticeable, only +/-2.5 KHz, we do not even need to change the transmitting frequency

because the wideband of ham satellites are over 5 KHz, the same as our FM

transceivers.

To sum up, we must try to improve the UHF received signals. When an antenna

is attached to an HT, the feed line or no exist or it is too short that we do not have feed

line losses, so to set a preamplifier is a nonsense. Then we only had a way, to improve

the antenna.

We were browsing the Net searching for a high gain UHF antenna to be attached

directly to the HT, but we only found whip antennas that we have just tested. So we

became again searching for a linear polarized UHF yagui, because if we work with a

hand held antenna, to install a circular polarized one is a nonsense. But it must be

small enough to be directly attached to an HT.

Photo nº3:

Photo nº4:

The BNC connector definitely installed.

CJU antenna ready to work, it has even

installed the rubber protectors at the

reflector endings.

Then we were looking around and we analyzed the antennas we usually use to

receive UHF signal with enough gain. The most veteran is the Arrow (we have just

reviewed it in the January 2005 Unión de Radioaficionados Españoles monthly

magazine). The Arrow antenna has seven elements in a 1.20 meters boom length, it is

too large to be attached directly to an HT.

We must search for a directional antenna with similar gain but with a less length

boom. We can only find this feature in the cubical quad antennas. Then we

remembered a known good reputation antenna into the satellites world, the IOio antenna

(We have just reviewed it in the January 2006 Unión de Radioaficionados Españoles

monthly magazine). The IOio antenna, in its UHF part, is a square radiator and a linear

reflector set in a 0.2 meters boom length. This antenna has a bit less gain than the seven

elements Arrow antenna because the IOio antenna is equivalent to a four elements yagui

antenna, but we have experienced that it has enough gain to receive the satellites

comfortably. So this is the option which fit to our necessities, we gave up searching and

became to work.

We needed a lightweight boom which it could be of plastic of 0.2 meters length

and 10mm internal diameter, because it is the BNC connector external diameter, so it

could be set into the plastic boom. We were searching around for some stuff suitable

but we did not find it, so I talked about it with my father EA4ABV who apart from ham

he enjoys raising canaries, and told me wait, perhaps the plastic stick where the canaries

perch on in the canary jails has this measurement. I used the inner diameter of the

perch and it was perfect.

To build the radiant and reflector elements I needed a steel wire, when I came

back from my father home to the mine a broken umbrella tossed in a trash can caught

me eye. The rods were perfect too, it was a lucky morning walk. To connect the

radiant element to the BNC connector I used a piece of RG223, a low losses 50 Ohm

feed line with the same diameter than the RG58.

You can see the “CJU” antenna details in the Scheme nº1. The antenna consists

of all the stuff you can see in the Photo nº1: the plastic stick, the umbrella rod, the BNC

connector, the screwed cooper clamps used in electrical installations and a compression

clamp to fix the BNC connector to the plastic stick.

In the Photo nº2 you can see the rod umbrella blended to the right length and the

BNC connector soldered to a piece of RG223, the other end of the feed line has been

uncovered a small length to solder later to the radiator element. The Photo nº3 shows

the BNC connector in its definitive place and the Photo nº4 shows the finished antenna

in which I have set a rubber protector at the reflector endings to avoid damaging

anybody while we are managing it. In the Photo nº5 you can see me working with the

antenna and in the Photo nº6 you can see the complete antenna system, a 1/4l whip on

the car to uplink and the “CJU” antenna on my right hand to receive the downlink.

Well, in a couple of afternoons I have just built the prototype, now Pedro EB4DKA had

to test it because he is the expert at working in portable conditions.

Photo nº5: Photo nº6:

EA4CYQ working with the ‘CJU’ antenna Complete EA4CYQ mobile/portable station.

A ¼ l whip on the car roof to uplink and

the ‘CJU’ in the downlink.

When I told Pedro what kind of stuff I have used to build the antenna we were

burst out laughing for a while and he quickly baptized the antenna as the Canary Jail

Umbrella antenna in relation to the stuff it was built. But in our minds were the same

question, Would it work?

Pedro has been testing the antenna for several weeks with all the V/U mode FM

LEO satellites, and each time he listen to the satellites he is amazed because the feed

line losses are nearly zero so it works as if a preamplifier was installed and the signal

never were worse than the signal he received with the Arrow antenna. He has even

received the FO29 with signal 5 and he has listening to the SO-50 from AOS to LOS

with any problem. I was surprised at his comments so I decided to build another one

and try my luck. I usually receive the satellites in my shack with 15+15 elements

crossed yagui with a switch capable to switch between right and left circular

polarization plus 25 meters of ½” feed line without preamplifier. I would not be able to

say which system works better, the only difference is being sitting in the driver seat or

in my shack.

The outcomes are amazing and I invite you to build the ‘CJU’ antenna because it

is very easy to build and you will be able to take advantage of its surprisingly

performance even in terrestrial communications. Pedro EB4DKA is updating its WEB

http://www.eb4dka.tk , and you can see us working with this amazing antenna in several

video recorders.

You need to learn some skills to work satellites so at the beginning you must

listening several passes before you push the PTT. You must take into account that a FM

LEO satellite is a repeater with a sole bigger than Europe so if you keep the PTT on for

several minutes to try to listening to yourself your are sending a carrier which interfere

with other stations, so IF YOU CAN NOT LISTENING TO YOURSELF YOU MUST

NOT KEEP THE PTT ON. The FM LEO satellites are one channel device, so we must

not take much time than necessary to make a contact. We must give other hams the

opportunity to make more contacts. We must never send a CQ, it is enough to say our

call sign or to call another station we have listened before.

We must take a lime flower tee before pushing the PTT the first time, because

when we listen to our self modulation you will get nervous and you will not be able to

say your locator and report signal properly which are the minimal dates to validate the

contact.

The following frequencies are exclusively for satellite use:

- VHF: between 145.800 MHz and 146.000 MHz all modes.

- UHF: between 435.000 MHz and 438.000 MHz all modes.

It is a pity to listen to hams, specially from our country, through the satellites.

This kind of behaviour interferes with satellite communications making them more

difficult that they are. When somebody uses these frequencies because they do not

know the rules we must try to explain them, we must always be polite.

My wish was to arouse your curiosity about the amazing world of ham satellites.

I think that with this tool attached to an HT in your left hand and with the microphone

of your mobile station in your right hand you will make satellite contacts successfully. I

am looking forward to listening to you soon!

I take advantage of this opportunity to say hello to all hams who work this mode

and all the hams from Vegas Altas del Guadiana, because their experience and advice

help us to bring out these easy projects.

EA4CYQ

EB4DKA

Juan Antonio Fernández Montaña

Pedro Pérez Álvarez-Cienfuegos

ea4cyq@amsat.org

eb4dka@amsat.org

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