Saturday, October 4, 2014

G5RV Vs Automatic ATU & Manual ATU Comparison

G5RV vs Automatic ATU & Manual ATU, and YAGI Antenna Comparison

One of the most common questions from any amateur new to the HF bands is, what antenna is the best? This is a question that is almost impossible to answer simply, and you can guarantee everyone has a different opinion! By the way, the word ‘antenna’ is interchangeable with ‘aerial’, they both mean the same!

Generally, a large antenna is best for the low end of the HF spectrum, where the wavelength is long, and a much smaller antenna will give you better results on the higher HF frequencies, where the wavelength is shorter.

This is the main reason many amateurs will use more than one antenna, but just as many will use one antenna, either a large wire one giving better results on the low bands, or a small antenna favouring the higher bands. As they are using just one antenna, they accept it will be a compromise and work better on certain bands than others.
If the antenna is resonant on a given frequency, this means it is exactly the right length. This also means the correct impedance is seen by the transmitter, and all of the power generated by the transmitter can be radiated through the antenna. The antenna is said to be a good match.
If you have an antenna that is too long or too short for the given frequency, the antenna will not be resonant, and the transmitter will not be able to transfer full power, the antenna is therefore a poor match.
Fortunately, if the antenna is not too far away from resonance, it can be matched with a matching unit, otherwise known as an Antenna Tuning Unit.
The same is true for received signals, the longer or shorter the antenna is from the resonant length, the poorer the incoming signal will be unless matched. If the antenna is far too long or far too short it may be impossible to match, depending on the matching unit.
If you have a small garden, the most practical solution will be to have just one antenna. Fortunately, one antenna can be made to have multiple band characteristics, and there are a variety of methods employed to give low impedances on multiple bands. The antenna will still be a compromise on certain bands, but not everyone has the space needed for an Antenna Farm!
In my experienced, it can be important for a blind operator to use a low impedance antenna. If the antenna  has low impedance characteristics on multiple bands, it is likely the operator will be able to match the antenna using the automatic antenna tuning unit built into the radio. This built in antenna tuning unit or ATU will only have a limited range, and only be able to deal with small impedance variations.
If you cannot tune the antenna by using the built in Automatic ATU in your rig what you should do? Well  I have an experienced in 1994, I have a chance to bring back Yaesu  FT-1000D to my shack which I can’t afford to buy it at that time , you know this is like a FERRARI at that time running 200 Watts bare foot with built in Power Supply. 

In my case through my experienced and experiment I found out that the built in ATU can’t tune my G5RV antenna. So what I did was I bypass the built in ATU and used my manual Tuner and it work fine, I am puzzle at that time why the built in ATU can’t tune my G5RV on 40M. I went to my back yard and look at my antenna and the feeder. The feeder was quite long and it was lying on the ground, I think this is why the builtin ATU can’t tune….what I did I took the coax cable and hang it up…and I went back to the shack I dismantle my Manual ATU and connected the coax cable back to the FT-1000D…than I tune it by using the built in Automatic ATU….It works now the ATU can tune. Than I make some research by reading some books yes now I understand that  the impedance of the antenna change when  our feeder on ground and on air on that particular frequency. Now I understand it well the automatic ATU have a limited range and only deal with small impedance variations compare to our Manual ATU which have wide range of impedance. 
This is what i used when i can't tune my antenna way back in the 90's they called it Antenna Coupler !!                          
The antenna  I have used for many years is the G5RV which hang up on the pole running down as an inverted V. It is a wire antenna and is inverted V shaped in profile. The feeder rises vertically to a T piece at 20 feet high, and the signal is radiated by the wire element, extended each side.
My second HF antenna is a Yagi beam. It is a Mosley 4 element Yagi, and the elements mechanically adjust to the correct length for the chosen frequency. The advantage of a beam is its ability to focus the signal in the chosen direction. Whilst most serious DXers (hams wanting to work long distances) will use a beam, they are relatively large, and require a strong mast and a method of turning or rotating the beam. The Mosley is a 4 element beam on 10m to 20m.
With all antennas, it is important to get it off the ground and as far from surrounding obstructions as possible. In my case I used a  60 feet tower.

For local 40M QSO in Malaysia please use a Dipole. Don’t ever use a vertical antenna because most of our QSO between 10km - 500km. A vertical antenna is Good for DX because it radiate on low angle but for short distance QSO within the range of 10 to 150km this will be a problem to other station because they can’t copy you well but if that station TX from Penang to JOHOR they will copy you 5/9 but if the other station was in IPOH for sure this station will copy you (from Penang) maybe around 4/6 or less than that and very hard to copy, if band is noisy you will be drown in the noise.....So my advice try to make one dipole for 40M for local QSO.

            This CP-6 antenna is the most popular easy to put up but only good for DX.....

1 comment:

  1. I hope you can explain and give advices on this 'problem'

    Here are the two ways/places to put SWR meter or ATU.

    A) Transceiver +ATU/SWR+-------coax---------+Antenna
    B) Transceiver +-------coax---------+ATU/SWR+Antenna

    Which one is correct?

    IMHO, I choose B), because
    1) the coax cable's impedance is always 50 Ohm. Yeah, there are still +- several Ohms.

    2) From the name ATU itself, Antenna Tuner, it tunes the ANTENNA, not the coax cable. :)

    Another question is..

    If I got SWR 1:1 near the transceiver (A), does it mean, I also get 1:1 when I measure near the antenna (B)?

    Thank you, for the great, simple to understand article.