Icom 802 AT tuner with dipole

[galbizua]

Hy
I have an icom 802 and AT Tuner 140. I want to install it in my house with a dipole Antena but I don't know how to make it.
The tuner don't has coaxial output, it has ground connection and other antenna connection.
I think that one option is connect the coaxial that came to the dipole to te Antena output tuner and the other to ground, it is correct????
Please help !!!
Thanks!!!
Guille

[GordMay]

Greetings and welcome aboard the CF, Guille.

➥ http://www.icom-france.com/files/not-AT-140-angl.pdf

[PommyDave]

A dipole antenna is a single-band antenna that is fed at its center by a coaxial feeder. It is a simple antenna, however you basically need a different size dipole for each HF band you plan to transmit on. The ancient formula for a dipole is 468/frequency in MHz. Therefore an antenna for 7.1 MHz (a popular Ham band) would be about 468/7.1 = 65.9 feet or 65 ft 10.8 inches from end to end.

The exact dimensions depend on the thickness of the wire antenna, whether it is bare wire or insulated wire, and the height of the antenna about the ground (or deck of your boat, or the sea itself. And then it is different again if the antenna is hung as an "inverted vee" (with the center much higher than the ends of the antenna "legs", or as a normal dipole).

Each location and installation differs slightly, and antennas are usually fine-tuned by transmitting a low-powered carrier (maybe 3 watts or less) and measuring the antenna's impedance with an antenna analyser or by using a VSWR meter (often called just an SWR meter).

Most modern radios are designed to work with an antenna that shows 50 Ohms impedance. (This is totally different from 50 Ohms resistance). If the transmitter "sees" a high SWR or a different impedance it should cut back its transmit power to low, to save itself from damage. Old, valve radios were much less prone to such damage from a mismatched antenna.

What is normally used on a boat or ship is an antenna with an automatic ATU (antenna tuning unit) at the base of a long whip or end-fed wire antenna. The ATU "fools" the transmitter into thinking it is sending to a resonant (tuned) antenna that shows 50 Ohms impedance, so it transmits at full power. That way you don't need ten different antennas for ten different bands.

[ka4wja]

Guille,
Sorry I didn't reply earlier, I've been quite busy with personal matters ashore...

You CANNOT expect to use a coaxial-fed dipole on ANY OTHER BAND/FREQUENCY than it is cut/designed for.....no matter how good of a "match" your tuner may represent to your radio....
Most of your transmit energy will be lost in the mismatched coaxial line and in the tuner!!

If you can return this "dipole" (whatever one you purchased), get you money back, and simply source some inexpensive copper wire....90' to 225' of it, of any gauge from 18awg to 12awg....
And string up this wire, thru some trees / shrubs, etc.....or support it from some poles/masts, etc....

If you cannot return the dipole, then use its wire....but NOT its coax...as your antenna...

The 2 easiest ways to do this set-up, are:

1) String up a wire (of any size you have access to) of approx. 175' to 240', in some sort of a loop / any configuration/shape you can manage (square, triangle, hex, octagon, circle, etc.), at a height of approx. 20' minimum and 50' maximum (30' - 35' high is good)....
Attach one end of the wire to the AT-140's "antenna output terminal" (the screw stud on the ceramic insulator), and the other end of the wire to the AT-140's "ground terminal" (the screw stud on the other end of the AT-140)....
This antenna will provide you with excellent regional coverage from 0 - 300 miles or so, on the lower bands (3.6mhz, 4mhz, 6mhz)...decent regional coverage, from 0 - 500 miles on the middle bands (7mhz, and 8mhz)....as well as good nighttime coverage for longer ranges on these lower and middle bands....AND, will also provide decent long-range coverage for some higher bands (12mhz, 14mhz, 16mhz) with some odd nulls and lobes in the pattern, the higher in frequency you go...
But, understand that the larger you make this loop antenna (up to 250' in circumference), the better it works on the lower bands, but the more lobes and nulls you make on the higher bands....
A good compromise is a length/circumference of 175' to 225'...

The AT-140 will tune this antenna perfectly, with no effort and minimal losses...

Understand that the exact length/circumference, the exact shape, and exact height is NOT critical at all!!
And, where you place the tuner (low near the ground or on a pole, etc.) isn't critical either, just run the antenna wire from the tuner's attachement terminals, up to wherever you can string up the wire!
You do NOT need to measure anything precisely at all....simply roll out about 200' of wire, and string it up....attach it to the tuner, connect tuner to M-802 (coax and tuner control wiring)

This horizontal loop antenna is an excellent wide-band antenna, which presents a rather narrow range of impedances (compared to trying to use a dipole on various bands!), it is easy for the AT-140 to tune, and presents you with an excellent regional-range antenna for the lower bands, and a decent long-range antenna for the higher bands...
And, it is totally non-critical....and cheap/inexpensive!!


2) A second choice would be to simply string up a dipole, cut for the lowest band of operation, and accept some possible tuning difficulties at the 2nd and 3rd harmonic (such as a 4mhz dipole on 8mhz and 12mhz), and the deep nulls and narrow lobes on the higher bands (3rd and 4th harmonic)
You'd simply attach one wire to the AT-140's "antenna terminal" and the other to the AT-140's "ground terminal"...
If the 4mhz marine band is your lowest frequency of interest (typical), then two wires each approx. 57' long would be good....but, if the 8mhz marine band was your lowest freq of interest, you could use two wires, each approx. 28.5' long....
If you are looking for the best overall compromise "dipole", just use two wires, approx. 40' to 42' long, each...
And, string them up at the same approx. height (20' high minimum, to 50' high maximum)....

Originally Posted by galbizua

Hy
I have an icom 802 and AT Tuner 140. I want to install it in my house with a dipole Antena but I don't know how to make it.
The tuner don't has coaxial output, it has ground connection and other antenna connection.
I think that one option is connect the coaxial that came to the dipole to te Antena output tuner and the other to ground, it is correct????
Please help !!!
Thanks!!!
Guille

Please understand that what you're trying to accomplish in either of the above two examples (and your query) is a wideband antenna directly fed with a remote auto-tuner....
These two examples above are the two easiest / simplest approaches to this....(and #1, the loop, is a very good antenna!!)



Guille, I have no idea where you are located, nor what bands/frequencies you wish to use your M-802/AT-140 on from your house....please advise us of all of this, as it will make a big difference in what we can recommend specifically...


I do hope this helps!

fair winds...

John

[ka4wja]

Guille,
I hope you found the above info helpful?
If not, please provide further info, and I'm sure we'll be able to ofer you more assistance.
fair winds...
John

[galbizua]

Jhon, I saw your excellent explanation,
I apologize for replying so late.
Guille
CP6GA

[continuouswave]

There is nothing about a dipole antenna that requires it be fed with an unbalanced coaxial transmission line, and, in fact, a dipole is a symmetrical antenna and SHOULD NOT be fed with an unbalanced coaxial transmission line.

The antenna tuning unit you describe is intended for feeding a MONOPOLE antenna, not a DIPOLE antenna.

There is nothing intrinsic in a MONOPOLE antenna compared to a DIPOLE antenna that makes it have a broader impedance bandwidth. The impedance bandwidth of any antenna depends on the antenna Q, which is better when lower and can be achieved by making the radiator elements from large diameter conductors.

The comments about transmission line loss are accurate, but omit the notion that when the ATU is directly connected to the end of a monopole antenna, there is NO TRANSMISSION LINE in the system. You could accomplish this same approach to feeding a dipole antenna line by just elevating the ATU to the height of the center of the dipole and using an appropriate BALUN.

A BALUN is a word formed from BALanced-to-UNbalanced. So to use an unbalanced ATU to feed a dipole--a balanced antenna--you would use a 1:1 balanced-to-unbalanced BALUN. There is no perfect balun with no loss, and this is particularly true when the balun is terminated in very strange impedances. Thus a balun could introduce added loss into the system when trying to operate a dipole antenna at a non-resonant frequency when its feedpoint impedance will be more than 1,000-Ohms.

Comments about loss in the ATU are not specific to use with a dipole. A monopole will have very large impedance excursions with frequency, and it will present a very high impedance to the ATU, just as a dipole will. The ATU has no idea what is causing the high impedance and it will have the same losses in the ATU with either a dipole or a monopole when they are operated at non-resonant frequencies.

It is not particularly difficult to make a FAN dipole where several different lengths of dipole antennas are wired in parallel with a common center feed point. This makes an effective dipole broadband antenna that will resonate at multiple frequencies.

Generally a horizontally polarized dipole antenna of half-wavelength that is operated at least a quarter-wavelength above ground will give much better performance than a random length vertical monopole fed directly with an ATU and operated without any effective counterpoise.

So don't give up on a dipole.

As a general rule, you should be careful about accepting advice about antennas, as a great deal of bad advice gets passed around--of course, including mine.