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Author Topic: What antenna should I look at building?  (Read 7209 times)
KG6YSF
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Posts: 81




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« on: September 27, 2013, 08:38:27 PM »

I have a Drake TR-7A, an MFJ 969, and I am getting ready to ship the radio for a once over i.e. a good cleaning and what ever repair realignment and so on it needs. While it's gone I am wanting to work on some antennas. I like to build wire antennas and was thinking of putting one up to radiate N/S as well as one to radiate W/E obviously on a switch and then be able to use the one that is in the best orientation. As well while the radio is gone getting the full spa treatment I am setting up to run the radios on a pair of L16 batteries. They will be fed by a float charger for the time being and eventually by a solar cell and charger.
The other equipment is a Yaesu FT-8900, and some LED lighting. So it is a very simple set up. But back to the origional topic. What should I look at to do for antennas?   
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
NU1O
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« Reply #1 on: September 28, 2013, 12:55:52 AM »

What band or bands, and what will you use to support the center of the two dipoles?  Also, how high will be the tower or mast you use for support?
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WX7G
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« Reply #2 on: September 28, 2013, 02:24:41 AM »

I assume you want to work 80-10 meters with your MFJ-969 tuner and TR-7. A 100 to 130' dipole or inverted-vee center fed with ladder line will do the job. The vast majority of hams with such an antenna have only one and not two. The high the better of course but even at 30' you will make plenty of contacts.

If you do install two antennas that require an antenna tuner, and you want to switch between them instantly, two tuners are needed.
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W2WDX
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Posts: 188




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« Reply #3 on: September 28, 2013, 02:38:26 AM »

I always find it interesting how people buy something before they know what it is going to be used for. The tuner in this case.

Like most things the type of antenna will determine the best choice of tuner, not the other way around. Your antenna choices should be chosen on the installation site available and not the gear you have. If you cannot raise the antenna at least up beyond a 1/2 wavelength for the frequency of operation it will tend to be more omnidirectional in its radiation pattern, with a high angle of radiation. So constructing two antennas is not gaining anything directionally.

Also balanced wire antennas are much more efficient and have much lower losses, and exhibit substantially better multi-band performance as an overall system, but only if tuned using balanced feed-line and a true balanced tuner. Single-ended tuners, baluns, traps and coax are not preferred and exhibit relatively higher losses in a simple multi-band dipole. The same problem compounds in diploes using traps, OCF designs or snub tuned systems like G5RV.

A simple random length high dipole fed with balanced transmission line and a simple link-coupled tuner will almost always tune easier, have much lower losses, and operate on most bands well. Even if not mounted high. This is when compared to many of the compromise antennas, like OCF and trapped dipole heralded by their makers as the savior of Hams.

I've been through that frustration using OCF's, trapped dipoles, G5RV and even resonant monobanders. Now I use a simple Extended Double Zepp (210' long) fed with simple 14 AWG 430ohm ladder-line and a 60 year old Johnson Killowatt Matchbox (I did own a 969 and a Palstar 5k and a Murch). It is very high (nearly 270' above ground level) and it is the best antenna system I have ever used, by far. My total calculated losses are under 1.7dB compared to the 6dB to 12dB in loss I had with baluns, coax, traps, and single ended tuners.

I had so much loss on these systems, that depending on frequency I was losing as much as 70% of my power by the time it reached the feed point of the antenna. Basically that's taking 1200w and turning it into 360w. Or 200w and turning it into 60W. Now add to that ground losses and other losses in the antenna and I am amazed anyone heard me!  Smiley

Just a thought ...

John, W2WDX
« Last Edit: September 28, 2013, 02:42:26 AM by W2WDX » Logged

KG6YSF
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Posts: 81




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« Reply #4 on: September 28, 2013, 01:45:35 PM »

Okay to fill in the blanks. I am sitting on a thousand acres so length and space are not an issue. I will be supporting the ends and center on 30' masts. I know it isn't very high however I don't have money for towers. I would like to be able to work 10 - 80 on this system. I do not own the property it is my cousins. He lets me live here in trade for watching over the place and feeding cattle when he isn't here. He lives in San Francisco about 4hrs away. Back to topic, I have the equipment I do from barter. The drake I got for 2 cords of firewood. The tuner I got from my brother in law for helping them move. Money is an issue for me so I am trying to do the best I can with what I have. I am sending the radio out hoping that by having it taken care of it will last longer. The reason I am setting up on batteries is because I was given the batteries and we are out of power up to a week a year. So I still want to be on the bands and since frequently we are out of power due to wild land fire. Oh as well there is only one way in and one way out of the valley we are in. I work with ARES and Red Cross for those times. Any way long story short I only want to spend money where it can be best utilized.
Thanks for the input I do appreciate it.   
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
KI5FJ
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Posts: 37




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« Reply #5 on: September 28, 2013, 03:41:25 PM »

Jason, please consider four 30 Ft masts in a square shape. If you can space them 558 Ft apart and feed in a corner with
450 Ohm ladder-line(window line) you will enjoy low noise receiving. NVIS on 80-40. Significant gain at Low TOA at higher frequencies.
I have a similar loop up for the past 16 years. I have modeled it on 12-Meters. If you are interested in a pdf just email me at QRZ address.
I suggest you contact local club members about experiences with large loops. 73 Joe O NNNN
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N4JTE
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Posts: 1147




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« Reply #6 on: September 28, 2013, 04:54:27 PM »

http://www.eham.net/articles/29061 This article might help you focus your antenna plans.
Bob
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KG6YSF
Member

Posts: 81




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« Reply #7 on: September 28, 2013, 08:41:10 PM »

I thank you for the reading and the idea for the loop. I had tried a fan dipole array and did well on 15, 20, 40, and 80 but as soon as I tried to add the rest of the bands everything went to crap. As well my power supply for the HF went down, and I want it back! Grin Not only do I want it back but I want it to be gooder, much , much gooder. Cool Yeah I know my English 1A profesor about had a coronary over that one.
Now if I feed an antenna with twin lead should I use 300ohm or 450ohm. My MFJ 969 has a 4:1 balun built in.
As I am sure by now most of you have figured out that I don't "know" the electronic theory well. I have memory issues. Bad head trauma in the Army so I'm sorry that I seem so uneducated for a licensed general class ham. 
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
WB6BYU
Member

Posts: 12977




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« Reply #8 on: September 28, 2013, 10:38:37 PM »

Not a problem - if everybody knew everything to know there would be many fewer questions
asked on these forums!

The 300 ohm twinlead is lighter and cheaper, and somewhat more fragile.  The 450 ohm twinlead
is sturdier and has a bit lower loss.  You can also use open wire line (two wires with periodic spacers
holding the apart, which can be homebuilt with some #14 house wire and spacers cut from PVC pipe.) 
Any of them will be operating at a high SWR on most bands, but losses should be reasonably low
as long as the antenna is long enough for that band (preferably longer than about 0.35 wavelengths.)
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KG6YSF
Member

Posts: 81




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« Reply #9 on: September 29, 2013, 11:17:37 AM »

Okay I had thought about "making" twin-lead that way not realizing that it was what was being refered to as "open wire." That I will do. You said home wire, I assume you mean solid copper or copper clad and not stranded? Stranded wire should work for that shouldn't it?
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
WB6BYU
Member

Posts: 12977




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« Reply #10 on: September 29, 2013, 03:25:32 PM »

Just about any sort of wire will work.  There are mechanical limitations (thin or stiff wires, or
soldered joints in stranded wires, may not hold up when it flutters in the wind) and some
types of wire materials are less suitable (iron and steel wires are more lossy; CopperClad is OK
as long as the copper layer is thick enough relative to the skin depth at that frequency, so
stranded CopperClad may be more lossy on 80m and 160m.)

I've used stranded, insulated hook up wire strung between nails on the top of a fence, with
no other insulators in a span of 75'.  Indoors I've used two pieces of thin magnet wire held
together with Scotch tape.  If you have some type of wire on hand, use it.


And you should NOT need to thread the end of the wires through a bunch of insulators to make
it work.  Generally the approach is to stretch out the wires and secure the insulators to them,
sometimes with a tiewrap or short piece of wire passed through holes in the insulator and
twisted around the wire itself.  There are lots of ways to do it, but if you are passing the end
through the hole in every insulator, you should look for a better method.
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KG6YSF
Member

Posts: 81




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« Reply #11 on: September 29, 2013, 09:58:35 PM »

Been reading a lot and the wife just handed me the ARRL "More Wire Antenna Classics" book. She surprises me some times. There again she may have ulterior motives being a ham as well; she is a pretty gabby one at that. Grin I am toying with the a design for an OCF 130' dipole and a Random or long wire. My tunner has provisions for multiple antennas. 
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
WB6BYU
Member

Posts: 12977




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« Reply #12 on: September 30, 2013, 12:20:01 PM »

Using a smaller loop (about 70' on a side) will still give you good coverage of all bands,
and may be more practical (less sag in the wires, among other things.)  That only takes
1 more mast than a dipole (assuming you are planning a mast in the center to support
the weight of the feedline, though it isn't always needed.)

I've had success tuning the loop for about 3.55 MHz with a 4 : 1 balun at the feedpoint
and having relatively low coax loss on most HF bands, though you can also feed it with
twinlead or open wire line.  Maximum radiation is in the directions of the corners of the
loop on 40m, 20m and 15m, and it should give pretty good coverage around the state
on 80m.

There are many other possibilities, of course.  I'd certainly recommend having more
than one antenna, not only for filling in nulls in the pattern, but also so you can compare
two antennas and see which one you like best, then trying something else.  This is
easiest if you put pulleys and halyards on your antenna supports so you can swap out
antennas without lowering the masts.

If you do go with the loop, I'd recommend spacing the masts about 100' on a side and
using rope from the masts to the corners of the loop - that gives you about 140' across
each diagonal, so you have room to string a dipole as well.
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KG6YSF
Member

Posts: 81




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« Reply #13 on: October 02, 2013, 02:27:39 PM »

I like the idea of the loop. I will try to get another mast or two.
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"Rangers Lead The Way!"  "Sua Sponte"   "Litalis Velox Silens"
When all else fails ham radio is there!
FT2900, FT8900, VX6, Ft60, TS940SAT, Drake TR7, MFJ 969
WB6BYU
Member

Posts: 12977




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« Reply #14 on: October 02, 2013, 03:45:51 PM »

You can do a triangular loop rather than square if that is easier - it shifts the
radiation pattern slightly.  Maximum tends to be in the direction away from the
feedpoint on the higher bands, but there isn't a lot of Front/Back ratio.  The
shape has a minor impact on the resonant frequency - when in doubt, aim for
the same wire length (just over 1 wavelength on the lowest band) and you
should be fine.
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