Author Topic: Help with HF dipole set up  (Read 3338 times)

Offline 23skido

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Help with HF dipole set up
« on: May 17, 2014, 08:22:09 AM »
Trying to set up HF multiband dipole antenna outside of my house. Antenna is 100 feet long. I do not have a street mounting location for such a length. I do however have mounting locations that would put the dipole at something around 172 160°. Will this kink in the dipole set up a fact transmission and reception? The dipole will be mounted at Centerpoint from edge of roof with each leg extending out two trees on my property. There may be much more here that I am not addressing. All new to me. Any help appreciated.

Offline UnderTheRadar

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Re: Help with HF dipole set up
« Reply #1 on: May 17, 2014, 09:27:19 AM »
The simple solution that let me work mucb of the world was a dipole installed as an inverted V.  I was renting and used bungie cords to attach a mast to a fence post and rope to pull the wires to a out 45 degrees.  The mast was two 12 foot pool cleaning poles connected together.

20 meters is short to keep it stealthy and I used an LDG tuner to make it work for all bands.


Offline Carl

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Re: Help with HF dipole set up
« Reply #2 on: May 17, 2014, 10:38:13 AM »
  Antennas react with the earth,nearby metal objects,and themselves...so anything you do will effect your antenna...as you are using a multi-band antenna ...do you have a manual or automatic antenna tuner? When MULTI-BAND there is always a compromise is efficiency of an antenna anyway,but they are a good compromise rather than installing multiple antennas for each band.

Though most HAM bands are in near multiple frequencies to each other the tuner is needed to make sure the RADIO has a good impedance match so it won't 'let the smoke out' of your transmitter. NO antenna will do HF multi-bands without major compromise so you can HOPE but expect to CHANGE and ad a tuner to you system.

The antenna is DRAWN in straight lines because it is easier to draw strait lines,changes in antenna direction or shape will not change much of your transmission pattern or take-off angle.The angle you refer to would not produce any change in signal that you would notice.

  My antenna is a 20 meter inverted "V" and a 40 meter inverted "V" at a common (1 to 1 balun) feed point they slope from 30 feet down to small 8 foot posts along the fence,due to my narrow property (50 feet) the 40 meter (65 foot total length) actually is also "V'ed" more to the rear of the property in a 100 to 110 degree "V" besides a vertical "V".And I can tune and transmit on ALL bands from 6 meters to 80 Meters and am able to talk to most any station that I can hear.

NO ,it is not the textbook BEST way...but it works just fine. The match to your antenna is important to protect your radio.

I must give a hearty AMEN to the LDG automatic tuners,at close to the same cost as manual tuner,they protect you radio and tune your antenna to give you more time to communicate and less time fiddling with antennas.

http://www.ldgelectronics.com/

Offline austinrob

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Re: Help with HF dipole set up
« Reply #3 on: May 19, 2014, 10:44:19 AM »
yup... put the antenna up as best you can, don't bend it too sharp (you don't want it coming back close to itself) and get on the air.  The SWR will be slightly affected, the radiation pattern slightly as well.  The takeoff angle, not much at all.  That's more dependent on height above ground.

I had a windom cut for 80m band and it was mounted from my roof into the trees behind my house.  Kind of a "U" pattern.  I worked the world with it though.

The multi-band compromise...  yes, every multi-band antenna is a compromise.  If money and size weren't a concern, I'd have a huge antenna farm and a mono-band antenna for each band I wanted to use.  Unfortunately, I'm in an HOA and built a windom with insulated wire and tossed it over my roof, connected it to a 4:1 balun and my MFJ-993B.  Now I work 40m through 6m not as efficiently as I could with multiple monoband antennas, but sometimes good enough is good enough.  :)

Offline handsonham

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Re: Help with HF dipole set up
« Reply #4 on: May 19, 2014, 02:54:19 PM »
Any antenna that you can get up is better than none!

A slight bend in the antenna at the center point is not a deal-breaker.  In fact you can partially bend the individual legs of a dipole a bit to fit where you need it to go.  Just be aware that any deviation from a flat, perfectly aligned dipole will bring about some consequences.  Matching impedance and resonant frequencies will change.  The feedpoint can go unbalanced and cause RF to come back on the shield.  The antenna can become a bit more directional, and can have some rather funky 'lobes', meaning you may be able to talk from California to New York, but not be able to talk to Pennsylvania, as that there may be a lobe and a null.  Lobes become more pronounced as wavelength gets longer.  You mentioned multiband, so the other thing to be aware of is that there will be more lobes and nulls on higher frequencies. 

I use and highly recommend OCF dipoles for multi-band operation.  There is a ham I know that makes some of the best, and they are very reasonable.  Check out:
http://www.hypowerantenna.com/products/off-center-fed-antenna

Offline Carl

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Re: Help with HF dipole set up
« Reply #5 on: May 20, 2014, 06:52:22 AM »
Let me ramble on a bit about this.

You cut your antenna to what is KNOWN to be the resonant,most effective and efficient length.

You put it up in a good location.At the end of coax ,that has LOSS,CAPACITANCE,REACTANCE,and RESISTANCE.

And then you measure SWR and start cutting length out (making it NON-RESONANT) in order to minimize a reading that has little to do with antenna effectiveness or efficiency ....WHY???

To make you happy, or the radio if SWR is too high.( OR "because it's what we do")

Once you TRIM the carefully measured antenna and CUT it...it is no longer the finest example of efficiency or effectiveness.

NOTE that a true DIPOLE is about 70 ohms...1.4 or 1.5 is as great as SWR should get...remember loss in feedline sways the measurements too, 3 db loss (for the sake of easy math) means HALF of your 100 watts makes it to the antenna, and when measuring reflected power...ONLY HALF OF THAT WILL MAKE IT BACK TO THE METER...so what does the SWR meter tell us about the antenna? Really very little.( I think it as more a measure of the smoke retention of the solid state radio)

This is why we use a TUNER,In my case an AUTOMATIC TUNER, as they cost about the same as manual tuners and do a far better ,and faster,job than I at making the radio a HAPPY NON-SMOKER.

An analyzer is a great tool for experimenting with new antenna designs and configurations.And is OK as a measure of SYSTEM performance(Antenna + Feedline +environment) as related to the radio .A FIELD STRENGTH METER will tell you much more about your antenna, but you gotta' work to do it.

SWR is about as good as the "OIL" idiot light in your auto. It lets you know something is wrong..NOT what is wrong.
And usually we start repairs by doing the wrong thing.(OK ,we add oil, but later discover the oil pump is bad)

If a TUNER was actually named ANTENNA SYSTEM EFFECTIVENESS ADJUSTER AND RADIO PROTECTOR, then everyone would correctly acquire one right along with the radio ,feed line, and antenna.

OK, this is just more of my rambling,but as you read it...maybe it made you think.