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Author Topic: Hy-Power Dipole way out of band  (Read 1646 times)
W1AJO
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Posts: 108




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« on: May 04, 2013, 07:22:20 PM »

Last June I purchased a Hy-Power 2 band dipole 2B2040LQ and finally got it installed today. 

As I live in an HOA subdivision, I had to install it in my attic.  I just noticed in the instructions that it is not recommend it for indoor use.  Perhaps that is why I am having SWR & resonance issues with it.

The antenna runs along the peak in the attic and does not touch any part of the structure.  It is fed by RG58 coax to the ham shack 1 floor below the attic (2nd floor).  The house is up on a hill, 2nd highest point in the subdivision.

My radio is a Yaesu FT-817 5 watt with a 50 watt linear amp (Tokyo Hi-Power).  I use a LDG antenna tuner.

I have a number or homemade QRP rigs that I do not use antenna tuners with so I strive to get my antennas tuned as best as possible.


After I installed the Hi-Power 2B2040LQ and ran the coax to the radio location, I analyzed the antenna with my MFJ-259B antenna analyzer. 

The antenna is resonant (SWR is 1.0) at 13.538 MHz (20 meters) and at 6.835 Mhz (40 meters), way below the ham bands.  Since I do QRP phone my target freqs are:

20 meters: 14.285 MHz (SWR is 2.5)
40 meters:  7.285 MHz (SWR is 7.7)

This tells me I need to shorten the antenna. 

I assume I need to tune the 20 meter segment of the antenna *first* then tune the 40 meter portion second.  Is this correct?

Per the instructions I need to cut 3 inches per leg of the 20 meter section (17’10” portion) for a rise of 170 KHz of frequency. The difference between 13.538 MHz (resonance) and 14,285 (target) is 747 KHz.  I calculate that I need to cut about 13” from each leg to get the antenna to resonate at 14.285

Once I do this I assume it will effect the 40 meter resonate frequency as well.  But let’s assume that the antenna is still resonant at 6.836 MHz. A 3" cut in the 40 meter section will get a rise of 110 KHz.  I calculate that I need to cut 12” from each end of the 40 meter segment to get the antenna to resonate at 7.285 MHz. 


Have I done my math correctly?  I need to be sure before I start cutting wire!

Also, the instructions state that I should use a BL 6-160-5KW balun if I choose to use a balun.  Should I use one?  Where does it go?


Thanks!

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KB4QAA
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Posts: 2409




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« Reply #1 on: May 04, 2013, 08:30:28 PM »

Forget their numbers.  That is for the antenna hung in ideal outside conditions.

You can only do one thing at a time.  We must start with the "inside" portion of the antenna, 20 meters.

(resonant F - Desired F) / resonant F  = Delta of Freq (in Percent) needed to change

Percent * antenna length = Amount to trim/add

So...

13.538 Mhz - 14.285 Mhz = 0.747 Mhz
0.747 / 13.538 = 0.0552  or 5.52% "too long"

17'10" (leg) *2 = 35.66ft (Present length)
35.66ft * 0.0552 = 1.97ft  to shorten 20m antenna
1.97ft /2 = 0.98ft * 12" = 11.8" to shorten each side.

-I recommend not cutting the wire, just wrap around main wire until you sure of the length.  You may have to adjust once or twice more.
-Keep the whole antenna intact, re-hang it and make measurements again.

40m will be done the same way.    bill

This method will work for essentially any antenna assuming the adjustments are linear.  It can save a ton of walking back and forth.
« Last Edit: May 04, 2013, 08:36:32 PM by KB4QAA » Logged
K3VAT
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Posts: 731




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« Reply #2 on: May 05, 2013, 12:39:53 AM »

KB4QAA provides sound advice on how to 'tune' your dipole.

An attic can be one of the worst environments for an amateur radio antenna.  Why?  Basically significant and often quite detrimental interactions with the nearby structures of the house and specifically with electrical house wiring, ventilation ducts, home security (smoke detectors) wiring, outdoor metal gutters and downspouts, etc.  These interactions play havoc with SWR, element balance, radiation pattern; e.g., especially when one section of the antenna is sitting within a few meters of the A/C unit or runs parallel to your metal gutters.

For this environment, I would definitely recommend the use of their balun.  Get some decent coax also - you need all the help you can get and something like LMR400 provides added shielding.

Hy-Power Antennas make quality products: excellent materials, good design.  Most products can work 'straight-out-of-box' where one doesn't even need a tuner.  But because they use loading coils there is a sacrifice in bandwidth and there are losses associated with the coils themselves.  (I personally would like to see them add optional 'low loss coil/higher Q' coils) Your particular installation should work once you get it tuned for the frequencies where you want to operate.

GL, 73, Rich, K3VAT
(no connection to Hy-Power Antennas)
« Last Edit: May 05, 2013, 12:47:48 AM by K3VAT » Logged
W9GB
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Posts: 2626




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« Reply #3 on: May 05, 2013, 04:25:41 AM »

Quote from: W1AJO
Last June I purchased a Hy-Power 2 band dipole 2B2040LQ and finally got it installed today. 
As I live in an HOA subdivision, I had to install it in my attic.  I just noticed in the instructions that it is not recommend it for indoor use.  Perhaps that is why I am having SWR & resonance issues with it.
Your Newnan neighborhood is HOA?
I think you should be able to install a dipole or wire antenna at your pine tree line.

Like the W9INN(sk) and Alpha-Delta antennas that use loading coils (inductors) to shorten the antenna's length -- nearby objects, especially metal, will easily de-tune them (high SWR).

I don't know Barry, KU3X tuning setup for these antennas, but Bill, W9INN(sk) tuned his antennas at 35 to 40' above ground.
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W1AJO
Member

Posts: 108




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« Reply #4 on: May 05, 2013, 06:16:33 AM »

Quote from: W1AJO
Last June I purchased a Hy-Power 2 band dipole 2B2040LQ and finally got it installed today. 
As I live in an HOA subdivision, I had to install it in my attic.  I just noticed in the instructions that it is not recommend it for indoor use.  Perhaps that is why I am having SWR & resonance issues with it.
Your Newnan neighborhood is HOA?......

Yes it is.  It's a new subdivison started in 2005.  It seems that EVERY new subdivision started in the Atlanta area since 1990 is HOA controlled.
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W1AJO
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Posts: 108




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« Reply #5 on: May 05, 2013, 06:17:50 AM »

Thanks all for the replies!  I will do as advised and post the results when I'm done.
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W9KDX
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Posts: 771




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« Reply #6 on: May 05, 2013, 06:22:26 AM »

One thing to watch out for, I got caught.  After everything is done and perfect, resist the temptation to cut off the extra wire you have wrapped back around to shorten the length.  Even though everyone says it should not make a difference, it can and did for my dipole.  I wound up splicing it back in.

Good luck and be ready for a lot of back and forth.
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Sam
W9KDX
W1AJO
Member

Posts: 108




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« Reply #7 on: May 07, 2013, 01:33:55 PM »

Update:  I sent HY-Power an email and Barry, the owner replied quickly:

"What you want to do for starters is:
Remove 8" off of the ends of each wire on the 20 meter part of the antenna where it attaches to the coils.

At the same time remove 6" off of each end of the 40 meter leg next to the end insulator.

Both bands interact with one another. Take SWR readings again and then trim to the final frequency per band that your are shooting for.

20 meters: removing 3" per leg will shift the resonant frequency up the band by 170 khz 40 meters: removing 3" per leg will shift the resonant frequency up the band by 110 khz

It's more work, but go a little at a time on each band. The antenna uses isolation coils and they act different than traps.

If you have any other questions feel free to email us again at any time.
Barry, Owner
Hy Power Antenna Company"





Wow!  Great customer service! I will follow his advice.


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