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Author Topic: Inverted L 160/80M matching  (Read 955 times)
KL2GN
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Posts: 31




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« on: March 29, 2010, 04:59:20 PM »

All -

I had previously posted about my inverted L (matched at the base with a SGC-237) and looking for ideas to switch in and out various matching networks for 160 and 80M to be able to run higher (600-800W) power so I didn't fry the SGC.
I have decided to take the SGC out of the picture and use it on a different project and dedicate the L to 160/80M.

I am looking for suggestions with regard to length and matching of the L for 160 and 80.
I have about 42' vertical might get 43' and can run the horizontal section as long as needed.  I was thinking of making this a 1/4 wave end fed on 160M which would leave me with a 1/2 wave end fed to have to match on 80M.  I have looked at using either a L network or tank circuit to switch in and out for use on 80M.  I know, very high impedance and robust components needed.

Or, I could leave the L shorter then a 1/4 wave on 160M and it would require 2 matching networks (160M and 80M) but the matching requirements would not be as robust as the end-fed half wave on 80M.  I already have an extensive ground field under this and will be adding more once the snow melts.

Any thoughts or suggestions are very much appreciated.

Thanks,
Tim, KL2GN
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VA3XH
Member

Posts: 6




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« Reply #1 on: March 29, 2010, 06:05:56 PM »

I use a common feed point for both my 160 and 80 inverted L's. A little trimming and everything works fine.

Peter,, VA3XH
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KL2GN
Member

Posts: 31




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« Reply #2 on: March 29, 2010, 06:35:39 PM »

Peter -

How closely spaced are your L's?
How do you have them set up?

Thanks
Tim
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WB6BYU
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Posts: 13126




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« Reply #3 on: March 29, 2010, 07:19:39 PM »

Try making it around 3/8 wave on 160m, which will be close to 3/4 wave on 80m.
You may be able to match it with a just series capacitor on 160m, and perhaps
nothing on 80m if it is close to resonance.

Try about 200' total combined length and see where it resonates on 80m, and
how it does on 160m with just a variable capacitor.
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VA3XH
Member

Posts: 6




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« Reply #4 on: March 29, 2010, 07:36:33 PM »

Hi Tim,,I'll try to describe my ant. as best as I can. Its actually a 40,80 and 160 on one feed. 40 section is 30 ft of cheap TV tower with ten feet of tubing on top. There are two 4 ft 2 by 3 spreaders, one 2 ft from the bottom and the other at 30 ft. 80M  section is 12 gauge stranded copper about 66 ft long running up the end of the spreader and out to a nearby tree (too close to the tree, it is really into the tree). 160M section runs up the other spreader and over a near by tree the slopes downward, element is about 130 ft. 80 and 160 are tied together at the base of the 40M element. Fed with coax to an I.C.E. static discharge. This set up works VERY well for me. It IS over a considerable ground field. Good luck with your install and let us know how it end's up!
73 Peter
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W9OY
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Posts: 1293


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« Reply #5 on: March 30, 2010, 05:08:26 AM »

Put up 2 wires one resonant on 80 and one resonant on 160 use a relay to switch between the wires and use the same radial field for both antennas.  The advantage of doing it this way is each antenna can be optimized separately.  There is very little interaction between the antennas if you do it this way.  I would use a hairpin coil across each feed point to match each antenna to 50 ohms.  The advantage of this is there are no networks to worry about and the switch point is low impedance so you don't need high voltage relays.  

You can switch between the 2 using the coax to send the switching voltage for the relay using a Bias T injector.  You can add a 3rd relay and switch 3 antennas if you like.

73  W9OY
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N6AJR
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Posts: 9913




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« Reply #6 on: March 30, 2010, 11:29:43 AM »

look up K6MM.com and look at his home brew 160 antenna
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N6AJR
Member

Posts: 9913




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« Reply #7 on: March 30, 2010, 11:31:02 AM »

look up K6MM.com and look at his home brew 160 antenna
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N6AJR
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Posts: 9913




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« Reply #8 on: March 30, 2010, 11:31:16 AM »

look up K6MM.com and look at his home brew 160 antenna
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G8JNJ
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Posts: 485


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« Reply #9 on: March 31, 2010, 03:39:07 AM »

Hi,

Take a look at the G7FEK design.

http://www.g7fek.co.uk/news.php?page=80m_Antenna_for_small_gar_49493

This would scale up quite nicely to 160 & 80m and seems to work nicely.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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