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help with AM dipole design

 
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help with AM dipole design
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static-radio
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Joined: 19 Aug 2008
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Post help with AM dipole design Reply with quote
i recently built a center fed Dipole for my AM MAX II DSP AM

its 20ft from ground level, i have a 50ohm Balun 1:1, fed by RG213.
I am using a MFJ 941 E ATU.

When i use the Bypass mode the signal seems better but the SWR is still high but better.
I Have the Antenna cut for 1251Khz but works better on 1395Khz, (Possibly too short)possibly too short)

using 1395Khz i got about 6 miles at night.

Question 1: is my array correct? Transmitter to ATU to Balun?

Question 2: is 20ft high enough for a dipole?
Mon Nov 10, 2008 1:45 pm View user's profile Send private message Visit poster's website
SonnetRadioEurope
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Joined: 03 Nov 2008
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Post Re: help with AM dipole design Reply with quote
static-radio wrote:
i recently built a center fed Dipole for my AM MAX II DSP AM

its 20ft from ground level, i have a 50ohm Balun 1:1, fed by RG213.
I am using a MFJ 941 E ATU.

When i use the Bypass mode the signal seems better but the SWR is still high but better.
I Have the Antenna cut for 1251Khz but works better on 1395Khz, (Possibly too short)possibly too short)

using 1395Khz i got about 6 miles at night.

Question 1: is my array correct? Transmitter to ATU to Balun?

Question 2: is 20ft high enough for a dipole?


I'm sure for a dipole to be effective it should be at leat 1/4 height above the ground (very high) but a horizontal dipole is not the ideal antenna if you want to broadcast locally, you'll be genrating skywave signals and hardly any ground signal. Skywave signals introduce all sorts of reception problems such as phasing (Fading) which can make LPAM unlistenable for ordinary listeners. Anoraks love abit of hetrodyne mixed with fading though

Yes, TX - SWR / ATU - Balun is correct. The ATU will tune but your bandwidth will be quite narrow if your dipole lengths aren't near the 1/4 wave lengths. What are the lengths of each leg of the dipole?

Still, not bad for 6 miles, what was the output level of the transmitter?
Sat Nov 15, 2008 4:33 pm View user's profile Send private message Visit poster's website
static-steve
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Joined: 20 Apr 2006
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Location: Mayo, Ireland

Post Reply with quote
thanks very much SonnetRadioEurope for your help.

57 meters, each side. at the moment its 10w (60w Max) i intend to get 1000w amp for it once i get an ideal antenna.

when you say "at leat 1/4 height above the ground" do you mean by 1/4 of total wave length?

my first intension was to build a inverted V antenna, but the gound was too wet to get a crane in to lift up all sections.

im considering the inverted L to be a better option for local broadcasting.

for the ground radials i pursume the have to be of equal length but does the pattern matter?
Sun Nov 16, 2008 12:51 am View user's profile Send private message Visit poster's website
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