High Reflect on Maco 7 Element Beam

[spongbob]

Hi, Spongbob again with antenna problem. swr 1.3 low end and 1.5 high end but reflect is high. 500 watts in and 60 reflected back.Need help how to lower reflect.

 

[DainBramage]

gee. I dunno. @ 1.5:1 VSWR, you reflected power should be about 4% (20 watts)

!. test again, but into a dummy load.

2. use a different meter

IF you really have 60 watts reflected, then your VSWR is really about 2.2:1

BTW: all of that reflected power, eventually does get radiated

 

[midnight special]

because of harmonics low power should be used to test swr, after that then put amp in line,,,, amps and souped up radios tend to put out harmonics and cause false readings,,,

 

[Road Squawker]

... low power should be used to test swr, after that then put amp in line,,,, amps and souped up radios tend to put out harmonics and cause false readings,,,

my VSWR doesn't change with output power level changes, if yours does, it is probably CMC or RF affecting the meter, not "harmonics"

 

[Captain Kilowatt]

my VSWR doesn't change with output power level changes, if yours does, it is probably CMC or RF affecting the meter, not "harmonics"

It depends on the meter being used. Some meters "see" the harmonics and display it as a high SWR because the meter cannot tell the difference between in-band and out of band frequencies. An amp would have to be fairly dirty for that to happen however.

 

[M0GVZ]

An amp would have to be fairly dirty for that to happen however.

500W CB amps usually driven by a CB over modulating like a dog makes the signal being fairly dirty a given.

 

[spongbob]

Thanks guys but I left out some information. The boom length is suppose to be 37.5 ft long but I have it 40 ft, will that be the cause of the high reflect problem? If so what should I change with out changing boom length to lower reflect.?

 

[hotrod]

Thanks guys but I left out some information. The boom length is suppose to be 37.5 ft long but I have it 40 ft, will that be the cause of the high reflect problem? If so what should I change with out changing boom length to lower reflect.?

i dont believe the boom lenth would do this. however if ya modifed the lenth of this then idgo thru the rest of the antenna and check all measuements and make sure there exactly as they should be. then recheck spacing and make sure thier exactly as they should be. then as last resort put the boom to lenth instruction say.

 

[DainBramage]

...go thru the rest of the antenna and check all measuements and make sure there exactly as they should be.

... then recheck spacing and make sure thier exactly as they should be.

... then as last resort put the boom to lenth instruction say.

ya might wanna re read this

 

[M0GVZ]

Thanks guys but I left out some information. The boom length is suppose to be 37.5 ft long but I have it 40 ft, will that be the cause of the high reflect problem? If so what should I change with out changing boom length to lower reflect.?

It won't. Altering the boom length affects the forward gain and the front/back ratio.

 

[wavrider]

It won't. Altering the boom length affects the forward gain and the front/back ratio.

If only the boom length is changed then yes, but if the element spacing is changed then impedance is also changed.

If using a gamma match then should see very little change in impedance, if direct fed then changing the spacing of the elements will change the impedance.

Seems like it is a VSWR meter issue.

Or water intrusion on the coax.

 

[vkrules]

You can't just add two and a half feet to a yagi randomly. Spacing and element length are all related. It will change the gain the front to back and the impedance.
Some designs are more critical than others and you could have easily cost yourself some gain and changed the match.
Put it back to spec.If you want the longer boom' model it with software and see what you have to do to get it right.
Adjust the gamma match for swr.(if it has one.)

 

[Road Squawker]

You can't just add two and a half feet to a yagi randomly. Spacing and element length are all related. It will change the gain the front to back and the impedance...

exactly

 

[spongbob]

Thanks guys for all of the good advise and information but due to severe weather and high winds the antenna was destroyed. I will be building a new one and sticking to specs.