Re: 432MHz ATU?


Mark GM4ISM
 

Julian

A 6:1 VSWR is about 3dB Return Loss. Think of it of this way, if your feeder has 1.5dB  loss (not unreasonable)

and you had no antenna at all, just an open cct, you would get 3dB Return Loss (feeder loss x 2)  I suspect that whatever is left of the connection to the yagi will not radiate that well... 

Whist matching that is theoretically possible, the  'good' match would likely  be very narrowband and  changing frequency may  make the mismatch worse, risking damage  anyway.

 If the mismatch changes in any way  the matching cct will make it worse,  risking damage.

 If you must use this  a 6dB power attenuator rated at the full TX power would add 12dB to the  return loss,  The rig will probably survive 15dB return loss 1.4:1 VSWR  That sort of attenuator is not common

You will hear and work even less but the rig would be reasonably safe

 Best option is to pop a dipole on a long fishing pole and use that as an antenna. It will probably work better than what is left of your MET

I do not recommend trying to use the MET antenna until it is fixed.

Mark GM4ISM



On 15/02/2021 23:03, g4zod@... via groups.io wrote:

I have a long term problem with my 17 element MET Yagi. The VSWR is rather high at about 6-1 and I cannot risk blowing my new radio!

I have no way of taking down my pump up mast to adjust the matching on the antenna. The current restrictions mean I cannot get my fellow club members around to help me drop the mast.

As this means my activities on 432MHz have to be put on hold for possibly many more months I need to find an interim solution. In the mist and cobwebs of mind I recall an ATU for UHF frequencies. I did a quick search and nothing came up.

Can any group member confirm if an ATU for 432 MHz is practical and if so any reference to one?

Many thanks

Julian G4ZOD


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