[Amps] bi-directional coupler question

[Dan Sawyer]

Thank you. The coupler I have is too high frequency for my current 
needs. I am interested in a 1 to 100 MHz bi-directional coupler. However 
bi-directional couplers are much less common then uni-directional ones.  
There appear to be uni-directional couplers in the HF and VHF range 
available.

Are couplers 'reversible, that is can the output be applied to the 
input? The purpose if this would be to make a bi-directional coupler 
from 2 uni-directional couplers.  Is this practical?

Thanks again - Dan

m.ford wrote:

>
> ----- Original Message ----- From: "Dan Sawyer" <dansawyer at earthlink.net>
> To: "amps" <amps at contesting.com>
> Sent: Friday, November 18, 2005 4:10 PM
> Subject: [Amps] bi-directional coupler question
>
>
>> All,
>>
>> This journey started several months ago with the purchase on an 8405a 
>> to measure an antenna. One of the items listed at that time was a 
>> bi-directional coupler. Finally I have found one and am beginning to 
>> experiment. The first readings seem to show that the coupler may be 
>> supplying readings that are out of phase? Direct input to the coupler 
>> terminated in a 50 ohm dummy load produce readings that appear to be 90
>
>
> Hi Dan,
>    A bi-directional coupler has a mainline input and mainline output. The
> other two ports are the coupled ports. One is zero degrees phase shift 
> and
> the other is 180 degrees phase shift because it is looking at the 
> reflected
> power coming back to the mainline output. It is very useful because you
> can see forward and reflected at the same time using two meters.
>
>    If you are seeing 90 degrees phase shift then you may have a 
> quadrature
> hybrid which is a four port device that will give you two outputs that 
> are
> 90 degrees out of phase when any port is fed and the opposite port is
> terminated.
>
>    A 180 degree hybrid is similar however in this case there are two 
> ports
> that will be in phase when the opposite is terminated and two that will
> be 180 degrees out. A bi-directional coupler is essentially a special 
> type
> of 180 degree hybrid.
>
> Hope that helps,   Mike
>
>> degrees out of phase. Is this correct? Is it a coupler design issue? 
>> I am a novice in this area so I am not sure what is normal and what 
>> is not.
>>
>> Is this one of those cases where the 8505 is biased to read 0 phase 
>> angle into a known termination and then read the difference in the 
>> circuit under test?
>>
>> Thanks in advance - Dan
>> _______________________________________________
>
>