AD8302 - directional coupler - part #3

Discussion in 'Homebrew and Kit Projects' started by AA7EJ, Nov 6, 2018.

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  1. AA7EJ

    AA7EJ Ham Member QRZ Page

    Call me old fashioned , but ...
    how good is a schematic of DIRECTIONAL coupler without (I/O) pins / terminal numbers and without # of turns and without "dots" indicating winding directions ?

    Probably the "direct in / out " is a single turn, bout source and load .
    I do have some doc about number of "coupling turns", but the directions are just guess.

    I have not figured out why the first app has the K1 relay / switch.
    Will do some more reading on it.

    Screenshot from 2018-11-05 20-01-53.png Screenshot from 2018-11-05 20-16-37.png

    Attached Files:

  2. VK4HAT

    VK4HAT XML Subscriber QRZ Page

    The primary will be 1T and the secondary will be however many turns you require to get the required level of coupling. K1 is just bypassing the transformer so 100% of power it passed to the detector.
    Last edited: Nov 6, 2018
  3. AA7EJ

    AA7EJ Ham Member QRZ Page

    Using the schematic with numbers
    is 1 - 2 winding ( 1 turn ) in same "direction" as 5 - 4 ( 1 turn)
    or does it makes a difference ?
    How about 1 - 3 /G and 5 - 3 /G ?
    I need some better description about "directional coupler".
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    You need to observe CW and CCW winding.

    Have Fun.
  5. VK4HAT

    VK4HAT XML Subscriber QRZ Page

    The winding 1-2 is a single wire passing straight through the core. The winding 1-3 will be N number of turns to get the required coupling. Something like 37 turns to get -30db of coupling. So a signal of 100w on the primary will be 0.1w on the secondary, for the forward reading, and on the reverse reading the opposite is required. The primary will be N number of turns something like 10 turns and the secondary will be a single wire passing through the core. The reason why the coupling is different is because the reflected power is lower. But in both cases you might be looking to present a 0.1w maximum signal to the detector circuit.

    This video might help you understand the concepts a little easier.

    KA9JLM likes this.
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    As much as I do not care for u-tube - this is one of the best , no nonsense articles.
    It really helped to have the incident / reflected hardware drawn as he did.
    In an essence - there is ONLY one connection (TL) in the VNA - source to load.

    The usage of coax as TL carrier and using the coax braid as shield is the most revealing part of the article,
    but I fail to see the need for metal shield between the coaxes.

    Perhaps more of mechanical than electrical function.

    I hope I can apply this to "binocular core" where the "isolation" between incident / reflected PRIMARY windings is not so apparent , at lest to me.
    VK4HAT likes this.
  7. VK4HAT

    VK4HAT XML Subscriber QRZ Page

    The shielding between cores improves directivity, which is the measure of isolation between the ports. In your application a low say 10 or 15db directivity might be enough, in another aplication 20db directivity might be required and shielding helps that a ton.

    All his videos are great. he explains complex topics in a real no nonsense way. glag you found it helpful.
  8. AA7EJ

    AA7EJ Ham Member QRZ Page

    Found yet another article on directional couplers.
    This one explains the "mechanics " of "binocular transformer ".
    Welcomed addition to the project .
    I think it is time for me to thank Mr Al Gore for inventing internet.
    Atta boy Al!
    K3KIC and VK4HAT like this.
  9. K3KIC

    K3KIC Ham Member QRZ Page

    Interesting. I now work for the company that the author worked for in the 90s. And yesterday I was working on some 2 GHz binocular core couplers for a project I'm working on. These happen to be 75 ohm.
    Back at the time the article was written I worked for a competitor that has since been bought by the successor to Antec. And this morning we find we are bought once again.
  10. AA7EJ

    AA7EJ Ham Member QRZ Page


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