Question related to imped. transformer winding in phased arrays

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK4NSF, Mar 24, 2020.

ad: L-HROutlet
ad: l-rl
ad: abrind-2
ad: Left-3
ad: Left-2
ad: Subscribe
ad: L-MFJ
  1. KK4NSF

    KK4NSF Ham Member QRZ Page

    As some of you know, I've been working on a phased array system for a few months now.... and a question has developed for which I can't find an answer in the standard books:

    The elements in my array require a 4:1 impedance matching transformer... which is quite easy to build. I've got 6 elements in the field now. BUT one of the elements doesn't seem to play well with it's team-mates. It is an excellent antenna by itself, but when I add it to the array it degrades the performance. Since it is identical in every way to it's siblings... and the problem occurs no matter where I put it in the array, (and all of the connections are good) the only thing I can think of is that it might be out of phase for some reason. I'm wondering if the direction of the winding in the one transformers could be causing the problem.

    So here is the question: does the direction of the windings in the transformer matter as far as phase goes? assuming of course that the primary and secondary are in the same direction? If 1 thru 5 have transformer wound clockwise, and number 6 is counterclockwise, could that be a problem?

    I know, I know.... go outside and look at them. Well, I can't. They are all sealed in place with Epoxy inside their little boxes.... so I'll just have to chuck box #6. BUT I'd like to avoid the problem in the future.

    Oh yeah... for reference purposes, it is a receive only loop similar to KK5JY's but a different size with different impedance values.
  2. W1VT

    W1VT Ham Member QRZ Page

    I think this is a common problem. It is surprisingly easy to introduce an unexpected 180 degree phase shift.
    Someone will buy two identical baluns and they will be wired differently.

    Or people will stack Yagis and flip one so it looks more symmetrical.
    KK4NSF likes this.
  3. KK4NSF

    KK4NSF Ham Member QRZ Page

    I think that is what has happened here. If I were to chip open Number 6, I bet I'd find it is wound the wrong way.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'm not sure about winding orientation, but swapping the input or output terminals the balun windings are connected to would certainly flip the phase.

    You might wind up a simple 1:1 transformer and place it between the existing transformer and the antenna feed point and try flipping the terminal connections on one side of that new transformer to see if one orientation resolves your issues. If so you know it's a phase issue and could rewire the 4:1 transformer accordingly or just leave the phase inverting 1:1 transformer in place if it doesn't cause excessive loss or other problems.
    KK4NSF likes this.
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    Perhaps you could use a signal generator and a two channel scope to check each transformer for a phase reversal or phase shift.
    KK4NSF likes this.
  6. KK4NSF

    KK4NSF Ham Member QRZ Page

    All of the above are good ideas. A friend of mine has a mult-channel scope.... so I'm going to call him and we;ll figiure it out.
  7. AI3V

    AI3V Ham Member QRZ Page

    Absolutely could.

    Everything a ham should know about phasing transformers , courtesy of W2AEW:

    N8ZL, WA6KNW and KK4NSF like this.
  8. EA1DDO

    EA1DDO Ham Member QRZ Page

    To be sure where the problem is, just exchange two transformers. For example #5 and #6 and see if problem moves to antenna #5, or stays on the antenna #6.
    That simple test will confirm the transformer #6 is not good.

    73, Maximo
    UA3TW likes this.
  9. KK4NSF

    KK4NSF Ham Member QRZ Page

    Agreed. I'm still relatively new to phased arrays, and simply overlooked this particular problem. But hey.... that is what the test-loop array project was intended to do: identify potential problems to watch out for.

    that was my first test... and here is the result:
    1- All 6 antennas work the same with regard to received signal / /null and so forth when tested individually.
    2- Numbers 1 thru 5 work the same no matter where in the array they are located.
    3- Number 6 produces a decrease of signal when used in the array no matter where in the array it is located.
    4- I also tried physically reversing the orientation of each element 180 degrees, one at a time. Same result. #6 still appears to be out of phase to me.

    That's a good idea. I may make the device for testing later.

    That is also a great idea. I discussed it with an EE who is a friend of mine. Such a rig would also be excellent for adjusting the phase of both boradside and end-fired arrays, checking our calcs on dealy line lengths, and all sorts of other tasks related to the project.

    After working on this much of the day yesterday, I did an experiment. I made two identical impendance matching boxes (they are quiet inexpensive) , one with the turns going clockwise, one counterclockwise, the other counterclockwise.... and intalled them into #6 one at a time. The CCW version had the same problem as the original #6. The CW worked like numbers 1-5. (and no.... CW and CCW is not an accurate description when talking about toroidal cores. It just as well could be described as "over" and "under". Winding direction on those gizmos always messes me up. )

    So.... I'm convinced that the winding direction was the key difference. Does that mean #6 was out of phase? I don't know for sure yet. It may be something we're not thinking about. (like my tape marks indicating side A and side B being reversed) I want to do the test recommended by WA7F and see what it shows.

  10. KK4NSF

    KK4NSF Ham Member QRZ Page

    Rege... thanks for posting that link. It was really helpful in visualizing what is going on.

Share This Page