IC-7300 and SWR

Discussion in 'General Technical Questions and Answers' started by W8WJC, Jul 4, 2021.

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  1. W8WJC

    W8WJC Premium Subscriber QRZ Page

    Hello Everyone and Happy 4th of July!!

    So I’m trying to understand my new 7300, I feel like the SWR is high while transmitting on SSB voice. I’m using a 100w alpha mag loop with this. So I put it in RTTY and transmit a carrier so I can tune. I can get a 1:5 match just tuning the mag loop alone. Put it back into SSB and transmit, the swr meter is moving around while I speak. Is this normal? I feel like as the swr bounces over 3:1, the 7300 starts to fold back. Is this normal to have the swr on SSB voice to fluctuate? TIA
  2. G0GSR

    G0GSR Ham Member QRZ Page

    VSWR is always expressed as a ratio of "some number" to 1.

    If you really mean that you have a VSWR of 5:1, that is excessive, your loop should do better than that.

    Yes, it will. With SSB, the RF power is constantly varying with speech. You can only get a meaningful VSWR reading by measuring with a steady carrier.

    WA2EIO, KS4W and KB2SMS like this.
  3. W4HRL

    W4HRL XML Subscriber QRZ Page

    Your feeling is correct. At SWR's greater than about 3:1 the 7300 will start to fold back to protect itself.

    The 7300's internal tuner will not tune any SWR's greater than 3:1. But if you go to Emergency mode, the 7300 will limit power to 50 watts (max) but the tuner will then tune SWR's greater than 3:1. I am not sure (I have never seen this discussed) whether Emergency mode should be a sometimes thing (i.e. an emergency for real) or whether it is OK to use on a long term basis.

    Mike in Poquoson VA
    K0UO likes this.
  4. W8WJC

    W8WJC Premium Subscriber QRZ Page

    My bad, sorry for the typo. It should say, 1.5:1. I guess I should have proof read it better.
  5. K8JD

    K8JD Ham Member QRZ Page

    VSWR is not dependent on modes, it's strictly a property of the antenna system. , Reading it is, since you need a constant RF source to meter the SWR of the antenna system.. .
    Seems to me you have to take a closer look at this antenna and make sure you have it adjusted properly, it probably only works over a very narrow freq range and needs to be reset each time you change freq much.
    Your QRZ page shows antennas a lot better that the mag loop you mentioned here !!
  6. K8XG

    K8XG XML Subscriber QRZ Page

    Do not tune your alpha loop in RTTY, Use CW. If you can't make a CW key out of a headphone wire and tie the wires together to use for tuning, than at least use AM and do the tuning of the Alpha loop at 5-10 watts not 100. It is only rated for 100 watts on SSB, not RTTY or AM or CW or Data, all those modes are lower ratings.

    I own an Alpha 100 loop FYI
    K0UO likes this.
  7. W8WJC

    W8WJC Premium Subscriber QRZ Page

    Yes I’ve learned that the loop is very narrow and I need to retune it about every 10khz. I’ve been trying to use the Alpha Mag Loop up at the lake as a portable type setup, but not have much luck. It seems to RX well, but TX, not so much.
  8. W8WJC

    W8WJC Premium Subscriber QRZ Page

    I appreciate the heads up. I’ve been tuning in RTTY with the power down to like 20-25% but maybe I’ll try CW. What I was doing is a pain because I’m constantly flipping back and forth between SSB and RTTY and adjusting the power. One time I accidentally tuned up more than 25% power into the loop on RTTY, whoops, hope I didn’t damage it. Just curious, how well have you made contacts on your Alpha Loop? From Michigan, I’m struggling to work the east coast. Just trying to determine if this is normal or not. I realize the loop has its limitations.
  9. K8XG

    K8XG XML Subscriber QRZ Page

    I last used my Alpha loop last year in the living room of my home, and made JS8Contacts into NC. I also made JS8call contacts from a Motel Room in Indiana to KS an OK.
    Is your loop outside?

  10. K8XG

    K8XG XML Subscriber QRZ Page

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