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Antennas for QRP

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W7CJD, Oct 11, 2015.

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  1. W7CJD

    W7CJD Ham Member QRZ Page

    I like to try different antennas of different designs at different locations.

    I have 30-acres undeveloped land for wire antennas (no towers).

    I am interested in these designs:
    Random wire
    End-fed
    Delta Loop
    Big loop
    Lazy H
    Trap dipoles
    Bazookas
    etc.
    coax fed
    75 ohm coax fed
    balanced feedline

    all modes
    HF VHF UHF

    I am also interested in the phased Lazy H.

    I have 1:1, 4:1, and 9:1 baluns on hand and 14 guage to more lightweight wire intended for QRP operation.

    I have managed, so far, with MFJ Travel Tuner and MFJ Auto Tuner Extender. However, I have limited my antennas to dipole, fan dipole and purchased end fed.

    End Fed Scorecard:
    Radiowavz end fed - good
    eBay wire j-pole - bad

    I want to do better than 50-50 chance I will destroy the transceiver.

    I recently purchased a You Kits FG-01 antenna analyzer to find resonance and other frequencies of acceptable SWR on the antennas I already have, without having to carry an antenna tuner for portable operation. I thought that would be fun.

    It is not expendable $$$
    I do not want to "pop" my FG-01.

    I think my next purchase will be the Bluetooth Mini60. I have a computer tablet.

    Expense is a constraint.

    I will have to learn how to use the information from that antenna analyzer. It is a SARK100 design.

    I think this is how to "gear up" for reasonably safe antenna construction or purchase, after having "burned" the 2-meter finals on my ICOM-2710H.

    I do not want to "burn" finals on my HF transceivers.

    Antenna tuners, manual or automatic, seem to be sold as either 9:1 or 32:1 maximum SWR handling, and how much voltage maximum they can handle.

    I am not the only one with this problem: how do I try new antennas and not destroy my radio amateur equipment?

    At Yahoo Groups, one QRP radio amateur "popped" his brand new Elecraft automatic antenna tuner that will handle 9:1 SWR.

    In another thread, here, I asked about a MFJ-939 automatic antenna tuner: If he doesn't operate over 200 watts, what antenna would push the limit of 32:1 SWR?

    I got one answer so far: avoid multiples of half waves, and feedline length losses control SWR.

    This answer indicates feedline length can bring an antenna down to a maximim 9:1 or 32:1 SWR but how to determine feedline length for the antenna?

    I would think it would be better to have an antenna that will not damage or destroy the tuner or the transceiver, then determine the feedline length.

    Perhaps more to the point: How do I find out the antenna design is over 9:1 SWR limit or the 32:1 SWR limit, to know it will not work for me or bring it down with what feedline length, except to apply low power and then "pop" or "smoke" the not at all cheap automatic antenna tuner or transceiver?

    The design work is not done for me by others because practically no one mentions SWR maximums in their antenna design writeup or commercial antenna either.

    I like to try antennas of different designs.

    How do I try these designs and avoid damaging my QRP and 50 watt maximum transceivers?
     
    Last edited: Oct 11, 2015
  2. KH2G

    KH2G Ham Member QRZ Page

    I would urge u to buy and study the following books - Building and using baluns by Jerry Sevick and ARRL's Wire Antenna Classics volumes 1 es 2. I am sure it will answer your questions es enable u to reach greater than your present goals. Enjoy 73 Dick KH2G
     
  3. W7CJD

    W7CJD Ham Member QRZ Page

    I will look into it, but I have been disappointed in every ARRL book I have purchased, over many years.

    I am 67.

    I hope to hear experience, not buy more books than I have over many years.

    I am looking for practical how-to details I specified, not the antennas but how to not destroy my antenna tuner, or, transceiver with designs in books and online as well as commercial antennas weak on details, specifically excess SWR.
     
    Last edited: Oct 11, 2015
  4. W7CJD

    W7CJD Ham Member QRZ Page

    I do not want to ruin the transceiver or tuner, while I am trying different antennas.
     
  5. KH2G

    KH2G Ham Member QRZ Page

    I believe the books will help you. On any antenna I've ever built in a bit over 60 yrs of hamming it up and down I have one rule of thumb I do adhere to and that is to Never test an antenna with more than 5 Watts until I have a good idea that it is doing what I expect and then I start bring the power up a bit at a time while checking for balun heating etc. I do this because in the islands I often had to experiment and make do with other than optimum parts etc. I never smoked any equipment doing that and with newer equipment you have to keep it low or the fold-back circuits will trick you into thinking things are different than what they appear. Enjoy 73 Dick KH2G
     
    KC8VWM likes this.
  6. KH2G

    KH2G Ham Member QRZ Page

    BTW you said no towers but I assume you have some trees or other means of getting the antenna(s) off the ground :cool: Dick
     
  7. W7CJD

    W7CJD Ham Member QRZ Page

    "old growth" Englemann Spruce

    I also have rough terrain, with a prominent knoll and at the East end of the property a sharp drop off. The South side of the property has a reasonable drop off, as well. Looks North. Ridge top, plus large mountain 1-mile distant West.

    altitude: 5,640 feet average
     
  8. W7CJD

    W7CJD Ham Member QRZ Page

    I had a paid for roll-up wire j-pole fry the finals on low power setting of my ICOM 2710H.

    I searched and finally found the part, in Indonesia.

    I like my transceivers, HF VHF and UHF.

    I also like the YouKits FG-01.

    I think I will like the Bluetooth Mini60 SARK100 design.

    I want no more fried components.

    I appreciate the practical advice.

    I do know that one.

    I am hoping to find out about these other antennas max SWR, and, especially, how to avoid maxing out the 9:1 or 32:1 on antenna tuners or the antenna analyzer when I "look at" the antenna for the first time.
     
  9. AG6QR

    AG6QR Premium Subscriber QRZ Page

    I've got one of those analyzers, and I really like it for portable operations. Small, light, easy to sweep a frequency range and see what the SWR is, and where it's lowest.

    It's next to impossible to "pop" an analyzer. The analyzer has its own low-power oscillator, and the monitoring circuitry is designed to safely handle any voltage or current that can be produced by that low-power oscillator when it's fed into any kind of antenna. The only way you can damage an analyzer is if you allow dangerous power levels to get into it from elsewhere. Don't hook it up to a transmitter, of course. And don't use it to analyze an antenna that is set up very close to a powerful transmitter that is actively transmitting. Finally, it's not a bad idea to drain any static electricity from an antenna before connecting the analyzer, by touching the shield of the analyzer to the shield of the antenna feed line, and then shorting that against the center conductor of the antenna feed line momentarily.

    You don't say what transceiver your using, and I'm not familiar with your tuners. So my advice has to be a bit generic. But here are some suggestions:
    1. Tune at low power. An SWR that would be damaging at full power can often be safely handled at 1/10 power or so. Start at the lowest power you have available, or the lowest power that will give reliable SWR indications and allow your tuner to have enough signal to tune.
    2. If your rig isn't rated to safely handle all SWRs at the power you use for tuning, then use an absorptive bridge between your rig and your tuner to protect your finals while tuning. This also has the effect of lowering the power seen by the tuner (and the antenna), but the big thing is that it lowers the SWR seen by the radio during the tuning operation. An example of an absorptive bridge is here: http://www.qrpkits.com/swrindicator.html You can build your own with three 50 ohm power resistors (or a 100 ohm resistor and a 50 ohm). The schematic is shown on that page. The resistors are the only super-important part, but the indicator light with its tapped inductor, diode, capacitor and LED is a nice optional addition. Be sure any absorptive bridge you build/buy is uses resistors sufficient to handle your rig's power.
    3. Another option is to use that analyzer to build/trim your antenna so that the SWR is low to begin with at your desired frequency of operation, and then you may not even need to use a tuner at all.
     
    WB5YUZ likes this.
  10. W7CJD

    W7CJD Ham Member QRZ Page

    I have made dipoles and fan dipoles.

    I purchased 1:1, 4:1, and 9:1 baluns to protect my transceiver and antenna tuners I already have.

    I thought that might be "belt and suspenders" for the other antennas I try.

    I am not clear about the "bridge".

    I am surprised what you said about the YouKits FG-01.

    I read it handles up to 9:1 SWR.

    I have these transceivers:
    TenTec Scout 555,
    TenTec Argonaut VI,
    YouKits TJ2B MKII,
    Yaesu FT817ND.
    ICOM 2710H,
    Wouxon UV3D
     

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