Antenna Type, SWR and ATU’s for HAM Muti-band application

Discussion in 'General Technical Questions and Answers' started by VK3FDCA, Nov 6, 2019.

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  1. VK3FDCA

    VK3FDCA QRZ Member

    Hello,
    I am a relatively new HAM for nearly one one year here in VK-Land (Melbourne, Australia) and I have a question regarding the advantages and disadvantages of an antenna whose SWR is adjusted via an ATU versus a second antenna where the SWR is adjusted by changing the physical length of the antenna.
    However, let’s complicate this a little for application in the real HAM world by assuming we want to use a vertical for multiband application across a number of HAM Bands with two antenna options:

    ANTENNA 1 - Is a 5.5. metre Multiband Vertical (I assume this antenna uses some sort of matching coil at the base of antenna to match it to 50 Ohm for the coax feed-line) with only one option to adjust the total length of the antenna for the SWR adjustment. This antenna is therefore used in conjunction with an ATU to allow it to be used across a number of HAM Bands.

    ANTENNA 2 - Is a Multiband Vertical which uses separate traps spaced along the length of the antenna which are used to fine-tune the SWR for each HAM Band. This Antenna therefore does not requires an ATU to function properly across a number of Bands.

    CONCLUSIONS:
    Normal SWR principals favour Antennas that can be adjusted to a low SWR. For this reason some might claim that, ANTENNA 2 is the preferred option because the SWR can be adjusted for each Band and because this antenna does not require an ATU to achieve a good SWR. However, the Antenna Traps used with ANTENNA 2 would also create an in-efficiency (Q) as does an ATU.

    We know that ATU’s do a really good job of matching the Impedance as well as acting like a Low-pass Filter; so is simply using ANTENNA 1 with an ATU such a bad thing to use?
    A key factor might be the insertion loss and inefficiency caused by inserting an ATU between the Transmitter to Antenna chain? But this is offset by the inefficiency of a number of TRAPS used in ANTENNA 2.

    So I’m concluding that Neither Antenna is better than the other and perhaps ANTENNA 1 is the simpler system and might have better efficiency because the multiple TRAPS used in ANTENNA 2 might add a greater in-efficiency compared to a single ATU used in ANTENNA 1.

    Are my above conclusions correct?
    What other, disadvantage/advantage of ANTENNA 2 versus ANTENNA 1 ?
    Can some of you more experienced HAMs please elaborate if you have any further thoughts about this?
    Thank you!
    Dean.
    VK3FDCA
     
  2. AA5MT

    AA5MT Ham Member QRZ Page

    This is an old discussion. Hy-gain makes both of these antennas. See AV-18AVQ and AV-6160. Both work well. The difference is the tuner required for the non-resonant option. With traps, you have a limited bandwidth. With a tuner, you can go anywhere frequency wise.

    My personal preference is to use a tuner with the non-resonant antenna. I think it receives a little better, as it works along the entire length, not just up to the trap.

    Tom
     
    VK3FDCA likes this.
  3. AA7EJ

    AA7EJ Ham Member QRZ Page

    I think it receives a little better, as it works along the entire length, not just up to the trap.
    Can you elaborate on this ?
     
  4. AA7EJ

    AA7EJ Ham Member QRZ Page

    Dean,
    electrically they are same.
    The traps loses are there, but for all practical (!) purposes inconsequential.
    I woudl opt for no traps for mechanical reasons and added weight and just KISS

    The tuner design / its range may be an issue with "no trap" system.

    73 Shirley
     
    VK3FDCA likes this.
  5. N3HGB

    N3HGB Ham Member QRZ Page

    Radio > coax > tuner > antenna is VERY different from radio > tuner > coax > antenna.
    Which one are you proposing?
     
    WB5YUZ and AI3V like this.
  6. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    On 80 and 40m, if both antennas are installed intelligently, I don't think you would notice much difference between them.

    From 20-10m, though, the trap vertical is going to have the advantage for DX due to the increasing number of lobes appearing on the 15.5m vertical. Below are the theoretical patterns for a 15.5m vertical on 80, 40, 20, and 10m. (It is quite intuitive to extrapolate what the patterns on the bands in between would look like.)

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  7. VK3FDCA

    VK3FDCA QRZ Member

    Everyone,
    This is all really good feedback and very much appreciated.

    Please correct me if I am wrong but:
    (i) a trap is simply another tuned circuit similar to the way an ATU is designed and both will have losses associated with insertion and due to quality/efficiency of Inductor/Capacitor.
    (ii) furthermore multi-trap antennas must have these traps in series for the antenna to work over a number of bands (..is this correct?) ....which according to my thinking; means that trap insertion and inefficiency increase as the band increases because more traps are in series. If this is correct it means that losses on a trap antenna are highest for 160 metres and least for 10 metres. Do we agree with this?

    So in reality the quality (Q) of the Traps are important but the number of traps in series are also perhaps a bigger loss factor because of the in-series cumulative effect; so this becomes more consequential when decreasing frequency from 28 Mhs to 1.8 MHz. Therefore, based on my initial thoughts and the above feedback the simple setup consisting of the Vertical Antenna and ATU setup is the simplest setup with the least losses.

    In terms of advantages and disadvantages:
    (A) Thanks very much Tom (AA5MT) for your initial feedback! ..you make a very valid point that ".....With traps, you have a limited bandwidth.....". This makes sense because upon installation of a trap antenna; once the trap is tuned to the desired frequency for optimal SWR you have no easy way of re-tuning the trap without bringing the whole antenna down from the mast. Doing this is not practical. Whereas with an ATU you can conveniently tune in the Ham Shack over a wide Bandwidth with ease!

    (B) Shirley (AA7EJ) also points out that "......I would opt for no traps for mechanical reasons and added weight and just KISS....". O.K. this is a good point because the trap antenna's are mechanically more complicated with more weight and more hardware to break down over time while exposed to the elements.

    (C) Shirley you also referred to "....and just KISS....". I had to do some research on what you are referring to here. Is this in reference to setting up a ground plane system? Note FYI my current vertical multi-band antenna is a "Sigma Euro-Comm SE-HF 360 Fibre Glass Vertical antenna". I originally bought it as a start-up antenna to experiment with because it's design athletically has a less visible profile in the neighbourhood. My original plan was to experiment with this first antenna and eventually replace it with a Hustler 6-BTV. However, as I have learnt more and based on the feedback here it looks like I'm staying with this simpler Sigma Vertical antenna. The antenna is currently setup on a tilt mast but I have added four metal guy wire lines to support the extended mast; directly under the antenna mounting slopping down 45 degrees which I'm hoping will also act as a suitable ground plane (as well as supporting the mast). Would anybody like to provide feedback on this setup?

    (D) Another factor which is important in my suburban environment is the athletics and visibility of the antenna in the neighbourhood. In this regard; the Vertical trap antenna is visibly less athletic to look at than a thinner vertical (no traps antenna) with the less visible profile.

    (E) N3HGB also points out the important point that "....... Radio > coax > tuner > antenna is VERY different from radio > tuner > coax > antenna. Which one are you proposing?....." Note I am aware that an ATU located at the Antenna feed point is better than in the shack but I would like to get a technical explanation of why this is the case. Can you please elaborate with more detail to explain this?
    (NOTE: In my case I do not have the option of having a ATU at the antenna feed point because this sort of ATU adds un-wanted extra weight to my Tilt Mast which I cannot afford to add. Add to this the additional cabling required by the remote ATU simply adds to the complexity of the tilt mast which is already dealing with Coax and four guy lines! It would also means that I need to purchase a more expensive remotely controlled ATU as compared to my current MFJ-949E ATU which in the shack). Nevertheless, I'm interested to hear about the relative advantages of the "Radio > coax > tuner > antenna". Thanks.

    Dean.
     
    Last edited: Nov 7, 2019
  8. K0RGR

    K0RGR XML Subscriber QRZ Page

    It depends on where you are mounting the antenna and the ATU.

    I have the MFJ version of the HyGain 6160 in the back yard. It has a 4:1 un-un at the base, and it's fed with about 100' of very low loss LM400DB coax.

    On 60 meters and up, it works fairly well. The best bands are 40, 30, and 20. On 80 and 160, it's possible to match the antenna using a wide range tuner, but the SWR losses are excessive. Still it works well for DX on 80. MFJ offered a kit in the past that featured a remotely switched loading coil for 80 and 160. This would greatly improve it's operation on those bands. If you were to remote the ATU at the base of the antenna, that would be even better on all bands. You MUST have a large number of buried radials to make this antenna work. I'd recommend at least 20, which is what I have, others will suggest more.

    It is a really good 40 and 20 meter antenna.

    Now, the trap vertical, roof mounted, with three 'tuned' radials for each band, would beat the ground mounted vertical all day long. Ground mounting a trap vertical would be particularly poor, because the higher band elements would be closest to the ground. I've never had a lot of luck with ground mounted trap verticals.
     
  9. K8JD

    K8JD Ham Member QRZ Page

    The answers I see, here, seem to skip over the cons of using a non resonant antenna with coax feedline and the tuner in the shack. this tuner can not reduce coax losses between the antenna and tuner.
    A non resonant antenna may actually have some gain at certain freqs (like an EDZ).
    BUT needs matching right at the feedline connection point OR, use a low loss, high Z feedline like twinlead. to reduce the loss factor and then using a balanced line tuner in the shack can do it's job of Z matching.
    The good thing about a trap vertical is it will be a good match to the coax feedlines on each band it's designed to be used on ! the traps will not have much loss at all.
    The tuning stubs work like traps in the Butternug HF siries of antennas, and a few other brands, but have virtually no losses.
    Your broad questions at the origional post can have hundreds of solutions!
     
  10. AA7EJ

    AA7EJ Ham Member QRZ Page

    I am sorry, I did not finish reading after "KISS" remark.
    It is mostly used by computer geeks - "keep it simple stupid"
    Sorry about that, mate .
     

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