How Close Can I Mount Antennas To Each Other?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI4VVA, Mar 10, 2021.

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  1. KI4VVA

    KI4VVA Ham Member QRZ Page

    Hey everyone, I was curious how close can I safely mount vertical base antennas to each other. I currently have a Diamond Triband VHF/UHF vertical mounted about 3 feet from a CB vertical. I have a Discone antenna I want to put up for my scanner and I would like to put it on the same side of the house as my other two antennas for secure mounting and proximity to my shack (home office). I may also possibly be getting a GAP Challenger vertical as well from someone and I may wish to mount it in the same area. I just don't know if they will interfere with each other or act as radials or some other weird coupling affect. Let alone I don't want to fry some front end or something. Yes, I may possible use all of them at the same time or at least two at a time.

    Any thoughts, suggestions, wisdom?
  2. KM3F

    KM3F Ham Member QRZ Page

    Some of them will react with each other depending on what band is in use at any given time.
    How close, how much and which band combinations will affect match, Tx and Rx is hard to tell .
    The fields couple to each antenna depending on the near resonant size or each of the elements, the same way a Beam works and would affect the patterns and direction.
    Thoughts, but no suggestions other than space them out a few wave lengths and see what happens.
    Verticals couple with other vertical elements the same as horizontal elements couple with other horizontal elements the most.
    Vertical to horizontal usually is not an issue even very close.
    AK5B likes this.
  3. US7IGN

    US7IGN Ham Member QRZ Page

    I would spread them by at least one wavelength. The diagram will be distorted, but the propagation will correct the situation)
    AK5B likes this.
  4. KI4VVA

    KI4VVA Ham Member QRZ Page

    I've been using the VHF/UHF and CB antennas for a couple years now and can't tell anything is wrong, but that may be my inexperience and I could be getting much better performance if I moved them.

    This side of the house is the best spot, I can't put them in front of back because of the heavy snow. I have each pole attacked to a 10 ft 4x4 buried 2 ft and each 4x4 is attached to each other for added stability via two 2x6s. Needless to say I don't want to put them elsewhere because I don't want to guy anything. The poles are 20 ft tall (two 10 ft chain link fence horizontal pipes).
  5. US7IGN

    US7IGN Ham Member QRZ Page

    In the case of using primitive antennas for near field communications, it makes no difference how to position them. To understand how important the location of the verticals is, I recommend reading about vertical driven arrays or phased verticals.
  6. N7WR

    N7WR Premium Subscriber QRZ Page

    The only one I would suggest be placed as far away from the others is the HF (GAP) vertical and only so that it does not become de-tuned by close proximity to other metal surfaces. If transmitting on V/UHF has not harmed the scanner's front end (unlikely) HF and V/UHF will not "hurt" each other. I have had V/UHF antennas and scanner antennas very close to each other for decades with no issues.
    KI4VVA likes this.
  7. KI4VVA

    KI4VVA Ham Member QRZ Page

    Wlad, I'm not sure what you mean by "primitive" antennas. I get good performan out of both verticals.

    For HF I currently use a Classic Windom, I have for 14 years. But I'm going to replace it soon with a MyAntenna brand end fed in an inverted-v formation. The GAP could be interesting since I've never used a vertical HF except for my Wolf River Coils TIA, which is way too fiddly and provided horrible performance even after tuning it with my Rig Runner. For portable I'm going to do what I should don't from the beginning and buy a Chameleon MPAS 2.
  8. KI4VVA

    KI4VVA Ham Member QRZ Page

    N7WR, thanks, that helps. I guess I should be fine for all the V/UHF antennas then.

    That CB vertical I have (Solarcon I-MAX 2000) gets great reception. I'm in North Idaho and was hearing people in Louisiana.
  9. US7IGN

    US7IGN Ham Member QRZ Page

    Everything is relative. Simple antennas are when they are no more than one or two elements. Then it starts interesting. When you realize that you need more amplification in one direction and more suppression in the other. Then you need to take into account the influence of both the elements of one antenna on each other, and the antennas among themselves.
    In the case of simple antennas and their extremely low efficiency, much does not matter and the difference is easily leveled by the propagation.

    I started with shit, cobwebs and sticks and went up to 16 elements on 3 bands. Then the war started and I lost everything. Now I am forced to wander through the woods with wire light antennas.

    During this time, I learned a lot about what to do with low power and bad antennas, but I remember what antennas should be and I work in this direction.
    AK5B and WD0BCT like this.
  10. KG2RG

    KG2RG Ham Member QRZ Page

    If I have a single mono pole vertical installed for 20m and a 1:1swr at 14.2Mhz reading on the Rig Expert, then take another identical 20m verticals and lay it on the ground about a 1/4 wave from the installed one, they couple and the SWRs drop down band about 100kc.

    I think there may be a unique and distinctive SWR curve that appears when antennas are interacting and coupling but I’m not positive. I’m actually here for the same question.

    my experience in phasing verticals leads me to think that 1 wavelength or more of separation is safe, but if you have a 1/2 wave for 160m, then you need to buy a farm.

    the only thing I can think of is to collect all the data you can from an antenna analyzer on each antenna already installed, then compare new data with old data every time you install a new antenna.
    If you’re wondering about if the new antenna is getting negative interaction buy your other antennas, match it with the data from your new in antenna that you collected at a test location, like a near by park. Yes, ground resistance may factor in between two locations, buts it’s close enough and May not even factor in for wire ant

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