2m/70cm antenna with lots of trees.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KG5BSR, Mar 26, 2020.

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  1. KG5BSR

    KG5BSR Ham Member QRZ Page

    I'm new to amateur radio and I want to get a rig set up at my house. I've bought the Kenwood TM-V71 and a power supply. My next move was to buy a dual band antenna with coax. As I was looking around my house to see where would be the best place to set it up. It dawned on me that I'm completely surrounded by very large pecan trees. Should I go above the tree line? If I do. Would I be getting anywhere with the coax loss?
  2. AI3V

    AI3V Ham Member QRZ Page

    Would you rather have a sturdy steel bucket filled with dollar bills, or a flimsy plastic bag from wallmart filled with hundreds? :)

    Height is king at vhf/uhf. You gain more range with height than you loose with longer coax.

    For casual use, pick a coax with less than, say, 3 db loss for the length you will need.


    Edit: for ordinary uhf/vhf fm radio, sometimes called "strong signal" work, the classic prediction of radio range is 4/3 the distance of the optical (line of sight) horizon.

    Here are many websites that will allow you to calculate the distance to the optical horizon compaired to your antenna height. Add 33% to get your reasonably expected radio distanc.

    Keep in mind that the other stations height adds directly to the distance, you can usually expect to talk to a station with the same antenna height as yours at double your 4/3 distance.

    Last edited: Mar 26, 2020
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  3. WA7F

    WA7F Premium Subscriber QRZ Page

    Getting above the trees would be good if it’s practical. You need to consider the terrain and how far your QTH is from the repeaters or simplex stations that you want to work. Line of sight is best but, don’t get too hung about it. Maybe you can try a temporary set-up or use a HT to see what height is needed before jumping in head first on the permanent installation.
    WB5THT, N1LOU and KG5BSR like this.
  4. KF5LJW

    KF5LJW Ham Member QRZ Page

    Distance is determined by coax loss. It is your job to achieve 2 dB or less loss. At VHF is somewhat a challenge, and at UHF a real challenge. Instead of using .2 inch diameter coax may require .6 inch diameter or larger coax. So look at your highest operating frequency, coax distance, and determine if you can afford to play radio or even if it is possible. This is why broadcast has to use 1-5/8 hard line. Has become such a challenge, carrier's put the radios on top of the tower and use fiber optics lines to interface with CPRI SFP's to gain those lost dB's back. So get a table out and look at 500 Mhz loss and see how far you can go.

    What you will find is a brick wall where going any further is pointless. Any gain gained going higher is ate up with coax loss and you loose going higher. Unless you put the radio on top of the tower.

    Edit note: Before you go throwing money at a problem that may not exist is get a list of repeater frequencies within say 20 miles of you. Try a HT or Mobile in your drive wayto see what you can hit. You may find out just a antenna in the attic is more than adequate to meet your needs.
    Last edited: Mar 26, 2020
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  5. AI3V

    AI3V Ham Member QRZ Page

    It's hard to come up with accurate numbers of just how much signal is lost going thru trees.

    Type of tree.
    Moisture in the tree.
    Time of year (leaves/no leaves).
    How many trees and how thick are they.

    All have a effect.

    When you get above the trees, the various formulas become quite accurate.

    AJ5J and KG5BSR like this.
  6. KM3F

    KM3F Ham Member QRZ Page

    You have little choice but to go with the conditions you have to deal with.
    Any repeater with marginal signal strength will be affected by temperature inversions on the longer paths, wet trees around the antenna and time of year leaves or no leaves..
    I find the strongest signals on the lower signals occur when the temperatures drop fast in the mountain areas and verified by area weather reports.
    Use the highest gain antenna you can afford, get it up as high as possible.
    Do not expect the same distances on the 70cm band.
    I have lots of experience with long distance repeater access using the highest gain Co- Linear vertical types available and do very well at up to 100 miles over the mountains in my home state and two nearby states on 2m and 222 band.
    I also run stacked beams on 2 bands that are noticeably a bit better. They are fed with 7/8 inch Helix for the distance so that counts for a lot.
    The Co-Linear gives a very good account of it's self being closer and a bit lower, fed with LMR 400.
    Lets look at the practical operation. The repeaters are usually located high, run Gain antennas, run powers in the 50 to 100 watt range for your receiver to hear. That's good for you in terms of effective radiated powers.
    But you don't have the same conditions and may need to get as close to it as you can afford with antenna gain and transmitter power. Ht's don't cut it very well except in your local area.
    Good luck.
    Last edited: Mar 26, 2020
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  7. KG5BSR

    KG5BSR Ham Member QRZ Page

    Thank you for the advise gentleman. I really appreciate it.
  8. WA7F

    WA7F Premium Subscriber QRZ Page

    IMO, The best advise so far is:
    1. determine what repeaters are in the area and where are they located.
    2. See what repeaters you can hit with a HT. If you don’t have one maybe a buddy does. Use it to determine where the best signal is obtained.

    Just keep it simple for now and learn as you go. You can always add more capability down the road if you are having fun with the hobby.
    N1LOU likes this.
  9. EA1DDO

    EA1DDO Ham Member QRZ Page

    For get over that you can install a Rx preamplifier at the antenna mast.
    It is power feed by the same coax (using a Bias-T), and you override the coax losses.

    73, Maximo
    KG5BSR likes this.
  10. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

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