Author Topic: Question for HAMs and GMRSrs  (Read 372 times)

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Offline Trekster

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Question for HAMs and GMRSrs
« on: December 15, 2021, 10:16:27 AM »
Hey all!
I just got my GMRS card and am finally embarking upon Technician classes and had a question.
Currently (for GMRS) I have a 20w mobile setup as a base station and my question is relating to antennae,

Despite being listed as working with VHF, UHF, wideband, this stick antenna (stubby) doesn't seem to run proper.
So I connected an approx. 48.5' length of TV coax and wowza! It's alive!

EDIT: It's probably an even 50' cable. (connectors on both ends).

But...

Will this extreme length of most likely 75 ohm impedance cable coax damage my unit?
I have no SWR meter and thus am at a loss of how to calculate correct length to cut the cord, if necessary.

I know shorter is better in the UHF spectrum, but this single, unsplit length of coax seems to work fine. My theory is that the lossy nature of TV coax is likely working in my favor at least for short-range comms and repeater use.
Shall I cut it shorter?

Please advise,
-Z-
« Last Edit: December 15, 2021, 10:52:17 AM by Trekster »
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Offline Mad-max

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Re: Question for HAMs and GMRSrs
« Reply #1 on: December 15, 2021, 03:19:41 PM »
I have my general but I am far from an expert
  There are a bunch of ham forums.  That's where you'll get answers...lots and lots of answers.  Lol.  Maybe I should say opinions.  Definitely go for your tech.  It's easy peasy.  YouTube vids and you can ace it.  General is a little harder but if I can do you can too.  Technician is a gateway to a whole new world.  Good luck.
huh?

Offline Mad-max

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Re: Question for HAMs and GMRSrs
« Reply #2 on: December 15, 2021, 03:29:24 PM »
One more thing get a band chart.  Stay in your licensed band.  Nobody is going to kick down your door and arrest you (we're self policed)  but there are some hams that will triangulate your position and drop a card in the mail to let you know they know.  Then there are the Karen's that will get crappy with you if you break protocall on the air.  Just change freq.  Remember you can receive on any freq.  But transmitting you should be sure you're allowed there.  Overall you'll find most hams to be very friendly, helpful, and humble.  In fact it's in the mission statement.

Have you got a Fred (mentor) to help you?  Big advantage.
« Last Edit: December 15, 2021, 03:36:54 PM by Mad-max »
huh?

Offline Pete Bog

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Re: Question for HAMs and GMRSrs
« Reply #3 on: December 16, 2021, 03:00:08 AM »
Trekster, I've been dinkin' with radios for 60 years. I'm a licensed FCC radio technician and CET certified. I hold a general class Ham radio license and have owned and/or operated a two-way radio service shop for 40 years. I know my radio crap.

  Making a 75 ohm TV coax work with a GMRS transmitter will require a solder iron, a little experience and a bit of black magic. Field expediency says to get rid of the TV coax before you ruin your transmitter output finals. You can listen with no harm, but transmitting will put your rig in peril.

    Set the 75 ohm coax aside and get some 50 ohm RG8 or RG58 coax. A two way shop will throw many feet of it away every week.
   Look up how to build a center fed dipole antenna.
    1.) strip off 6 inches of the black outer plastic to expose the outer braid.
    2.) tease the braid open right at the end of the black plastic and pull the center conductor and its plastic insulator through the opening.
    3.) you'll be left with a 6 inch center conductor and a 6 inch piece of braided outer shield on the end of your coaxial cable. Tape these to a non
          conductive stick. (wood or plastic) so they are pointed in opposite directions. When you hold it up, the coax will hang down and the assembly
          will form a "T".  it is important that neither arm of the "T"  runs parallel to the coax so keep keep the leg of the "T" at least 6 inches or more
          away from the arms of the "T".

      Polarization: TV antennas are horizontally polarized. Communications antennas are vertically polarized. So your wooden stick will have to stand vertically for best performance.
       Length of your coaxial cable is important only in that the longer the cable the more signal loss you will have. Think of a 300 foot garden hose compared to a 25 foot garden hose.  The longer garden hose has a sorry dribble of water out the end. The same holds true for Coaxial cable. The longer it is, the less signal is available at the far end. At GMRS frequencies, try to limit the length of RG58 coax to 25 feet and RG8 to about a hundred feet. Different frequencies have different limitations.
        This basic design will work with MURS, but instead of 6 inches, use 18 inches. For a HAM radio 2 meter rig, use 21 inches instead of 6 inches.
        I used to put these together for undercover cops using rental cars. I'd just duct tape the antenna to the tinted side window and away they'd go.   I used to teach game wardens how to do this with just a pocket knife when things would go bad for them out in the field. Antenna scraped off the roof in the woods, etc.. It's certainly not the best antenna, but it'll get you by / get you started until something better comes along.
        ARRL (Amateur Radio Relay League) Has a lot of good information on antennas.
        An experienced Elmer or a Fred is a great source for some good no nonsense help. They take great pride in getting a new HAM on the air.