FAQ

KB9VBR-J-Pole-Slim-Jim-Antenna-Header

Since 2001 I’ve built and sold thousands of the J-Pole antennas. I’ve also answered hundreds of questions about installation, operation and performance. Since there is no such thing as a bad question, I’m listing the most frequently asked questions here.

What are the all copper J-Pole antennas constructed with?

My J-Pole antennas are constructed out of Type M solid copper pipe for the ultimate in durability and weather resistance. All joints are soldered with rosin core solder. An SO-239 connector is soldered onto the antenna at the point of lowest SWR.

Related Post: Why build antennas out of copper and not aluminum or stainless steel.

Why copper, isn’t that expensive?

Yes, copper is expensive; but it is also one of the most efficient conductive materials available. One of the common elements more efficient than copper is silver. Aluminum is only 60% as efficient as copper. The high efficiency of copper means that more of your signal will be transmitted into free space and not burned up by the electrical resistance of the material. Antennas made out of stainless steel or aluminum may look pretty and won’t tarnish, but they don’t have the efficiency that a true copper antenna can provide.

How do these antennas compare to the wire antennas on the market

216573-r1-6aI’ve seen lots of plans and sites selling J-Pole and Slim Jim antennas out of 450 ohm ladder line or 300 ohm TV twin lead. These make good antennas; they are lightweight and can be easily packed when camping or hiking. I use them myself for portable and emergency situations. But you make a tradeoff in durability and efficiency when you go with a thinner material. All Copper J-Pole and Slim Jim antennas will have more sensitivity, lower noise floor, and more bandwidth than a comparable wire antenna. The greater surface area of the copper tubing makes the difference.

How do your two meter J-Poles perform on the 440 MHz band?

The two meter J-Pole is tuned for maximum efficiency at the 2 meter band where the SWR is 1.2:1 or less at 146 MHz. It is a pretty good performer on the UHF band where the SWR is 2:1 – 2.5:1 between 445-450Mhz. This is still within the range of what modern radios can handle.

Can you build antennas for any other frequencies?

I can build you a custom antenna for any frequency between 40 MHz and 500 Mhz. If you have a special antenna need, please email me and I’ll give you a cost estimate.

I need an antenna for my HF, 10 meter, or CB radio. Can you help?

At this time I do not produce any antennas for the HF spectrum. This would include antennas for short wave, hf, 10 meter or CB radios. But I am investigating new products, so check back from time to time to see if I have any new offerings that may meet your needs.

How are your antennas shipped?

I use USPS Priority Mail to ship my antennas. I find that Priority Mail gives you the best price, speed, and deliverability. The 6 meter antennas are shipped UPS Ground service which works best due to their length. International orders are usually shipped USPS International Priority. More on shipping can be found on the Ordering Information page.

Can the antenna be painted?

As the copper J-Pole is exposed to the elements, it will develop a dark brown patina.  This dark tarnish or patina is only cosmetic and won’t affect the performance in any way.

You may paint the antenna with nonmetallic paint to protect it and help it blend into the surroundings. If you want to keep the antenna looking shiny and new on the tower, you can also paint it with a clear enamel paint.

I recommend the following procedure if you are planning to paint the antenna. First shine the antenna with some fine ’00’ steel wool. Then clean the antenna with a rag or paper towel soaked with isopropyl alcohol. Alcohol is flammable so do this in a well ventilated area. Also let the rag dry out in the open before throwing it away to prevent spontaneous combustion. Tape the connector up with masking tape and apply one or two coats of spray enamel paint.

Related Post: Painting the J-Pole Antenna

Is there any special way in which the antenna needs to be mounted?

The antenna is naturally at dc-ground, so it does not need any isolation from the mast. The antenna can be mounted directly to a metal mast with hose clamps or U-bolts. The J-Pole can be detuned by nearby large metal objects. You should keep it at least 6 feet away or above metal buildings and the like.

Related Post: Do J-Pole antennas need to be grounded?

Related Post: Lightning Protection for Antennas.

I live in an apartment. Can I still use your J-Pole antenna.

Using the KB9VBR J-Pole antenna on the patio

Using the KB9VBR J-Pole antenna on the patio

You will definitely see an improvement with an antenna like a J-Pole when you compare it to the rubber duck antenna found on today’s HTs. Try clamping the antenna to the balcony or deck railing, to planting it in a flower pot filled with landscape stones. Try putting it into the attic space if you have access. As a final result, prop it up in the corner of the room. If you do that, follow RF safety guidelines and keep the transmitter at a lower power setting.

Related Post: Mounting Ham Radio Antennas in the attic

How to I connect your antennas to my hand held portable radio?

While the J-Pole antennas are designed to be superior base station antennas, they will all work very well with your HT or hand held radio. In fact I highly recommend the breakaway model for portable use. The antennas have an So-239 connector on them, and I recommend using coax cable with Pl-259 connectors to connect the antenna to the radio. You willl need an adaptor to connect the standard coax with Pl-259 connectors to your portable radio. Radio Shack does sell an BNC to SO-239 adaptor and an SMA to SO-239 adaptor. If you can’t find the adaptors at Radio Shack, try Tower Electronics or Ham Radio Outlet. These adaptors will let you connect an HT to any antenna using standard coax cable. It’s a good idea to have a few of these in your go bag just for these reasons.

Related Post: Mounting external antennas to a Wouxun handheld radio

Related Post: Connecting an external antenna to an HT

How much power will a J-Pole antenna handle

J-Pole antennas have been designed and constructed out of a wide variety of materials. The choice of construction materials can greatly affect the performance and power handling of the antenna. Typically, the 2 meter all copper J-Pole antenna will handle 250 watts or more of power. Copper is a very efficient conductor and will tolerate and dissipate heat energy very well.  I’ve personally tested my 2 meter antenna at power levels up to 170 watts without issue and am confident that the antenna will go higher. 

Related Post: How many watts can a J-Pole antenna handle

How far will this antenna transmit or receive?

VHF and UHF communications are primarily line of sight, your range will be dependent on antenna height, transmitter power, and terrain. For example, if you mount the antenna 20 feet in the air, it would not be uncommon to be able to hear portable radios in a 2-3 mile circle, mobiles 5-10 miles, and repeaters up to 50-60 miles. If you live in a very hilly or urban area, these figures could be reduced. Read my testimonials for real world examples of the antenna range.

Related Post: How does antenna height affect VHF communications.

Related Post: HAAT Calculations: which antenna will work best for me.

Can I use your antenna on a repeater

J-poles will certainly work well as a repeater antenna . They have an omnidirectional doughnut shaped radiation pattern. This makes them a good choice as an antenna for low to moderate elevation levels and would be a great choice as a remote base or receive antenna on a repeater system.

My Slim Jim antenna is a perfect choice for a repeater. It has a folded dipole design that gives it more gain and a lower angle of RF radiation, (7 degrees, vs 20 degrees). The Slim Jim concentrates more RF energy towards the horizon.

Related Post: J-Pole and Slim Jim Repeater Antennas.

How does your six meter antenna perform?

The six meter antenna works really well. I had one ground mounted and was able to hit a repeater 40 miles away with 5 watts. The return signal was about half scale on the on the radio and I had excellent signal quality going into the repeater according the other half of my QSO. Another person mounted his on his chimney and is able to talk simplex with 100 watts for more than 40 miles and still have a full scale signal. These examples exhibit average behavior of the antenna, but your mileage may vary.

What type of coax should I use?

Coax size is dependant on a couple of factors, most notably the length of your run and the frequency of your antenna. VHF and UHF signals are more prone to attenuation in the coax, so a low loss cable should be selected. For a run of 100 feet, here are the loss figures in decibels for some of the more popular coax types:

 

Type of coax cable Loss at 146MHz in db per 100 feet Loss at 446MHz in db per 100 feet
RG-58 6.5 12.2
RG-8X 4.7 8.6
RG-8 2.3 4.7
9913 1.6 2.9

Related Post: Coax Feedline Attenuation Chart

A loss of 3 db will cut your power in half. A six db loss will cut your power into 1/4. I recommend RG-8 if your cable run is over 50 feet and RG-8X if it is less than 50 feet. You shouldn’t use RG-58 for VHF/UHF unless it is a very short run (less than 15 feet.). GMRS J-Pole users should only use RG-8 for short runs and Belden 9913 for longer runs. Loss figures for other frequencies and cables can be found at the Cable Experts.

The SWR is really high on my antenna. What should I check?

Here are a few things you can check if your SWR is high.
  1. Check the coax, make sure there are no problems associated with it. The connectors should be well soldered or crimped without any shorts and there should be be any apparent kinks in the cable.
  2. Check the mounting location, nearby buildings will affect the SWR. Keep structures at least six feet away from the antenna, or make sure the antenna is above the structure.
  3. Make a balun to keep RF from coming back down the coax. Make a coil of about 5 loops of coax with a coil diameter of about 6 inches. This coil should be located about a foot away from the feedpoint of the antenna. Secure the coil with cable ties or electrical tape.
  4. Inspect the antenna itself. Is the solder loose or cracked at the feedpoint. If it is, let me know.
    Click for a full size image
    Balun Coil at the feedpoint


    Didn’t find the answer to your question?

    Drop me  a line on my contact form. I’d be glad to answer your particular questions concerning J-Pole antennas and my antennas in particular.

18 Responses to “FAQ”

  1. John Berkey August 28, 2011 at 10:26 am #

    Most impressive web site. Full of information. I want one.

  2. KK4EUA November 15, 2011 at 4:20 pm #

    <img src="http://occupations.phillipmartin.info/occupations_ham_radio.htm&quot;
    Cool, I am a new ham. Might just have to buy one…

  3. brad February 25, 2012 at 1:41 am #

    what is the gain in DBD ???

    how much to make one for me on 104.9 mhz ?

    thanks
    brad
    at kqrp-lp

  4. Michael February 25, 2012 at 7:28 am #

    The LPFM J-Pole antenna is a half wave antenna by design and has about 2.15 DBD of gain. Price for the LPFM antenna tuned to 104.9MHz is the same as the other low power fm j-pole antennas, that is $49 + $12.00 shipping.

  5. Tim Boyd April 30, 2012 at 10:33 pm #

    I purchased a j-pole 2 meter from you a few months ago, and wow, does it ever work. I live way down in a valley, with an approximate 700 ft drop from the main road, and I have no problem at all, hitting my local repeater. I am getting ready to extend the height of my antenna mast, and I think I will get even better transmit and receive, as I am right against the side of my metal roof. I appreciate your help, and will most likely buy another for my scanner. Thanks again! Buy this antenna; you WILL NOT be dissapointed!

  6. Charles Milstead May 8, 2012 at 10:04 am #

    Radio Shack makes a SWR meter I believe is geared towards CB antennas. Would it work for the 2 meter dual band j-pole? Or is it not accurate enough? Suggestions?

  7. Michael May 8, 2012 at 12:47 pm #

    Thank you for your interest in my antennas. The SWR meter that Radio Shack sells works well for the HF bands under 30MHz, but will give you inaccurate results if you try to use it on VHF/UHF frequencies. You are correct, the meter is geared towards the CB band.

    Michael

  8. Dave Akins May 28, 2012 at 11:07 am #

    Just ordered your 220 unit and read about keeping it 6′ away from other metal objects. How about mounting it 3′ above a horizontal pair of 75m horizontal hamstick dipoles, with the 220 J pole and dipoles sharing the same mast on the rotator? Any performance degradation or problems to watch for? Should I use a non-conductive mast?
    Thanks,
    Dave Akins, AK1NS

  9. Michael May 30, 2012 at 5:58 am #

    If the antenna is alongside large objects and structures, then you will want to keep it at least six feet away so that the antenna does not couple with the structure. If you are are mounting the antenna above the structure, then you will be fine. Objects below the antenna won’t affect it, so you can mount it on the same mast as your hamstick dipoles. Since the J-Pole is a half wave antenna by design, it doesn’t require a groundplane or special grounding. You can mount it on a non-conductive mast.

  10. Jason November 30, 2012 at 10:12 pm #

    Good stuff. I found what I needed. My SWR was in the red. I made balum coil and it dropped to .5 for 70CM and 2M. Thanks.

  11. joe February 5, 2013 at 4:32 pm #

    is there a benefit or disadvantage to using solid copper rod v/s copper tubing? if so, how does diameter affect quality? i have access to 3/16 to 1 inch rod. just curious, thank you in advance.

  12. Michael February 18, 2013 at 1:46 pm #

    There is really no advantage to using solid copper rod vs tubing to build an antenna. The reason is that RF energy travels along the surface of ‘skin’ of the metal and not through the core like electrical energy does. Therefore surface area is more important than thickness, especially for the higher VHF and UHF frequencies.

  13. Brent June 21, 2014 at 9:48 pm #

    I have some extra 3/4″ copper rigid plumbing line. Will this wok like the 1/2″ or is the surface area an issue ?

  14. Michael Martens June 22, 2014 at 6:05 am #

    Brent,

    3/4 inch tubing will work just as well at 1/2 inch. In fact the surface area will give you a little bit more bandwidth, so go ahead and use up your leftover copper for the antenna.

    Michael

  15. Robert July 11, 2014 at 11:21 am #

    Just ordered one….

    Am planning to mount it atop a 10 foot galvanized metal mast that I have. You say that the antenna doesn’t need any isolation and can be mounted directly to the mast but he picture you show at the top seems to have the antenna isolated from the mast by a section of PVC pipe.
    Why?

    Can you explain?

  16. Michael Martens July 11, 2014 at 12:44 pm #

    Robert,

    Thanks for point that out, I should rewrite the FAQ so that it is a little more specific. The J-Pole antenna is a half wave vertical antenna, and can be mounted to a metal or non-metal mast without affecting it’s performance. The antenna pictured at the top of my FAQ page is the 2 meter Slim Jim antenna. Both antennas are similar in that they use a J style matching system consisting of a 1/4 wave stub, but the difference between the two is that the Slim Jim is a half wave folded dipole antenna. It performs best if it is isolated from the mast. That’s why I provide a short section of PVC pipe to use as an insulator.

    I hope this answers your question, let me know if you have any others.

    Michael

Trackbacks/Pingbacks

  1. The J-Pole as a low power radio antenna » KB9VBR J-Pole Antennas : Amateur Radio VHF and UHF antennas for sale - December 5, 2010

    [...] The other reason these antennas work well with low power radios is their portability. The breakaway J-Pole antenna breaks down into two pieces less than 34 inches long. This makes it very easy to transport the antenna or to make it a part of your go kit. There is more information on connecting a portable radio to my antennas in the FAQ. [...]

  2. Painting the J-Pole Antenna » KB9VBR J-Pole Antennas : Amateur Radio VHF and UHF antennas for sale - January 4, 2011

    [...] outline the steps in which to go about painting the antennas in my Frequently Asked Questions section, but to recap, the steps to paint can be found after the [...]

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