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Thread: Homemade quarter-wave ground plane base antenna

  1. #21
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    Oh ok. Good luck buddy. Hope you don't get any damage.


    Sent from my iPhone using Tapatalk
    Happy DXing

  2. #22
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    Btw, it's an antenna tuner. Not an amp. At least I think it is. I do know that it isn't an amp.


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    Happy DXing

  3. #23
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    You are right. Maybe if I took my head out of my ass I would have noticed that LOL!! That is a nice one actually and should work on 11 meters. Best way to try is to place it in line after the amp if will handle the power. Then place it on 10m and tune the 2 knobs for lowest VSWR with a decent carrier on AM. Using a little more than 4 watts may be the way to go as well as you normally don't see some issues until power is applied. If you can get your amp to key up around 20-30 watts of carrier on AM mode, try tuning it on the 10m setting, first tune the left knob then the right one. Might work. Also for first time testing use only your radio as to not blow anything up!! If possible use the cheapest radio you have on hand just in case!! JMHO's. Like I said it would take me som time to look more into that particular unit as my mind is elsewhere at the moment. Worried about my house and antenna as well as we live about 3-4 miles max from the coast!! So we are going to get pummeled if this storm moves any more west than it has already. Wish I didn't have to work today so I could focus more on my house and getting my mast lowered down, but to get it lowered isn't an easy job due to coax being taped to the mast, and isolated with 1/2" coax grommets. And also the bolts that need to be pulled as well as hose clamps snd such!! Not an easy 5 min job unfortunately!! Anyways, I'll get back to you as soon as I can! Until then try what I said and see if you can get it to work properly. If it works you should be able to tune the VSWR to 1:1.

  4. #24
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    Ok. Thank you very much. I will try that as soon as I get off work and I will post you my results. I'll wait on your reply as well. I hope you don't get hit too hard from hurricane Matthew.


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  5. #25
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    Here is the manual for the unit you have in the pics Matt.
    http://www.qsl.net/ea4bb/EA4BB/Old_R...les/MN2700.pdf

  6. #26
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    It's a link to the instruction manual. Save it to your computer or phone. It should explain what you need to know and I will also keep looking into whether it's useable on 11m or not.

  7. #27
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    First off. Sorry for the long post but there is a lot of good info.

    From what I have quickly read, this unit came with an optional 4:1 balun as well, accessory model #B1000.
    Here is the description from eham.com

    Description: Drake MN-2700 with optional accessory B-1000 Balun. Quality as usual from RL Drake. No complaints. I prefer it over the roller inductor tuners (fast QSY). Accurate wattmeter/SWR bridge and ability to match a wide variety of antennas. Once common at Hamfests and in the Yellow Sheets, they are now "locked" in the custody of their current owners who will probably never part with them. I saw this coming, so I acquired a mint one with B-1000 Balun for my long term collection. Unsung hero. Havent seen one on Ebay in over 6 months. Optional B-1000 Balun known to easily command $100.
    Also from reading i have seen many saying it doesn't work too well with 50 ohms antennas. It's more for a long wire. Also have a look at the frequency range listed in the photo I took. Appears it doesn't cover 11 meters or 27mhz area.



    Like I said before, you can try to use it on 11 meters and see what you get. If your VSWR is reading below 1.5:1, I would not even worry about using it. That is JMHO. It's a good unit, but without the accessory B1000 4:1 balun and also knowing it might not work too well on 11 meters if at all, you may want to place it to the side until you decide if you want to get your amateur radio license. But hey it's worth a shot at least to try it with just a radio and a known antenna with a bad match. This includes impedance as well as VSWR. Read the manual and get an understanding of how to use it and go from there. Just be careful and don't use a radio you much invested into. A cheap CB radio will work fine.
    Just something to think about here, maybe sell the unit and put the money toward an antenna analyzer. Then you can tune antennas the correct way. The MFJ269C or the rig expert aa-30 antennas analyzers are what you want to look into getting. The rig expert I believe is a better analyzer, but the MFJ269C might be easier to use.
    And to properly tune an antenna with the above analyzers you will need to cut an electrically tuned 1/2 wave coax jumper cut to your desired frequency. Here is the formula for making one. Also you don't need to have an antenna analyzer to perform tuning. You can use a known good SWR meter. But you need to make sure to use a 1/2 wave electrically tuned coax from the radio to the SWR meter and from the SWR meter to the antenna. This keeps everything in 1/2 wave increments or multiples of it. Hope all this makes sense. Read on down as it explains more in detail as to how to make this coax jumper and why. If this is a magnet mount antenna for your vehicle, use a 12" or shorter jumper from the radio to your SWR meter, then connect the coax from the magnet mount to the antenna port of your meter. If you use an antenna like the Wilson 1000 or Sirio 5000 performer, they are already most likely matched or closely matched to 50 ohms. That is what the loading coil is for. It a matching network basically. And you want the tallest antenna you can get as well for a mobile or one as close to 108" as possible. The Sirio performer trucker series antenna is about the longest one I have seen. They are longer then he Wilson antennas and much longer than the k40 antennas. Again. This is for a mobile install. For a base station install follow the directions below and you should be good to go. Once you have tuned the antenna with the 1/2 wave electrically tuned coax jumper or jumpers, you can then use whatever length you want. Whatever will reach from point A to B and leave a bit of extra coax for just in case you get a bad connector or if your coax gets kinked or gets water intrusion or some other issue, but try not to leave too much extra as this can but more then you truly need as you can get issues like common mode currents along the coax of its too long. Again, not trying to confuse you, just want to give you as much information as possible! Below is a chart for part of the formula that requires you know the velocity factor or VF of your coax.
    Some coax companies like Times Microwave or Andrew, and most other quality coax companies will list the velocity factor for their coax as well. Below are just some common numbers. But you will find that different coax may have a different VF then the ones listed below. Like Andrew/Commscope LMR400 type coax has a VF of 85%. That is faster than anything listed below. So make sure you use the correct VF when making your coax jumpers.
    Here are the velocity factors of the various Belden coaxial cables:

    RG-59 .66
    RG-59/U (foam) .79
    RG-8 .66
    RG-8/U (foam) .80

    Here is how to figure out your true 1/2-wave:

    492 x (Velocity Factor) / Frequency (MHz)

    For example, I want to figure out the true half wave coax length for RG-59/U (foam) on my home channel (ch. 33 - 27.335):

    492 x .79 / 27.335 = 14.22 feet

    Now add 14.22 to itself to determine your 1/2 wave multiples. Remember to use every other number. See the example below:

    14.22 feet 1/2-wave multiple

    28.44 feet 1-wave multiple

    42.66 feet 1/2-wave multiple

    56.88 feet 1-wave multiple

    71.10 feet 1/2-wave multiple

    85.32 feet 1-wave multiple

    and so on . . . .

    Use only the lengths that fall on the 1/2-wave multiples and you will be all set.

    Now in order to get the true SWR of the system, you have to throw away that 3-foot jumper cable for now. The SWR meter has to fall on a 1/2-wave point on the coax run. Using the example above, you need a 14.22 foot jumper from the radio to the SWR meter, and a 1/2-wave multiple length from the SWR meter to the antenna. If my antenna is 65 feet away from my radio, I need a 14.22 foot jumper from the radio to the antenna, and a 71.10 foot length between the SWR meter and the antenna.

    Further Considerations

    Now that we've said all this, we should discuss the trade-offs between having the perfect lengths of coax vs. having the shortest possible run for efficiency purposes. If it is possible to test the SWR while the antenna is installed, by all means do so. After you have your match as flat as possible, reduce the coax length to the shortest possible run. Your SWR will remain the same as far as the antenna is concerned and you may reduce the overall length of your coax enough to add more efficiency to the overall system. Experiment with this and have fun!

    I hope that this will help you well. Have a good one. Bracing for a bad situation here!! Going to be nasty as all get out and hopefully my Antenna will survive all the crap that is coming. My fingers are crossed and I added extra guyed ropes and ratchet straps to my mast pipe just about 5ft from the base of the antenna. Best I can do is to also lower the antenna 10ft, but I am still worried like heck! Anyhow, have a good one and again. I hope all is well up toward your way!!
    73 and God Bless
    Sean.

  8. #28
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    Thanks Sean for all of the useful info! I will work on that this weekend. I will have to lower my antenna down (witch is the homebrew I made) and take the coax off to measure. Once i get that done, I will post what I have got from it all.
    Happy DXing

  9. #29
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    What about the cable between my radio and amp? Does it need to fall in that 1/2 wave?
    Happy DXing

  10. #30
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    also. the biggest problem i am running into currently is the antenna warning light on my radio when i have my transistor amp on high. on high that amp puts out about 150 watts. My standing wave is 1.2:1. it is really aggravating me. i know my vertical element and radials are the right lengths. im using the homebrew antenna that i originally started this post with.
    Happy DXing

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