Help with MFJ-1622, APARTMENT ANTENNA, HF, 40M-2M

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KD5FQF, Jul 3, 2020.

ad: L-HROutlet
ad: l-rl
ad: Subscribe
ad: Left-3
ad: L-MFJ
ad: Left-2
ad: abrind-2
  1. KD5FQF

    KD5FQF Ham Member QRZ Page

    Greetings!!!

    Have been on somewhat of a amateur radio hiatus over the last 15 years or so... Recently dusted off my Icom IC-718 HF rig and have been trying to patiently work 20 meters through recent torrid band conditions with my portable MFJ-1621 (black box vertical antenna). Works well considering...

    I also have an MFJ-1622 apartment coil vertical antenna that I never used since taking the hiatus. Now I realize the 1622 has historically not gotten the best reviews, but I am determined to remember how to properly tune this beast and starting working 20 meters on it as well. I have no antenna analyzer or tuner. Just using the SWR meter on my 718 and checking the SWR while on RTTY mode @ 28 watts of power.

    Needless to say, it has been a headache this week trying to find the proper sweet spot on the MFJ-1622 for 20m with regards to the coil tap and counterpoise length and position. I can't seem to get any better than 2.75 to 3.2 : 1 on 20m. I used to use a Barker and Williamsson AP-10A back in 2000 on 10 meter and was able to tune like a champ... I guess mental rust has settled in...

    Using my MFJ-1622, my configuration for 20 meters consists of this (attached 2 images):

    - MFJ-1622 mounted via bracket on my backyard deck ~ 11.3 feet off the ground.
    - Using the telescopic vertical whip/radiator which measures 5.5 feet in length.
    - 50 feet of RG58 coax with 30 feet of it set in a choke 18 inches from the antenna.
    - Loading Coil tap currently set on the 9th coil (have been experimenting between 8-9 coil).
    - Counterpoise - now here is my primary headache source:
    - the provided counterpoise wire is 35 feet.
    - I know that for this configuration, the counterpoise wire should be less than 1/4 wavelength of the desired frequency (using 14.2875 Mhz as my desired frequency) therefore the sweet spot should be somewhere between 20 feet and 33 feet of the counterpoise wire (of which the excess is wrapped accordingly in a small coil 3-4 inches in diameter).
    - However, here are my 2 questions:
    -- should this counterpoise wire (20-33 feet) be draped down from my deck and on the ground or does it need to be elevated much like a radial?
    -- because the antenna is 11 feet above ground is my math correct with regards to the counterpoise length? Seems a little high/long?


    Any insight/help/guidance would be appreciated as I am trying to get my sea legs back with ham radio...

    Thanks and 73:
    Vince (in Colorado)
     

    Attached Files:

  2. W6MK

    W6MK Ham Member QRZ Page

    Just experiment with the counterpoise length until something works. You can shorten it without cutting the wire by simply doubling the wire upon itself.
     
  3. KK4OBI

    KK4OBI Ham Member QRZ Page

    Try a counterpoise wire 17 feet long.
     
    AK5B likes this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's a lot easier to use a small, cheap SWR bridge installed right at the antenna (maybe within a foot or something, so you can reach the antenna and read the meter at the same time), run much lower power than 28W (1W is good), and tune the antenna "live" and while transmitting.

    Your 8th-9th coil tap may not be close to where it should be. As stated, a 16-17' counterpoise wire is certainly a lot better than a 35' (or 20-35') one. A 33' long wire in theory shouldn't do anything worthwhile on 20m, but would be the right length for 40m.

    I used to adjust these all the time "live," while transmitting, just using very low power. Run the clip up and down the turns until the SWR dips. Won't hurt a 100W transmitter when running just 1W or so, and unlikely to get an RF burn, either (I never did at that power level on HF), but if there's a worry about burns, wear gloves.:)

    Of course, an antenna analyzer which is a very QRP transmitter and SWR bridge built into the same box and requiring no connection to your transmitter, makes this easier (they run about 10 mW output power, typically) but since you don't have one, a cheap "CB" type SWR meter ($10) and your transmitter will work fine, but only if the meter is at the antenna so you can read it while adjusting.
     
  5. KD5FQF

    KD5FQF Ham Member QRZ Page

    Hey.... thanks for the quick tips... I did a complete checkout of the entire antenna assembly this morning and started from scratch. For 20 meters, I have the loaded coil tap at around the 9th coil, and this time, I allocated about 16.5 feet of counterpoise wire (wrapping the excess in a coil about 4 inches in diameter). However, this time, laid out the counterpoise wire along the patio deck instead of letting it drape down to the ground/lawn below. This appears to have worked; resulting in a 1.5:1 SWR at 14.280. So hopefully the bands are little better tomorrow to try again. I also dusted off some old Atoc Technologies IronHorse Ham Sticks and started trying to see if I could tuned those on my car license plate mount. Was about to successfully tune the 10m and 20m sticks and tune the 40m stick on the high end of the band. Ran out of energy to mess with the 80m stick, but tomorrow is another day... No contacts today since bands were crummy, but it looks like I now have some options on 20 meters for my Icom 718. Looks like I need to invest in some sort of antenna analyzer. I use to have an old CB/10meter Radio Shack SWR meter, but can't seem to locate it...

    Anyways... thanks again for the help!!
    73
    Vince
     
  6. AK5B

    AK5B Ham Member QRZ Page

    I'd try shortening the counterpoise wire, perhaps even cutting it in two and run out 180 degrees apart if possible. I'd also experiment with making a makeshift cap hat out of a pie tin or wire as that base-loaded 5.5' radiator can use all the help it can get.

    What's going on with that big coil of coax underneath, too? EDIT: I just took a second look at your initial post and photo with the coil---that looks to be a very ineffective choke as is---ugly baluns need to at least be carefully wound with no overlapping turns for the best performance and choking ability. I'd suggesting re-winding on a plastic form such as 4 or 5 inch PVC pipe or better yet, ditch the coax coil and use a ferrite donut instead. G3TXQ's and K9YC's sites have all the good info and charts to help you with that and a simple search in this forum will reveal the direct links for them.

    While that balcony antenna may have it's share of bad reviews, remember that any shortened vertical can be vastly improved with the addition of sufficient radials/ground plane and loading methods such as a cap hat at the very top Elevated radials are great but will need to be tuned for best results.

    With some minor changes you should a significant improvement; good luck!

    73,

    Jeff
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    ^I agree, but actually using that particular antenna with no choke (at the antenna) at all can often work better, as it allows the outer conductor of the coax to be another counterpoise; whether this helps or not depends a whole lot on the length and routing of the coax.

    To prevent CM from interrupting operations in "the shack," a current choke balun can be installed close to the station instead...that can stop CM from screwing up stuff in the house while allowing the coax itself to still radiate a bit. I've found in some "apartment" type situations, it can actually improve performance.

    Since that's an easy thing to experiment with, and doesn't really cost anything, it's worth playing around.
     
    AK5B likes this.
  8. KK4OBI

    KK4OBI Ham Member QRZ Page

    Vince,

    you could get out better if you could mount the wire as high as possible and use the whip/coil as a tuned ground. Its angle controls the SWR... probably 30 degrees up to horizontal range.
     
    AK5B likes this.
  9. K8JD

    K8JD Ham Member QRZ Page

    Tuning Tips
    The antennas are more importaint than all the other stuff in a ham station !
    First off , either find your SWR meter or get a newer one, I am happy with a Diawa brand that cost me under 100 bucks.
    Don't just take a reading on your favorite freq on a band and try to guess what to do.
    Get some Graph paper and Make charts from below the band to above and the curve will show you if the ant is above or below where you want it,
    change things to move the resonance up or down to match how it charted.
    After adjusting make a new chart. This will tell you if what you did was good ,or to go the other way !
    Remember to use as little power as you can to get a good reading on the SWR meter, keep transmissions just long enough for the meter to settle and read it quickly.
    Have fun.
     
  10. KE4LH

    KE4LH Ham Member QRZ Page

    I believe you have a simple answer. All conventional antennas MUST have a return path just like a magnet has one. And just like a magnet, the return path is unbreakable. Your problem from the first photo is that big coil of feedline coax you have right below the antenna. And as have already found out, it must be uncoiled to allow for a good return path, also known as a counterpoise. That coil is forming a choke and resisting your return path and the result is a high swr.
    Good luck,
    Ke4LH
     
    WA7ARK likes this.

Share This Page