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

Jul 2nd, 20:56

kd5fqf

Joined: Jun 9th 2013, 15:17
Total Topics: 0
Total Posts: 0
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:

- 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)
Jul 3rd, 11:03

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
The counterpoise may be too long. A quarter wave on 20 meters is approximately 16-1/2 feet. If you wrap the excess into a coil that should be done at the far end. And that will add capacitance to ground, lowering the resonant frequency.

Zak W1VT
ARRL Senior Lab Engineer
Jul 3rd, 23:11

kd5fqf

Joined: Jun 9th 2013, 15:17
Total Topics: 0
Total Posts: 0
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
Jul 4th, 04:06

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Happy to help out. Yes, an antenna analyzer will help out. If you are on a budget you can get one that just covers HF.
VHF/UHF coverage gets expensive.

Zak W1VT
ARRL Senior Lab Engineer

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