Category: Projects

Full-wave loops are very popular antennas. They are especially useful on 80 and 40 meters where they perform well at modest heights. These are closed loops that are one full wavelength long. Horizontal loops may be fed at any convenient spot. For best performance, make your horizontal loop into a square, especially if it is to be used on several bands. The Vertical Loop is a good DX antenna. The shape can be a circle, square, rectangle or a triangle. The larger the area of the loop the better it will work. Feed square and rectangular loops at a corner. For best results, triangular loops should be supported apex-down. This puts less of the antenna parallel with the ground and increased the effective height. Feed triangular loops either at a corner or in the case of apex-down loop, at the apex. Use ladder line and a wideband transmatch (a naturally balanced tuner, like a Johnson Matchbox) for multiband operation. The RemoteBalun 4 is recommended if you will have problem getting ladder line to the operation position. Multiband operation is possible when feeding the loop with coax. The losses will be slightly higher, but the convenience of the coax may be worth the slight signal loss. The designfrequency, the feedpoint impedance, will be between 80 and 150 ohms. Coax fed loops will usually have an SWR between 2:1 and 3:1. You may feed this antenna with a 4:1 balun. If the loop is in the shape of square or large rectangle, the SWR can be below 2:1, but will not get much below 1.5:1. If you decide to feed your loop with coax, I’d suggest using RG-8X or RG-213 and a high power, high performance 1:1 or 4:1 Current-type balun. Experiment with full-wave loops. You may find them to be excellent multiband antennas. Antenna wire can be #14 hard-drawn antenna wire. Use #12 wire for large loops on 160 or 80 meters.

Center Frequency Total Length in feet
3.5 MHz 287
3.6 279
3.7 272
3.8 264
3.9 258
7.0 MHz 143
7.2 139
Center Frequency Total Length in feet
10.12 MHz 99
14.0 MHz 72
14.2 70
18.12 MHz 55′ 6″
21.0 MHz 48′ 10″
21.2 47′ 6″
24.93 MHz 40′ 4″
Center Frequency Total Length in feet
28.0 MHz 35′ 10″
28.5 35′ 3″
29.0 34′ 8″
29.5 34′ 1″


With this particular antenna, a RemoteBalun and Ladder Line are used to permit multiband operation. If you have a naturally balanced tuner (i.e. a Johnson Matchbox), the RemoteBalun 4 is not needed. Click on the Balun Index do check out the the RemoteBalun’s application notes.


Icom appears to delight in charging outrageous prices for all transceiver accessories, so many Hams improvise instead. A few circuits have been published for CI-V interfaces, most of which use the MAX232 IC.  Here is a very simple CI-V interface, originally described by OK2WY.  I’ve made small changes to the modem control signals connections. Although the circuit doesn’t conform exactly to the RS-232 specification, it does work well and has the advantage of being easily constructed inside a 9 pin D-type shell. Please note that the resistor value 4K7 means 4700 ohms.  The transistor types are not critical, I just happen to have plenty of 2N2222As.I’ve used this interface on various PC’s and also Dell Latitude Notebooks with both an IC735 and IC706MkIIG. No problems have been experienced even at 19200 baud with the IC706. It has also worked successfully when using a USB/Serial adapter from a notebook.  If a PTT function is required from the COM port, pin 7 (RTS) can be used to provide this facility.The circuit is powered by DTR (pin4).  I experienced some problems with YPLog using this power source. If YPLog is configured to use PTT from either the Parallel port or a different serial port from the one used by the CI-V Interface, the program drops the DTR signal, resulting in no power to the interface.   This is easily resolved by powering the circuit from RTS (pin 7) instead of DTR (pin4). To test and/or debug the interface, I would strongly recommend using AA6YQ’s CI-V Commander program.

Although I have successfully used the interface with a serial-USB adapter, I have seen

USB CI-V cables from China at very cheap prices on eBay. Consequently, it’s hardly worth

the effort of using the alternative.

Disclaimer: Although I have tested and used the above circuit on my own IC735 and

IC706mkIIG with no problems, I do not make any representation or guarantee that this

circuit will function, nor do I accept any responsibility whatsoever for any damage or

malfunction arising from the use of this circuit.

Here are some links to software for use with CI-V controlled Icom rigs:
CI-V Test by DF4OR - Freeware program to test CI-V bus
CI-V Commander by AA6YQ - Freeware program to control Icom rigs and monitor CI-V bus
RadioComm by KE7ZZ - Careware program to control and load memories of Icom rigs
YPLOG by VE6YP - Shareware Icom Rig control and logging program
Ham Radio Deluxe by HB9DRV - Bloatware Icom control program

ICOM CI-V interface to RS232 using transistors, fits in DB9 case

pro: No external power needed.
pro: Very small, fits in DB9 connector case (with SMD components)
con: Requires standard compliant serial port, may not work on all notebooks.

Alexander from Russia writes:

Concernig scematic for CI-V adapter. I drew down it from real pcb so I specified part value for readable components only. They all are smd.
C1 – ceramic (looks strange but it’s true),
R5 – at least 0.5W
Q1 and Q2 I guess can be any switch transistors.
I checked this adapter with CI-V Explorer software, everything’s ok.

Tune Your Metal Tubing Slim Jim to Perfection!

If you are reading this you most likely have built the Slim Jim antenna for the 2 meter band using either copper or aluminum tubing. After your final tuning, you may not have seen that “perfect” swr reading of 1:1 that many look for and could not get any lower to reach “perfection”. View full article »

The 4 Element Hentenna Beam for 2 Meters

by N5NNS


Having been a ham for 27 years and knowing that the most important part of any station is the antenna, I have built, designed, and redesigned antennas for over two decades. View full article »