Loop antennas may be constructed in many forms including horizontal full wave loops in square, rectangle or triangle (delta) shapes. They can also be in the vertical plane and are most often in the same shapes with the delta being very popular as it has both vertical and horizontal polarization. The impedance at the loop resonant frequency is approximately 100 ohms but will very slightly on harmonics. Loops are “quiet” antennas compared to verticals and dipoles and are omni-directional. The also exhibit gain on harmonic bands. Once you try a loop antenna you will know why they are so popular with old timers but still a secret to newcomers. Shown below are some typical designs:
Full Wave Horizontal Loop Antenna (a.k.a Skyloop)
This antenna is horizontally polarized and should be mounted as high as possible but works well at low heights of 10-30 feet. They are quieter than a dipole or a vertical, have a broader bandwidth and will usually out perform a dipole antenna.To determine the approximate circumference in feet of a full wave loop antenna use the formula:
1005/Freq in Mhz = length in feet.
The feed point impedance of a full wave loop antenna is theoretically in the vicinity of 120 ohms and requires a 2:1 impedance transformer (for single band loops or a 4:1 balun to match on multiple bands) with 50 ohm line. You will also need a feed line choke or better yet, just get the Hybrid 4:1+1:1 in a single box.
Vertical Delta Loops
Vertical delta loops can be oriented several way but the most popular is to have the “pointy” end at the top (usually a single support) and the lower horizontal ends just out of reach of humans and animals. Best feed point is 1/4 wavelength (246/f(mhz)) from the top point down one side. Vertical delta loops use the same 2:1 baluns as the horizontal loops or 4:1 for multi-band operation.
Palomar Engineers RFI Filter Kit for VHF/UHF Base Radio Transceivers up to 2 GHz uses a combination of ferrite mixes useful from 1-2000 MHz.
BUY THIS KIT NOW TO SOLVE YOUR RFI/EMI NEEDS! WORKS WITH MANY BRANDS OF HAM/COMMERCIAL RADIO RIGS
Purpose
The RFI kit is designed to be installed on your radio transceiver to reduce Radio Frequency Interference (RFI) caused by common mode current on the outside of the coax braid at the output of your radio. Additional chokes are included to reduce common mode currents on the amp relay keying line (7 pin Din), rear audio in/out for digital modes (13 pin Din), computer control line (DB-9) and the DC power cord.
This kit will help reduce or eliminate:
1. “Hot mic” RFI caused by poor grounding of antennas or common mode currents from linear amps feeding unbalanced (coax fed) antennas without baluns/line isolators.
2. RFI to neighbor’s electronic devices including audio/video systems, computers, telephones, garage door openers, etc.
3. RFI to your other radios, audio/video systems, computers, telephones, etc.
A side benefit is a reduction in noise floor in your receiver depending on the amount of noise being introduced by common mode currents (which are blocked/reduced by the chokes in this kit).
These chokes use a special mix of ferrite core material that is effective in suppressing radio frequency interference from Ham Radio amplifiers.
The split beads beads are easy to use, don’t require modification of the protected equipment and work in almost all cases, even when plug-in filters fail.
This kit is designed to choke common mode currents going into or exiting from your transceiver. Chokes are supplied for the RF Out (1 antenna only), Amp Relay Cable (7 pin DIN), Computer Control Cable (DB-9), PSK31/Digital Mode Cable (13 pin Din) and DC power line. Use of the chokes often helps cure SWR problems between transceiver and a linear amp and between transceiver and antenna tuner or direct to antenna. The DC power line choke helps keep common mode current out of the power line which could cause interference to other devices connected to the same power line if not suppressed.
Included are the following chokes and installation guidelines:
RF Input: F240 Ring Toroid for noise reduction – 3-5 turns of RG-58/RG-8X size coax cable through center
DC Input: F240 Ring Toroid – 3-7 turns of DC power cable
I/O Cable 1: FSB-1/2 – multiple turns through choke – ½” diameter hole
I/O Cable 2: FSB-1/2 – multiple turns through choke – ½” diameter hole
I/O Cable 3: FSB-1/2 – multiple turns through choke – ½” diameter hole
Also make sure you connect a good RF ground to the transceiver ground post.
For additional RFI suppression, use a feed line choke at the antenna to suppress common current on the coax feed line – see our store for feed line choke alternatives for use at the antenna.
If you use a linear amplifier we have RFI kits for linear amplifiers that help suppress RFI in your shack or in your neighbor’s house.