6M HO LOOP TUNING DETAIL
For base station installations, objects such as towers, large diameter masts, trees, roofs or buildings
near the HO Loop can cause some detuning. Be aware that some tuning of the HO Loop or HO Loops
in their final position or under similar conditions may be necessary. For mobile installations, tune the
HO Loop in its final position on your vehicle.
When tuning multiple HO Loops in a stacked array, tune each HO Loop individually and recheck them in
their final positions. After individual tuning and testing, add the phasing lines and power dividers and re-
test the complete system one final time, making fine adjustments as needed.
Note:
Be sure to reverse one feed block to account for the 180° phase shift in the 6M HO Loop 2
Port Power Divider. See “Mounting and Stacking Options” for more information.
BASIC TUNING
Be sure the feed block assembly is set to the starting dimension in figure 4. This dimension controls the
FREQUENCY. Likewise, ensure the shorting bar is set to the starting dimension provided. The short-
ing bar position controls feed point IMPEDANCE, and also has a small effect on frequency.
Tune the frequency first by adjusting the feed block assembly. Increasing the dimension will lower the
HO Loop in frequency; decreasing it will raise the frequency. Once the HO Loop is at the desired fre-
quency, make small adjustments to the shorting bar for best match. After tuning is complete attach the
support tube as shown and tighten all hardware.
REMEMBER: HORIZONTALLY POLARIZED ANTENNAS ARE AFFECTED BY THE GROUND SO
THE HIGHER YOU GET YOUR
HO LOOP,
THE BETTER.
The ground can be your friend as well,
providing as much as 6 dB additional ground gain at some angles above the horizon. That angle is de-
fined by the frequency and height above ground. At one wavelength (236” at 6 meters), the typical an-
gle of maximum radiation will be about 14 degrees. At two wavelengths, the angle is 7 degrees and at
four wavelengths the angle is 3.5 degrees. Net gain improves with height because the pattern hits the
ground at a shallower angle, giving up less energy to the ground.
In most mobile installations 10 to 11 feet is about the practical limit for most driving conditions. The HO
Loop can be tuned to work as low as 18" above a vehicle roof with some compromise in performance.
However, you will find more people to talk to and more DX if you can get the HO Loop up to at least the
10 foot level.
POWER CONSIDERATIONS
An HO Loop can handle up to 800 watts and a stacked pair can handle up 1.5 kW. Users often report
long distance QSO’s using HO Loops and modest power. We hope you enjoy your new
HO Loop
and
please keep an ear out for those rare but wonderful 6 meter openings to other parts of the world!
M
2
ANTENNA SYSTEMS, INC.
4402 N. SELLAND AVE.
FRESNO, CA 93722
(559) 432-8873 FAX: 432-3059
www.m2inc.com Email: [email protected]
