Hello,
Is the freq range of 156 to 163 MHz (receive only) too much to probably
consider a yagi for ?
That's less than 5% width, so it's probably reasonable. Yagi antenna
design involves a bunch of tradeoffs - Yagis which are optimized for
the highest gain at a specific frequency (or for the greatest
front-to-back ratio) may tend to be more narrow-band than a Yagi of
similar boom length which has a somewhat lower gain or F/B ratio.
There have been some interesting developments over the past few years
with OWB (optimized wide-band) Yagis... I gather that it's now
possible to put together a Yagi which can cover the whole 144-148 MHz
spectrum (and beyond) with very decent performance over the full range.
Yagi behavior tends to deteriorate more rapidly at the upper end of
the frequency range, if I recall correctly, so you'd probably want a
Yagi which is optimized for somewhere around 162 MHz.
If so, any suggestions for type(s) that have intrinsic Gain ?
Can, and probably should be, be very directional.
Log-periodic antennas are known for having a wide SWR bandwidth, and
decent gain and directional characteristics. Depending on the number,
spacing, and taper schedule, it's not difficult to cover a frequency
range of 3:1 with decent gain and with an SWR of no worse than 2:1.
Log-periodics are often used as TV/FM antennas, precisely because this
application requires decent directionality and a wide frequency
coverage.
It's possible that a commercial TV/FM antenna might do the trick for
you. A full-sized VHF-TV-plus-FM antenna would work from 45-88 MHz
(VHF TV low-band), 88-109 or so (FM), and 174-216 MHz (VHF TV
high-band). It's not uncommon for such antennas to use the longer
elements in two modes - they resonate on their fundamental frequencies
for VHF low-band, and on their third harmonic for VHF high-band. If
you see a TV antennas whose longest elements are "swept forward" (with
their tips aimed at an angle in the direction that the antenna is
pointing) then it's likely that the antenna is using this particular
trick.
If so, then there's a fairly good chance that it would cover the
marine-band frequencies as well, since those also fall within the
range of the third harmonic of the VHF low-band frequencies.
So - you could buy yourself a VHF TV antenna, log-periodic type, which
has swept-forward elements, and just rotate it into a vertical
orientation (i.e. mount it sideways on the mast, held out some
distance from the mast so that the mast doesn't de-tune it).
--
Dave Platt AE6EO
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