Which VHF-Hi ONLY antenna or other solution? - Page 4 - Canadian TV, Computing and Home Theatre Forums

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post #46 of 361 (permalink) Old 2010-09-23, 08:02 AM
 
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any thoughts on efficiently joining a vhf-low antenna to a vhf-hi/uhf combo antenna ?
An HLSJ from either Holland Electronics or Pico-Macom. Both are very efficient devices.
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post #47 of 361 (permalink) Old 2010-09-24, 01:13 AM
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Thanks, I do remember those.

I was thinking more in line with twin lead lead joining. I recall some formulas for twin lead lengths for the hi - low join.

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post #48 of 361 (permalink) Old 2010-09-25, 03:08 PM
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When dis-similar antennas are joined by simply twisting the twin-lead wires together, the
resultant impedance is anybody's guess. On any given channel, the fairly low SWR presented
by the "correct" antenna can be easily destroyed by an extremely low or reactive impedance
presented by the "other" antenna.

Since there are no frequency filters on either antenna, it is also possible for the "other"
antenna to destructively interfere with the "correct" antenna if the signal strengths are
fairly close....which may or may not be a problem, depending on both Gain curves.
The "other" antenna is also injecting more received noise into the system....

HLSJ Diplexer has low loss bandpass and band reject filters to prevent the above problem.
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post #49 of 361 (permalink) Old 2010-10-01, 01:41 PM
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How well would your Loop Reflector work in combination with an Antenna Craft U8000?

I have the U8000 sitting at the top of a 10' mast segment.
The loop reflector would mount on the same mast, under the U8000.
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post #50 of 361 (permalink) Old 2010-10-03, 09:03 PM
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Shouldn't be a problem as long as you mount it about half-way up the mast to keep it
as far away as possible from the U8000 and the roof below. You'll have to figure a way
to mount it to the mast so that it is isolated (no metal-to-metal contact).....
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post #51 of 361 (permalink) Old 2010-10-03, 11:24 PM
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Yeah, for vhf hi you would really want it away from the mast about 6 inches or so at least.

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post #52 of 361 (permalink) Old 2010-10-06, 04:32 PM
 
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No disrespect intended, but I'm not sure I see a conclusion here as to what antenna design is best for VHF-HI. I'm guessing it's a yagi, but that's just a guess. Maybe a big reflector-less bowtie?
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post #53 of 361 (permalink) Old 2010-10-06, 06:48 PM Thread Starter
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my initial post was misleading, the fact is i needed the most directional, high gain, channel #13 antenna, preferably compact....

but yes i have to agree, looks like nothing will beat a single channel yagi given the above!
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post #54 of 361 (permalink) Old 2010-10-06, 07:16 PM
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Originally Posted by byebye_cable View Post
No disrespect intended, but I'm not sure I see a conclusion here as to what antenna design is best for VHF-HI. I'm guessing it's a yagi, but that's just a guess.
I haven't seen many Yagi VHF antenna designs, except for single channel cut ones. Log periodic designs are more common (they are often mistaken to be "Yagi" antennas).

For maximum gain, I would recommend a large log periodic model.

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post #55 of 361 (permalink) Old 2010-10-06, 10:02 PM
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It is impossible to declare any particular Hi-VHF antenna "best" without knowing the "criteria":
1) Most Gain (or F/B) DIY irrespective of size (do you have room for a 20-element Yagi or Log-Yagi???),
2) Most Gain (or F/B) in a commercial antenna for a "typical" attic installation (100-inch boom Log-Yagi???)
3) Most Gain (or F/B) DIY for a given H, W and/or D (e.g. even smaller, such as K6STI's 5-Element Yagi):
http://www.imageevent.com/holl_ands/yagis
4) Easiest (and/or least expensive) DIY with High Gain (perhaps Zig-Zag Log Periodic or LPDA).
5) Easiest (and/or least expensive) DIY with Moderate Gain (2-Bay or Circular Loop, with or w/o a Reflector).
6) Least expensive commercial antenna with Moderate Gain (perhaps Antennacraft 60-in boom Y5-7-13)
7) Compact commercial antenna with Moderate Gain (perhaps A-D C5).

Very few Yagi designs provide good Gain, SWR and F/B Ratio across the ENTIRE Hi-VHF Band,
with the exception of K6STI's 5-Element Yagi (7.5-9.5 dBi Gain). Commercial Log-Yagi's, such as
W-G YA-1713 (100-in) and Antennacraft Y10-7-13 (120-in) provide about 10 dBi Gain and so-so
F/B Ratio....or about the same as a 100-inch long Zig-Zag Log Periodic Wedge or a DIY LPDA with
a 100-inch Boom length constraint.

A Hi-VHF antenna with more than 10 dBi of Gain will likely NOT cover the ENTIRE band and might
only cover a single channel, such as the following Ch7 12-Element Yagi, which is 4.7-meters long:
http://imageevent.com/holl_ands/yagis/12elyagi
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post #56 of 361 (permalink) Old 2010-10-07, 08:24 AM Thread Starter
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It is impossible to declare any particular Hi-VHF antenna "best" without knowing the "criteria":

agreed, but this thread allowed for a rather concise summary and useful breakdown of the various options, thank you
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post #57 of 361 (permalink) Old 2010-10-07, 08:45 AM
 
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Holl ands, I'd just say max gain within reasonable constraints on size, outdoor, F/B not significant, both DIY and commercial.

A major component of my job is "dumbing down" complex technical issues for non-technical people so I can get their agreement on how to move forward. I suppose I view the conclusion of this thread in the same light.
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post #58 of 361 (permalink) Old 2010-10-07, 09:15 AM
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I'd just say max gain within reasonable constraints on size, outdoor,
Max gain is not always what you want. Generally, the higher the antenna gain, the narrower the beamwidth. Beamwidth can be very important. Say you have two transmitting towers 35 degrees apart. A high gain antenna will probably only catch one well without a rotor. A lower gain antenna may do both well without a rotor.
TVFool data and the FCC coverage charts provide a wealth of info to determine what you need. The FCC coverage charts assume 4 db for vhf-low and 6 db for vhf-hi. Outside of the FCC coverage area, youre heading into DXing area.

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post #59 of 361 (permalink) Old 2010-10-07, 10:52 AM
 
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Agreed, max gain on the assumption the antenna would be pointed right at the tower. Those VHF bowties on Holl_ands site look enticing, not to prejudice any conclusion I suppose those could easily be tuned to a specific frequency?
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post #60 of 361 (permalink) Old 2010-10-07, 12:28 PM
 
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Again, that's not always the desired outcome. I can think of many areas in the DC/Baltimore metro that would need broader beamwidth to catch the VHFs from both markets. Your solution would work for me, since the two markets are nearly on the same azimuth from my location.

However, I have VHF DX opportunities 180 degress from Baltimore, so that implies yet a different solution. A table of options is probably the best outcome for this thread.
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