How to build a UHF antenna... - Page 164 - AVS Forum | Home Theater Discussions And Reviews
Baselworld is only a few weeks away. Getting the latest news is easy, Click Here for info on how to join the Watchuseek.com newsletter list. Follow our team for updates featuring event coverage, new product unveilings, watch industry news & more!



Forum Jump: 
 7Likes
Reply
 
Thread Tools
post #4891 of 4909 Old 02-25-2016, 08:48 PM
Member
 
Kenp51's Avatar
 
Join Date: Jan 2016
Location: Modesto, Ca
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 0
I bet a 5" raindrop would really flatten ya!

I had sat tv once. Rain and especially snow whacked the heck out of reception. Just for fyi, what frequency range is sta tv in?

Ken

"As for Me and My House, We Will Serve the Lord"
Kenp51 is offline  
Sponsored Links
Advertisement
 
post #4892 of 4909 Old 02-26-2016, 12:56 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
Picture = 1000 Words:

www.propagation.gatech.edu/ECE6390/project/Fall2012/Team02/6390%20Webpage%20Updated%202/6390%20Webpage/styled/files/3.png

In N. America, OTA TV Band goes up to 0.7 GHz....and 0.8 GHz in Europe & elsewhere....

Last edited by holl_ands; 02-26-2016 at 01:01 PM.
holl_ands is offline  
post #4893 of 4909 Old 03-05-2016, 09:24 AM
Member
 
Kenp51's Avatar
 
Join Date: Jan 2016
Location: Modesto, Ca
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 0
I had a possible eureka moment while using my framing marking up some wood to cut. Marked a couple of 45 degree lines (X) to find center. It dawned on me that if the lines were conductors (phase lines) that there should not be (or at least minimal cross inductance) where the lines cross since they are right angles, exactly 180 degrees to each other.

So my question is could I have just crossed my phase lines on my FF6 (6-Bay) and not had to fuss and fight to maintain 3" separation. Just used a plastic space at the center of the X.

Am I correct about no cross inductance if at a right angle? And does that apply here? Can you just run the phase line 3" apart then cross them with an X?

Or was I just running a brain fever with this thought?

BTW, UHF reception has never dipped below 96% with this unit. And I still haven't bothered to properly aim it. Maybe I just got it right by accident. Some day when I am not so busy, I will go play with the aim and see if I can just for giggles get some remote stations. That won't be today. Have to fix my mom's electric gate. The original installers were either stoned, drunk, or had no scruples about taking advantage of an old lady. So I am the one that gets to do the job right and correct some really glaring installation issues (already fixed the worse issue). But this is a subject for elsewhere.

Ken

"As for Me and My House, We Will Serve the Lord"
Kenp51 is offline  
post #4894 of 4909 Old 03-11-2016, 04:05 PM
Member
 
Joe Pal's Avatar
 
Join Date: Mar 2010
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 11
I am planing to build another M4 antenna. What effect, if any, would a bowtie with the end twisted as shown in the photo have. Would I have to compensate in the overall length?
Attached Thumbnails
Click image for larger version

Name:	Twisted bowtie.jpg
Views:	63
Size:	78.8 KB
ID:	1308153  
Joe Pal is offline  
post #4895 of 4909 Old 03-11-2016, 05:22 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
For modeling purposes, Whisker Length is measured from the INTERSECTION of the Feedline with the Whisker....so measure from the middle of the eyelet, ALONG the Whisker to the tip if it happens to be bent, ignoring all of the extra "capacitive loading". And "don't sweat the small stuff"...and 1/4-in error only moves Gain or SWR numbers by about a 0.1 of a dB (or SWR)....which would be impossible to notice in the REAL world.
holl_ands is offline  
post #4896 of 4909 Old 03-11-2016, 05:29 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
Quote:
Originally Posted by Kenp51 View Post
I had a possible eureka moment while using my framing marking up some wood to cut. Marked a couple of 45 degree lines (X) to find center. It dawned on me that if the lines were conductors (phase lines) that there should not be (or at least minimal cross inductance) where the lines cross since they are right angles, exactly 180 degrees to each other.

So my question is could I have just crossed my phase lines on my FF6 (6-Bay) and not had to fuss and fight to maintain 3" separation. Just used a plastic space at the center of the X.

Am I correct about no cross inductance if at a right angle? And does that apply here? Can you just run the phase line 3" apart then cross them with an X?

Or was I just running a brain fever with this thought?

BTW, UHF reception has never dipped below 96% with this unit. And I still haven't bothered to properly aim it. Maybe I just got it right by accident. Some day when I am not so busy, I will go play with the aim and see if I can just for giggles get some remote stations. That won't be today. Have to fix my mom's electric gate. The original installers were either stoned, drunk, or had no scruples about taking advantage of an old lady. So I am the one that gets to do the job right and correct some really glaring installation issues (already fixed the worse issue). But this is a subject for elsewhere.
I have NO CLUE what you are talking about...and esp. don't know what "3-inches" refers to. In my FF6, the Feedline Crossovers between each Pair of Bowties are NOT half-way between them...indeed there is quite a bit of difference. You need to very carefully follow the detailed plan, including the Crossover OFFSET Dimensions...it DOES make a difference in FF6, just as it makes a difference in the FF4. If you make ANY deviations from what the OPTIMIZER found, there is no telling how BAD it can get....
holl_ands is offline  
post #4897 of 4909 Old 03-11-2016, 06:26 PM
Member
 
Joe Pal's Avatar
 
Join Date: Mar 2010
Posts: 16
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 11
Quote:
Originally Posted by holl_ands View Post
For modeling purposes, Whisker Length is measured from the INTERSECTION of the Feedline with the Whisker....so measure from the middle of the eyelet, ALONG the Whisker to the tip if it happens to be bent, ignoring all of the extra "capacitive loading". And "don't sweat the small stuff"...and 1/4-in error only moves Gain or SWR numbers by about a 0.1 of a dB (or SWR)....which would be impossible to notice in the REAL world.
Thank you Holl_ands
Joe Pal is offline  
post #4898 of 4909 Old 03-11-2016, 09:12 PM
Member
 
Kenp51's Avatar
 
Join Date: Jan 2016
Location: Modesto, Ca
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 0
When I made my FF6 I also made a spacer gauge to keep the lines the same distance apart not only along the straight parallel sections but thru the twist where they crossed each other.
Was just wondering if that effort was needed. The drawings of f the FF6 are obviously 2 dimensional. But I kept the phase line spacing the same thru 3 dimensions. That is why I made the little spacing gauge.

Can the phasee lines simply cross each other (at 90 degrees) with just a small gap between them.

Ken

"As for Me and My House, We Will Serve the Lord"
Kenp51 is offline  
post #4899 of 4909 Old 03-12-2016, 02:21 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
I can actually ANSWER that specific question. OPTIMIZED Antennas are JUST THAT....if you elect to CHANGE anything, it's likely you will DEGRADE performance in one way or another.

I ran 4nec2's Parametric SWEEP [under START OPTIMZER tab] on my FF6 VDAR 4nec2 model, varying the Separation between the Feedlines at each Crossover, where I had ASSUMED Hop = 1.0-in (based on lots of experience) and the subsequent Optimization operated within this specific Constraint. As the below charts clearly indicate, increasing or decreasing this value DEGRADES performance, where I've elected to show only Gain and SWR at 698 MHz. It also clearly shows the "Don't Sweat the Small Stuff" mantra....a 1/4-in Change was nearly undetectable in the MODEL Results....and would be impossible to detect in OTA Reception:

BTW: In order to show them here, I had to add them to the FF6+VDAR Analysis Webpage:
http://imageevent.com/holl_ands/mult...6baybowtievdar




Last edited by holl_ands; 03-12-2016 at 02:29 PM.
holl_ands is offline  
post #4900 of 4909 Old 05-29-2016, 03:39 PM
Member
 
aeromojito's Avatar
 
Join Date: Mar 2011
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 10
alternative reflectors

I have built a 4-bay bowtie with 10 X 9.5 elements based off the Super M4. It does work but reception is about the same as my old antenna and it doesn't receive CH13, my only VHF. I can't get any fence material for a few days but wanted to try a reflector. I have 5 4ft. mop handles, which is what the main support is made of. I also wonder if I could use some individual strands from CAT5 network cable on a frame. Either way, what has to be electrically connected for a reflector to work? This is only temporary
aeromojito is offline  
post #4901 of 4909 Old 05-29-2016, 05:18 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
HORIZONTAL wires and the Spacing between them (1 to 2-in is best) are the only ones that are MOST important....optional Vertical Wires (whether just on outsides....or every 2 to 4-inches) also have an effect but it is secondary....and just to keep things interesting, Optimum Width for Grid is DIFFERENT than individual Reflector Rods....as I investigated using M4 4-Bay. If it's temporary, perhaps you might want to try covering some Cardboard with Aluminum Foil until you locate the stipulated materials...it will be closest to performance with a Double Angled Screen Grid Reflector....which is about 1 dB improvement over a typical FLAT Reflector with FLAT Bowties:
http://imageevent.com/holl_ands/multibay/4bayrefl

I have concerns re using "individual wires" from CAT-5 Cable. At UHF Frequencies, wire insulation can degrade performance, esp. on the higher channels. So you would need to use BARE WIRES....which would be a bit TOO SMALL [Model presumes AWG12 or larger wire size]. I have also used 1/4-in O.D. RG-58 and RG-59 Coax where the WOVEN SHIELD WIRES act as the Antenna Elements (Mylar Foil types, like RG-6 usually do NOT use woven Shield Wires and hence are NOT suitable). At UHF Frequencies the outer insulation needs to be stripped off but can be left on for VHF Only Antenna.

Last edited by holl_ands; 05-29-2016 at 05:48 PM.
holl_ands is offline  
post #4902 of 4909 Old 05-29-2016, 05:32 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,825
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 278 Post(s)
Liked: 90
As a minimum you would need 4 reflector rods 24 inches long, with a vertical spacing of about 2 inches, behind each of the 4 bays. That would require 16 rods; you don't have enough handles. You could straighten some wire hangers, with care. They don't have to be connected; just make them horizontal. You could also use metal plant stakes.

If you want to use wires, stretch them across a frame with 1 inch vertical spacing.

Wire fencing should be 1 x 2, with 1 inch vertical spacing of the horizontal wires.
Quote:
It does work but reception is about the same as my old antenna and it doesn't receive CH13, my only VHF.
Your UHF 4-bay antenna will not work very well for real CH13.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 05-29-2016 at 05:49 PM.
rabbit73 is offline  
post #4903 of 4909 Old 06-03-2016, 09:11 PM
Member
 
aeromojito's Avatar
 
Join Date: Mar 2011
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 10
Finally got a reflector. It's a 48 x 36 inch piece of 1x2 fence. I had limited time before the rain so I put the whole piece on there. There is an improvement but mostly on the lower UHF channels and VHF. Here are my UHF channels using RTLSDR Scanner. I have also found that any antenna works better a few feet lower than this one. Can someone show me a way to mount one of these anywhere on the mast instead of at the top?
Attached Thumbnails
Click image for larger version

Name:	uhf w reflector.jpg
Views:	30
Size:	216.1 KB
ID:	1476873  
aeromojito is offline  
post #4904 of 4909 Old 06-04-2016, 07:24 PM
AVS Special Member
 
rabbit73's Avatar
 
Join Date: Apr 2008
Location: S.E. VA
Posts: 1,825
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 278 Post(s)
Liked: 90
rabbit73 is offline  
post #4905 of 4909 Old 06-05-2016, 04:24 AM
Member
 
aeromojito's Avatar
 
Join Date: Mar 2011
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 10
Thanks. I've looked at this a few times and never realized that kit mounted the reflector to the antenna and the mast. I used some old phone cord for now and it seems to be working. I'll probably benefit from a curved or angled reflector and maybe shorter whiskers for the weak high channels.
aeromojito is offline  
post #4906 of 4909 Old 06-14-2016, 10:22 AM
Member
 
aeromojito's Avatar
 
Join Date: Mar 2011
Posts: 19
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 10
I need help optimizing my M4 10 x 9.5 for my weak channels. I rechecked and my elements are 10 1/8 to 10 1/4 inches long because I never trimmed them. Should I trim them to 10 or 9 3/4? My trouble channels are UHF 41 and VHF 13. VHF 13 is not as weak but I know the design is not for VHF. How much difference does a curved reflector make?
aeromojito is offline  
post #4907 of 4909 Old 06-14-2016, 12:25 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
SINGLE CHANNEL (Ch22) 9-ELEMENT FOLDED DIPOLE YAGI:

I just uploaded 4nec2 Analysis for the subject Antenna, Optimized for 8 MHz Bandwidth (to ensure no problems on the band edges...esp. if ReScaled to higher channel) centered on Ch22 [518-524 MHz]. Note that nikiml's EVAL [listed in summary below] calculates somewhat higher F/B & F/R Ratios than 4nec2 Chart. Note that nikiml's EVAL function [for Horizontally Polarized signals, listed in summary below] calculates somewhat higher F/B & F/R Ratios than 4nec2 Chart [for TOTAL Gain = Horizontal + Vertical Gains].

Ch22 9-El FD-Yagi - 300ohm OPTimized:

Ch22 Raw Gain = 12.9 to 13.1 dBi, F/B & F/R Ratio Min. = 34.3 dB and SWR (300-ohms) Under 1.5.
Also note the F/B Ratio NULL directly to the Rear (which you might have to STEER toward severe Interference).
Forward Sidelobes are fairly good, being suppressed about xx dB on 521 MHz.
Note that there is a Deep NULL in the Elevation Pattern, which could be used to advantage to suppress Ground Bounce using an Antenna Tilter to aim the Antenna somewhat UPWARDS.
BOOM LENGTH = 1045-mm, and is UNCONSTRAINED.

BTW: Gain for Ch22 9-El FD-Yagi Optimized for 75-ohm was not quite as Good.

CORRECTION (14Jun2016 at 6pm PDT]: Replaced this morning's version with correct version.


TOP VIEW [1 large square = 125-mm]:






AZIMUTHAL PLOT:


ELEVATION PLOT:

Last edited by holl_ands; 06-16-2016 at 08:55 AM.
holl_ands is offline  
post #4908 of 4909 Old 06-14-2016, 12:46 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
SINGLE CHANNEL (Ch22) 9-ELEMENT FLAT-LOOP-FED (FLF) YAGI:

I just uploaded 4nec2 Analysis for the subject Antenna, Optimized for 8 MHz Bandwidth (to ensure no problems on the band edges...esp. if ReScaled to higher channel) centered on Ch22 [518-524 MHz]. See Dr. Hidetsugu Yagi holding an example: https://www.jpo.go.jp/seido_e/rekish...tsugu_yagi.htm
Dimensions were determined using nikiml's Python Optimization Scripts. Similar to Folded Dipole, except rotated (with SOURCE towards REAR) so Co-Planar with rest of Yagi. ALL X,Y,Z Dimensions Optimized. Note that nikiml's EVAL function [for Horizontally Polarized signals, listed in summary below] calculates somewhat higher F/B & F/R Ratios than 4nec2 Chart [for TOTAL Gain = Horizontal + Vertical Gains].

Ch22 9-El FLF-Yagi [Flat-Loop-Fed] - 300ohm OPTimized:
Ch22 Raw Gain = 13.2 to 13.4 dBi, F/B & F/R Ratio Min. = 40.2 dB and SWR (300-ohms) Under 1.7.
Forward Sidelobes are quite good, being suppressed about 22 dB on 521 MHz.
Note that there is a Deep NULL in the Elevation Pattern, which could be used to advantage to suppress Ground Bounce using an Antenna Tilter to aim the Antenna somewhat UPWARDS.
BOOM LENGTH = 1019-mm, and is UNCONSTRAINED.

A Yagi has about the SAME Gain whether driven by a Stick Dipole or a conventional Folded Dipole (see K6STI 5-El Yagi Analysis):
http://photos.imageevent.com/holl_an...dFD%20Gain.jpg

HOWEVER, when the additional Element in the Flat-Loop-Fed Yagi is rotated to be Co-Planar, it becomes ONE MORE ELEMENT that can add Gain to the Traveling Wave Signal....it ALSO makes the Yagi LONGER, which we've learned also indicates MORE GAIN....so perhaps we should call this a 10-El Yagi, where the second and third Elements happen to be interconnected at their extremities, forming a Loop.

Note that Flat-Loop-Fed (FLF) Yagi's date back as "PRIOR ART" at least as early as 1940's. Justin Johnson (G0KSC) has (FWIW) Copyrighted some "similar" Loop Fed Array (LFA) Yagis, designed to have a VERY LOW IMPEDANCE [under 50-ohms], but until he has an approved PATENT, it's up in the air as to WHAT UNIQUE FEATURE(S) make it an LFA. More info on this subject: http://www.hamradio.me/antennas/loop...-yagi-uda.html

BTW: This Random Optimization Search found Circumference = 51.1-cm [wavelength = 586 MHz] which is NOT one-wavelength at 512 MHz CM [57.58-cm] or anywhere else in the desired 518-524 MHz Band.




TOP VIEW [1 large square = 125-mm]:







AZIMUTHAL PLOT:


ELEVATION PLOT:

Last edited by holl_ands; 06-16-2016 at 08:54 AM.
holl_ands is offline  
post #4909 of 4909 Old 06-14-2016, 06:12 PM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 4,589
Mentioned: 4 Post(s)
Tagged: 1 Thread(s)
Quoted: 312 Post(s)
Liked: 148
SINGLE CHANNEL (Ch22) 9-ELEMENT 75-OHM FD-YAGI, per MTM SCIENTIFIC DIMENSIONS:

I also analyzed a 9-El FD-Yagi using Dimensions found in an MTM Scientific Article. Unfortunately (like K7MEM Designs), it was NOT OPTIMIZED and was a very poor Design for Ch22 with Excessive SWR:
Crescent City, CA: Building a Yagi for Ch 22
holl_ands is offline  
Sponsored Links
Advertisement
 
Reply HDTV Technical

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off