How to build a UHF antenna... - Page 58 - AVS Forum
Forum Jump: 
 1Likes
Reply
 
Thread Tools
post #1711 of 4829 Old 02-16-2009, 07:30 PM
AVS Special Member
 
IDRick's Avatar
 
Join Date: Feb 2006
Location: Eastern Idaho
Posts: 1,033
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 24
Thanks mclapp! Always appreciate your great advice. Your comments earlier this winter were very instrumental in improving my second build.

Just for the record, I should have stated how I attached the whiskers and phase lines in this post: http://www.avsforum.com/avs-vb/showt...3#post15834673

I used 1 inch tall nylon spacers (1/2 inch diameter). On top of the spacer, there is a "sandwich" with two nylon washers and the whisker/phase line junction in the middle. I soldered the whiskers and phase line junction before attaching the top washer. I also used a spacer to ensure that I had a 1" phase line spacing throughout the crossover.\\

In the original build, a sandwich was also used with the whisker/phase line junction located between two large metal washers. No solder was used in the first build.
IDRick is offline  
Sponsored Links
Advertisement
 
post #1712 of 4829 Old 02-16-2009, 07:41 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


that's a signal discarding device.

I like that. I think I could build one of dem signal discarding devices, heh.

Quote:


with Delaware's average height above sea level being about 11 feet you may want to reconsider your position on global warming

Hmm, gimbal mount my antenna mast on a boat, maybe.
300ohm is offline  
post #1713 of 4829 Old 02-16-2009, 07:49 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


On the other hand, the 300 ohm commercial open wire I have is spaced a little further. Ill post the dimensions tomorrow.



Its exactly .55 inches center of 18ga wire to center of 18ga wire. The plastic spacers are 1/4" in diameter by 7/8" long, spaced every 6 inches. The wire looks like it was melted into the plastic.

Extrapolating from the data, it looks like it should be about 385 ohms. Hmm, there is nothing on the cardboard spool that says it 300 ohms. Just a catalog no. C-3-100-6. Maybe Lafayette Radio screwed me.
300ohm is offline  
post #1714 of 4829 Old 02-16-2009, 08:02 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


Sorry if this legitimate restraint in faith was misunderstood.

OK, no problem. It wasnt meant for you personally, but just in general.

Suprisingly, even when I have exceeded the limits, like on my foldable GH design where I used 1 inch wide aluminum elements, the actual field testing of the build produced results very close to the model.
300ohm is offline  
post #1715 of 4829 Old 02-17-2009, 08:07 AM
Senior Member
 
MikeySoft's Avatar
 
Join Date: May 2008
Location: about 21 miles from Boston's TV antennas
Posts: 213
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Last summer I build the maclapp and gave a report at http://www.avsforum.com/avs-vb/showt...php?p=14299317 I did not use a reflector because I needed bi-directions.

My mclapp is in the attic and was a somewhat sloppy build. No standoffs, no separation with the phase line crossover, and oversize washers. I planned to build a better one but it looks like I don't have to.

Today, digital RF 57 changed to RF 11. Before I would sometimes have problems with digital RF 57 and usually just watch analog 11 when I wanted to watch that station. Today digital RF 11 is a lot stronger then when they were on RF 57 according to the signal strength meter and I no longer have problems with breakups.

Digital RF 42 will be changing to RF 7 when they switch. I expect no problems because analog 7 is presently very strong and clear.


Photos of the antenna and my tvfool plots are on the original post.
MikeySoft is offline  
post #1716 of 4829 Old 02-17-2009, 08:29 AM
AVS Special Member
 
IDRick's Avatar
 
Join Date: Feb 2006
Location: Eastern Idaho
Posts: 1,033
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 24
Great news for you Mikesoft! I think the main problem on my original build was the too wide separation between phase lines. The oversized washers become even more of an issue in my circumstance. Plus I maybe further away from the towers than you. My NM from tvfool were mid to low 50's for most channels and 41 for the ch 31.
IDRick is offline  
post #1717 of 4829 Old 02-17-2009, 09:49 AM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
OK. 300 ohm, I stripped down all of that wire, (all 84 feet) and do not know whether this stuff is even copper. It has more of a "brassy" looking color, similiar to a goldish color, rather than copper. The neighbor friend who used to do a lot of electrical work, back in the hey-day says it's what they used to call "copper-brass." He says it was popular during the war, due to copper shortages, in homes built in that era. He claims it's just as good as copper, has all of the same properties, conductivity, and is actually a blend alloy of 50 % copper, with tin, aluminum and zinc added. I don't know if he's pulling my leg or what. Either way, unsure exactly what it is, But I'm still planning on using it.

Interesting spool of wire, there. It gives me kind of a better idea now.- Little pieces of plastic about every foot or so. Hmmmm.

Still unsure what the poster meant regarding, "signal discarding device," regarding the home-made balun. Nybbler, would you care to elaborate on that? I'm trying to understand why/why not fabricate your own balun, and if my idea will work. It seems unreasonable that it would not work. If there is a reason, or something you know that you haven't included as to why replacing the hair-fine wires with thicker wires would work, then please state your reason and explain.

Incidentally, 300 ohm: Regarding my DBGH. VHF high stations worked ok, but were still not all that hot. I also seem to recall you mentioning adding 4 pieces of metal above and below each bay. Cannot recall your exact dimensions, or what it was exactly that you recommended, but if there's any promise in that for improving VHF high, I'd like to try that. UIn doing that, does it also compromise any of the UHF ?

Many thanks, in advance.

Regards,
Eric
nepaeric is offline  
post #1718 of 4829 Old 02-17-2009, 11:44 AM
Advanced Member
 
johnpost's Avatar
 
Join Date: Mar 2008
Posts: 783
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
wire for power, single or in a cable assembly, will likely have some brown copper oxide on its surface, the various amounts of that will give it a various range of color. depends on its age and production conditions and insulation.

power wire is an alloy, it is not pure copper.
johnpost is offline  
post #1719 of 4829 Old 02-17-2009, 12:33 PM
Advanced Member
 
Join Date: Jun 2007
Location: Good Ole' Copper Fan
Posts: 773
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 146 Post(s)
Liked: 61
Quote:
Originally Posted by nepaeric View Post


Still unsure what the poster meant regarding, "signal discarding device," regarding the home-made balun.

nepaeric
Take one of your discarded Balun, dissect it with a Dremel or hammer
Snap a picture or two in Macro and share your findings. Making a small home-made-mess in the pursuit of understanding seems logical.

OR

Admire the ingenuity of:
Martin E. Meserve Feed Setup for use with 75 Ohm Coax
Woobieizer is offline  
post #1720 of 4829 Old 02-17-2009, 03:59 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


Incidentally, 300 ohm: Regarding my DBGH. VHF high stations worked ok, but were still not all that hot. I also seem to recall you mentioning adding 4 pieces of metal above and below each bay. Cannot recall your exact dimensions, or what it was exactly that you recommended, but if there's any promise in that for improving VHF high, I'd like to try that. UIn doing that, does it also compromise any of the UHF ?

You can follow my many posts on it here : http://www.digitalhome.ca/forum/showthread.php?t=99907


Its still a work in progress.

Quote:


Still unsure what the poster meant regarding, "signal discarding device,"

A lot of people end up building "signal discarding devices", heh.
300ohm is offline  
post #1721 of 4829 Old 02-17-2009, 04:07 PM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Thanks, Woobieizer, for your reply. Unfortunately, I have tried, in the past, to post photos here, to no avail. It's a glitch within my computer I haven't figured out yet. I have e-mailed some of my antenna photos to a couple of guys here, who contacted me by P.M, but none of them have posted these yet. Anyway, simply put, the balun has tiny wires that are as fine as a hair which are broken, and you'd need a microscope to see the break. Soldering those baluns would be an even bigger challenge and probably a waste of time.

On the brighter side of things, I was able to locate an old matching transformer balun labeled, "SMK," "Made in Japan," as 300 ohm suggested, and WOW! What a difference since installing that! (Found it at the Salvation Army, as part of a video game for $3.) I will now use this balun for all testing to get consistant and fair results when comparing my Mclapp antennas. I also have 10 Channel master baluns on order. (I did not take the Japan balun apart for inspection, but must surmise it is beefier than the Chinese ones I've been using.) I also assume I'll obtain better results with the CM balun, as well.

I did finally finish my vertical stacked 8-bay, and felt, based on my initial impressions, that it performed well, but about as good as it's 4-bay equivalent by comparison. Paid particuarly close attention to length and even, equal distribution with balun connection. I was more impressed with the results of the DBGH on the high UHF side and still want to modify this to get those VHF high channels better. I can't remember what exactly was the recommendation, but I recall an element installed above and below each bay to make the GH respond to VHF.

Also, thus far, I am beginning to believe things to be a toss-up between the 8-1/2" x 8" and the 9" x 8-1/2" reflectorless Mclapps to be the best comprimise of all sizes built. They may give away a little on the VHF channels over the 9-1/2" x 9", but appear to substantially improve the upper UHF channels. I will form more accurate opinions and results with time, now that I have solved a balun issue, which may have skewed my initial results.

I am currently using the Philips/Magnavox baluns on all the other antennas, but for test purposes, I will only use the Japan one, until the CM's come.

Best Regards,
Eric
nepaeric is offline  
post #1722 of 4829 Old 02-17-2009, 04:07 PM
Member
 
wmbjr's Avatar
 
Join Date: Aug 2007
Posts: 89
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I have a mclapps 10 X 9.5 antenna up in my attic. I received all channels fine, including real channel 8 but 8 was weak. I added the reflector (1X1 screen) to the antenna. I am now having some trouble with real channel 41. 8 comes in good as does 48 and 31, but 41 is having trouble. Could the reflector have caused the trouble with 41? Or is it more likely that it was weak before and I just did not notice it? It is a pain to get in and out of the attic other wise I would just remove the reflector and see what happens, but thought there might be an answer here. Thanks.
wmbjr is offline  
post #1723 of 4829 Old 02-17-2009, 04:18 PM
Senior Member
 
MikeySoft's Avatar
 
Join Date: May 2008
Location: about 21 miles from Boston's TV antennas
Posts: 213
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by wmbjr View Post

I have a mclapps 10 X 9.5 antenna up in my attic.....

Could you post your tvfool.com plot and maybe a photo of your antenna?
MikeySoft is offline  
post #1724 of 4829 Old 02-17-2009, 04:48 PM
Member
 
wmbjr's Avatar
 
Join Date: Aug 2007
Posts: 89
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by MikeySoft View Post

Could you post your tvfool.com plot and maybe a photo of your antenna?

Attached is the tvfool plot. I will have to wait until tomorrow to do a picture of the antenna itself because it is already dark here and it is in the attic and not easily or quickly accessible. It is based off the PVC version mclapps provided schematics for quite a few pages back.
LL
wmbjr is offline  
post #1725 of 4829 Old 02-17-2009, 04:56 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


On the brighter side of things, I was able to locate an old matching transformer balun labeled, "SMK," "Made in Japan," as 300 ohm suggested, and WOW! What a difference since installing that!

Ah so, heh. Yeah, I believe the video game makers had a keen interest in providing some of the best baluns for their systems. Of course, they are designed for indoor use, so youll need to weather proof it yourself. Pure silicon sealant is one way.
300ohm is offline  
post #1726 of 4829 Old 02-17-2009, 05:10 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


8 comes in good as does 48 and 31, but 41 is having trouble. Could the reflector have caused the trouble with 41?

Hmm, try repositioning the antenna. Attics can cause havoc with reception.
300ohm is offline  
post #1727 of 4829 Old 02-17-2009, 05:24 PM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Pure 100% silicone rubber sealant (GE silicone II) is what I used, and that's exactly what I did with the balun for outdoor use.

I checked that GH thread out, and from what I gather, these "NARODS" used for VHF reception are merely a 10 guage piece of straight wire about 28" long mounted 1/2" above the upper stubs and below the lower stubs on each bay.-(4- 28" sections, in all for a DBGH) Would that be correct? Also, If need be, one could use any tubular metal or wire up to 3/8" in diameter?

Thanks a lot for your help. Can't wait to get this DBGH VHF ready and hooked up with some 14 guage 300 ohm ultra-low loss!

Best Regards,
Eric
nepaeric is offline  
post #1728 of 4829 Old 02-17-2009, 05:43 PM
Advanced Member
 
Join Date: Jun 2007
Location: Good Ole' Copper Fan
Posts: 773
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 146 Post(s)
Liked: 61
Ok.. so I either will have a "Face Palm" moment tomorrow, or jump off the roof LMAO.. but here she is..


Balun from almost nothing


PS nepaeric: good thing you purchased 10 CM.. makes it hurt less on the shipping.
Woobieizer is offline  
post #1729 of 4829 Old 02-17-2009, 05:54 PM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Yeah, I guess, why pay shipping on just one balun, so in light of the problems I had, why not get extras, with the shipping cost.

I can't figure out what it is you posted in the photo, Woobieizer. Is that a homemade balun, and if so, how did you make it?

Eric
nepaeric is offline  
post #1730 of 4829 Old 02-17-2009, 06:03 PM
Advanced Member
 
Join Date: Jun 2007
Location: Good Ole' Copper Fan
Posts: 773
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 146 Post(s)
Liked: 61
Quote:
Originally Posted by nepaeric View Post

I can't figure out what it is you posted in the photo, Woobieizer. Is that a homemade balun, and if so, how did you make it?
Eric

It is either a home made balun or a signal discarding device.. background image is from:
Martin E. Meserve Feed Setup for use with 75 Ohm Coax

If it works.. I will tell all ..lol

Edit noticed that the URL is parsed..(you may copy paste, as I sourced his Web page title) two exceptional web pages that describe, visualize, and promote antenna construction, and balun. Detailed enough to satisfy the engineers, yet presented with the DIY "wannabees" (like me) in mind.

http://rtr.ca/yagi_antennas/index.cgi?z0205655+large

Martin E. Meserve - K7MEM - VHF/UHF Yagi Antenna Feed Design
Building custom yagis for UHF/VHF television reception
Woobieizer is offline  
post #1731 of 4829 Old 02-17-2009, 06:18 PM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


checked that GH thread out, and from what I gather, these "NARODS" used for VHF reception are merely a 10 guage piece of straight wire about 28" long mounted 1/2" above the upper stubs and below the lower stubs on each bay.-(4- 28" sections, in all for a DBGH) Would that be correct? Also, If need be, one could use any tubular metal or wire up to 3/8" in diameter?

Keep in mind, there are different lengths for different ranges of VHF-Hi channels. Its very easy to flip the gain direction using the wrong range. Yeah, up to 3/8" would be fine. Just keep it 1/2" center of wire to center of wire.
300ohm is offline  
post #1732 of 4829 Old 02-17-2009, 10:48 PM
Member
 
RONNIE KD5YTE's Avatar
 
Join Date: Jan 2009
Location: Collins Mississippi
Posts: 85
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Been reading all posts and some are looking for good wire to build with my favorite is 6mm power line wrapping wire its aluminum , and to get it straight I pull it with a engine crain about 6 or 8 feet at a time it will stay straight till I cut it up also built a bending jig
for the whiskers ,the reflector is aluminum stucco mesh with 1x1 openings can be found at most bigger hardware stores
RONNIE KD5YTE is offline  
post #1733 of 4829 Old 02-18-2009, 07:27 AM
Member
 
Johnrmckee's Avatar
 
Join Date: Aug 2008
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Here is insertion loss data I measured on a Philips outdoor 300 to 75 Ohm matching transformer. I purchased two of these at a local Lowes Hardware store.

I measured two transformers connected back to back (300 Ohms to 300 Ohms) with an Agilent E5071B network analyzer along with two HP 50 to 75 Ohm minimum loss matching pads.

I set up the analyzer using a segmented sweep covering only the VHF LOW TV and FM broadcast bands, VHF HIGH TV band, and the post transistion UHF DTV band.

After calibration with the analyzer's 50 Ohm autocal box, I connected the matching pads and performed a thru cal on the analyzer to remove the cable/connector/adapter/matching pad losses and set my reference line to zero.

The S21 (forward gain/loss) trace data was saved as a .csv file and imported into Excel. I divided the total loss by two to give me insertion loss for a single transformer.

Hope this is useful. I would like to measure several different brands of transformer to see if there's any significant difference between them.

 

BALUN TRANSFORMER LOSS.pdf 76.3515625k . file
Attached Files
File Type: pdf BALUN TRANSFORMER LOSS.pdf (76.4 KB, 41 views)
Johnrmckee is offline  
post #1734 of 4829 Old 02-18-2009, 08:03 AM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Woobieizer, I'm anxiously awaiting the results of your balun build, to see how it works out. Keep us posted, and please don't jump off the roof!

I still don't understand why some don't think my homemade balun idea will work, as no one has indicated thier reasons. Since I haven't heard any reasons why, I will likely attempt this to see what it does on one of my antennas.

300 ohm, would the 28" length "NAROD" be the proper size for VHF hi channels 11 and 13? Also, in your experience, do these modifications enchance or hinder UHF performance in any way? Please also keep in mind, I am using my DBGH reflectorless?

Mclapp, I am interested in knowing how my findings are in keeping with what modeling says for the 4-bays. Also, my reflectorless 8-bay vertical stacked 9-1/2" x 9" performed about the same as the reflectorlesss 4-bay equivalent. Further tests also demonstrated, in my situation, at my location, that reflector 4-bays only provided a modest gain above the same reflectorless ones, but became more directional. On balance, the loss on stations behind it was greater than the gains in front of it. Was wondering your thoughts on all that, and also if it would be worth my while to bother rebuilding this 8-bay into a side by side stacked, instead, or if I would likely experience similiar findings as the vertical stacked.

Many thanks to everyone's continued support here.

Sincerely,
Eric
nepaeric is offline  
post #1735 of 4829 Old 02-18-2009, 08:08 AM
Member
 
nepaeric's Avatar
 
Join Date: Dec 2008
Location: Scranton/Wilkes-Barre area, Northeastern Pennsylvania
Posts: 150
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Johnrmckee, interesting read. My Philips/Magnavox baluns, purchased at Lowe's, Home Depot, and Walmart have proven themselves to be inconsistant. One was garbage brand new, another failed after a few weeks, and the other three are working fine, but for how long.- Who knows. Based on my experiences, I'm not optimistic or encouraged.

Regards,
Eric
nepaeric is offline  
post #1736 of 4829 Old 02-18-2009, 08:25 AM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


Been reading all posts and some are looking for good wire to build with my favorite is 6mm power line wrapping wire its aluminum , and to get it straight I pull it with a engine crain about 6 or 8 feet at a time it will stay straight till I cut it up also built a bending jig
for the whiskers ,the reflector is aluminum stucco mesh with 1x1 openings can be found at most bigger hardware stores

Yeah, that wire would be great to use, and cheaper than copper, except none of my electrical supply houses around here dont carry it anymore.
You can also straighten it by putting one end in a vice and the other end in vice grips and then hitting the vice grips hard with a hammer or small sledge. 6 gauge takes a little more muscle than the thinner stuff.

Aluminum stucco mesh is also hard to find around here. Most Ive seen is galvanized or plated steel and the wires are bent on an angle to catch and hold the cement.
300ohm is offline  
post #1737 of 4829 Old 02-18-2009, 08:35 AM
AVS Special Member
 
300ohm's Avatar
 
Join Date: May 2008
Location: Somewhere in Delaware
Posts: 1,823
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:


300 ohm, would the 28" length "NAROD" be the proper size for VHF hi channels 11 and 13? Also, in your experience, do these modifications enchance or hinder UHF performance in any way? Please also keep in mind, I am using my DBGH reflectorless?

Yep 28.0 inches for the NAROD and NAROD reflector. 10.0 inches between the NAROD and NAROD reflector.

It puts a 1 db or so dip in the uhf gain curve at around 623 mhz. Im still trying to figure out how to get rid of the dip. I too will probably be building two reflectorless DBGHs, one with the NAROD and NAROD reflector, one without. The dip occurs in the wrong spot for me, so I have to figure it out, heh.

Quote:


One was garbage brand new

Nah, it was just mislabeled on the package. It should have been sold as a commercial signal discarding device.
300ohm is offline  
post #1738 of 4829 Old 02-18-2009, 08:49 AM
Advanced Member
 
mclapp's Avatar
 
Join Date: Apr 2008
Location: Delaware Co. ,NY
Posts: 717
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by nepaeric View Post

Mclapp, I am interested in knowing how my findings are in keeping with what modeling says for the 4-bays. Also, my reflectorless 8-bay vertical stacked 9-1/2" x 9" performed about the same as the reflectorlesss 4-bay equivalent.

In general the best you can expect to see is about 2-3 db sometimes less than 2 because of mismatch losses at certain frequencies. A best it's about the same as adding a reflector to a 4 bay.

How did you connect the (2) 4 bays together?
Quote:


Further tests also demonstrated, in my situation, at my location, that reflector 4-bays only provided a modest gain above the same reflectorless ones, but became more directional. On balance, the loss on stations behind it was greater than the gains in front of it. Was wondering your thoughts on all that, and also if it would be worth my while to bother rebuilding this 8-bay into a side by side stacked, instead, or if I would likely experience similiar findings as the vertical stacked.

The rejection of the stations behind the reflector should be 10-20db depending on the reflector material but the forward gain will only be 2-4db so I would say what you observed would be consistent with this.

A side by side stacked 8 bay will not have any more peak gain than a vertical stack but the signal pattern will be changed a lot, the beam width will be much narrower and somewhat taller. There is a lot more to receiving radio/tv signals than just flat out gain, the beam width and take off angle are big factors in reception.

Simply put max gain needs to be at the right elevation and azimuth angle for your signals.

Probably the horizontal stack won't work any better for you than the vertical stack but with your terrain who knows. The horizontal stack works better for multi-path problems or if your signals are coming in from a slightly higher angle.
mclapp is offline  
post #1739 of 4829 Old 02-18-2009, 09:21 AM
Advanced Member
 
nybbler's Avatar
 
Join Date: Sep 2006
Posts: 697
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by nepaeric View Post

Still unsure what the poster meant regarding, "signal discarding device," regarding the home-made balun.

The 300-to-75 ohm devices used for TV antennas do two things

1) Handle the impedance mismatch between the 75-ohm coax and the 300-ohm antenna.

2) Prevent the coax from acting as part of the antenna.

The device you described, a piece of 75-ohm wire attached to the 300-ohm terminals with short pieces of wire, does neither of those. So a significant portion of the signal will be reflected by your device, and never make it into the coax. Additionally, the coax will act as part of the antenna, rendering the shielding ineffective and distorting the antenna pattern.
nybbler is offline  
post #1740 of 4829 Old 02-18-2009, 09:46 AM
Member
 
alphanguy's Avatar
 
Join Date: Mar 2008
Posts: 175
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I think after much research, my best for what I want is to try and make a high gain, cut channel yagi for channel 17. I used an online antenna designer, and for a gain of 16Db, which is what I'd need... the antenna needs to be 179" long. It just so happens that I have a 180" boom from an old antenna in great condition... so it seems like it's a matter of cutting my elements to the proper lengths and proper spacing, right? I'm going to be using 3/8 inch hollow aluminum (old elements) in the designer program, for element diameter, I type in .375 inches, so that should be right? My question, is can I use the old active element from my existing antenna? And exactly where should it go? (the program didn't tell me that). and suggestions for attaching the hollow elements to the boom so theyr'e secure, without crushing or splitting them?
alphanguy is offline  
Reply HDTV Technical

User Tag List

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