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Building DB8

post #1 of 25
10/8/08 at 4:42pm
Thread Starter 
I have bene doing a lot of reading over the last few weeks after building a successful DB4 antenna.

The stations I am trying to pull in are 54-59 miles from my house. the antenna is placed ona first story roof for now but will be mast mounted after I build the finished product. (~25' elevation. Will eventually have to add a lower VHF on their as well)

My problem is, I added a second DB4 like the channel master antenna does in "side by side" mode. I picked up a diplexer from home depot... oops its for sateliette and antenna. Returned it and purchased an antenna diplexer at radio hut, oops it seperated VHF and UHF.

So I tried a regualr splitter, of course, no love.

With proper atmospheric conditions, I can pull in all channels perfectly. But when I couldn't. (Like on a nice warm day) I was started looking at signal strength and realized that the diplexer and the splitter both led to 0% increase in signal strength.



From my reading I see that vertically aligned antennas offer good gain in a narrow beam. Which is fine for me, as all the stations I want are in one location.

So if I build a DB8 on a single 2x4. Would I cross only the top and bottom bays to reduce phasing? Or would I have 4 sets of "crossover" conductors like in the side by side antennas? Also should the "crossover" go in the same direction on both top and bottom?

I also read that reflectors are not recommended for fringe/near-fringe reception, but it seems I only get one local digital station if I do not use a reflector. Anyone else have this experience?


(Oh. antenna web says I should not get any channels. tvfool says I should get them all with a decent antenna. Highest was -70db gain.)

Have not added an amp/filter to the line yet, as currently using only a 10' linedrop until I get a suitable signal. Then will pick up a decent amp for the 100' line drop to run the signal to the living room.

Thanks


EDIT: Should point out this is the "coat hanger" DIY antenna found on lumenlabs. I posted over there, but its a pretty dead forum.
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post #2 of 25
10/8/08 at 5:50pm
You may want to look at the How to Build a UHF antenna thread http://www.avsforum.com/avs-vb/showthread.php?t=798265
Side by side will make the beam narrower and more directive, vertically stacked will squeeze the beam width vertically.

Either way you do it both antennas must be fed with the exact length of feed line and be in phase (no x over). When using 2 baluns and a combiner (2 way splitter in reverse) the baluns have to be the exact same and connected in phase. If you were to attach a proper reflector to your db4 clone you would probably gain more than stacking 2 non reflector db4's, of course 2 properly stacked db4 clones with a reflector is even better. Depending on your terrain a properly built 4 bay style antenna with a reflector should get you 50 mi. + range.
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post #3 of 25
10/9/08 at 11:22am
Thread Starter 
Hey thanks for the advice and the quick reply. A LOT of the links in that post are dead or redirected. But enough were good that I got even more reading done. I think if I did not have a short 15 week class in electronics warfare my head would have fallen off instead of just be spinning.

The only difference between the two antennas I built was the reflectors. I watched all whisker lengths, conductors, used same screw sizes and washers, and identical baluns. I ran out of large pieces of cardboard so that is why there is a differnce between the reflectors. This was trying to be done as cheaply as possible, hence why I have not purchased a CM7777 yet either. I will if it works... but can not see buying one until then. (Oh even the wood was the same type.. not that it matters of course)


50+ mile is good I am aiming for a little more so that only in truly foul weather does the signal become too degraded.



So


Vertically aligned DB4s will be good yes?

Reading that I need to connect them with 300 ohm twin lead wire, which looking back is the spaced wires you have coming off the antenna, leads me to wonder...

I seem to recall them being ~1/2" apart. Is this why most of the Online DIY guides suggest the V's being mounted 1/2" apart? the commercially built ones look like they have a lot of room between them though. And 1/2" apart leads to either using washers too small to hold a wire as thick as a coat hanger... or using larger washers, then they are touching. (or is 1/2" space needed between washers, meaning 1" seperation between mount points?).

Off of that... Is there an alternative to having to purchase 300 twin lead wire? for instance... standard speakers wire. Or if the 1/2" rule applies.. can I take each conducter and tape it either side of a nonconductor that is 1/2" thick?


Thanks for helping out a seriously confused, overthinking moron.
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post #4 of 25
10/9/08 at 5:27pm
Quote:
Originally Posted by nettronic View Post

The only difference between the two antennas I built was the reflectors. I watched all whisker lengths, conductors, used same screw sizes and washers, and identical baluns. I ran out of large pieces of cardboard so that is why there is a differnce between the reflectors.

What length whiskers did you use and what is the vertical spacing between them? What reflector spacing did you use and what actual channel #'s are you trying to get?
Quote:
50+ mile is good I am aiming for a little more so that only in truly foul weather does the signal become too degraded.

A properly tuned 4 bay should do that no problem over flat ground.

Quote:
Vertically aligned DB4s will be good yes?

Either vertical or horizontal stacked will be fine it's just a matter the reception pattern.
Quote:
Reading that I need to connect them with 300 ohm twin lead wire, which looking back is the spaced wires you have coming off the antenna, leads me to wonder


I seem to recall them being ~1/2" apart. Is this why most of the Online DIY guides suggest the V's being mounted 1/2" apart? the commercially built ones look like they have a lot of room between them though. And 1/2" apart leads to either using washers too small to hold a wire as thick as a coat hanger... or using larger washers, then they are touching. (or is 1/2" space needed between washers, meaning 1" seperation between mount points?).

Off of that... Is there an alternative to having to purchase 300 twin lead wire? for instance... standard speakers wire. Or if the 1/2" rule applies.. can I take each conducter and tape it either side of a nonconductor that is 1/2" thick?...

300 ohm twinlead would be good to connect the 2 together, I'd stay away from speaker wire it's too flimsy to keep properly spaced apart among other things. Bare single conductor #10 to #14 wire spaced 1 to 1 1/2" would work well for connecting two 4 bays.

All the 4 bays I have built use 1 1/4" or wider spacing between V's like the commercial ones do. I've also found that it's best to keep contact between any of the wires and other objects to a minimum.

I did some testing with a spectrum analyzer and found that a 4 bay antenna mounted on a dry wood frame with a 1" contact area at each mounting point was about 1-2 db less that the exact same wires mounted on a PVC frame with a 3/8" contact area. 2 db is about all the gain increase you can expect from stacking two 4 bays.

Here is the link to the post on the test results, I've also posted many more results from other tests later in that thread and some dimension diagrams and pictures of some of the antennas tested earlier in that thread.

http://www.avsforum.com/avs-vb/showt...7#post14714047

I would suggest getting one 4 bay optimised for the channels you need first and if that's not enough then worry about stacking 2 together.
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post #5 of 25
10/9/08 at 8:27pm
Thread Starter 
Thanks for the info.

The wood is only temporary, I was thinking of building a nice aluminum mast one when finished with testing. Using some type of non conductive block. (I figured wood is not long lasting, and PVC too flimsy for the shore) Not sure about what to use to paint the whole thing with later. (Need to protect it from salt air and also to try and match the house)

Specs are

7" Bowties. (14" bent in V) 3 inches between whisker points.

7" vertical spacing

Crossover conductors are slightly longer then the others (7")


Channels desired

Now

26 32 42 54 64 67


Post transition

6 17 26 32 34 42

(will deal with needing one VHF station later)

EDIT: Trying to read that long thread now.

EDIT EDIT: Looking at 26-42 as the "average" range I need. Hopefully not too much drop off at 64 and 67 now.. I really do not see why so many people suggest 7" whiskers. That puts the average at over channel 60 somewhere?

(I guess I assumed the conductors and balun had some type of synthetic aperature effect on the antenna to pull in lower frequencies then it was designed for)

Will calculate dimensions for channel 34 and build anew from there.
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post #6 of 25
10/10/08 at 12:57pm
Quote:
Originally Posted by nettronic View Post

Thanks for the info.

The wood is only temporary, I was thinking of building a nice aluminum mast one when finished with testing. Using some type of non conductive block. (I figured wood is not long lasting, and PVC too flimsy for the shore) Not sure about what to use to paint the whole thing with later. (Need to protect it from salt air and also to try and match the house)

You could make a wood -PVC hybrid for test purposes just attach PVC pieces as stand off blocks to the wood.

Quote:


Specs are

7" Bowties. (14" bent in V) 3 inches between whisker points.

7" vertical spacing

Crossover conductors are slightly longer then the others (7")


Channels desired

Now

26 32 42 54 64 67


Post transition

6 17 26 32 34 42

(will deal with needing one VHF station later)

If you are going to rebuild you my want to consider building a Gray-Hoverman style antenna. They are much easier and more foregiving to build than a bowtie antenna and the gain is almost a toss up on UHF. Just google gray-hoverman and you'll find all sorts of stuff on how to build them. If you are sticking with the bowtie style then take a good look at the chart I linked to in the last posting and you will see how different size bowtie antennas perform at different frequencies. I computer modeled those antennas and built them from those specs. and the chart shows the actual gain curves not simulated.


Quote:


EDIT: Trying to read that long thread now.

EDIT EDIT: Looking at 26-42 as the "average" range I need. Hopefully not too much drop off at 64 and 67 now.. I really do not see why so many people suggest 7" whiskers. That puts the average at over channel 60 somewhere?

(I guess I assumed the conductors and balun had some type of synthetic aperature effect on the antenna to pull in lower frequencies then it was designed for)

Will calculate dimensions for channel 34 and build anew from there.

9 or 9 1/2" would be where you want to be post transisition but if the channels in the 60's are your hardest to get and you want them now you may have to go with 8". Bowtie antennas fall off very fast in gain above thier peak compared to below so you have to build to the high side of center to get full coverage or cheat towards your weakest or most desired channel.

Here is a picture of a 9 3/4" x 9 1/2" 4 bay I built using custom made plastic spacers mounted to a piece of EMT and uses 2"x4" wire fence as a reflector.


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post #7 of 25
10/13/08 at 4:32pm
Thread Starter 
Thanks for all the help mclapp. It is all good now

Stuck with the 7" design since because two of the stations I need for now are in the high 60's.



With 25' coax line, autoscan pulls in 21 analog and 15 digital channels

Moved to 100' linedrop to put TV downstairs, RG-59 (will be replaced with rg6 and also going to get an amp, so thats the next research project) I lost NBC but all other channels are still working perfectly! Amazing


I built myself a quick bending rig to make the crossover lines. Works perfectly. (put 4 screws in a piece of wood. shapped wire.. hammered the center to make it curve up (or down) and then trim to size.) I also got frustrated with the wires trying to shoot out from under the washers when I cranked down on them. So I ran to the dollar store and grabbed a box of spade connectors. Trimmed the lines cramped them on nad much faster assembly time.

Found some unused aluminum screen windows that I can use for a reflector but Am going to work on permanently mounting hte antenna to the roof right there first

I would like to meet the people that can build one of these in 15 minutes. This took me about 4 hours today and I did not have to make the elements just reshape them and resand them.

Going to get the painting done on friday. Mount two small pieces of 2x4 to the side of the porch roof there. A couple of wedges to that... then the antenna to the wedges.. (this will keep it pointed at philly). Would love to mount it against the wall of the house but not really sure how to mount to asbestos shingling.

Mounting it here




One last question. I had to resand all of the coat hangers today, because of oxidation. Is it safe to paint everything? I would hate to just try out painting it and losing half of the TV signals and having to start over with new components


Thanks again

Rich
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post #8 of 25
10/13/08 at 5:15pm
Everything you would possibly want to know and then some:

http://www.digitalhome.ca/forum/showthread.php?t=85987
http://www.digitalhome.ca/forum/showthread.php?t=81982
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post #9 of 25
10/13/08 at 6:24pm
Thread Starter 
Thanks.

There is already a super long thread that I could not read all of here on avs, about uhf antennas, with what appears to be a few of the same people posting at both forums


I answered my painting question with a quick google search and I surmised correctly that a thin coating of non conductive/capicative paint should be just fine.

Will hit the hardware store on thursday to try and match the house paint and do a refinishing to remove ever last trace of oxidation before I paint.


Time to start the next project I guess, fixing up the HTPC with an ATSC tuner and figuring out the best 10' ui for it (just using VMC now)

EDIT: Will update this thread when I get around to building a "final" one in february with a PVC mast and longer whiskers. I see the grayhooverman type tossed around alot as easier to build but I had access to clothes hangers, I do not have access to 3 foot long malleable conductors, short of purchasing some 12 gauge solid core from the HW store.
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post #10 of 25
10/13/08 at 8:32pm
Quote:
Originally Posted by nettronic View Post

Thanks for all the help mclapp. It is all good now

Stuck with the 7" design since because two of the stations I need for now are in the high 60's.

for the high sixties 7" is fine

Quote:


I built myself a quick bending rig to make the crossover lines. Works perfectly. (put 4 screws in a piece of wood. shapped wire.. hammered the center to make it curve up (or down) and then trim to size.) I also got frustrated with the wires trying to shoot out from under the washers when I cranked down on them. So I ran to the dollar store and grabbed a box of spade connectors. Trimmed the lines cramped them on nad much faster assembly time.

The x overs are important it's worth the time to do them right.

Quote:


Found some unused aluminum screen windows that I can use for a reflector but Am going to work on permanently mounting hte antenna to the roof right there first

Window screen has a lot of wind resistance keep your eyes open for some scrap 2x4 wire fence
Quote:


I would like to meet the people that can build one of these in 15 minutes. This took me about 4 hours today and I did not have to make the elements just reshape them and resand them.

I've also heard of alot of people that said they don't work could be the same ones

One last thing I noticed that you attached the balun in the middle of the antenna. That is fine but if you do that you need put an x over in every line except the one that the balun is hooked to which means you need to add 2 more x overs, 1 in the lower half and 1 in the upper half.

The best way to connect those 2 antennas is to connect a line from the center of the lower one (where you would normally connect the balun on a single antenna) to the center of the upper one and then attach the balun to the center of that line (a coat hanger probably wouldn't be long enough). If you have any twin lead (300 ohm) you could run equal lengths from each upper and lower half to a common point and attach your balun to that.
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post #11 of 25
12/30/08 at 1:39pm
Thread Starter 
Been w hile since I updated this LOL

Mounted a couple of short pieces of 2x4 to the side of the porch eave. Then a couple of cedar wedges to try and get hte right angle on the mast to point towards Philly.

Probably should have spent more time on that part, since I am about 10-15 degrees off :S (Would have been more accurate, but holding a 8' 2x4 up with one hand while driving 16 penny nails with the other at the top of a flimsy aluminum ladder was not my idea of a good time and I just wanted done with it)

Anywho, I painted the whole thing, and attached the Aluminum screen I mentioned, and it blew off in a week LOL

Since I got a PA-18 for Christmas I am out to rebuild this thing properly, using a pipe for a mast (to make adjusting angle easier) and this time, im not going to mess around with coat hangers but going to "splurge" and pick up some solid core wire (and make sure to get enough so that I can ground the mast as well.

Have not decided if I am going PVC or aluminum mast yet, whichever is cheaper I will probably do. Will make a base for the mast to rest on where it is mounted now with some pipe strap loops to hold it against the house, while I fine tune the angle. Then a couple of long coarse thread screws through the mast into the 2x4 pieces I already have mounted to keep the antenna from spinning should keep it ready to rock and roll.

Will see if I can pick up any twin lead 300 ohm wire locally for cheap, or I will just make more cross over points.. as you mentioned mclapp.

Meanwhile I just have to get my AIW HD to work on my 790GX motherboard and then my super HTPC will be complete!


Oh one last question.

I am going to wire up the PA18 in the attic (I have some old school 2 line wire up there I can attach to an outlet (just gotta find the right breaker first LOL) although I did detach it while it was live...

Would it be okay after the 100' line drop to run a splitter right at the TV, to run a 3' line to the HTPC and a 3' line to the TV? So we can record and watch 2 seperate channels?

The power insertion point will be 100' away.. so not sure how this will work...I just now that you do not put the power insertion between a splitter and the antenna...not sure about the other direction....
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post #12 of 25
12/30/08 at 2:14pm
Quote:
Originally Posted by nettronic View Post

Been w hile since I updated this LOL

Mounted a couple of short pieces of 2x4 to the side of the porch eave. Then a couple of cedar wedges to try and get hte right angle on the mast to point towards Philly.

Probably should have spent more time on that part, since I am about 10-15 degrees off :S (Would have been more accurate, but holding a 8' 2x4 up with one hand while driving 16 penny nails with the other at the top of a flimsy aluminum ladder was not my idea of a good time and I just wanted done with it)

Anywho, I painted the whole thing, and attached the Aluminum screen I mentioned, and it blew off in a week LOL

Since I got a PA-18 for Christmas I am out to rebuild this thing properly, using a pipe for a mast (to make adjusting angle easier) and this time, im not going to mess around with coat hangers but going to "splurge" and pick up some solid core wire (and make sure to get enough so that I can ground the mast as well.

Have not decided if I am going PVC or aluminum mast yet, whichever is cheaper I will probably do. Will make a base for the mast to rest on where it is mounted now with some pipe strap loops to hold it against the house, while I fine tune the angle. Then a couple of long coarse thread screws through the mast into the 2x4 pieces I already have mounted to keep the antenna from spinning should keep it ready to rock and roll.

Will see if I can pick up any twin lead 300 ohm wire locally for cheap, or I will just make more cross over points.. as you mentioned mclapp.

Meanwhile I just have to get my AIW HD to work on my 790GX motherboard and then my super HTPC will be complete!


Oh one last question.

I am going to wire up the PA18 in the attic (I have some old school 2 line wire up there I can attach to an outlet (just gotta find the right breaker first LOL) although I did detach it while it was live...

Would it be okay after the 100' line drop to run a splitter right at the TV, to run a 3' line to the HTPC and a 3' line to the TV? So we can record and watch 2 seperate channels?

The power insertion point will be 100' away.. so not sure how this will work...I just now that you do not put the power insertion between a splitter and the antenna...not sure about the other direction....

So you want the power adapter in the attic or behind tv#1? as long as no splitters come in between the pre-amp and power injector, you are fine, the distance between them is "not" important as far as the power is concerned, although the RF begs to differ with long runs.....
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post #13 of 25
12/30/08 at 2:17pm
Thread Starter 
I would love to have the power injector behind the TV... would make life a heck of a lot easier I figured putting it in the attic would reduce the distance to the preamp and help with noise etc.
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post #14 of 25
12/30/08 at 3:08pm
Quote:
Originally Posted by nettronic View Post

I would love to have the power injector behind the TV... would make life a heck of a lot easier I figured putting it in the attic would reduce the distance to the preamp and help with noise etc.

The distance the power travels, does not matter, worry about the rf signal. Make the runs as short as possible (without going insane) usually 50-100ft is normal, over a 100ft is a little more loss, about 3dB per 100ft for RG6 coax...
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post #15 of 25
12/30/08 at 3:15pm
Thread Starter 
Quote:
Originally Posted by gjvrieze View Post

The distance the power travels, does not matter, worry about the rf signal. Make the runs as short as possible (without going insane) usually 50-100ft is normal, over a 100ft is a little more loss, about 3dB per 100ft for RG6 coax...

Currently using RG59 (yikes!)

Will upgrade it to RG6 after all else is done... but it was why I got the preamp. Just to cover the loss in the 100' line drop. It will not actually improve the signal of the antenna right?
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post #16 of 25
1/7/09 at 9:31pm
Thread Starter 
Okay, I hit lowes picked up some 12 gauge wire for the whiskers and 2 5' antenna masts (mount one build antenna on other drop it in, align then pop in a set screw to hold it in place


mclapp

Going to try what you said about running a wire from the top antenna to the bootom and mouinting the balun to that.

I cant find any 300ohm wire locally, can I use the 12 gauge wire that I am building the rest of the antenna with to connect them? Or should I use some shielded cable?

Not really sure what makes 300ohm wire differnt then another (umm, I am guessing resistance?) lol, figured there must be something that can be used. Wondering if the rest of the antenna is not at 300 ohm, why would the lead wire need to be right? For that matter, should the material the whiskers and everything are made of be "tuned" to 300 ohm somehow?
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post #17 of 25
1/8/09 at 10:35am
Quote:
Originally Posted by nettronic View Post

Okay, I hit lowes picked up some 12 gauge wire for the whiskers and 2 5' antenna masts (mount one build antenna on other drop it in, align then pop in a set screw to hold it in place


mclapp

Going to try what you said about running a wire from the top antenna to the bootom and mouinting the balun to that.

I cant find any 300ohm wire locally, can I use the 12 gauge wire that I am building the rest of the antenna with to connect them? Or should I use some shielded cable?

You can use #12 wire is long as you keep the spacing equal through out the length. Keep it away from other objects as much as possible the same way you would with the phase lines of the antenna.

Quote:


Not really sure what makes 300ohm wire differnt then another (umm, I am guessing resistance?) lol, figured there must be something that can be used. Wondering if the rest of the antenna is not at 300 ohm, why would the lead wire need to be right? For that matter, should the material the whiskers and everything are made of be "tuned" to 300 ohm somehow?

The distance the wires are spaced apart and the size of the wires make up the ohm (impedance) value of the feeder wire.

The antenna hovers around a 300 ohm impedance so the 300 ohm twin lead would be a good match but anything close will work fine.

If you make open wire feeder line out of #12 and space it the same distance apart as the phase lines you should be in the ball park

I computer modeled a tapered open wire line for a vertical stacked antenna I'm building but with the holidays and cold weather here I haven't finished it yet.

The nice thing about the pre-made 300 ohm line is that it's already spaced properly and less prone to negative effects of the weather or near by objects like totally open wire line is.

The nice thing about making your own open wire line is you could make a tapered line which may allow you to get a better impedance match over a wider range of channels but that takes a lot of experimenting or special test equipment to get right for a very small gain.
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post #18 of 25
1/8/09 at 12:41pm
Thread Starter 
Well on a whim I stopped at Radio Shack today to see if they had 300 ohm twin lead

They did! But they do not sell it anymore.

So got a nice long roll for $1

Problem though. The spacing is not the same as my antenna, and it is 24 gauge.



Will this be okay? Or should I jsut do as you said and just make sure to keep spacing even and use the 12 gauge?


nm: stupid question. If the antenna is at 300 Ohm impedance on its design and the twin lead is at 300 Ohm impedance on its design (smaller gauge and only 1/2" spacing) then it really should be okay.

If not I make sure i get enough extra parts at the HW store tonight so that if I need to use the 12 gauge I can

Double edit:

REread the whole thread and see that this was already answered in my first couple of posts by mclapp. 300 ohm it is
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post #19 of 25
1/8/09 at 7:52pm
Thread Starter 
Almost finished with the rebuild, have all my elements and rods ready to mount. Before I do that I was going to mount the reflector (since I will not be able to flip it onto the front after whiskers are installed)


So quick question.

Got the whiskers mounted on vinyl, spaced ~2.5" off the mast (1.25" D) Going to use some 3/4" thick 20" long boards to help stablizie the reflector (and gives me 8" on each side to bend in ). Was going to sandwich the reflector between the boards and the mast.... so it is also grounded when ground the mast. For additional safety protection.

But I am not really sure if this will disrupt or complete cancel the reflective properties of the screen.

Thanks..
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post #20 of 25
1/13/09 at 3:41pm
Thread Starter 



Little weak on channel 29.1 Getting EVERYthing else just great

Got enough extra pieces (except for screen) to work on next project

Reflector should be bigger, 3x6' was more than enough for a 7" antenna, 9.5" though I am short about 3" of reflector on top and bottom. Its covered but no overlap...

The 300 ohm twin lead made a big improvement.

Have to watch the NFC championship game in Analog though unless I can tweak 29.1 in the meantime...
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post #21 of 25
1/18/09 at 1:32am
Thread Starter 
Couple more questions

I have a pa-18 installed. I am going to upgrade the drop line to RG-6 in hte next week or so (hopefully this helps with dropping 29.1 (42). I am thinking about the next build though, and also running a splitter since I have a PC in the bedroom, and another TV with digital box in another room upstairs.

I know you can not put a splitter between the power injector and the preamp..so how does one use a preamp if they are going to split the signal?

I figure I can do a 20' line to the attic, run hte splitter then 2 short cable to 2 bedrooms and one long one back down to the living room. I can get power to the attic, for the power injector, will this juice the signal enough to handle splitting it? Or will I need a powered splitter?

Also in looking at designs for a new antenna to experiment with. I will need chan.6 after the transition. I see the grey hooverman style tossed around alot, with the LONG conductor length on that help pull in the VHF band or does the design preclude that from happeneing?

Or should I just build a small antenna specificially for 6 and another for 17-50 UHF?

Thanks
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post #22 of 25
1/18/09 at 2:31am
They make splitters that will pass DC. If you use one of those, you should be able to put the injector where you like (within reason of course). Most any preamp will give you more than enough to make up for splitter loss.

300ohm has a new design mod for the standard GH that gives it some gain on upper VHF (7-13), but that wouldn't help on channel 6.

As a lark I put a 58" NAROD and NAROD reflector, with 25" reflector spacing, into his design and 4nec2 shows about 7 dBi forward gain (and 10 dBi rearward gain) on channel 6. 58" and 25" was just a random guesstimate; it could probably be optimized better. It might be worth a look.
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post #23 of 25
1/18/09 at 3:54pm
Quote:
Originally Posted by nettronic View Post

Couple more questions

I have a pa-18 installed. I am going to upgrade the drop line to RG-6 in hte next week or so (hopefully this helps with dropping 29.1 (42). I am thinking about the next build though, and also running a splitter since I have a PC in the bedroom, and another TV with digital box in another room upstairs.

I know you can not put a splitter between the power injector and the preamp..so how does one use a preamp if they are going to split the signal?

Put the power injector at the point where the coax enters the house or anywhere before you split or do as kedirekin suggested with the DC passing splitters just make sure they don't pass DC to anything other than the Preamp.

You can try some different lengths of 300 ohm wire for your problem channel, try a pair 2" longer and 6" longer. Just make sure to keep each half the same length. Also try to keep the twin lead from touching anything but where it's connected, I know it's not possible but keep it to a minimum.

If your reflector screen is a little short it's best to split it and center each half behind each 4 bay.

It's hard to tell by the picture but do you have the whiskers bent forward away from the reflector? With the forward angled reflector you should angle the whiskers forward about 2" to match. It will give you a narrower beam, more gain and may also help with that problem channel.
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post #24 of 25
1/18/09 at 4:01pm
Thread Starter 
Thanks mcclapp.

I have played around with bending them forward or leaving them flat, it apprently make 0 differnce according to my gain meter.

(I only checked problem channel though)

Now if I make twin lead not touch anything... is it okay to have it betwe4en reflector andwhiskers? I have it strapped to mast right now... but will try removing that...cant really play with this one... sincve its "in productions:


Dunno why i didnt think of spliitting the reflector.... vut really will only leave it short in the middle i think at 6'
wil lget more and play around though
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post #25 of 25
1/19/09 at 9:24am
Quote:
Originally Posted by nettronic View Post

Thanks mcclapp.

I have played around with bending them forward or leaving them flat, it apprently make 0 differnce according to my gain meter.

(I only checked problem channel though)

In computer modeling and field testing the angled reflector and forward elements show about a 2 db difference. Gain of one without the other varies depending channel. A meter on a most converter boxes or digital TV's my not even show the difference.

Quote:


Now if I make twin lead not touch anything... is it okay to have it betwe4en reflector andwhiskers? I have it strapped to mast right now... but will try removing that...cant really play with this one... sincve its "in productions:

It's ok for it to be between the whiskers and the screen, it can touch but just keep it to minimum.

Quote:


Dunno why i didnt think of spliitting the reflector.... vut really will only leave it short in the middle i think at 6'
wil lget more and play around though

Splitting it will get a more equil amount of reflector behind each set of bowties for better balance.
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