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Discussion Starter #1
I live in Bloomington IN about 60 miles from the Indianapolis stations I'm trying to receive. I just installed a CM 4228 and CM 7777. I tested on a single 10' mast before raising and seemed to be OK, though a little inconsistent. This weekend, I put the antenna about 35' in the air and can no longer get a decent signal out of Indy. A local station (WTIU) is overloading the pre-amp.


The AntennaWeb chart shows that WTIU is at 13 degrees, while Indy stations are at 19 degrees. WTIU is about 9 miles from my house.


Can I notch the two WTIU frequencies (470Mhz and 566Mhz) between the antenna and pre-amp? Will the atenuation on the pass band kill my already weak Indy stations? Who makes a good trap?


OR


Can I use the CM 4248 (stacked?) to avoid the interference? I can't seem to find beam width numbers on the 4228 and 4248, but I'm pretty sure the YAGI 4248 will give me a much more narrow beam. Of course, it also lists a 10.8 gain and 45 mile range compared to 12.0 and 60 miles for the 4228, so that could be a problem. Maybe the 6 degree seperation is too small even for a highly directional antenna?



Thanks for any help or suggestions.


Jerry
 

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Quote:
Originally Posted by jfath
Can I notch the two WTIU frequencies (470Mhz and 566Mhz) between the antenna and pre-amp? Will the atenuation on the pass band kill my already weak Indy stations? Who makes a good trap?
That's what I would probably do instead of stacking to improve directivity, given that you've only got a 9 degree seperation to work with ... I've never had the need to knock down a ATSC signal(or tune a tunable trap to do so) though, and I don't know if there is a good notch filter designed for it, or how some of the notch filters designed for NTSC would work. Then again, Knocking down WTIU 30 analog might be all you need to do.


Blonder-Tongue makes nice tunable channel traps ... They are on the expensive side, though(About $250 retail I believe for MWT-4). Here's Stark's page on them(link to their pricing sheet is available via a link from this page as well) :

http://www.starkelectronic.com/btp48.htm


I use a older verison of MWT-3 to knock down a local on 7, and I certianly like its performance. I also have a Dx'er friend using 3 MWT-4's to knock down UHF analogs 4 miles distant from him, and he likes them. With the VHF trap I'm using, as you can see from the specs at above link, it does quite a narrower bandwidth notch than the UHF version ... But, I've seen no detrimental effect on other frequencies besides what it's tuned to knock down.


If I recall correctly -- the CM7777 shouldn't pass any VHF frequencies on it's UHF input, but especially if you are going to be using a VHF antenna as well - If you are close to WTTV 4, that one may be even a bigger problem for you.


Another less expensive option that might do the trick would be Winegard UT-2700 tunable UHF trap. It won't do a 60db notch like the B-T, but will knock down one channel -15db, or 2 different channels -8.5db. I use an older version of one of these to knock down a blow torch analog on 22 that is 12 miles distant, and I haven't noticed any problems on other channels - Including weak signals via tropo DX.


Info on UT-2700 can be found about 1/2 way down the page at following link :

http://www.winegard.com/offair/trapsfilters.htm


BTW, I also use a few Winegard "TRT-LO"(for Lo-VHF), and 1 TRT-HI(for Hi-VHF) tunable notch filters before preamp to knock down blow torch local analog signals -- they also "work"(a 12.5db notch over 2MHZ) but, it doesn't look like winegard still makes them.


With the VHF traps given they notch fairly narrow slices of bandwidth, I tune seperate traps(the MWT-3 has 2 adjustable "sides") to knock down visual/audio carriers/etc. from blow torch signals on 2+7 for maximum effectiveness. The end result concerning what is left over on the notched signal does end up looking very ugly ... With the UT-2700 however, it seems to pretty evenly knock down the signal across the channel(and you could probably tune it to some extent with a little extra attenuation in feedline+by maximizing "snow"), without effecting weak 1st adjancet channel signals.


In my case, I was fortunate in that I got hold of these traps "for free" from a fellow who lost the TV Dx'ing bug ... Perhaps you can run into some luck along those lines as well ...


Hope that helps ... There may be other notch filters which may work for you as well.
 

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The Blonder Tongue MWT-4 is their midband dual notch trap. The UHF model is MWT-u.

I've used dozens of MWT 2s and 3s, but never an MWT-u because they cost too much.. The Winegard UT-2700s cost me under $20 each. The only downside is, they are in plastic cases that leak like sieves, so I have to do some careful planning to incorporate them into my multi-antenna headends such that they do no leak in unacceptable levels of undesired signals. That won't be a factor for most of you to concern yourselves with.


It is not easy to meaningfully notch adjacent channels without the use of a spectrum analyzer.


I think Tin Lee in Canada has tunable notch traps for about 1/2 to 2/3s of what Blonder Tongue sells them for.
 

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Quote:
Originally Posted by AntAltMike
The Blonder Tongue MWT-4 is their midband dual notch trap. The UHF model is MWT-u.
Thanks for the correction -- I was either being dyslexic lining up the columns on the stark MWT chart, or had a typo error, not sure which ...

Quote:
Originally Posted by AntAltMike
It is not easy to meaninglully notch adjacent channels without the use of a spectrum analyzer.
Very true. I had a friend offer to tune mine with his spectrum analyzer ... And I may take him up on that next time I'm in his area, as I expect If I ship it to them, the pots on some of the traps could easily move a bit in the process ... Then again, If *I* hit a pothole that might happen as well ....


But, I do think I have them awfully close to how I want them however ... While it would be very difficult to properly describe exactly how I did it, and It did, I believe involve a bit of "luck"(and a lot of patience) --- follows is a bit of an expanation :


I am lucky in that I was able to "tune" the traps by minimizing(eliminating it as far as I can tell, in fact) the intermod or harmonics created from the too strong signals(and/or a mix thereof) that I desired to "knock down", which showed up on certian portions of certian "cable" channels -- I did this With the use of a bit of a "unique" TV with internal NTSC tuner in it that not only lets you turn off its AFT and do manual(electonic) tuning, but, it also has an "extra" LNA inside the TV that it lets you switch on/off for any specific channel. this TV also doesn't put up a "blank screen" nor does it mute audio on weak or "interference laden" channels - (well, after some work in the service menu it doesn't) - While at the same time, I was also able to detirmine the signals were "effected" On channel, and as far as I can tell, I'm getting good results on 1st adjacent channels(or anywhere else), and I have indications that the traps are effective in reducing intermod, and seems to be keeping the preamp or front end of receiver from overloading.


Again, I'm just lucky however that for instance ... that when I turned the TV's internal "LNA" on for cable channel 39+adjusted manual tuning to hear the station on 22's audio carrier(and a bit of "video noise" showing up from the station on 22 as well), I was able to make it "go away" by tuning the UT-27 trap appropriately - while still be able to detirimine that it was channel 22 being notched(by adding add'l attenuation in feedline as the signal is quite strong) and not 21+23(still being able to receive weak adjacent channel signals).


Also lucky because "Intermod" from the stations on 2+7 I was knocking down also showed up in a similar fashion on Cable channels 22, 25+99. I experimented with knocking down a nearby station on 16 a bit(which as far as I can tell doesn't seem to be causing any problems, even though it is quite strong), but I couldn't find anything that would allow me to see if the trap was tuned correctly.


Is it as "good" as could have been done with a spectrum analyzer? Probably not, but then again, it was a very "fine tuned thing" to get rid of the noticable intermod on the cable channels, and from what I'm seeing with "DX signals"(1st adjacent channel in same direction of the signals being knocked down, lack of any "visable" signs of intermod anywhere/etc/etc) I can't imagine how things could be much better ..


It certianly however was NOT an easy process to undertake(and it could drive one a bit crazy), and was quite time consuming - and, tuning those traps was certianly a very "sensitive" thing. I don't think I would have been able to do it at all for a ATSC signal without a spectrum analyzer.


I did notice however that the MWT-3 I have was tuned to knock down a analog on 10 by the previous owner, and it did "seem" to knock down a local digital on 10 with his "settings" to at least some extent. At least in the sense that this fairly strong station wasn't "showing up" on my digital receiver's "signal quality meter" ....


BTW, the Winegard UT-27 I have(an older version of UT-2700 I believe) Is in a Metal case .... It certianly does not look waterproof, and I would not want to test it to find out ....


Update : LOL ... I just realized we were talking about different sorts of "leaking" ..... Sort of like that other thread concerning where the "sticks" are ....


Along the lines of the sort of leaking you're talking about -- I ran into some problems at first when tuning the traps(the way I had to do it anyway) because I needed more RF shielding, especially as we are talking about stations that come in "off the screws" .... BTW, My traps are in a ammo box, but it was amazing what just taking the lid off it could do ... and that's just one reason why trying to look "on channel" results to tune the traps doesn't work very well ....
 

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Quote:
Originally Posted by Nitewatchman
,

BTW, the Winegard UT-27 I have(an older version of UT-2700 I believe) Is in a Metal case .... It certianly does not look waterproof, and I would not want to test it to find out ....
By "leaks", I mean RF ingress leakage. The Winegard and Channel Master outdoor devices are not "hermetically sealed" (whatever that means), but the cases basically are five of the six sides of the rectangular form, so as long as the vulnerable side is down, the water will stay out.


My problem is, a lot of my customers are in Arlington, VA, where I am within a mile of my channel 27 DTV transmitter, so the cheap traps (UT-2700s, and Channel Master Jointennas) leak in unacceptable levels of undesired channel 27 which corrupts my desired channel 27 signal.
 

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Antaltmike,


Yep, I laughed when It dawned on me what you had actualy meant by "leaks" and was evidently in the process of updating my post(see update above) as you were posting your new post ;)


My traps are actually inside in attic as is my VHF preamp(CM7778). 30FT of RG-6/Ground block/etc. goes from VHF antenna(PR-5030) with Balun to a CA-8800 FM/TV band seperator(so I can get FM before I trap it). Then TV side from CA-8800 to the VHF traps then the preamp - with FM trap engaged - lots of blow torch FM's around here as well.


The UT-27 I have just before the "tuner", not before the preamp which is a Winegard AC-4990(300 ohm input - antenna is Antenna's directXG91 with it's included balun/balun box removed) on mast, VHF/UHF combining via CM0549 is in attic as well.


Traps(and VHF preamp) are in attic Mainly because I want to be able to easily remove the traps for DX purposes when I catch the locals off air on the channels I'm knocking down ....


Good to know though that water won't get in if I ever do end up putting the UT-27 on the mast ...


I'm in a very forested, small, steep valley(terrain issues in most directions), and in my case it's the local VHF's(the ones 12 miles distant especially) that blast in here the strongest. But, I think the transistors in the UHF preamp still may be just slightly "oversaturated" with signals with the antenna aimed towards Dayton antenna farm(12 miles), so I think getting the UT-27 out on the mast+before the preamp would be better, and may be something I might do ...


On the other hand, was receiving stations such as WNED 17 Buffalo, 23 akron and other Cleveland/Akron stations on the same heading as Dayton(some of which I'm knocking down - I use a seperate antenna/feedline for local Dayton reception BTW - The "Main" antenna setup described here is for Cincinnati local reception+DX) via a bit of Tropo Sunday morning just fine, and don't have any problems with local reception, so I suppose why mess with it if it ain't broke ....


And, I doubt I'll be using or needing any off the traps after analog shut off. I certianly won't need any VHF traps and would need to retune the UT-27. And, I also see no reason to climb the tower more often than is needed ....
 

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Quote:
Originally Posted by Nitewatchman
...I think the transistors in the UHF preamp still may be just slightly "oversaturated" with signals with the antenna aimed towards Dayton antenna farm(12 miles), so I think getting the UT-27 out on the mast+before the preamp would be better, and may be something I might do ...
No! No! No!. It's the polyunsaturated fat that causes the problems, not the oversaturated...


Oh. never mind.
 

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HA! ...


Must be a bit like "Extra Stout" ... As I do get bigger the more I drink ...
 

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Discussion Starter #9
Thanks for the great info, guys. I ordered a couple of UT-2700s.


I was planning on putting them up by the antenna along with the CM 7777, but reading your posts, I wondered if I would lose much if I brought both the pre-amp and the filters down to the bottom of the 25' mast? Sure would make tweaking easier. I'm pretty much on the edge with some of the stations I'm going for, so I'm trying to maximize gain and minimize noise/loss where possible.


Thanks again.


Jerry
 

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Jerry,


Mike can probably give you better input, as I've only done much messing around with my own antennas+and few friends setups ... And, I've rarely been able to master the "short post" with this sort of discussion, unfortunately ...


but I dunno -- It might be OK, but if possible(or desired) I'd probably put the preamp as close to antenna as possible. Gain wise, you'd probably only lose a little over a db or so on upper frequencies in that amount of coax, and that probably won't be noticable, but then again, in your sort of situation seems like every little bit could help. I don't know if it might hurt noise figure(NF) to any appreciable extent, but I think there can be other benefits to having it near antenna as well. I didn't really think too much about how it might be the case, but I'd read a seemingly knowledgable article once that indicated it can even help VSWR.


In any event, If there's a good reason why you might want to do it, or if you just want to try it ... I'd say You'll probably just have to try it and see how it goes ....


What I'm doing here (on the VHF side anyway - I have 6 strong locals on VHF) is a bit different case than yours, and there is more room for "compromise" in my case -- as I have good signals from all the Cincy/Dayton stations(all within 39 miles - 36 of them if you count all the digitals/analogs and LP's!), and I don't need the traps at all in order to still achieve excellent local reception ... Also, not as much loss in coax on lower VHF frequencies, that's part of my "reasoning" anyway ....


I probably wouldn't want my UHF amp that far away from the antenna, though And for weak signal Dx'ing I even perfer to use a preamp with 300 ohm input+the preamps internal 300 ohm~75 ohm conversion rather than use a ferrite core balun with antenna .... while I don't know if that's really any noticably "better" than say a balun + CM7777, nevertheless I at least have the "idea" that I can rest assured that minimal loss is occuring across the band ...


Not that it really matters, but what I don't know is if the UHF preamp is perhaps overloading a bit and raising the overall NF a bit(perhaps only on certian channels) with antenna aimed towards/near Dayton, and whether I might achieve a bit better performance (weak signal DX wise) in that direction if I get the UT-27 before the preamp ... It doesn't "seem" to be the case, but I have no way of knowing for sure, and of course I don't want to diminish performance with weak signals in other directions, especially considering some of the terrain issues I have here ...(Goes up 300FT higher than my antenna within a few miles to my West, for instance, and about 50ft higher than my antenna within a few hundred feet of the antenna to East or West) .... I expect I might even see a slight change for the worse concerning some of my more "distant" local UHF analog LP's if I made such changes, but again it's hard to say without trying it, which is something of course I really have no reason to do, unless I get a wild hair or something ....


Oh ... I'd think You should also be able to do your "tweaking" by bringing the preamp+traps inside first if you want, then after getting the traps set like you want them move them outside ... I had the preamp in different places in feedline when tuning the traps and don't think I ran across any problems moving it around -- except the RF shielding thing with the ammo box lid off, and I did "doublecheck" things with the traps in the attic involving making sure those audio carriers that shouldn't be there on the cable channels were still gone with the use of wireless headphones ... It's hard to say(as I did some do some "fine retuning" at that point) but I don't think I actually changed anything on the traps from where I had them set when I had the preamp+traps in next to the "unique" TV I was talking about ...


---------------------------


By the way ... I was just curious ... Are you going to add a VHF antenna as well? Such as for WISH-DT 9 Indy(CBS HD)? PAX digital Louisville is also on VHF -- WBNA-DT 8, and A couple of other Lou/Indy stations have chosen to move back to VHF after analog shut off. WHAS-DT Lou ABC HD to 11 after analogs shut off, currently on 55, and If I recall correctly, WTHR-DT 46(currently) NBC HD Indy to 13.


If you don't need any of the lo-VHF analogs or FM, seems like a Winegard YA-1713 VHF Hibander(ch 7-13) might be a good choice for VHF for you to add to the mast. Here's the specs on it from Winegard site :

http://www.winegard.com/offair/pdf/ya-1713.pdf


Or, you might also try sending a PM to "Max HD", who is somewhat near you in Greensburg, IN -- He did have a number of European model Hi-VHF antennas in his garage he was selling that should have quite good performance, I don't know if he has gotten rid of them all or not. Max HD might also have some good thoughts for you concerning your reception in general.


Anyway - Good luck+let us know how it goes.
 

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Discussion Starter #11
Believe me, your 'tutorial type' posts are very much appreciated. I'm afraid my ignorance would be hard to overcome with a 'short post'. :)


It's a little hard to get the mast up and down in my setup, but it sounds like putting the pre-amp and filters down low for a while might be a good idea. I'll raise them when I'm happy. FWIW: I have 25' of mast braced to the rafters of an open 'car port' type structure (and guy wires of course). The antenna is at a barn 600' from my house because the barn sits 40' or so higher than the house and the roof of the house is too steep for my taste. I use a good Channel Master amp with variable tilt to get the signal from the barn to the house. I do lose a little signal going from the barn to the house, but I'm doing all my signal testing at the barn.


Your information on the VHF situation is good (and surprising). I had decided I could live without the current VHF stations, but wasn't aware of the post-analog moves. WHAS and WTHR are necessary, so I'll investigate the options you mention.


Thanks again.


Jerry
 

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Jerry,


Hopefully those traps will help you out ... 600 Feet - WOW! That's a long run ... Very cool you've got that to work from a "fringe area" ....


On the post-analog moves, there will be some moving around on UHF as well. If you go here :

http://www.fcc.gov/dtv/


under 6/23/05 Date there are a couple of spreadsheets FCC released with post-transistion "tentative channel designations" for most stations. You might want to read the associated public notice as well. I think Most if not all stations you'd be interested in are probably on that list.


But if not -- Choices for post-transistion channels from About 150 stations that participated in the first round of channel elections "didn't fly" because of interference conflicts, but they've already sent in their "conflict resolution forms" which specifies what they are going to do to solve the conflict" -- You can get info on these by going to following link - under service choose "Television station", under application choose "First Round Conflict", Under application status choose "tendered for filing" (currently anyway - you might need to choose something else soon), hit the "submit" button, then "yes" after the next page pops up.



A list of 187 stations which received "interference conflict" letters from FCC concerning their first round choices, and sent their forms in telling FCC how they wanted to solve the conflict will pop up. Next to each "entry" on the right side, there is a(blue text) "info" link, and "application" link. If you click on the "application" link, the actual conflict resolution form the station sent to FCC will pop up, and in section 2 of the form "First round conflict decision" you'll see the stations choice -- especially If they chose option "b" (to use their current digital channel allocation after analog shut off), It's most likely to "stick" ...

http://svartifoss2.fcc.gov/prod/cdbs...d/app_sear.htm


---------------------------------------------


There are 3 rounds in the Channel election process, and the whole thing isn't going to be over and "set in stone" until 2006. However -- MOST stations made their election in the first round, and due to the way the "rules" for channel election are set up, (FCC for instance needs to know where the stations in the first round will be after analog shut off so they'll know what channels are going to be open for those few stations that will be participating in 2nd and 3rd rounds, and for DTV LP's to some extent).


I think the vast majority of the first round elections will stick ... At this point, especially those that are on that "Tentative channel list" from FCC from back in June -- I could be wrong, but I don't expect many, if any of those to "change". I'd think they should be issueing a new tentative channel designation list soon, with many, if not most of the "adjusted choices" for the stations that sent in their first round conflict resolution forms.
 

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Discussion Starter #13
Help! I know I was warned that tuning the UT-2700 without a field strength meter was hard, but I'm having trouble even getting started.


The tuning instructions say that the variable caps will rotate through 360 degrees, and warn not to turn the screws too much, but it isn't clear whether the cap tunes the whole band in a single turn (seems like that would be really touchy), or 10 turns, 100 turns, ... If more than one turn, are there stops?


I put one in, turned off the pre-amp and turned the rotor to knock the signal down a bit (some snow in the picture). I assumed multiple turns so I started slowly turning, but got worried after about 20 turns without change and started to rotate really slowly through a single rotation. The signal was affected slightly at some positions, but nothing significant. Maybe I already managed to damage the dialectric as they warn.


Before I do further damage, could somebody tell me how many turns I should expect when tuning the UT-2700?


Thanks very much.


Jerry
 

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Jerry,


I'm using the older version of it(UT-27), and don't know how much different it would be with the newer one ... but with it anyway, it is EXTREMELY "Touchy" .... on it, WAY LESS than 1 turn tunes the entire UHF band .... For instance, I did check this - but didn't write it down so this isn't really very "exact" : "tuned" to Channel 22 and 45 respectively was probably about the difference between a 1 o' clock posistion and a 3 o'clock posistion - and, actually I think it was a bit less than that.


As I said earlier, In my case I really needed that visable/audible "intermod" from the station I was knocking down to show up on UHF cable TV frequencies, and the capability to turn the AFT(automatic fine tuning) on the tuner so I could do manual tuning on those cable channels and FIND that "intermod" to really tune it most effectively(as far as I can tell anyway) without a spectrum analyzer ...


Note 12:35am upate - Some of the following is updated, as I realized I'd misread your post at first --- sorry about that!


Oops! Don't know how I missed this! I see you said you saw a "difference" in how much snow there was after turning off the preamp/etc in certian spots when tuning, but that it wasn't much of a difference ... Well, it probably WON'T seem like much, as you're only knocking it down ~8db off each "side" of the filter, and since you are only 9 miles away, you've likely got a very strong signal coming in, which you would probably have to knock down by at least 40db(with the preamp being supplied power) to see "any" change at all ....


So, you are not knocking it down all that much "relatively speaking", but you probably shouldn't NEED to knock it down much .... All you want to do here I think is keep the preamp(or tuner) from getting too high of a signal input level(If that is actually what is occuring that is causing your problem) ...


I'd think in your case You probably don't need to knock down the "blow torch" signals MUCH to acheive this .... in other words, You shouldn't have to make the signal "disappear", and, the end result will probably be that it won't even be "snowy" after/if the traps are properly tuned, and you remove add'l attenuation from feedline you were using so you could "see something" in order to be able to tune the traps ... 1st adjacent channels will likely appear a little "cleaner" though ....


I ended up using the "intermod" on cable channels as described above, but I found I was also able to get somewhat close via using another method which should hopefully be possible for you to some extent as well .... I was able to first get in the ballpark by adding some extra attenuation in feedline(about 20db), tuning to a weak analog signal on 25, and aiming antenna off target to a bit of a "null" - seeing the "effect" when I "turned the screw" to where it effected ch 25(more snow when it was "tuned" somewhat in the range to knock down 25). Then, I was able to do the same thing On channel I am knocking down channel(22 - analog signal - in this case) ... BUT, I had to add a lot more extra attenuation in feedline(about 40db) as well as rotating the antenna off target for a "null" .... And, it certianly wasn't easy, and I had to look REALLY closely to see the difference(certian video - such as the letterboxed "black bars" made it easier to see) and you wouldn't believe how "small" the difference was in the posistion of the caps for 22 compared to 25 ... It was a VERY TOUCHY VERY sensitive thing ...


For such a strong signal, In my case, using that method ... As I had/have the UHF preamp BEFORE the notch filter I likely had to add more attenuation in feedline than you will tuning the traps with it inline BEFORE the preamp. I'm not having problems with a overloaded UHF preamp, it was NTSC tuner which was getting "too much" for good results concerning weak adjacent channel "DX" signals in same direction as some of the "blow torch" locals ....


IF you can do that, you still probably won't be able to tune it so the traps will be most effective(I couldn't do it via that method without also slightly effecting either 21 or 23 for instance) -- but hopefully you'll be able to tune it so its "effective enough" for your needs.


I really don't know how you'd be able to tune it to knock down the digital on 14, though. Maybe using WKPC 15 analog Louisville could get you close(and update - Mike's suggestion about the UHF modulator seems like it would work). Otherwise, Hopefully, you'll get lucky, but the "signal meter" on your DTV receiver might not be able to tell you anything ... IF it would, I'd guess you'd still have to add a lot of temporary "attenuation" in the feedline(as well as again, luck) to be able to see any sort of "change" when you "find" the proper place when "turning the screw" ....


Let us know how it turns out and good luck ...
 

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You could buy a cheap two or three output residential UHF modulator on eBay for maybe ten to twenty bucks, and feed any old A/V into them from a single source using "Y" cables, and then tune a notch filter to degrade one while minimal degrading another. This works best if you initially pad each output to nearly the point at which graininess becomes visibly degrading.


Or you can pay someone a hundred and fifty bucks to do it with a spectrum analyzer.
 

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If you are trying to attenuate an adjacent channel coming from another direction, the best way is to point a second antenna directly at the undesired signal source, bandpass filter and reduce the output of this second antenna to match the the output of the main antenna, and then phase cancel them either by moving the second antenna or by precisely setting the coax cable length. This is something I've done to eliminate FM radio harmonic interference on VHF high-band channels. But again, you'd need to have a professional do this for you.
 

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Quote:
Originally Posted by AntAltMike
You could buy a cheap two or three output residential UHF modulator on eBay for maybe ten to twenty bucks, and feed any old A/V into them from a single source using "Y" cables, and then tune a notch filter to degrade one while minimal degrading another. This works best if you initially pad each output to nearly the point at which graininess becomes visibly degrading.
Seems a good possible option to me for what Jerry wants to do ....

Quote:
Originally Posted by AntAltMike
If you are trying to attenuate an adjaxcent channel coming from another direction,
I wouldn't think there should be any 1st adjacent channel/receiver selectivity issues involved in Jerry's case for which phase cancelling would be beneficial.


Judging from 1st post of this thread, he said wants to knock down a strong local analog on 30 and digital on 14(9 miles) because he says it is swamping his preamp to the point it is "disrupting" reception of weaker, more distant signals on nearly the same heading.


I do think he should have a couple of other nearby stations. A Pax on 63/27 digital, a lo-VHF analog on 4/low power digital on 54 - I think they're running 4KW ERP currently. I think that is about it on the TV bands between Louisville and Indy.
 

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Some of the Euro stuff that I use might be beneficial in Jerry's situation.I'd use two Triax A/E combiners(20db out of band rejection),one behind a wideband UHF antenna to block everything below 38,before preamping,and another one to combine an unamped deep-fringe Band A antenna.25 from Indy is strong and 26 from Lou is also strong,so preamping might not be necessary for channels below 38.If this setup would work,the 600ft run is just a matter of line amplification at the right places to keep the signals "up".


I still have several of the Highband PSP 1922's.Would be a very good application for the Bloomington area,I would think.


Edit:

Only one combiner would be needed as they can be configured to pass DC for a preamp on either,or both legs.


Greg B
 

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I misread Jerry's last post a bit and updated my response -- In short here - I'd missed the part where he said :

Quote:
Originally Posted by jfath
The signal was affected slightly at some positions, but nothing significant. .
Since each side of the trap only provides about a -8db notch, and he's dealing with a very strong signal -- proper tuning of the trap *is* only going to "slightly effect" it in a "visable" way ..... ...


The goal here I think is only to lower the input signal level the preamp(or tuner) is getting so it doesn't get "swamped" ... That probably shouldn't take all that much, I wouldn't think ... IF it is properly tuned, First adjacent channels should be "cleaner" as well ...


I don't think you should need for the strong signals to "disappear" or even be "snowy/weak with "normal" operation with the preamp in line+no add'l "attenuation added. I'd think that would likely take a -40db notch or more.
 

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Discussion Starter #20
Once again, I'm overwhelmed by the helpful responses.


My hope in tuning was that if I attenuated the signal to the point of some snow by turning the antenna away from the strong transmitter, the affect of the filter would be more visible. At that point, I would have thought bringing the signal down 8db would be more noticeable, but I simply couldn't get consistent results. Using a plastic screwdriver, I would tune until I saw slight degradation, but removing the screw driver would change the results. I do have a three channel modulator, so I like the idea of loading it up with some attenuators and tuning with that - fewer variables. As a last resort, I'll beg, borrow, or buy a field strength meter.


Thanks again.


Jerry
 
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