Where to buy signal attenuators locally? - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 15 Old 12-26-2006, 08:08 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I'm looking to pick up a few coaxial signal attenuators (like this), but I'm not sure where to look. Surprisingly, Radio Shack doesn't seem to carry them. I can find them online but I need them ASAP and they only seem to come in packs of 10. Since I don't know how much I need the signal reduced I'd like to pick up a few different ones and I don't want to buy three boxes at $17 each. Any suggestions on where I might find these?
sd_smoker is offline  
Sponsored Links
Advertisement
 
post #2 of 15 Old 12-26-2006, 08:39 AM
AVS Addicted Member
 
Ratman's Avatar
 
Join Date: May 2002
Location: Collingswood, N.J.
Posts: 14,457
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 167 Post(s)
Liked: 286
http://cgi.*********/75-Ohm-Bidirect...QQcmdZViewItem
Ratman is online now  
post #3 of 15 Old 12-26-2006, 08:54 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Okay, here it goes... I've got a CM3016 antenna in my attic with about a 30ft run of RG59 to the STB. Of the stations I'm interested in, all but two come in at between 90 and 100% on the signal meter. I know that the TV/STB meters aren't totally accurate, but they're strong signals nonetheless. However, two of the channels come in between 70-80% and drop out intermittently. Being that one of the channels is CBS (i.e. Super Bowl) I need to get this resolved soon.

Here's what I was planning on doing. First, swap out the RG59 for RG6. I've gotten conflicting info on whether this will help, but it can't hurt. Second, I wanted to try a low-gain pre-amp so as not to overload the strong channels. I found a 13db dist. amp, but I don't know if that will do what I need. The lowest gain pre-amp I found has a gain of 16 for VHF and 23 for UHF. I was going to pick up the attenuators to try to fine tune the amount of gain. I have a feeling it will be a balancing act between boosting the weaker channels and overloading the strong channels.

If all else fails I'll look into moving the antenna outside, but that will be a PITA so I wanted to exhaust my other options first.
sd_smoker is offline  
post #4 of 15 Old 12-26-2006, 08:57 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Here is the info for the relevant stations. The ones I'm having trouble with are in red...

yellow - uhf KWTV-DT 9.1 CBS OKLAHOMA CITY OK 320° 18.9 39
yellow - uhf KETA-DT 13.1 PBS OKLAHOMA CITY OK 320° 18.9 32
yellow - uhf KFOR-DT 4.1 NBC OKLAHOMA CITY OK 320° 18.9 27
yellow - uhf KOCB-DT 34.1 CW OKLAHOMA CITY OK 316° 16.7 33
yellow - uhf KOKH-DT 25.1 FOX OKLAHOMA CITY OK 314° 16.2 24
green - vhf KOCO-DT 5.1 ABC OKLAHOMA CITY OK 316° 17.0 7
sd_smoker is offline  
post #5 of 15 Old 12-26-2006, 09:39 AM
AVS Special Member
 
Speedskater's Avatar
 
Join Date: Mar 2004
Location: Cleveland, Ohio
Posts: 2,031
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 18
Radio Shack 6dB Attenuators
Old Part Numbers:
#15-1257 F jack to plug
#15-1258 F jack to jack

Kevin
Speedskater is offline  
post #6 of 15 Old 12-26-2006, 09:50 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Rick0725 View Post

I would start with replacing the rg59 with rg6.

Will do. I'll be crossing my fingers that this works.

Quote:
Originally Posted by Rick0725 View Post

The preamp suggested in your case would be the winegard hdp269 preamp with only 12 db gain and very high overload tolerance.

I missed that one. Thanks. It says it's designed to work with the SquareShooter antenna, but I assume it's not limited to that application...

Quote:
Originally Posted by Rick0725 View Post

You can try using the hdp 269 preamp and only amplify the uhf signal and pass vhf. This would cut down on the channels/signal going into the hdp269 and lessen the chances/severity of overload (if you have an issue).

Being that one of the channels I need amplified is VHF and all the channels at risk for overloading are UHF, I don't understand how this would solve any problems. Can you elaborate a bit?
sd_smoker is offline  
post #7 of 15 Old 12-26-2006, 11:11 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,407
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 31
Replacing the RG-59 with RG-6 is your best shot.

If that doesn't fix it, some Radio Shacks may still have their Variable Attenuator in stock. While there, see if they still have the little FM Trap, as well. Try them both, individually.

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #8 of 15 Old 12-28-2006, 03:08 PM
AVS Special Member
 
bfoster's Avatar
 
Join Date: May 2001
Location: Weeksville, NC
Posts: 2,131
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
I wouldn't put to much faith in changing from RG-59 to RG-6. Unless the cable you have is defective or some real poor quality stuff, you are going to only realize about .3 dB on channel 39 and even less on channel 7.
bfoster is offline  
post #9 of 15 Old 12-28-2006, 05:43 PM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I went ahead and turned the antenna around so it's facing NNW (that's the best I could do) and replaced the RG59 with RG6. It was just laying around in the attic unused so I figured it could't hurt anything. The combination of those two things seems to have fixed my problem, although I wish I would have done them one at a time so I could see how much difference each one made. Every single station is in the 90's, with a couple at or very near 100%.

In fact, NBC (ch 27) is pegged at 100% and I'm seeing a little bit of noise that I don't think was there before. Is it possible to have an overloaded signal using only an antenna? Will I need to attenuate the signal just a bit even though I didn't end up using a pre-amp/amp?
sd_smoker is offline  
post #10 of 15 Old 12-29-2006, 08:22 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
After a little more investigation, I think the noise may have just been the particular show I was watching (What About Earl?). I later watched The Office and The Tonight Show and saw no noise.

The antenna was in the attic when we bought the place. It looks like the 3016, but I suppose it could be the 3017 or even a generic that looks just like those models.
sd_smoker is offline  
post #11 of 15 Old 12-30-2006, 07:15 AM
AVS Special Member
 
kenglish's Avatar
 
Join Date: Jan 2000
Location: Salt Lake City, UT, USA
Posts: 5,407
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 31
Quote:
Originally Posted by bfoster View Post

I wouldn't put to much faith in changing from RG-59 to RG-6. Unless the cable you have is defective or some real poor quality stuff, you are going to only realize about .3 dB on channel 39 and even less on channel 7.

The problem is, RG-59 has terrible shielding. So, as the signal leisurely plods it's way thru the cable (at about 66% of the speed of light), the rest of the signal is blasting in at full speed, and they sum together at all sorts of wierd timings.

This blurs an analog signal, and it blurs the data of the OTA or Cable Digital signals, making them more likely to fail. Also, the poor shielding allows all sorts of household electrical noise to get in....my own STB radiates a good bit of noise, and the nearby satellite receiver spews digital garbage across the VHF high band.

Ken English, Sr. Engineer, KSL-TV.
"The postings on this site are my own and don't necessarily represent the Company positions, strategies or opinions."
kenglish is offline  
post #12 of 15 Old 12-30-2006, 08:18 AM
AVS Special Member
 
Speedskater's Avatar
 
Join Date: Mar 2004
Location: Cleveland, Ohio
Posts: 2,031
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 18
Not all RG-59 has a "Nominal Velocity of Propagation" of 66%.
For some it's 78% (Belden # 9659, 8221, 9240)
But most any common co-ax has a "Nominal Velocity of Propagation" of 66% to 78%.

Kevin
Speedskater is offline  
post #13 of 15 Old 01-04-2007, 05:38 AM
AVS Special Member
 
bfoster's Avatar
 
Join Date: May 2001
Location: Weeksville, NC
Posts: 2,131
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by kenglish View Post

The problem is, RG-59 has terrible shielding.

C'mon Ken, you know better than this.

You can good or bad quality RG-59 and RG-6.
bfoster is offline  
post #14 of 15 Old 01-04-2007, 07:11 AM - Thread Starter
Senior Member
 
sd_smoker's Avatar
 
Join Date: Dec 2002
Location: OKC
Posts: 436
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Rick0725 View Post

The debate over coax here is beginning to get trivial in comparison to the other issues involved as part of the upgrading process (which was not even mentioned here)!

Care to expand on that a bit? I'm happy with the results of the modifications I made, but I'm intrigued nonetheless...
sd_smoker is offline  
post #15 of 15 Old 01-04-2007, 07:30 AM
AVS Special Member
 
AntAltMike's Avatar
 
Join Date: Nov 2001
Location: College Park, MD
Posts: 3,569
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 15 Post(s)
Liked: 25
The old, RG-59 commonly used twenty to forty years ago has copper braid shield and leaks like a sieve, causing the blurriness that Ken alluded to. If someone is in a region were an ignorant contractor or fledgling cable company had once made it their conductor of choice, then they may be working in environments that are not representative of the world in general. Whenever I run across copper braid shielded RG-59, it is a piece added onto the system by a do-it-yourselfer. I have no leakage problems with foil shielded RG-59.

As has been explained so many times, the signal meter numbers are not just unreliable measures of signal strength, they are so far removed from being indicative of signal strength that they are nearly useless in estimating it. They are the resultant of unique algorithms that reliably principally on the amount of error correction being performed. You can vary signal power a thousand fold without the receiver signal strength number changing.

If someone is 18 miles from full powered transmitters and is using any conventionally designed consumer grade antenna, they will not experience any signal level problems that can be remedied through amplification. When signal level numbers jump from 70 to 80% down to zero or thereabouts, it means that there is multipath interference that fluctuates around the threshold level of canceling the desired signal to the point of rendering it unusable. The remedy is an antenna remedy, either reaiming it within the attic, replacing it or putting it on the roof.

While the original poster now has a situation that satisfies him, he has no way of knowing how much of a performance margin he has, because digital signals, unlike analog signals, only display avalanche failure symptoms. If any channel craps out again, the only practical solution is to put the antenna on the roof, where the signal quality is invariably, significantly better.
AntAltMike is online now  
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