Source for Signal Attenuators

[Mike123abc]

I am using an antenna for over the air HDTV on the 6000. I had to put up a large antenna to pull in the distant stations. My problem is that some of the stations are local (within 10 miles) and some are 40 miles away. The local 2 VHF stations are so strong that if I use any amplifier at all they over power the amplifier.

So, I can either get 5 single channel amps and try to amplify the other channels or I could get some way to attenuate those channels. They are channels 3 and 6, the rest of the channels are in the VHF-hi or UHF bands.

Anyone know of a source for single channel attenuators? Or a way to tone down the VHF-lo band?

p.s. BTW we had 2 digital channels go live this week... 6000 picks them up great!

[boba]

Mike according to www.100,000watts.com you are not receiving KFDX-DT & KAUZ-DT on VHF. Their digital channels are UHF 28 & 22 respectively. If they were as you posted VHF & UHF I would have suggested bandseparators then you could amplify them separately and recombine them.

[Mike123abc]

Well my problem is ABC (channel 7) is not digital and is not going to be for a long time. I tried a UHF only amplifier and they overpowered it also, of course it was an inexpensive Radio Shack one. A bandseparator could be a way to go. I am still stuck trying to amplify channel 7. I found some BT amps on the net, but a single channel amp and powersupply is $200. I was hoping to get a passive device for a lot less.

[AntAltMike]

If just 3 and 6 are strong, and if you are indifferent to 2, 4, and 5 (as most people in markets with a 3 and a 6 are), then the HLSJ band separator is the way to go. You can get them for a few bucks each and put a little padding on the lowpass line, or use a Radio Shack variable attenuator which has zero to about 20dB of attenuation. If FM is a problem, the HLSJ will route that to the lowband where it will be attenuated also.

Companies also make notch traps for individual cable channels, so a dealer for Eagle Comtronics or Microwave Filter could probably furnish you with channel 3 and 6 interdiction filters, but in single quantities, you might pay $20 or so each, whereas your local cable company might have paid a dollar or two each when they bought 10,000 at a time when these were commonly used to filter off HBO and Showtime.

By the way, these 50dB notch filters do NOT clear out the channel good enough to allow reinsertion of a modulated channel there. They just kill the RF energy in the visual carrier unusable.

[Mike123abc]

Well since it is the weekend I came up with a temporary work around. I run the antenna into a 4 way splitter, then a 2 way splitter then an FM trap. This dropped strength down enough that I could amplify the UHF signals without the VHF overwealming it.

Thanks for the info about Eagle Comtronics and Microwave Filter I will have to see what they have. Right now I am looking at getting a VHF Hi/Lo splitter and then putting Atennuator Pads on the VFH-Lo side (I ordered a selection from 3-20 DB to play with).

[AntAltMike]

You've now got about 11dB of padding on the entire RF bands, plus another 20dB or so on the FM band. If that is working for you, then there is just no reason to waste your money on the notch filters. For your application, they won't even work as well as the HLSJs. The channel 3 and 6 notch filters are narrow, narrow notch filters that will kill the 61.25Mz channel 3 visual carrier and the 83.25Mz channel 6 visual carrier, but they will hardly affect the 65.75 channel 3 aural carrier and the 87.75 channel 6 aural carrier. You might pass more total RF energy from the channel 3 and 6 broadcast signals with the notch traps than with the HLSJs and in either case, your channel 7 will be over 10dB further above the noise floor than it is with your make-shift splitter arrangement

You will then find out whether the overload you experienced was solely a matter of lowband VHF overload or whether some of the local UHF analog and digital stations are too strong also. You may benefit from a lower gain amplifier. How much gain does your present amplifier have? What make and model is it?

[Mike123abc]

Ok my amplifier is a Channel Vision CVT-2/4 PIA http://www.channelvision.com/specs/CVT-2-4.pdf

I have ordered 2 of:

Channel Master:
VHF Lo/FM – VHF Hi/UHF
Joiner/Separator
Model 0534 (75 Ohm)

Joins any VHF Lo band antenna and any VHF Hi band/UHF antenna to one downlead. Low loss, high isolation.
Input 1 54-108 MHz Loss 0.5 dB
Input 2 174-900 MHz Loss 0.5 dB
Isolation 30 dB

I will split the antenna, use attenuator pads (have a variety of them on order ranging from 3 to 20db) to tone down the lower VHF band then will combine the antenna back using the second band splitter. With a bit of work I think I will be able to nicely equalize the strong VHF-Lo.

Antenna -> band splitter -> attenuator -> band combiner -> amplified splitter

The signals are split again (and some again) as they work their way through the house using passive splitters.

[AntAltMike]

Looks like a plan. The amplifier has 15dB of gain. All that rating information on the spec sheet is inadequate to assess the maximum input capability of this amplifier. They need to specify the load (# of channels and input level) at which the various distortion levels are developed, but it has a reasonable amount of gain for your situation, so hopefully, you will be in good shape. The 100,000 Watts site shows only a 200KW CBS digital transmitter in what appears to be your locale, so that isn't likely to be a problem for you.

[Mike123abc]

I have 7 local stations, will have 13 when all broadcast in digital. So, should not be too many channels for the amplifier. It is hard to test right now because the CBS-DT channel is part time and 1/4 power I think (50kw when I talked to the engineer on Friday).

All in all the splitters & attenuators combo ended up being less than $30 including shipping. I get to cancel basic cable so will save almost $10/month. The picture on all except the ABC station is far better than cable, it is still getting interference from the CBS/NBC stations.

[Mike123abc]

Well I got the band splitter and the attenuators in and they worked pretty good. I ended up attenuating the VHF-lo band 13db. It was a compromise between channel 3 (NBC) being over attenuated and channel 6 (CBS) being too strong. Both are 100kwatt stations within 10 miles but the antenna points more toward channel 6 since that is also the direction of channel 7(ABC).

I really want to see ABC go digital, it does not have the best picture yet.

NBC is broadcasting in 480i here and CBS in 1081i. The problem is that CBS is up-converting their whole programming day to 1081i and is stretching the image to 16x9. They do not have the equipment for the 1080i feed from CBS yet, so end up with a 4:3 image stretched to 16:9, not the best.

[AntAltMike]

You can now further finesse it with a channel 3 or channel 6 jointenna. Use that to separate them, pad accordingly, and then bring them back together with a two-way splitter.

[Mike123abc]

Yeah it makes you appreciate why so many gave up on TV antennas when cable came out. Perfecting all the channels simultaniously is quite the challenge. It would be a lot easier if all the channels were on the same transmission tower and all at the same power. I will probably work on the reception some more, it bugs me not to have a pristine picture on every channel.

Right now compared to cable 6 of the 8 channels are far better picture (std definition ones). One (7-ABC) is much worse and one (18-FOX) is just a bit worse. Of course cable does not carry the 2 HDTV stations (CBS/NBC).

It would be nice to have a device that could give you a signal level on every channel... That way one could try to balance them all to the same number. Well I am sure they exist, but would be nice if they were affordable.

Found an useful site for TV antenna reception: http://www.tvantenna.com/

[Mark Lamutt]

Well, Mike - look at it this way...you could be trying to pick up a 3kW ABC station broadcasting from the top of a 6 story building that is located right in the low point of a valley, and 3 other stations broadcasting at 5kW broadcasting from the top of a 27 story building that is right between 2 other buildings that are as tall or a little taller. And then couple that with another station that is broadcasting at about 25kW from almost exactly the opposite station. At least all of my stations are in the UHF band. With a large UHF yagi antenna on my roof, I'm getting all of them reliably through 3 passive splits to my 3 HD receivers, but the 3kW (ABC) station was tough, and I'm only 3 miles from their building. Good thing all this stuff is "fun"...:)

[Mike123abc]

Well I have improved my channel reception yet again. I now attenuate the VHF-Lo band 23db, then pass all the antenna into a 15db amplifier. Then I pass this into the 15db amplifier splitter (plus input from my RF modulators). Amplifying 15db the fox and abc station really cleared up their signals, but I had to knock down the VHF-lo band another 10db before I could amplify them.

Hmm just had a thought while typing that out... maybe put the amplifier in the mix while the bands are still split then I would not have to attenuate VHF-lo so much to just amplify it back... Will try that this afternoon and report back. Yes it is fun working on it because you can see instant progress or setbacks.

[Mike123abc]

Well that solution did best, I put the amplifier after the band splitter on the VHF-hi and UHF side and put 9DB attenuation on the VHF-lo side to make it balance out nicely... Get a better than cable picture on every channel, and most are very nice reception.