Just a couple more!

[dePorange]

Hi, guys -

Here's the deal:

http://www.tvfool.com/?option=com_wr...81a30d1f810d7a

Homemade 8-bay 9" bowtie antenna http://farm4.static.flickr.com/3368/...67eedaa796.jpg

The antenna is in the attic connected to TivoHD via 25' coax.

Primarily looking for help with ABC WLOS for which I'm getting no picture. Tivo shows either 0 to 25 out of a possible 100 - but no picture.

Also, I get some articfacts on CBS and CW which would be great to fix, but aren't as important to me.

I'm wondering if adding a VHF specific antenna for ABC (13) would help? And a preamp? Or, does the antenna needed to be upgraded, which I would consider.

Installing the antenna outside on the roof is not really an option.

Thank you for your help!

[Dave Loudin]

First thing: NO PREAMP! You've got tons of signals bombing in, so a preamp will be overloaded and wipe out half of your channels. Do you actually have eight bowtie elements in your design? The picture shows four, which should be plenty.

You may have already done so, but be sure to consult the best site for bowtie array designs here. There should be a design that will fit the bill if you want to tinker some more.

I think your problem is an avalanche of FM. Try putting an FM trap in the line to see if that helps.

[John Candle]

Read and understand this , http://forum.tvfool.com/showthread.php?t=695 , Ground the coax cable with a coax grounding block and ground wire , this will help divert some of the strong signals that are bomb barding the coax shield to ground.

[dePorange]

Thanks for the ideas, guys. You're right, it's a 4-bay antenna 10" x 9" (followed the 9.5" design with the idea I could always trim down from 10"). I'll try the FM trap and grounding block and report back.

Based on TVFool, should I be able to get ABC 13? How about the other "yellow" stations?

[Tigerbangs]

Don't expect a bow-tie design to do much of anything on VHF: they are essentially a UHF antenna with MAYBE some incidental VHF reception.

A multi-directional antenna like a bow-tie design antenna isn't well-suited to an attic design because of their susceptibility to multipath. if you insist on using that antenna in an attic, you are going to have drop-outs and pixellation. Why can't you go outside with your antenna?

[dePorange]

Tigerbangs, thank you for your thoughts. I would consider upgrading the antenna. The homemade bowtie was really just a diy project and test to see if ota dtv was even feasible at my house. It proved it is feasible and is actually providing most of the TV we care for. That said, I can easily justify spending money for a better antenna if it will provide increased programming and quality, particularly in the areas I mention in the original post. I prefer to keep the antenna in the attic for aesthetic reasons and we do have space for a larger antenna in the attic - I understand that doesn't give extra height, if you think that is an issue.

Does my TVFool indicate I might have multipath issues? Since most signals are coming from the North, aren't multipath problems limited?

[Dave Loudin]

Tigerbangs, don't discount the VHF capabilities of the design I pointed to. That array has been pretty thoroughly modeled and tested. Granted, the gain at VHF-hi is not the same as UHF, but it IS more than a dipole and can be useful in many situations.

[Tower Guy]

Originally Posted by Dave Loudin

Tigerbangs, don't discount the VHF capabilities of the design I pointed to.

Unfortunately such capabilities aren't sufficient for attic reception in this case.

Add a Y10-7-13 or YA1713 for reception of channel 13. Use a UVSJ to combine the antennas together. I would not attempt a preamp.

[dePorange]

Wow, the Y10-7-13 or YA1713 have 120" and 100" booms - could anything less humungous do the trick? I think these could fit in the attic, but wondering.

[John Candle]

I suggest a Winegard HD7084P mounted on the roof and No preamp. Pointed at 355 magnetic compass. This will get you the channels in the north type direction and WMYA 14 My Network will likely be received through the back side of the antenna because the signal is very strong. Read this about Real and Virtual channels. http://forum.tvfool.com/showthread.php?t=695 . Also read this about placement of tv antennas. What it says is Yes you can put a Tv antenna and other antennas on the roof. http://www.fcc.gov/mb/facts/otard.html . Also read this about tv antennas , http://forum.tvfool.com/showthread.php?t=237

[Dave Loudin]

Originally Posted by dePorange

Wow, the Y10-7-13 or YA1713 have 120" and 100" booms - could anything less humungous do the trick? I think these could fit in the attic, but wondering.

As Tower Guy said, you need some real gain in order to overcome the losses from being in the attic. Doing the math... The predicted Noise Margin for WLOS is 22 dB. Take 20 dB out for losses through the roof and other stuff and yo are very close to no lock. Add a little cable loss and you're right at threshold.

As far as size goes, you can't fight physics.

[dePorange]

Originally Posted by Dave Loudin

As Tower Guy said, you need some real gain in order to overcome the losses from being in the attic. Doing the math... The predicted Noise Margin for WLOS is 22 dB. Take 20 dB out for losses through the roof and other stuff and yo are very close to no lock. Add a little cable loss and you're right at threshold.

That sounds reasonable, thank you for the explanation.

Could you speak to orientation? The smaller bowtie stands vertically facing North. I think the larger antenna might only fit in the attic such that its length runs East-West, essentially perpindicular to the source of most signals. Problem?

[GroundUrMast]

This link illustrates aiming of most antennas... http://www.dennysantennaservice.com/...na_aiming.html

Off aim by 90° will cost quite a bit in terms of signal strength and quality, possibly 20dB or more for a larger, directional antenna.

[dePorange]

Thanks, I'll have to take some attic measurements tonight.

[Tigerbangs]

Originally Posted by dePorange

Does my TVFool indicate I might have multipath issues? Since most signals are coming from the North, aren't multipath problems limited?

TVFool.com wouldn't indicate multipath issues, but your attic installation definitely would, as all attics introduce some degree of signal loss and reflections, which are the key components of multipath interference. Since attic installations are unpredictable, and based on the relative signal strengths of the signals available at your location, I would bet that yours is a multipath issue.

[dePorange]

After measuring, it looks like we can probably get a 120" antenna pointing in the right direction, so this should work.

I guess my question now is should I go for a VHF Hi antenna (e.g., Y10-7-13) to specifically address my Ch 13 problem; or, should I go for an antenna that will address that problem as well as possibly enhance my UHF reception, if that's possible, i.e., replacing my current bowtie.

Thoughts? Thanks again -

[Tower Guy]

Originally Posted by dePorange

I guess my question now is should I go for a VHF Hi antenna (e.g., Y10-7-13) to specifically address my Ch 13 problem; or, should I go for an antenna that will address that problem as well as possibly enhance my UHF reception.

Some have found that 2-edge signals don't always arrive from the expected direction.

Using your existing bow tie will be cheaper, and give you some flexibility in aiming the two antennas in different directions.

[dePorange]

OK - ordered YA1713, fm trap, grounding block, and UVSJ - will let you know how things end up.

[dePorange]

Could you confirm the following is the correct sequencing of the various components (apologies for the crude diagram):

(1) BOWTIEantenna __coax__FMTRAP__coax__UVSJ [ goto (3) ]

(2) YA1713antenna __coax__ UVSJ [ goto (3) ]

(3) UVSJ ___coax___ GROUNDBLK__coax___TUNER

[GroundUrMast]

If you move the FM trap to your #3 section it will be able to filter FM signals that enter through either antenna. (The bow tie antenna is less inclined to receive FM signals but some will be making it into the system)