Installed a Dayton VIT-1 video isolation transformer from partsexpress.com and it corrected the speaker hum and video issue I was having but now I think it is blocking some of my HD cable channels. It does say that it interferes with digital cable and satellite TV, but in all the posts I have read about this thing this issue never came up. Is there a better unit out there that will work? Has anyone else had this same problem when using this part?

First, check your ground block, make sure you are properly grounded.
Secondly, if your are on cable, make sure you turn the volume up on your converter box, so you can turn down the actual tv volume. Third, try to use optical audio whenever possible.

Parts Expresses's published specs (www.partsexpress.com/pe/showdetl.cfm?Partnumber=180-075) say it only passes down to 100 MHz, which will block a lot of signals. Those are the worst published specs for such a product that I have ever seen.

For $12.25, you will probably have better luck with this one, a model CCI-1 (www.cencom94.com/gpage.html8.html), from Holland Electronics.

As primitive as this sounds, you need a physically larger one because high-pass capacitors vary in capacitance with physical size and roll-off frequencies tend to vary inversely with capacitance.

Update: I just found it elsewhere (http://www.techtoolsupply.com/browseproducts/CCI-1-Cable-Isolation-Filter.html) for $9.95. If you care about a couple bucks, you'll have to compare the shipping, handling and minimum order prices.

(I paid $40 each for an order of ten of them about a decade ago. They were worth it, even at that price)

Parts Expresses's published specs (www.partsexpress.com/pe/showdetl.cfm?Partnumber=180-075) say it only passes down to 100 MHz, which will block a lot of signals. Those are the worst published specs for such a product that I have ever seen.

With an upper limit of 1 GHz, presumably covering the HD frequency QAM slots, anyone know how the lower 100 MHz limitation would block HD channels? Some feedback to the head end...registering what from the STB? What's a typical lower filter limit?

My 860+ Mhz NYC TWC system, as member Berk32's Excel spreadsheet (http://www.avsforum.com/avs-vb/attachment.php?attachmentid=96603&d=1197609415) shows, only carries 5 analog channels <100 MHz. Thanks. -- John

We have several digital channels on lower frequencies in Washington, DC. I believe that when they took out the analog-scrambled HBO and Showtime, which I think were in the VHF lowband, they replaced them with digital channels.

I think that most cable boxes send their upstream signals around 108 MHz, so those would work with the Dayton VIT-1, but internet modems send their upstream signals below channel 2, often as low as 10.5 MHz. I don't know if any cable tuner boxes use sub-band for upstream communication. I have never had a sub-band signal blocked by an isolation filter, but I have had them blocked by certain diplexers.

FWIW, when I recently sweep tested old CCI-1 isolation filters that were labeled to pass up to 1GHz, they passes signals up to 2 GHz with no roll-off.

Thanks for all the help so far. Anyone else want to put there two cents in?

Here's a unit from Jensen Transformers: the VRD-1FF
(data sheet: http://www.jensen-transformers.com/datashts/vrd1ff.pdf).

It has a quoted typical passband (-3 dB) of 1 MHz to 1300 MHz. It lists for about $60, though, so it's considerably more expensive than the Dayton product. Jensen Transformers is a very old and reputable transformer company. The DC blocking spec is confusing. In one place in the spec sheet it lists the max DC "input to output voltage" as 200V. At the bottom of the spec sheet, though, it lists the maximum "DC or peak AC voltage between input and output" it can withstand as 34V.

I'm considering getting a VRD-1FF for my system, but the 34 V max voltage may not be great enough for my application -- I measure 41 VAC between my cable and TV grounds. I had audio hum until I isolated the ground of my power strip, which cured that problem. But the obvious large voltage difference between my cable and TV grounds bothers me.

Prfssr

I have used one of the Jensen units for a number of years with no problems at all. If you look at the reviews on the Dayton VIT-1 a number of them say they had similar reception problems when using it.

prfssr: 41 volts is a whole lot of voltage to have between things that are suposed to both be grounded. I think you need to find out why this is happening.