^ Thanks for doing that. :)

Yes, I am using largish "Made in Japan"/Sony baluns that came with old TVs for now. I opened some up and the internal wire gauge is at least 10 bigger (and cores appropriately larger) than some similar-looking baluns sold at The Source etc. The wire in some of these is like 30ga, and on a tiny core...can't help at all.

Just would prefer to use a known-good type as I can't measure performance here. Don't know anything about the MTO2 matching transformer from Durham Radio, google doesn't help. Seems a bit too cheap to be good...but you never know.

I currently have a VHF/UHF antenna (similar to a winegard HD7082P) mounted about 1 meter above my roof line on a rotor and I would like to add a channel master CM 4221HD antenna pointed in a different direction. I currently get about 20 channels.

I have a channel master cm-7777 masthead pre-amplifier, not yet installed. Additionally, the plan is to use equal lengths of RG6 from each antenna to the cm7777. The output from the cm-7777 power supply will be split to 4 separate TVs using a PCT-MA2-4P. All cables are Belden 7916A RG6 quad shield solid copper core.

The UHF/VHF antenna is now normally pointed at azimuth 339 and the new 4221HD would be pointed at 136 to 149. There are about 40 channels within line of site (LOS) and only 4 channels are channel 9 or less, the most desireable VHF channels are at azimuth 148. The possible receivable UHF channels seem to be split evenly at 339 and 147.


Questions:

1. Is it ok to mount the 4221hd below the UHF/VHF antenna and what should be the separation distance?

2. Would it be best to install the cm-7777 and cm 4221HD and feed the VHF/UHF into the VHF port on the cm-7777 and the cm4221hd into the UHF port and set the cm7777 input to separate inputs? or should a splitter be used or a diplexer?

3. In order to get the best reception of UHF stations with the VHF/UHF antenna, should the end with the long elements be pointed in the desired direction or is it better to point the end with the short elements in the desired direction?

4. On the cm4221HD is the receiving side with the one with the X elements?

5. What direction should each antenna be pointed?

I followed the instructions from a document by industries canada about making your own filter out of a piece of coax.

I want to filter out VHF 12 from CFCF12 that causes interference to VHF13.

I did the following test:

- I tuned to Analog VHF13 and saw some ghost from CFCF 12

then I made the coax stub for VHF 12, I followed the instructions, I made the stub a bit longer and progressively cut out half centimeter at a time.

I must be missing something. The stub does not seem to filter out anything, CFCF12 still comes strong.

I have a preamp so the stub goes before the preamp, i.e. close the the antenna.

I did not have the T-connector so I sort of split the coax and tap into it to make my own T-connector, I hope that is ok.

http://www.digitalhome.ca/forum/picture.php?albumid=85&pictureid=571
http://www.digitalhome.ca/forum/picture.php?albumid=85&pictureid=570

Post the stub length range (max to min) that you tried, and the exact kind of coax used (printed on the coax itself).

Then someone here can double-check things.

Cheers

Channel 12 uses 205.25MHz as the center of the Video carrier (wikipedia (http://en.wikipedia.org/wiki/North_American_broadcast_television_frequencies)).

Assuming RG-6 coax is used, the velocity factor is usually about 0.75, though this will vary by batch and by brand.

So 1/4 wavelength is 27.4 cm, and that's the total distance from the point of the tap to the end of the coax for the 1/4 wavelength notch filter.

This won't get rid of channel 12, but it should reduce the signal intensity seen, and therefore reduce interference with adjacent channels.

Cheers

The coax I used says RG6 75 Ohm, no name on it. I bought a while ago on a 500-ft spool from Addison

The length of the stub was 30cm to 25cm cut about half centimer at a time

That should cover the frequency range of CFCF12 from 204-210 MHz and variations of velocity factor from 0.66 to 0.75

by the way, the dangling end of the stub is not shorter together right?

The instructions says to shorten it only if the stub is half wavelength

by the way, the dangling end of the stub is not shorter together right?
That's correct. It should just dangle, away from any unshielded portions of the system. The signal just reflects back upon itself from the open end.

Again, it won't get rid of the channel, but it should make it slightly weaker. You can add more of these tap/filters to increase the effect, but I'm not sure of the best spacing to use between them.

Mlord, I did not have any T-junction so I split the coax main line and tapped the stub into it. Is that OK?

alternately, can I use a 2-way splitter to act as a T-junction?

I did more testing and conclude that the stub I made to suppress VHF 12 is not sufficient to kill it because the signal from CFCF12 is so strong. Actually its suppressing bandwidth is quite wide, it completely kills also VHF 13 at some point if I cut it shorter than 25cm. I receive VHF 13 very weakly and in an attempt to kill interference from CFCF12, I made the stub but it turns out that it is not a good idea.

Is it an older TV set ? Do you have the same problem on other sets ? One drastic way around that problem would be to de-tune the tuner. Or maybe it is de-tuned or misadjusted now ? Older sets had detent tuners with ferrite slug coils that you could easily adjust from the front of the set.

300Ohm: I don't understand what you mean by de-tuning the tuner.

I have a recent ATSC TV manufactured this year, the latest ATSC chip I believe.

I am attempting to catch WVNY-DT on VHF13 and was suspecting that CFCF12 analog is interfering with the digital signal. That is what people from WVNY told me in an email.

300Ohm: I don't understand what you mean by de-tuning the tuner.

I have a recent ATSC TV manufactured this year, the latest ATSC chip I believe.

With the older sets, you could play around with the tuner. Im not sure because I havent played around with the tuners on newer sets, but you may not be able to adjust yours. (and you shouldnt if you dont have a full understanding of it, because it can be dangerous. In other words, dont try this at home, heh)
Its possible that its adjusted at the factory using a pricey software interface, not feasible to buy to do just one set.

Questions:

1. Is it ok to mount the 4221hd below the UHF/VHF antenna and what should be the separation distance?

Optimally the antennas should be 1/2 a wavelength apart so it all depends what the lowest channel number you are wanting to receive is. Some people use 1m as a rule of thumb, but this could be too close in some circumstances and further than necessary in others.

2. Would it be best to install the cm-7777 and cm 4221HD and feed the VHF/UHF into the VHF port on the cm-7777 and the cm4221hd into the UHF port and set the cm7777 input to separate inputs? or should a splitter be used or a diplexer?

Plugging the VHF/UHF antenna in to the VHF port will block the UHF signals from that antenna, so if you want to use it as a VHF only antenna, that is the best way to go. If you want UHF signals from both antennas then you will need to use a signal combiner, but that could cause other reception issues (including a minimum of 3.5 dB of signal loss). A diplexer is only for combining signals from different bands so is not appropriate for this.

3. In order to get the best reception of UHF stations with the VHF/UHF antenna, should the end with the long elements be pointed in the desired direction or is it better to point the end with the short elements in the desired direction?

It should be pointed with the small elements pointed towards the transmitter and large elements at the back (this is true for both VHF and UHF).

4. On the cm4221HD is the receiving side with the one with the X elements?

Yes

5. What direction should each antenna be pointed?

Impossible to say without knowing your location. Please post this question in the thread for your city.

Optimally the antennas should be 1/2 a wavelength apart ..
Err.. actually, it's not 1/2 wavelength (which is tiny for UHF). Rather, they should be arranged so that their receive aperatures are just barely not-touching. For UHF antennas, this measurement often ends up being close to a meter or so, but it really does depend upon the specific antennas.

Cheers

Err.. actually, it's not 1/2 wavelength (which is tiny for UHF). Rather, they should be arranged so that their receive aperatures are just barely not-touching. For UHF antennas, this measurement often ends up being close to a meter or so, but it really does depend upon the specific antennas.

Thanks for the clarification. I was basing it on information received from tvantenna.com (http://www.tvantenna.com/support/tutorials/combining.html), but I guess you can't trust everything you read on the web.

The yagi thread in the antenna R&D section has much better reference links for stacking.

This one, Stacking, Phasing, and Matching Yagis (http://www.grantronics.com.au/docs/StkYagis.pdf) explains the concepts in considerable detail. The article is about yagis, but the stacking principles can be applied to other designs.

Cheers

The yagi thread in the antenna R&D section has much better reference links for stacking.

This one, Stacking, Phasing, and Matching Yagis (http://www.grantronics.com.au/docs/StkYagis.pdf) explains the concepts in considerable detail. The article is about yagis, but the stacking principles can be applied to other designs.

Interesting article mlord, although it is focused on stacking antennas pointed in the same direction for the purpose of increasing gain. Things are quite different when the antennas are pointed in different directions like cigar7 is wanting to do.

Sorry if this question is stupid.

So Lets say I have two diplexers that do NOT block DC. I connect them in the normal way and do not have a preamp on my antenna. Will the DC voltage from the receiver act as a preamp on the antenna? Or what will this do to the antenna is anything?

Interesting article mlord, although it is focused on stacking antennas pointed in the same direction for the purpose of increasing gain. Things are quite different when the antennas are pointed in different directions like cigar7 is wanting to do.
Ah. I missed that, thanks.

Elsewhere in that same yagi thread, is a link (which I've lost track of now) that dealt with that situation as well. It turns out to use the exact same math, and suggests that for UHF *especially*, it is important to keep the other antennas outside of the receive aperature.

Or worst case, outside of 1/2 the receive aperature. So, same calculations apply.

Cheers

Sorry if this question is stupid.

So Lets say I have two diplexers that do NOT block DC. I connect them in the normal way and do not have a preamp on my antenna. Will the DC voltage from the receiver act as a preamp on the antenna? Or what will this do to the antenna is anything?

The simple presence of a DC voltage does not amplify an RF signal. What are you diplexing? If you're connecting a satellite dish and an OTA antenna to the diplexer, then you don't want the DC from the satellite receiver to go up the antenna. The satellite receiver uses a DC voltage to switch the polarity of the LNA on the dish; I don't know of any other type of receiver that outputs DC on its RF input.