VHF Challenges in San Diego

[hkinkade]

Here's my site specifics:

http://www.tvfool.com/?option=com_wr...5134219e430b5c

I get a large selection of channels with an old indoor Zenith (Zenith ZHDTV1 HDTV-UHf, yep it's been mounted outside for more than 10 years) all UHF. I Want to pull in 8 and 10.1, so I purchased a Clearstream 2v. It didn't help, even with the antenna pointed directly at the tower. There are no immediate obstructions in line of sight. The channels I am able to get are:

15.1, 15.2, 17.1, 17.2, 21.1, 26.1, 26.2, 27.1, 27.2, 39.1, 39.2, 50.1, 50.2, 50.3, 50.4, 51.1, 69.1, 69.2, 69.3 . . .but no VHF channels!

Based on the channel and strength data I would expect the two VHF channels of interest would be easy.

Other details include:

Antenna about 25 off ground 5 ft from roof surface.
About 100 feet of coax from antenna to distribution box.
Channel View model 0747 amp at distribution box.
Another 70 ft to TV

Any recommendations as to why I can't detect the VHF channels? What antenna do you recommend, note, I don't really want a large attenna due to location and being in predominate view.

[ADTech]

The C2V should be completely adequate for your location, therefore there is a problem. I see three distinct possibilities:

1. Verify you did not reverse the coax cables on the VHF module as that will cause your exact symptom.

2. Get rid of what you're calling the "Channel View model 0747", it does not belong in the system. Most likely, you have an old, leftover power supply from a Channel Master CM7777 or CM7778 preamp still in the system. I'll have to check once I get to the lab, but it may well have burned out the VHF module due to applying power where power doesn't belong.

3. Solar panels have earned a deserved reputation for radiating interference into the VHF bands. Without a spectrum analyzer, though, this can only be determined by a process of elimination which still leaves considerable opportunity for misdiagnosis.

[hkinkade]

ADTech:

1) Confirmed that I did NOT reverse the UHF / VHF connections (I checked twice)

2) I'll remove the power supply. It appears way in the past I mistakenly thought this was a signal amp, day??? I returned the Clearstream 2v. any suggestions on what antenna I should buy in preference over the 2V or would you stick with the 2V

3) Solar Panel interference, is this while they are producing power or strickly reflective?

[rabbit73]

3) Solar Panel interference, is this while they are producing power or strickly reflective?

The interference comes from the DC to AC inverter. Most systems have a separate inverter; newer systems have a small inverter integrated with each panel which are combined.

[shoman94]

I think the C2V is a good choice. It is possible that you would have to aim the dipoles separately but based on what I get with mine, those channels are plenty strong.

Originally Posted by rabbit73

The interference comes from the DC to AC inverter. Most systems have a separate inverter; newer systems have a small inverter integrated with each panel which are combined.

Is there a set distance one should mount an antenna away from them.

[rabbit73]

Yes, the dipole must be broadside (perpendicular) to the VHF signal.

The antenna must be far enough away so that the interference from the inverter is at least 16 dB weaker than the VHF signal. It's trial-and-error unless you have a spectrum analyzer or signal level meter. The coax should be grounded with a grounding block to reject interference.

[shoman94]

Originally Posted by rabbit73

Yes, the dipole must be broadside (perpendicular) to the VHF signal.

The antenna must be far enough away so that the interference from the inverter is at least 16 dB weaker than the VHF signal. It's trial-and-error unless you have a spectrum analyzer or signal level meter. The coax should be grounded with a grounding block to reject interference.

Is having the powered distribution splitter grounded to the electrical panel considered grounding the coax?

[rabbit73]

Is having the powered distribution splitter grounded to the electrical panel considered grounding the coax?

If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge, but the system will not survive a direct strike.

[shoman94]

Originally Posted by rabbit73

If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge, but the system will not survive a direct strike.

I've seen that image. Doesn't make sense to me to run 2 ground wires. Tie one wire to the mast and shield. The shield should be able to be grounded anywhere as long as its grounded wouldn't you agree?

[rabbit73]

It doesn't matter what I think; the NFPA NEC code dictates what is required and the local electrical inspector has the authority to enforce it. He is called the AHJ, Authority Having Jurisdiction.

The authority having jurisdiction (AHJ) is that person or office charged with enforcing the Life Safety Code. In many states the AHJ is the state fire marshal who has local inspectors work on his/her behalf.

https://www.google.com/?gws_rd=ssl#q...g+jurisdiction

https://www.google.com/?gws_rd=ssl#q...lectrical+code

Some satellite companies do something like your way, called piggy-backing, but it does not comply with the code.

http://www.dbsinstall.com/diy/Grounding-2.asp

Todd Humphrey doesn't speak for the NFPA that publishes the NEC code, but he has some ideas that are helpful. The local electrical inspector has the final say if you are willing to get him involved. Some inspectors are more friendly than others; a local electrician could tell you.

As far as I'm concerned, I ground the coax with a grounding block for personal electrical safety because I have had three close calls with electrical shock. The coax is connected to AC operated equipment, and all AC operated equipment has AC leakage current even when it is operating properly. Example here:
http://www.digitalhome.ca/forum/81-o...ml#post1457594
http://www.digitalhome.ca/forum/81-o...ml#post1457668

Some surge suppressor strips have coax grounding jacks, but I don't think it is a good idea to use them. They do ground the coax shield if the strip is connected to a good 3-wire outlet, but the strips often have a surge protection device that is connected between the center conductor and ground that can degrade the TV signal. Also, the center conductor can pick up electrical interference from the AC lines in the strip.

[rabbit73]

Interference from an inverter can be conducted through the power line or radiated through the air to the antenna, or both. Sometimes it is necessary to move the antenna away from the source of interference and run the TV on a separate small sine wave inverter like the Exeltech XP125.
http://exeltech.com/products/inverte...p/125-watt-xp/
http://www.solar-electric.com/xp-125-12.html

[rickbb]

Without the separate ground on the mast ALL of the current it may collect in a nearby strike WILL go into the coax.

A separate more direct and larger ground wire from the mast to the ground rod will divert more of this current and help keep it outside your house.

Remember only the outer braided part of coax is grounded, the center copper wire is not. It will carry some current too, you want to divert as much as you can to something else.

As rabbit stated, no grounding system is 100% effective and a strike close enough or direct will not be stopped. You'd have to make your house a giant 10 million volt capable Faraday cage to stop a direct strike.

[Tower Guy]

I would tend to agree that the likely culprit is interference from the solar inverter(s). One way to minimize the problem is a directional antenna. This helps in two ways, the direct signal from the TV station is amplified by the gain of the antenna and the interference is reduced when the antenna is aimed away from the solar panels and/or the wiring.
Take a look at this option: http://www.mcmelectronics.com/produc...-2475-/30-2475

It claims 12 db gain, but that's really a bit under 10 db referenced to the C2V dipole. Next is the reduced antenna response in the direction of your panels. It might be around 10 db, yielding a net improvement of 20 db. The antenna would be coupled to your UHF section of the C2V with the existing dipole coupler.

The directional antenna would also help if the problem was interference from another source or even ghosting due to multipath.

[ADTech]

The antenna would be coupled to your UHF section of the C2V with the existing dipole coupler.

Can't do that easily with the newest version of the C2V with the clip-on VHF attachment. The VHF balun and the UVSJ circuit are all integrated into the VHF module on this version. You'd have to disassemble the module, remove the dipoles, do some changes with the hardware, then use twin-lead to attach the VHF antenna to the module and it's UVSJ. Ugh!

Just call your nearest (surviving) Radio Shack and see if they have a 15-2586 left on hand. Otherwise, you'll need to mail order a UVSJ.

[hkinkade]

Thanks gang, I have some ideas to check out. I'll try again, if it isn't working I can turn the inverters on the solar system off. at least this should eliminate the noise source as a potential source of the problem. Also, I took the channel view 0747 out of the circuit and lost every channel! I actually think it is a power supply and antenna amplifier in one. It doesn't appear to be soley a power supply (see attachment). Anyway it helps the UHF signal!

[hkinkade]

I researched the CM 0747 some more. Yep, it's the amp, but my wiring hookups never included the preamp. Go figure, maybe that's why I became a mechanical engr. - duh. But, it is interesting that the amp without preamp helps me get UHF, without it I get nothing. I'm going to start over tomorrow with a new antenna, pointed to the VHF channel, without amp. If this doesn't pickup the VHF signals I'll turnoff the inverters. Any other test cases I should do? Any explanation for why the amp alone helped UHF, what issues this could create, and should I try a pre-amp/amp if I continue to have issues?

[rabbit73]

Sorry, but the CM0707 is not an amp, it is a power supply for the original 7777 and 7778 preamps. More exactly, it is a power supply/power inserter.
http://www.solidsignal.com/pview.asp?p=cm0747







There is no amplifier shown in the circuit diagram, only a power supply and power inserter. The power inserter is in the upper right corner, consisting of inductor L and capacitor C2 which allow the power for the preamp and the TV signals to share the same coax line to the preamp mounted near the antenna.

[hkinkade]

Rabbit 73, I should have taken the cover off. It's clearly just a DC power supply.
Does anyone have an idea why placing a DC power supply in-line helps with reception (without power supply no reception, with power supply over 20 channels received).

[rabbit73]

That is the way it is supposed to work when there is a preamp between the antenna and the power supply.

Did you inherit that system from a previous owner? Who put the 0747 in the system?

I'm going to start over tomorrow with a new antenna, pointed to the VHF channel, without amp.

What new antenna? A separate VHF antenna like the MCM 30-2475 or 2476 combined with the Zenith or a VHF/UHF combo antenna? For what, ABC?

[ADTech]

That is the way it is supposed to work when there is a preamp between the antenna and the power supply.

He had only the P/S installed, no amp.

Does anyone have an idea why placing a DC power supply in-line helps with reception (without power supply no reception, with power supply over 20 channels received).

Probably attenuates an interference, fixed an impedance mismatch, fixed a bad connection.... Dunno, shouldn't have made any difference logically.