Bizarre Intermittent Reception

Bobster · 12-Sep-2011, 3:52 AM

First, here is my report:

http://www.tvfool.com/?option=com_wr...8387b67abd9e9f

I have been having OTA reception problems. I had an old TV antenna and got sporadic reception on all the channels, so I recently installed a RCA-ANT751 and still had some stuttering, especially on 8.1 and 33.1 (odd as they are hi-VHF and UHF). I added an amplifier and all the channels worked wonderfully.

However, less than a week later the stations all disappeared. I could only get 13.1 (14) and 27.1 (36). I took the amplifier off and still only got 14 and 36.

I live near the old Carswell Air Force Base, and the Lockheed plant in Fort Worth, Texas, so I wonder if there may be some type of interference from their radio or radar transmissions.

Any ideas or information would be greatly appreciated. I live in River Oaks, Texas, just north and west of downtown. My antenna is pointed at 118 degrees south east where the transmitters are. I'm stumped and would really appreciate your input.

John Candle · 13-Sep-2011, 5:31 AM

Your lngth , Letting reception with out evhere are problems witectors or etc. nna?? e roof?? If in the attic is thountd by the building?? Heg transformerg transformer , the coax that is connected to the ma is the reception now??

Bobster · 13-Sep-2011, 1:59 PM

John, thanks for your input.
The antenna is on the roof of a single level house. It is pointed as LOS toward the broadcast towers. I actually used the TVFool map and a compass.

There are trees about 40 feet away which block the LOS but they extend across the back of the neighbors properties to the south and east so I can't move the antenna to get around them. They are very old and very tall so I'd probably need a 60 foot mast to get over them and I'm not ready for that.

The fact that there are so many strong signals is what completely perplexes me. I am using the brand new transformer that came with the RCA antenna and a brand new run of 50' RG6 coax. I do have a coupler to extend cable to a 25' run down to the TV and the amplified was added at the TV because of "stuttering" on channel 33 and no signal from 8. My reasoning was that the coupler would have less signal loss than an unneeded extra 25 feet of coax. You seem to suggest that I get a new 100' cable run (I don't have any 'known good cables') which will likely be my next course of action and try it without an amp. I don't look forward to spending time in the attic in the 100 degree heat!

I'd appreciate any other suggestions.

John Candle · 13-Sep-2011, 2:33 PM

Is the antenna o the com tter conductor.

GroundUrMast · 13-Sep-2011, 6:20 PM

I agree with John, close inspection of the matching transformer and coax is in order. In addition to the obvious short circuit caused by shield wire, is there any possibility that water could have gotten in to the coax? One of the least expensive items in a collection of 'test equipment' is a 100' section of RG-6 with good connectors, a matching transformer is even less expensive.

Testing would not require that you replace the existing run. Temporally run from the antenna to the set through an open window or door. If you prove trouble to the existing cable or transformer, then proceed with replacement.

It sounds like you are running the cable through your attic. I avoid working in my attic on a sunny 50° day.

MisterMe · 13-Sep-2011, 6:28 PM

Quote:

Originally Posted by Bobster

... the amplified was added at the TV because of "stuttering" on channel 33 and no signal from 8. ...

I'd appreciate any other suggestions.

I presume that you mean that you are perplexed by the fact that you have so many strong signals that you can't receive. You say that you have a stand of trees between your antenna and the TV transmitters. We know that trees block UHF, but I have read no post or link on this forum why this is the case. We also know that trees attenuate VHF, but they do not block it all together. Many tree leaves are about the same size as the elements of a UHF antenna. Somewhat like an antenna, green leaves extract the energy from UHF and send it to ground. VHF is much longer wavelength for which tree leaves do not act like an antenna.

This does not explain why you are not receiving WFAA (Real Channel 8). With the strength of signal that you should be receiving, you should receive something if only from the VHF low-power stations in your area. It might behoove you to survey your property with a signal strength meter or VHF/UHF set top antenna at the end of a long pole and connected to a portable digital TV to see what if you can find a signal anywhere. I would actually begin the survey with the rabbit ears connected to your regular TV. This would help to exclude connection issues with the big antenna and cabling.

GroundUrMast · 13-Sep-2011, 6:51 PM

Quote:

Originally Posted by MisterMe

... We know that trees block UHF, but I have read no post or link on this forum why this is the case. We also know that trees attenuate VHF, but they do not block it all together. Many tree leaves are about the same size as the elements of a UHF antenna. Somewhat like an antenna, green leaves extract the energy from UHF and send it to ground. VHF is much longer wavelength for which tree leaves do not act like an antenna.

...

Regarding UHF, block may be too strong a term. UHF frequencies are attenuated more than VHF, but less than microwave frequencies when passing through vegetation. Water molecules (rain, snow, vegetation, etc.) are excited by RF. Energy is dissipated as heat. Yes, trees are grounded, but the attenuation will still occur if a tree were isolated from ground The phenomenon is more pronounced as frequencies increase which is why microwave ovens operate at 2.4 GHz rather than VHF or UHF frequencies.

Given the predicted signal levels, vegetation attenuation does not explain complete loss of signal on all but two channels (IMO).

Bobster · 14-Sep-2011, 1:35 PM

@John Candle - The antenna itself is on a mast 6 feet above the roof. The RG6 runs through a hole into the attic and then downstairs. The roof is typical asphault shingle. I checked the cable and the shielding does not appear anywhere near the conductor.

@GroundUrMast - There's no chance water got to it. It's too high for the sprinklers and we haven't had rain here in months. The transformer is new (it came with the antenna) but I can get a cheap one and swap them out for the test. Thanks for the idea of not restringing the cable! I don't know why that didn't occur to me. Here in Texas the attic only cools below 100 degrees a few days in January and I don't want to wait that long for TV.

@MisterMe - I like the survey idea. The downside is that this is an intermittent problem. Last night, for instance, everything was working peachy. Not a glitch on any channel. Any chance a HAM radio operator could be on a frequency (or frequencies) that might be interfering with my reception when s/he's broadcasting?

Any additional input would be greatly appreciated. I'll keep you posted on swapping the transformer and cable (which I presume could have an intermittent short), which I'm hoping to do this weekend.

Thanks to everyone for their insights.

MisterMe · 14-Sep-2011, 2:22 PM

Quote:

Originally Posted by Bobster

...

@MisterMe - ... Any chance a HAM radio operator could be on a frequency (or frequencies) that might be interfering with my reception when s/he's broadcasting?

...

I can't give you absolute assurance, but the chances of a HAM interfering with your reception are vanishingly small. It is illegal for an amateur radio operator (HAM) to transmit using faculty equipment. He can be prosecuted. If the HAM deliberately transmits using commercial frequencies, then he stands a good chance of being incarcerated. Other HAMs take a very dim view of even accidental violations. The violator will be reported and apprehended.

BTW, HAMs do not broadcast. Broadcasting is a violation of the HAM's amateur operator's license. HAMs communicate on one-to-one basis or within a group of HAMs. Of course, they may also listen to anything that their equipment can receive.

If your TV reception suffers from HAM interference, then the faulty equipment is likely to be yours. If you know of a HAM in your neighborhood, then ask him to help you identify and fix your problem. This is not an imposition, it is a service that HAMs provide for their neighbors.

Bobster · 24-Sep-2011, 4:28 PM

@MisterMe - Sorry if it seemed I was implicating HAM operators, please know I wasn't. I just can't figure out why I get all the stations some days and only 2 on other days.

At this point I have tried John Candle's idea and run a straight coax (with a new transformer) and it did not make any difference. Some days it worked other days not. I also tried the survey idea, walking all over the roof on one of the days I only got 2 channels. No where I moved the antenna did it make any different. Of course, a few days later all the channels reappeared (with the antenna in its original spot).

At this point I'm thinking of getting a "deep fringe" antenna as a last resort. Any input of whether that may help. I'm afraid whatever is interfering with my signal currently will just keep interfering, but I don't want a monthly bill.

Thanks for your input, oh mighty ChannelMasters!

John Candle · 24-Sep-2011, 5:43 PM

When to trhbc jytxk

GroundUrMast · 24-Sep-2011, 7:08 PM

Rather than repeating the suggestions regarding coax and matching transformer -- Which you have already tried, let's start investigating FM interference... I don't see an obvious indication when I search the FM Fool data base but a Radio Shack 15-024 FM-trap is about $8.

Also it's time to consider the possibility that your converter box may be having problems. A bad F connector on the back perhaps?

Bobster · 18-Oct-2011, 4:56 AM

Thanks everyone for their input. I've checked all the cables, all the connections and switched out converter boxes (2) as well as using the built in TV tuner. Conclusion: it just depends on the day and time. I can't find a correlation between weather, heat or time of day.

I'm going to get an amplifier for the mast and see if that helps. My guess is it will help when I can't get signals now, but will overpower the signals when they "work". This has really been a strange experience!

GroundUrMast · 18-Oct-2011, 11:53 PM

An amplifier is at the bottom of the list based on your TVFR.

If you are going to spend the money, be sure to buy from a vendor with a liberal return policy.

Also, be sure to select an amplifier with high input capacity, you have a lot of signal, most amplifiers on the market are going to overload.

CPA-19 and HDP269 come to mind...

I'm going on the record as saying, "An amp is not going to fix the problem".

If it changes the situation, I won't be surprised... I expect it to make things worse.

There may be a source of local interference in the neighborhood or something is loose or corroded.

Bobster · 19-Oct-2011, 2:43 AM

GroundUrMast: Thanks for all your input but I've replaced every part of the system but the mast. I can't imagine what could be corroded and I've used multiple coax runs, transformers and tuners. I don't know how to check for interference from anything nearby (as I noted in my OP I'm near an air force base so maybe they are doing something) and frankly, I've lost faith in the TVFR. My neighbors report the same situation with their reception and they have a Winegard fringe antenna. As I said, I'm stumped so I'm going to try the amplifier route. After that I'm may look to a deep fringe antenna and then cable. I'll keep you posted!

GroundUrMast · 19-Oct-2011, 3:08 AM

This sounds like interference...

Do you know any HAM radio operators? In the HAM community you may find someone willing to help... who has access to a spectrum analyzer. That equipment in the correct hands can locate interference sources.

Sorry this is a tough one...

MisterMe · 19-Oct-2011, 4:50 PM

Quote:

Originally Posted by GroundUrMast

This sounds like interference...

Do you know any HAM radio operators? In the HAM community you may find someone willing to help... who has access to a spectrum analyzer. That equipment in the correct hands can locate interference sources.

Sorry this is a tough one...

I second this recommendation. If the interference is as ubiquitous as the OP implies, then local HAM operators will be aware of it and will have measures in place to mitigate the problem for their communications.