Trouble with my mast mounted antenna system

tvtom · 6-Nov-2011, 3:54 PM

Greetings, I am a newbe to this very interesting forum. It is possible if I searched long enough I could find and put together some answers to my questions. But decided ask.

1st a summary.
I have had a mast mounted system since 2002.
Winegard AP 8275 preamp (2006)
Winegard HDA 100 distribution amp (2006)
Recently changed (last week) from a CM 3023 to Terrestrial DB8 UHF antenna (no VHF)
On rotor
Antenna is about 39 feet up, and we live on a hill
There a the tops of a couple trees for the 1st 500 feet or so of the LOS
We are 41 miles LOS South South West of South Bend IN antenna farm (east of Winamac) about

Recently I had lost some channels (the weaker ones). Decided to try the DB8 as it had more advertized gain than the CM3023.

It did not help any. I decided the problem was in the preamp or the cable.
I purchased a Radio Shack preamp (they are close out here in the boonies) in case I needed if once I dropped the tower. I discovered that the cable shielding had deteriorated greatly apparently from a coax splice I had put in near the ground and sealed with tape.

I replaced the entire cable with new rg 6u cable. Did not replace the preamp.

The results were-
The channels with previously good signals came in very good. The ones with previous moderate signals (in the middle green band on my digital converter box) were helped slightly. The antenna seemed to have a narrower pointing angle than the cm3023. but the channels with previous weak signals (PBS WNIT the main one) were zip, nothing. This channel would come in often previously. Although it does not have much power 85KW, the tower is high, 1100 feet (according to my info); it seems I should be getting that signal good with the DB8.

1- My 1st question here is - Why would the DB8 seem to pull in the previous strong signals better than the CM3023?
2- Is there experience that the DB8 has a narrower pointing angle than the 3023.?
3- I am thinking of dropping the antenna again-
a- Can I put the CM3023 up with the DB8 and connect them in parallel through an inverse splitter into the preamp on the pole, and should that help, make no difference, or?
b- Should I replace the DB8 with the CM3023
c- Should I change preamps?

Although it is not too hard to drop the tower... it is not trivial.

Thanks very much for any comments....

TVTom

tvtom · 7-Nov-2011, 4:27 PM

If I understand it right my report is here-

http://www.tvfool.com/?option=com_wr...4bba0561c80519

GroundUrMast · 7-Nov-2011, 10:05 PM

Several questions,

How many feet of cable lay between the AP-8725 the the HDA-100?

Is there a splitter after the HDA-100? If so, how many feet of cable lay between the HDA-100 and the splitter? How many output ports does the splitter have?

How many sets are connected?

How many feet of cable lay between the antenna and most distant tuner?

tvtom · 8-Nov-2011, 1:02 PM

Starting at the top-
- There is about 1 1/2 feet of coax between the DB8 and the mast mounted 8275 preamp
- There is about 75 feet of coax between the preamp and the 8275 power source (mixer is it).
- There is about 2 feet of coax between the preamp mixer and the 100 distribution amp.
- I do not have a VHF antenna so there are no vhf uhf combiners.

- there is about 30 feet from the 100 to my distribution board and the splitter
[correction] - the splitter is a 1 to 4
[correction] - there are 3 TVs and 1 fm radio on the output of the splitter
- the cable length to these is about 25 +/- 5 feet.

<<<<How many feet of cable lay between the antenna and most distant tuner? >>>>
- I assume you mean the TV tuner... adding the above together
1 1/2 feet
75 feet
2 feet
30 feet
25 +5 feet

About 138 feet.

The system had been working pretty well until a while ago... a month, several weeks.... it may have been slowly degrading (like tire tread) and I had not really noticed it. The weaker channels appeared to be weather sensitive and sensitive to different TV sensitivities.

I have moved TV's around on different cables, and moved one to the output of the distribution amplifier (splitter disconnected) and also to the output of the preamp mixer. The results were very similar.

After reading a note from the cable guy, I decided I should have checked the cable between the mast preamp and the antenna. The connectors looked good but I did not check the shield. The shield on the downlead cable was very bad, and is why I replaced it. When the wx clears up I will drop the tower and check that cable.

Thanks
tvtom

PS- I after some wavelength calculations I have decided it is not practical to add the 2 antennas DB8 and 3023 together. It seems I would have to match the mixer within a mm or so to assure summing.

[added] PS2 Last eve (Monday) my weakest channel WNIT 34 (35 RF) was coming in STRONG signal bar way over to almost max. It was raining lightly had been all day.

GroundUrMast · 8-Nov-2011, 7:24 PM

Thanks for the details.

So, 138' of RG-6 will have about 9 dB of loss at the upper end of the UHF band. (Assuming 6.5 dB loss per 100')

The AP8725 is rated at 28 dB gain (UHF). The HDA-100 is rated at 15 dB gain. Both amplifiers are rated at about 3 dB NF which means that even if the HDA-100 is not overloaded by the preamplifier the combined noise figure of the two amplifiers is about 6 dB. The NF of each amplifier is a negative, a source of noise added to the signal.

I'd like to suggest an experiment.

Try connecting a single TV to the output of the AP8725. (I'm thinking that it may be easy to disconnect the cable from the input of the HDA-100 and connect that cable to a TV.)

My suspicion is that the new antenna and coax repair is delivering more signal to the HDA-100, overloading it to some degree. I'm also thinking the AP8725 is possibly over-driven... but I don't want to make you lower the tower unless we prove the need.

tvtom · 8-Nov-2011, 9:01 PM

Thanks for the info....

Today I did some 'serious' trouble shooting. After doing a lot of the stuff you mentioned I came to the conlusion that the Distrib Amp was bad. I disconnect all and moved down to the preamp out and the distribution amp out. It all of a sudden, it seemed went blank. I connected to the pre amp out and good signals... The thing I dont understand is the signals were reasonable wether the power was on or off the preamp.

Finally I hooked all back up, by passing the distrib amp, with all 4 loads on the splitter and we have all of our channels back again with good signal levels on the 'signal meter reading'. Amazing.

I am going to blame some on the wx.... Will know more tomorrow....

have to feed the dogs and then go to a Pathway construction meeting.

Thanks for the info...

tvtom · 9-Nov-2011, 3:26 PM

Signals still very good (Wed morn). Still very humid, rainy.

I can even pick up some Chicago UHF stations. Have never been able to to that. From the signal levels on my Convertor box, with a little more gain or antenna height I could pick up more.

But I am about maxed out... DB8 15.8 gain (advertized). And my mast height is at its limit, to keep it droppable and (relatively) easily home repairable.

Will check again in dry weather to see how it goes.

At a convieient future time I will drop the mast and check the antenna connections and seal with liquid tape...

Thanks for all the info on TVFool

Ps, I still find it amazing how much improvement I got by bypassing the Distribution Amp and feeding the Preamp output directly into the 1:4 splitter.

GroundUrMast · 9-Nov-2011, 3:54 PM

Rule of thumb: "One amplifier can be too many - Two amplifiers are too many."

Consider, would you connect a pump designed for low pressure or suction input to the output of a high pressure pump? Or, would you connect a public address amplifier to the speaker output of another public address amplifier?

I'm not certain the HDA-100 is bad, but I'm certain it was misapplied.