Ch 61 WB19

[techboy]

I am having an awful time getting a constant signal level from this station.  I have a 15 foot over the roof mounted 4 bay bow tie antenna pointed directly at the tower which is just 1 mile due south of me. No trees in the way!  And yet on my receiver the level meter fluxuates between 10 and 100 ( and anywhere in between ) at random intervals.  If it drops below 10 the picture freezes.  I don't have any signal level issues with any other DT channels.  Anyone else have this level bouncing trouble?  How much ERP are they running?   I get channel 25, 35 and 40 off the same tower perfectly.  Even Ch. 33 comes in 100 percent.  Sure Ch.61 is a higher frequency, but I'm only 1 mile away.

[techboy]

Well Sir:  It's not a problem of too much signal.  The issue is a signal level which can vary from moment to moment from very good to nothing.  Normally you might want to blame this on trees or some other multipath anomally.   But I have line of sight and about 1 mile to the transmitter.  Signal level actually was more stable during the summer when foilage was out.   I've a good deal of experience in UHF  RF as well, and I can't determine the cause.  The level meter in my receiver is not a true RF AGC indication, but rather a combination function of how much error correction is occuring as well.  My system also indicates that Ch 61 is running a 65mbps transport stream.  That's impossible, as 19.15 mbps is the max allowable.  So, I may have some other issue here.  If no one else sees this vasilating signal level, then I need to look beyond antenna issues.    BTW, I know that the Ch. 61 frequency assignment is temporary.  Anyone have an idea when the move to the permanent DTV channel occurs?

[techboy]

Well Sir:  It's not a problem of too much signal.  How else can I say that?  All I want to know from this forum is if any one else has a severely fluxuating signal level.  Apparently your level is stable and you have a lot of 3db pads laying around.  I didn't go into a lot of details in my post, but I have tried different antennas and in different locations around my home and they all exhibit the same level changing behavior.  I thought an antenna 15 feet over the roof would eliminate the possibility of multipath and tree absorbtion.  It didn't.  So, either the signal is actually changing in RF level, is out of spec, or I have a decoder problem.   I'd like to see this on a spectrum analizer, but I don't have access to one.   DTV is randomized so as equal modulation energy is applied across the full 6 Mhz.  If my antenna isn't flat, or my lead in has an impedance notch, or some damn balun is resonate, or I could go on and on.  Does anyone else see a fluxuating signal level on Ch. 61?

[wxndave]

Actullaly it can be a problem with to much signal.  It might not be to much on channel 61, but it can be interference from another high power TV/DTV transmitter overloading the tuner and may cause a mixing effect.  I have seen some STB and tuner cards have problems because of hot signal levels.  If you are a mile north of the transmitter then you are almost next to the channel 63 transmitter.  I'm not saying that Ch 63 has a problem, I'm just pointing out that you might have signal overload.

Channel 61 & 25 are transmitting the same power output from the same tower location.

Dave

[John L]

Originally posted by techboy
 BTW, I know that the Ch. 61 frequency assignment is temporary.  Anyone have an idea when the move to the permanent DTV channel occurs?

Perhaps JimBoy can best answer this question.  Afterall you are right that ch. 61 has to be temporary because the FCC plans to auction off channel 51 and above.

I would assume this to occur when the analogs are required to shut down.

So Jim does that mean eventually the DTV on ch. 61 will move to ch. 18 after the analog goes off?

-John L.

[techboy]

I checked the FCC's 6th report and order for Wisconsin DTV's and it indicates that Ch.61 is licensed to operate at 497.5 Kw and Ch.25 is licensed for only 106.4 Kw   I don't know what each is actually operating at, as the FCC has often granted waivers to lower power.   In any case, I've given some thought to the front end over load / intermod possibility.  My problem couldn't be caused by a DTV transmitter as they have nearly constant output power regardless of what's in the stream.  However, an analog TV transmitter's output power changes with picture content.  Amplitute modulation.  That is, black being maximum modulation, not counting tip of sync of course.  So, intermod from an analog transmitter ( frequency X?) with DTV Ch.61 could be causing my signal level to fluxuate as power varies with picture content.  (The degree of intermod varies with analog picture content.)  Now if I could just figure out which analog channel is it.  BTW, pads don't help.  All signals drop proportionately.  The answer will be in a bandpass filter for Ch 61 or a bandtrap for the offending analog channel.  Anybody got a spectrum analyzer or a tracking signal generator good to 800Mhz?

[Nels Harvey]

I wonder if Techboy's problem is multipath?  An actual analog signal strength measurement, not a digital indicator, might indicate he is UNDER the cone of the radiated signal.  If so, he could be subject to receiving a strong reflected signal, from a nearby reflector of some sort, that causes the RF level to vary based on a phase relationship.

Some TV transmit antennas employ beam tilt, others may employ less, or none, depending on the coverage desired.  Ch. 25 may have more beam tilt, or something.

My experience with TV measurements show problems under the umbrella of such TV antennas, resulting in the kind of multipath being experienced.

Possible solutions might be to reduce the antenna gain, or change direction of the antenna.  This is a very common problem on Milwaukee's east side, and in Shorewood.  I do wish you well.

Nels....

[techboy]

Thanks Nels:

I am indeed directly 1 mile east of the WABC / WCBS towers and so I'm possibly on the backside of them, particularly if they are running a cardiad pattern ( Lake Michigan null ) antenna. I don't know if they are patterned or beam tilted, but I have no issues with them.  I am 1- 1/2 north of the super tower.   I should be outside any usual "cone of silience".  I know Ch 28 is running cardiad and some uptilt as I was there when the antenna was purchased and installed.  No problem with them either.  Actually no problem with any signal other than ch 61.  Ironically. it has actually gotten much worse since the leaves have dropped.  The rooftop antenna signal is no longer stable enough for break free reception.  My bow tie antenna is very broad, and pointing it off to the sides has not helped.   What I have found is that a simple old style single UHF hoop on the end of about 30 feet of coax at ground level can work.  That is, it will work well in loacation A today, but no signal at location A tomorrow. Move it 10 feet away to location B and again it will be OK for a while, but ultimately, no one location is usable from one day to the next.  Weird.  So, yes I believe it's a multipath or intermod problem.  I just can't figure out why it changes so dramatically and dynamically.   I am a retired broadcast TV engineer with 35 years experience.   This has proved to be a most interesting (and frustrating) problem.  I mis the tek tools I had when I was working.