San Francisco, CA - OTA - Page 254

Very interesting report, Chuck! Thanks for sharing it. I'm jealous.

Larry
SF

KFTY is back on the air but the picture and sound is completely broken up. Better SNR though with the antennas in the new position. They must have the worst track record for problems.

Chuck

Sorry, I missed this. No, it's a manual crank-up. Motorizing is about $1500 plus I'd need to trench power 400' up the hill.

Chuck

don't take this message negatively, but your surname means cadaver, like dead body,

Don't know exactly what you're talking about since I've never given my surname here. If you're referring to "Calaveras" it means "skulls" in Spanish. It is the California county I live in.

Chuck

Based on the lack of references to KPIX, I assume nobody else here started having reception problems at the beginning of the month. Until this month, the KQED and KPIX numbers were lineball and weather was never a problem.

The antenna is a Winegard 7698, and reception has dropped so low on KPIX that programs that one hour shows being recorded (on TiVo) are only 40 minutes long. In a couple of cases, less than 30 minutes.

The TiVo's signal is worst during prime time.

9:00pm 5.1 peak in the 50's and dropping below 20
1:00am 5.1 peak in the 60's and not dropping below 60

9:00pm 9.1 in the high 70's and never dropping below 70
1:00am 9.1 in the low 80's and never dropping below 75

KQED does show a slight improvement in early morning, but KCBS shows a huge improvement.

If this was electrical, I'd go looking for a power sink but have no what would cause this type of problem with an antenna.

Can anyone here shed light?

Hi,

it all comes down to light, that is the sunlight coming from the sun affecting the earth's atmosphere, trees that grow and drop leaves and shift in the wind, grass that grows on the hills and dries out, rain that falls or does not, fog that appears or disappears, the temperature inversion and so on.

I had a problem with KPIX a few months ago and Sundays with rain have suddenly been bad for NASCAR on KTVU.

OTA is a crap shot here and always will be.

If weather was never a problem then something has changed, buildings go up, roofs are replaced with metal foil lined ones, trees may have been cut down ... It does not take much to increase multipath or lower the received signal levels to the borderline where problems occur. Moving your antenna might help.

I do not keep track of the signal levels but I see KAXT, KRCB, KFTY and KTNC appearing and disappearing many times during the day.

SHF

I've had the same sort of sporadic issues with TiVoed recordings of KPIX HD 5.1 on various nights over the past few years during primetime and recently one night on KTVU HD 2.1 during a storm. I have found that KPIX 5.1 has been the most unstable channel of the ones that we normally watch.

Usually I have found that these dropouts or pixilations occur during windy or stormy conditions and often when it rains. I am about 16 miles away from Sutro tower and can see the top half of Sutro from our back yard. However we have some Eucalyptus trees on the hill below us in the signal path that may be one of the reasons that our reception problems usually occur during wind and storms when their branches and leaves blow in the wind.

We have a large 8 foot UHF/VHF Radio Shack antenna (VU-110) which we've had in our attic for many years which usually gives us great reception on the stations that we watch- 2.1, 4.1. 5.1, 7.1, 9.1, and 11.1

Reception problems can be very hard to troubleshoot. I just fixed a problem today that I've had for several years but didn't even recognize I had until I moved my antennas to the new tower.

I noticed long ago that KGO peaked at 6-8 degrees farther north than any other station from SF. Of course, except for KNTV which I rarely receive, all the other stations are on UHF which are completely different antennas.

This didn't register with me as a problem because before the transition when KVIE was on 53, it also peaked up about 8 degrees farther north than it should have. All the other Walnut Grove station were on target. I just figured that KGO had some similar path problem.

When I moved the antennas last weekend to the new tower, KGO peaked in the correct direction. I chalked it up to moving the antennas south a little and 10' higher. Two days later KGO was back to peaking in the wrong direction. Uh oh, must be an antenna problem.

Now I took a careful look at all the VHF stations and they all peaked up too far north. KVIE, KXTV, and KSBW are so strong that it doesn't matter. The only other weak station like KGO was KCBA and I never paid any attention to it.

Now that I was paying attention, I saw that the SNR on everything but KSBW was down about 2 dB compared to the initial numbers. This sure sounded as though one of the two VHF LPs wasn't connected. The power combiner was the only component that could cause this.

This morning I replaced the power combiner and all the stations peak in the correct directions again and the SNRs are back to last weekend numbers. I'm not sure how disconnecting one antenna can alter the pattern, but it did.

This shows problems can come from all sorts of things and they can't always be blamed on the most obvious things.

Chuck

Very impressive channel list!

- Trip

> It does not take much to increase multipath or
> lower the received signal levels to the borderline
> where problems occur.

True, but in over 30 years of OTA have never seen a single station affected by these factors. This has the look and feel of a frequency issue to me, not a signal issue.

> I see KAXT, KRCB, KFTY and KTNC appearing and
> disappearing many times during the day.

Ran a check starting around 2:00pm today:

KPIX 5 peak in the 60's and not dropping below 30
KQED 9 peak in the low 70's and not dropping below 65

KAXT 1 peak in low 80's and nothing below 75
KRCB 22 peak in high 80's and nothing below 85
KFTY 50 no signal unless atmospherics are just right
KTNC 42 peak in mid 70's and rarely below 65 except for occasional momentary plunges below 30 (which are momentary).

KTNC has always been a puzzlement, these sudden dropouts are a characteristic of 42 that occurs on no other channels. Oddest of all is that they tend to cluster in the last 15 minutes of a movie.

> I have found that KPIX 5.1 has been the most unstable
> channel of the ones that we normally watch.

Interesting, maybe there is something to it being frequency related. If it was an independent it would be more understandable, but this is a national broadcaster. You'd expect better.

> This sure sounded as though one of the two VHF LPs wasn't connected.

That's the kind of issue I was wondering about, hoping that some component failure could cause a frequency-related dropout that was hosing KPIX.

Thanks for the input, will keep plugging away looking for a cause.

Sure seems like KPIX is a common problem.

I checked for the Sutro signals after midnight last night. I had a/v locks on 4, 5, 9, 20, and 66. I didn't find anything new after a search unfortunately. This was definitely my best reception from there so far. My highest signal, according to the tv, was 65%. Prior, I hadn't seen 50%. I watched 5 minutes of 66.1 without any drops. This is wild. Two nights prior, with the antenna aimed the same, only KPIX was getting through with dropouts.

There was very favorable ducting for me this morning. It's rare to see it good in multiple directions at the same time. Station/SNR follows.

SF: KGO/30, KNTV/24, KOFY/27, KPIX/27, KQED/25, KMTP/20, KRON/21, KTVU/20, KBCW/21

Fremont: KAXT/25, KICU/26, KTEH/25, KDTV/26, KSTS/27

Salinas: KSBW/32, KCBA/27, KLFB/31, KSMS/25, K38JP/20, KMMD/27, KION/31

I did a scan and KCSM still wasn't coming in. KTSF and KFSF are not possible here due to strong co-channel analog stations.

Chuck

I had very strong ducting down to Salinas again this morning. I took some images from the spectrum analyzer. For reference I included an image of KMAX taken at the same time. KMAX is my strongest Walnut Grove signal now and was up about 4 dB in this image.

Fremont Peak transmitters, KSBW, KCBA, KQET, KMUV, and KDJT were enhanced by about 20 dB. Mt. Toro transmitters KION, KLFB, K38JP, and KMMD were enhanced by about 30 dB.

All the UHF stations in that area are relatively low power with KQET running the most with just 81 KW. None of the UHF stations there have more than 17KW in my direction.

With my channel 19 filter moved to channel 18, I saw KMBY for the first time. It's picture was all messed up just KFTY was last week. KMMD is also messed up. Don't the owners monitor these LP stations to verify that they are working?

Chuck

I missed all the TV DXing fun! I was up at Yosemite enjoying the beautiful scenery and roaring waterfalls. I'm sure there will be more openings in the weeks to come.

Larry

Is this an all morning event ? What times did you see this ?
I don't closely monitor this, but I have seen 2 hour signal surges in the past around 9am to noon.

TvFool is showing a new station here, but I don't see it on the air yet here. KDAS-LP (48) 48 .... close to 47 in the north bay. ???
In the future applications it's showing KPIX moving to San Bruno Mt. ? Is that for real ?
And also showing KBKF-LP 6 (Radio 87.7 K-Love) to move to near Monument Peak ? Near that antenna farm.

Not sure how accurate that website is, but we'll see.

My friend in Placerville (who's on OTA only and keeps up with the latest station changes) and I plan to make many trips to Yosemite this summer to do panoramic photography from a number of locations. I've been there twice so far this spring. We're hoping to hike to "Oh My Gosh" point next week. You look up at upper Yosemite Falls from there and down at lower Yosemite Falls.

Chuck

It's best in the mornings, before 10 am.


TVFool is not the best source to tell what's on the air since they use construction permits as though they are stations on the air. KDAS shows to be on analog still on 48 but they have a construction permit to switch to digital.

KGO and KPIX have been granted Special Temporary Authority to operate a DTS transmitter from Mt. San Bruno to test coverage in a dead zone for Mt. Sutro. They are not moving to San Bruno. I see KGO has been granted a Construction Permit for the Fremont site on channel 35. This will wreak havoc for anyone who can receive KCRA in the south Bay Area.

Chuck

It's going to be interesting to see how the on-channel KGO and KPIX signals from Mt. San Bruno will work together with the higher powered signals from Sutro Tower in the areas where the two overlap. Take a look at the coverage projected for the KGO San Bruno Mountain channel 7 transmitter. It hits lots of area where the Sutro signal covers.

http://maps.google.com/?q=http://www...SCO%26state=CA

The KPIX coverage is similar.

Larry

Looking at the map for signal coverage, it shows KDAS digital 48 being located on Mt. Tamalpais, but the southern edge of their signal will just barely reach San Francisco. Most of their signal will be going north-northwest as far as Sebastopol with partial coverage of Santa Rosa.

KTLN's channel 47 transmitter is located on a short mountain, more like a hill, just west of US 101 in Novato.

Larry

I am LOS to Mt. Tamalpais, ... and coverage here is expected but weak.
KTLN ch 47 comes in good here. -- Even indoors on a double bow setup.
Things are easy when it's LOS.
I guess it helps too... the full power 1000 kw channel 47

KRCB on the other hand, very tricky. Huge yagi pointed towards Lafayette, Moraga The hills bring UHF signals down --- Way down
KFTY is so far ... not seen.

Still need to switch from MXU-59 yagi style to 4228 .... and see what that does ... if anything
Starting to test KUVS, 3, KION, KFTY, & KCBA plus "Try again" and see if any Full power UHF from Walnut Grove come in.

I was a lucky duck last night with KICU. I had consistent fractured a/v with brief locks. It was the first a/v I've seen from 36.1, which normally reads around 3% on the tvs signal meter. I hadn't changed the aim of the indoor antenna. Were I to have changed it, who knows. Sutro, at the same time, was not as lucky.

Ducting can work for you or against you. I posted just a few days ago about the great ducting conditions I had here. Yesterday morning made up for it. Conditions were awful. I thought my antennas were broken. Stations from every direction were way down or gone completely. I finally looked at KMMW on the spectrum analyzer as it is the only station LOS to me, close enough to not be affected by inversions, and not messed up for some other reason. It was completely normal. By the afternoon conditions had recovered and signals were nominal again.

So if you typically have good reception, and occasionally great reception, you have to expect occasional periods of poor reception too.

Chuck

most dtv users in nyc ota forum find ducting irritating to say the least im bit like you i want as much signal as i can get. sorry to report we not had any propogation yet this year.

My new tower is up and I really wanted to try a phased array of four 91XG antennas. I've attached a photo of the antennas. The highest antenna is at 70'. I removed the 300:75 ohm transformers and used 300 ohm twin led to connect all the antennas together. Four 300 ohm antennas connected in parallel is 75 ohms but still a balanced feedline. I used a simple ferrite choke balun to convert from balanced to unbalanced. There was no transformer or combiners to add loss.

The results were pretty much as I expected. Most signals increased but not the expected 3 dB. KCRA didn't increase at all but KOVR and KMAX increased 7 dB. I really can't explain this. Most of the DX stations increased around 3 dB as well as their signal-to-noise ratios.

The SNRs of the Walnut Grove stations did not increase at all. As far as I can tell they stayed exactly the same. I was hoping that they'd get better but no change was the expected result. My problem with Walnut Groove is multipath and the only thing that will improve that is higher front-to-back ratio (F/B) on the antennas. See my next post where I show test results on the 91XGs.

Phasing antennas does not increase F/B. It simple increases antenna gain up to 3 dB in every direction.

I'm really only getting a couple of stations that I didn't before. KPIX is in most of the time now. KQED is much more reliable. And I'm now seeing KSEE on RF 38 from Fresno most of the time although it is one of the most unstable paths I've ever seen. See attachment. Fresno is not as far away as either SF or Salinas but there are many high mountain ridges between there and here which makes it a very difficult path. KTEH seems much better too but with no HD I don't watch it much.

Chuck

I've never seen anyone try to plot the pattern of their antenna. I've only seen computer generated plots. So I decided to give it a try for the four 91XGs. See my previous post for a photo.

Attached are two plots of the horizontal pattern. I should point out that arranging the antennas into a square produces the same horizontal pattern as having two side by side. It narrows the vertical pattern but you'd never notice that unless you could tilt the antennas up and down.

The first plot is of KMMW on RF 28. I use that as my reference since it is LOS and just 14 miles away. The signal almost never varies. The plots are a little jagged because I took data points every 5 degrees. One degree increments would be better but it's too hard to position the rotor in such small steps.

You can clearly see the main lobe, the first nulls, the first lobes, and a little less obvious the second nulls and lobes. The front-to-back ratio (F/B) looks to run around 25 dB. You can see a lobe that points at 95 degrees. I have a strong reflector off the mountains there and all signals from the west have a peak there. Even a 147 MHz ham repeater above Palo Alto has a strong peak there. I suspect the antenna pattern is a little better than what it looks like at 95 degrees.

Now take a look at the antenna pattern for KOVR. I picked KOVR because it was close in frequency to KMMW and only 2 dB weaker. The F/B looks awful. This is because the mountains east of me are LOS to Walnut Grove and my antennas have 2 ridges to look over. I estimate those 2 edges attenuate the signals by 15-20 dB.

I need to find a way to increase the F/B on my antennas. I'm wondering if larger reflectors on the 91XGs would help? Taking an extreme example, a 20' x 20' sheet of metal would certainly block the reflections 100%. How big of a screen would be needed to block another 10 dB? I haven't found any good information on this.

I noticed in these plots that my antennas were pointing 3 degrees too far CCW. KOVR is 270.3 degrees, not 267.5 degrees as shown in the plot. I fixed that.

Chuck

That would also make a great kite. Not what you want in an antenna. Perhaps chicken wire, or some other metal fencing material. As long as the holes are smaller than about half the smallest element in your antenna, it should work as well as a solid sheet without as much wind loading.

I didn't mean to imply that I'd consider some huge piece of sheet metal. It was only an extreme example to illustrate that signals behind the antenna must be able to be blocked. I just don't know how big of a screen it would take to make an improvement. One inch square screening might be a good choice to try as an experiment.

Chuck

I would think anything 50% wider than the widest element would be a good start. The big question is how far back from the last element should it be so that the reflections from the front of the antenna come back in phase with the signal rather than at a random phase.