San Francisco, CA - OTA - Page 273

I got tired of not having a working rotor so that I could play around with my TV reception, so I hired a contractor, Crawford Electronics from Pinole, to come and fix my aging antennas and replace both rotors.

He used a telescoping 20 foot mast for my VHF 10 element yagi and CM4228 to find the height that's best for distant stations. We found a spot that added 4 to 6 dB to the stations from Walnut Grove, 8 dB for KTNC from Mt. Diablo and 7 dB for channel 50 from Mt. St. Helena. Channel 1 now comes in with an 18 dB SNR signal. After rescanning and searching last night, I ended up with 31 stations that locked in solid. If you count all of the sub-channels, I get 96!

I am also able to get KCRA 3 (RF35) again. By turning the antenna about 10 degrees to the south of the Walnut Grove peak direction, I'm able to null out the KGO signal from the South Bay enough to allow KCRA to come through. I don't know how stable it'll be... there's only about a 2 degree wedge where this works.

Larry
SF

For those of you still interested in antenna stacking, there's some great reading in these old Ham Radio Magazine articles from 1985.

http://www.archive.org/details/1985-04-hamradiomag

page 129 (VHF/UHF world: stacking antennas, part 1)

http://www.archive.org/details/1985-05-hamradiomag

page 18 (stacking Yagis is a science) and page 95 (VHF/UHF world: stacking antennas, part 2)

Ron

That sounds great! You'll have a lot more fun now. Can you receive any of the Walnut Grove stations that you couldn't before?

Chuck

Thanks for running these down Ron. There's lots of good info in these magazines if you can just find it. I downloaded the articles and will spend some time reading them. It does look though that the best you can do for wideband TV antennas is to space them for the lowest frequency and let the side lobes fall where they may.

Chuck

thanks Ron and Chuck that is what I recommended to DAP's issue using channel 7 as the target frequency.

I now get three new stations showing up with signals in the 13 dB range, but none strong enough to produce a picture:
RF 8 KDTS 52 Mt. Diablo
RF 26 KTFK 64 Walnut Grove
RF 48 KSPX 29 Walnut Grove

Maybe I'll get them when conditions are better.

Larry
SF

I could use TSReader data on KDTS should conditions allow it.

- Trip

I had some time to look over the old Ham Radio Magazine articles. Turns out the link above is the most important one for TV antennas. The second two are mostly aimed towards stacking mono band ham Yagis, especially for EME work.

I did some experiments today with my pair of 91XGs. Using the beam widths from the HDTV Primer page for the 91XG, I plugged those numbers into the formula for spacing. I used the 51/Beamwidth formula based on the side lobes shown in the plots.

Something I didn't expect turned up when I ran the calculations for the channel 14, 35, and 48. The spacing was identical. This occurred because the 91XG gain increases with frequency and produces a narrower beamwidth. A narrower beamwidth requires wider spacing. The two parameters canceled either other out. The recommended spacing was 30" at all frequencies. My antennas were spaced at 44".

My VHF antennas are log periodics with constant gain and beamwidth so the spacing for those antennas would have to be a compromise.

Using KMMW as a signal source, I measured the pattern for the 44" and 30" spacings. The first image below show the results. They are pretty close to what was predicted in the article but I think the spacing could be even closer if I wanted duplicate the predicted patterns. It could be the 91XG needs to use the 45/Beamwidth formula to correctly predict the patterns. That spacing would be 25". The wider spacing produces strong first lobes and nulls as predicted. The narrower spacing widens the main lobe and reduces the first nulls and lobes.

The second image below compares the patterns for KTNC 14, KCRA 35, and KSPX 48. This is as close as I could get to spanning the whole UHF band. I rotated the plot for KTNC 15 degrees so it was easier to compare to the other two. Mt. Diablo is about 17 degrees off from Walnut Grove. As expected the pattern gets wider on the lower frequencies. I only plotted the forward part of the pattern since moving the antenna in 5 degree steps and going to the other room where the spectrum analyzer is located is a tedious procedure.

There was no noticeable difference in gain between the two spacings. There were some differences on channels that suffer from co-channel interference because of the change in patterns. Unfortunately spacing has no affect on front-to-back ratio so I still cannot improve that.

I guess I'll leave it here for awhile before I decide if I want to switch the antennas back to their original spacing.

Chuck

DAP, try a rescan. I did pick up 86 channels now, including the channel 7 at channel 35.
comes in strong near LG.

I get nothing on channel 35. That is on the same tower as channel 1, that is 2edge from my location.

Larry,

I noticed that KDJT analog 33 is back on.

Chuck

Hmmm... they must be having problems getting the digital transmitter on the air.

Larry
SF

They'd have to have a digital permit first.

- Trip

Hi,


Something is not right! (67.1 twice)

SHF

I haven't been able to find one either but apparently this came from the W9WI report. This wouldn't be the first time that information has appeared there that I can't find. Where is he getting his information from?

Chuck

Larry,

It looks to me that the status of KRJR has changed from what I see on your list. I no longer see the CP for channel 34 (expired?) and the current CP is for channel 24.

Then there is this:

43-900312KG - callsign pending winner of lottery for channel.

I thought that I read that La Dov Educational Outreach won this channel but I can't find the FCC document pertaining to it anymore. I think it may have been in 2008. It seems to be dead though as no CP has been issued to anyone.

Chuck

Doug's info should be from the FCC. They recently filed to cover an analog permit, perhaps that's what people are thinking of.

- Trip

If you don't mind, I'm commenting on this here since I think I'd be a little OT for the Channel Change thread.


After the big wind storm I noticed a drop of 2 dB in the SNR on both KOVR and KTFK. These stations are on the same tower and are on adjacent channels. I cannot detect any change in their signal strengths. I don't know what happened. All the other Walnut Grove stations are unaffected, even KXTV which is on the same tower. It appears that the multipath has somehow gone up.

My friend in Arnold reports that he's now receiving KOVR almost 100% after the windstorm where before it was intermittent at best.

This Fall has had a minimum of temperature inversions that affect TV signals here in any way. I've had few good or bad days, mostly nominal conditions. The result has been few days where distant signals have been good but almost no problems with the local stations dropping out on recorded programs. I have found out that the nominal SNR for KGO is 18 - 20 dB which I get now most of the time. Not bad for 111 miles over the top of Mt. Diablo. Now if they would just increase power to 100KW......

The tree swaying problem is exactly what I had at my cousin's house in San Leandro. And trees get bigger every year which doesn't help.

It's also my perception that the seasons seem to be shifted about a month later compared to say 30 years ago. I don't remember so many wet springs but maybe my memory is faulty. I haven't looked at any historical data.

Chuck

there are a lot of stations missing or off the air this morning. 60,66,38,22

just went to channel 60 TV KCSM and a link to a PDF says it is sold.

I have not forgot about this; I've got some changes to make it more Linux friendly (Fedora has python3..) I want to get them back to the original author; however, I've attached the patch file to this post; just remember, YMMV, and you must have python3, tkinter, the previous program posted, and patch.

The previous program I posted about generates a 360 degree view of what your antenna can see; it looks like the attached view. The 3 white bars are the LOS stations - KRCB, KFTYDT, and KTLN-DT. This view also does not have the high VHF antenna attached.

 

dtv-linux.patch.txt 1.763671875k . file

My samsung TV is seeing a channel with PSIP of 14.6, on which color bars are displayed and a test tone.. No idea who, or what is broadcasting this, plus my HDhomeRuns do not see it.

Anyone have ideas?

Never mind; KTNC is broadcasting it..

I've never seen this graph before. The graph has no labels but I'm guessing that the X axis is channel # and the Y axis is a relative signal strength or signal quality with the antenna rotated every 22.5 degrees (16 steps) but I can't tell for sure what the directions are or what the colors mean.

Chuck

Thank you TDavis, I'll give that a try this weekend.


In TDavis's previous post, he had this link: http://www.silicondust.com/forum/viewtopic.php?t=11538
That has a link to the sourcforge page which explains the graph.

I don't have a rotator, I'm more interested to see what my signals do as a function of time.

I don't have a rotator, so I went up on the roof to do it by hand.. I figured out my 0, 90, 180, 270 marks, then subdivided them down..

Each row in the Y axis is a rotation. Each dot is the channel; brighter = better signal. It generates a CSV file, so you can save or reload it. You can also click on the dot, and it will tell you what it found on that channel (signal, quality, and symbol).

It also has a strip graph on it, which is in the lower right corner.

It is useful to see what is around you, and helpful in tuning to the proper station orientation..

Thanks for the update. Should I just remove 43-900312KG from the list?

Trying to keep up with the pending digital stations is next to impossible. I'm seriously thinking of removing the pending list altogether and only listing stations that are actually on the air.

Where do you look on the FCC site for current information? The file pages that I link to from my lists never seem to be up to date.

Larry

KCSM is up for sale, but hasn't been sold yet. As noted on their web site:

"A Request for Proposal for the sale of KCSM-TV was released on December 7, 2011 with bids due on February 14, 2012." Full details are at:

http://kcsm.org/misc/KCSM_statement_re_bid.pdf

Larry
SF

I finally got a lock and PSIP info from KDTS on Mt. Diablo (RF channel 8, virtual channel 52.1) but multipath or some interfering signal is causing the channel 8 signal strength to change radically from 12 to 17 dB. It locks, breaks up, locks, breaks up... continuously. I've never seen such radical changes in signal occur on such a constant basis.

Larry
SF

I get the same problem here with that station.
Now that you fixed the rotor, ... better chances trying KSBW than with that station.
KSBW comes in around 8 am to noon every day here. It varies.
I need to build a 20 foot yagi to fix that.
Here, 8 & 25 are the strongest Salinas stations.
For San Jose stations, 36 & 54 (RF50) are the strongest.