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Old 15-Apr-2014, 10:51 PM   #1
dbseeker
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Presumed FM interference

http://www.tvfool.com/?option=com_wr...5b9480256c9f67
Great forum!! Thanks to all that offer their expertise.
Current setup is a Winegard 7084p rooftop with 10' pole with 25 foot of RG6 into attic to a AP 8275 with FM trap on, done about 8 years ago. I have always had trouble with real channel 7 pixelating presumably from a strong FM station about a half mile away. Two years ago, I placed Radio Shack FM trap in line prior to preamp and the channel is watchable with minor pixilation. However, WEHT pixelates mildly since then presumably from the extra NM introduced by the FM trap. Surprisingly, channels 15 and 20 are rock solid but no channel 47. There is only 25 more feet of coax to one TV from the preamp. I have not tried adjusting the variable trap. I have tried the RCA preamp and a Kitz tech amp with no change in results. I have at my disposal a CM 4221HD and an HBU33.
Questions: Can I trim the VHF elements on the 7084 to the length of the VHF elements as on the HBU 33 and effectively make a 7698 out of it and reduce some of the FM interference that way? If so, what is the best way to trim an element?
Should I try either or both of the other two antennas with the Winegard or RCA preamp with FM traps and hopefully eliminate the Radio Shack component? Would I likely lose channels 15 and 20?
Appreciate all your input! Thanks!!
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Old 16-Apr-2014, 2:41 AM   #2
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Sorry about a mistake. It should have read WFIE channel 45 pixilates mildly since adding the Radio Shack trap.
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Old 16-Apr-2014, 3:44 AM   #3
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Post an FM Fool report. It may not be FM interference as you assume.

Re-run your TV Fool report at 30, 40 and 50 ft to see how far up you have to go to get RCH7 and RCH46 (your weakest stations) as a 1Edge or even LOS. I think a slightly taller mast will make a huge difference in your location.
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Old 9-Jun-2014, 2:59 AM   #4
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Just completed install of CM 4221HD with Antennacraft Y10713 at 40 foot height using RCA pre-amp, fm trap on, separate input selected and 4 foot distance from each antenna. Was able to eliminate radioshack fm trap and real channel 7 now rock solid. Channels 15, 20, 47 all rock solid with substantially lesser noise margin than WFIE that still pixilates mildly but watchable and solid after dark. Will assume mulitipath? Adjustments to aiming could hurt the lesser NM channels. Would appreciate any suggestions!!!
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Old 9-Jun-2014, 3:09 AM   #5
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Old 9-Jun-2014, 8:44 AM   #6
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+=>

In place of the CM4221HD install a CM4228HD.

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Can Call the WFIE Tv Station with a Telephone and Have a Voice Conversation With the Engineering Department About the Transmission and Reception Situations of WFIE and Your Reception Situation.

http://en.wikipedia.org/wiki/WFIE.

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A question.

Is , W06BD , Analog channel 6 being received??

http://en.wikipedia.org/wiki/W06BD.


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As always , for Reception of Tv Stations , trees and tree leaves , plants and plant leaves , have a Negative Effect on Broadcast Tv Reception and so do buildings and and other obstructions including you own building.

Some and not all Negative Effects are.

Absorbing and Blocking Reception.

Multi-Path Reflecting Tv Signals Bouncing All Around.

The Best Practice for Reliable Reception is to Install the Antenna/s at a Location that has the Least Amount to No Amount of Obstructions of Any Type or Kind in Directions of Reception Including Your Own Building.

Last edited by teleview; 10-Jun-2014 at 1:03 AM. Reason: Clarify information and typos.
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Old 10-Jun-2014, 6:00 PM   #7
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I agree that your problem is likely to be FM interference. Unfortunately, the frequency of the strongest station is 89.1 MHz, and almost all FM traps pass 89.1 with little attenuation. This is because channel 6 is on 82-88 MHz, the trap should not interfere with channel 6 reception, and the trap can't be designed with rejection that close.

A better solution for you is to install a HLSJ between your antenna and the preamp, and put a 75 ohm termination on the L port of the splitter/joiner.
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Old 10-Jun-2014, 7:26 PM   #8
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An HLSJ is an excellent suggestion.

The FM Filter we carry is a "full-band" filter and doesn't compromise FM suppression to save channel 6 (which it will also attenuate) so it can't be used in areas like Philly or Albany (Sorry, Fred!).

I have seen FM interference severe enough that two traps in series were needed to suppress really strong FM.
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Old 10-Jun-2014, 7:47 PM   #9
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Quote:
Originally Posted by ADTech View Post
An HLSJ is an excellent suggestion.

The FM Filter we carry is a "full-band" filter and doesn't compromise FM suppression to save channel 6 (which it will also attenuate).

I have seen FM interference severe enough that two traps in series were needed to suppress really strong FM.
I have seen tests that show that the AD FM filter takes out only some channel 6, so it might still work in a strong channel 6 environment. I doubt that the FM attenuation of the AD filter would be sufficient in this case.

That is based on an FM fool look-up using the 4 digit latitude and longitude data in the TV fool report. It shows that 89.1 is .7 miles away and +4 dbm signal level.
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Old 11-Jun-2014, 1:15 AM   #10
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Yep, that's a hot signal, alright.

I tested the Pico and Holland HLSJ devices a couple of years ago. The Holland attenuated 90 MHz by about 25 dB, the Pico was around 31-33 on a curve. Some of our FM filters tested close to 40 dB, but there was a variance all the way down to only 20 dB on some units.

I've got one of the current Radio Shack FM filters at the shop. I'll put it on our new office play toy (Agilent FieldFox N9923A) tomorrow and see what it looks like.
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Old 12-Jun-2014, 2:23 AM   #11
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Thanks to all who have replied and shared their knowledge base. T he fm interference on real channel 7 was eliminated with the Y10713 and the RCA preamp fm trap. Channel 6 was never received on the Winegard 7084p and is a high school channel of no significance. Channel 46 has remained a pixilation problem and as Teleview suggests, I have an email into the engineer for possible troubleshooting. The Winegard advertises a gain of 12 to 14 db on channel 46 so upgrading to a Channelmaster 4228 would be a gamble.
If anyone has ideas for eliminating the channel 46 problem, I am all ears.
Many thanks!!
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Old 12-Jun-2014, 12:07 PM   #12
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Quote:
Originally Posted by dbseeker View Post
If anyone has ideas for eliminating the channel 46 problem, I am all ears.
Try raising or lowering the antenna 6-12 inches. It may be sitting in a weak spot for WFIE & just needs a slight vertical tweak to see a more consistent signal.
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Old 1-Jun-2015, 4:05 AM   #13
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About one year later, I have been struggling with real channel 7 (ABC channel 25 Virtual).
Signal strength is good on a new LG 24 inch with signal strength meter only. Channel strength drops to nothing for hours and then returns to good and watchable at random with no correlation on time or electrical intereference or fm intereference. All fm traps (most recent a Winegard FT 3000) have been tried and in multiple series with no effect.. NO amp is used and cable run at 50 feet.
Poor connections come to mind, however all coax replaced within one year with RG6 and best fittings. RF 9 always solid and not intermittent.
As an experiment today, mounted an RCA ant751 about 8 foot below the antennacraft Y10713 to a separate tv tuner and picture watchable with mild pixilation on rf 7 with no reception on the Antennacraft. Again rf 9 receivable on both antennas.
I realize that signal layering issues occur, but for an antenna that has a 9.4 db gain to go from good strength to absolutely nothing strength seemingly at will and maintain channel 9 reception without issue would not suggest a connection issue.
Please comment and offer your expertise. This gremlin is on my last nerve!!
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Old 1-Jun-2015, 11:43 AM   #14
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Did you ever try raising or lowering the Y10-7-13. It may be sitting in a bad spot for RF 7.

How is signal strength on RF7 when it is good, compared to RF9. Is one more stable than the other at these times?

Do you happen to have one of the anaolog to digital converters leftover from the transition?
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Old 1-Jun-2015, 4:37 PM   #15
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Quote:
About one year later, I have been struggling with real channel 7 (ABC channel 25 Virtual).
Quote:
RF 9 always solid and not intermittent.
Quote:
mild pixilation on rf 7 with no reception on the Antennacraft. Again rf 9 receivable on both antennas.
Quote:
This gremlin is on my last nerve!!
Your gremlin is FM second harmonic interference that harms 7 more than 9.
http://www.tvtechnology.com/digital-...ference/202503

CH 7, 174-180 MHz, 1/2 = 87-90, WVJC 89.1 +4.2 dBm
CH 9, 186-192 MHz, 1/2 = 93-96, WYNG 94.9 -9.2 dBm, 13.4 dB less

see Attachment

Possible solution: two HLSJ in series between antenna and preamp

Ant > HLSJ > HLSJ > AD Juice Preamp > coax down > Power Injector > TV
http://www.hollandelectronics.com/ca...-Diplexers.pdf

The Juice preamp doesn't have an FM filter, but it is highly resistant to overload.

Is it safe for me to assume that your coax shield is grounded with a grounding block to help reject interference?

It is also possible that the noise level on VHF from electrical interference is high at your location. I have a VHF-High channel that would seem to be strong enough, but the noise level is so high the SNR for that channel barely makes it to 15 dB as shown on the Diagnostics Screen of my Sony TV. Sometimes I can receive that channel, sometimes not according to how high the noise level is at that time. I have been able to measure the strength of that signal and the noise level of the vacant adjacent channel with my old Sadelco 719E signal level meter (SLM) to confirm that. I have also used my Sadelco DisplayMax 800 SLM to make similar measurements of SNR.

OTA signals are constantly changing in strength, especially for 1Edge and 2Edge signals that are less stable than LOS signals. This is why you need to have a fade margin of at least 10 dB for your NM after adding antenna and preamp gains.
Attached Images
File Type: jpg dbseekerTVF FM est.JPG (120.2 KB, 271 views)
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Last edited by rabbit73; 1-Jun-2015 at 6:51 PM.
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Old 1-Jun-2015, 5:33 PM   #16
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Quote:
Originally Posted by rabbit73 View Post
Your gremlin is FM second harmonic interference that harms 7 more than 9.
Thanks, I was assuming the OP was still using the Radio Shack FM trap, but looks like he has removed it after re-reading the thread. He absolutely needs to have one. I would re-insert the RS trap & try that before ordering anything. It might be enough.
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Old 1-Jun-2015, 6:21 PM   #17
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The RS trap probably has insufficient attenuation at 90 MHz to be effective in this situation.
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Old 1-Jun-2015, 6:26 PM   #18
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Maybe / maybe not. I have successfully used one with a +8.3 db FM station .25 miles away (90.9) I would certainly try it first.
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Old 1-Jun-2015, 6:54 PM   #19
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All FM filters are not equal.




FM Filter
http://www.avsforum.com/forum/25-hdt...fm-filter.html
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File Type: jpg ADvsRSFMfilter.JPG (135.6 KB, 744 views)
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Last edited by rabbit73; 1-Jun-2015 at 7:01 PM.
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Old 1-Jun-2015, 7:24 PM   #20
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I know that, but the OP already has the RS unit. Why not try it first??????? Is this an informercial?
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