| Author |
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738
| | Posted on Monday, July 14, 2003 - 5:34 pm: | 
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I have always used TVI filters in the past, but always had a good ground. I'm in a apartment now (2nd floor) with plastic plumbing. I have found in the past that using the electrical outlet ground injects TVI. I'm planning on sneaking up and replacing my 2M Verticle with the "Top One" antenna because of my limited hight and the fact that 1/2 wave "Bigstick" type antennas seem to induce TVI because of there angle of radiation that close to ground. Question: all the TVI filters I have ever used had a ground lug that I grounded to a good ground. Will one function in-line without ground? I would assume it would, but would like a professional opinion.
BTW Love this group, you do a good job of filtering out "Trolls"! I'm getting ready to set it as my home page!
73 |
Tech833
| | Posted on Tuesday, July 15, 2003 - 10:00 am: |
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Duplicate |
Tech833
| | Posted on Tuesday, July 15, 2003 - 10:00 am: |
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A TVI filter is really nothing more than a 'rolloff' filter. This means that any frequency below threshold will pass, unaffected. Once frequency treshold is met, any frequencies that try to pass through will be shunted to ground. There are no internal 'dummy loads' in TVI filters, right? So where else would the RF energy above threshold go? Right! Unless grounded, the RF will not drain to ground, instead it will use the case of your radio and anything connected to it as a 'drain'. It is true that less TVI makes it to your antenna, but if the case of your radio is radiating TVI, and your neighbor's TV set is right below you, you will get a knock at the door.
It is also known as a capacitor rolloff filter. The number of stages is determined by the number of capacitors in parallel. The coils in series only break up the capacitor sections so they do not act as one. The capacitor value is determined by the impedance and the design threshold frequency. I build them all the time for broadcast. |
738
| | Posted on Tuesday, July 15, 2003 - 3:19 pm: |
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Excellent reply! I will have to find a ground at all cost! Well if I was able to sneak up a 6M loop and a ARX-2B 2M vert. then I guess I can find a way to ground. Duh.. came to me Bathtub has metal fittings, if I run a line from Bathtub to Breaker box ground to station that should do it!
Thanks! |
Ironmask
| | Posted on Tuesday, July 15, 2003 - 10:45 pm: |
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Tech 833
As usual your statements for the layman are easily understood and make great sense.
My question, based on your previous explaniation is; Will more than one TVI filter of the same cut off ratings in line decrease the performance of the other.
Example; having a TVI filter between the radio and amp and another between the amp and the antenna. Thank you |
Tech833
| | Posted on Wednesday, July 16, 2003 - 5:17 pm: |
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It will not cause one filter or the other to become less effective. I have seen installations that required more than one rolloff filter. One filter between the transmitter and the phasing common point, then another filter between the coax from the phasor and each tower tuning unit. One installation required 7 seperate filters. We needed to keep a nearby AM (higher in frequency) from mixing with the new AM.
You were aware that rolloff filters work both ways didn't you? |
Bigbob
| | Posted on Friday, July 25, 2003 - 11:55 pm: |
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738 wait,wait listen to what you're saying,bathtub?breakerbox? If the breakerbox has a poor ground you will get electrocuted at your next bath via a groundloop,oh god,I hope I'm not to late. |
Ironmask
| | Posted on Saturday, July 26, 2003 - 8:08 am: |
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Bigbob,
I was refering to the ground rod or equivilent used to ground the breaker box. NOT the ground within the box. Thanks for bringing that up. I agree with the tub not a good idea.
Thanks again for keeping us on our toes. |
738
| | Posted on Saturday, July 26, 2003 - 10:59 am: |
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I'm lucky I don't really fit in the small tubJ and only shower! Else I would have to buy feeder Gold Fish to test the water first! That's so funny, but a true issue. I do have the breaker box about 6' from my radio and will just use that. In addtion The antenna base will be about 10' from the A/C roof unit and I think I will run a heavy ground between them. The A/C feed is from the same box and it's directly over head about 6' from the box in my room. That's about the the best I can do from this 2nd floor Apartment. Boy that tub thing is so funny I could see it now! Anybody remember that old thriller movie "Cats Eye" think it was like 3 story's of what a cat see's in his travels and there was the one where they were shocking the guys Wife on the grid when they caught him smoking and she was dancing all over to the music they had wired to it? I could just see my Wife doing a Modulation dance! Boy would I be in the dog house!
73 Guys, and very good point! |
Kc0gxz
| | Posted on Saturday, July 26, 2003 - 3:11 pm: |
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Tech833
When building these filters, what factors are brought into the equasion? Lets use the multi filter system that you built and mentioned in your Wednesday, July 16, 2003 post. I am asking these questions because of my very limited knowledge of filters.
You said that it required 7 filters.
1-How was it determined that 7 were needed?
2-Are they all identical or step-up? (if there is such a thing)
3-Are they paralelled or in series?
4-What determines coil diameter and # of windings?
5-How do you determine the # of stages needed?
In your line of work, you are playing with thousands of watts of power. It would seem to me that there isn't much room for error which leads me to my two final questions.
6-At what stage in the transmitter chain are the filters installed?
7-And how much power is actually going through these 7 filters?
I find your line of work facinating. The more I read your posts, the more I realize just how complex a Broadcast radio station really is. It seems to me that your responsibilities as a Broadcast Engineer must be tremendous.
One more question...Are you free-lance or do you work one station?
PS: There's no hurry for an answer to this post.
Jeff, kc0gxz |
Tech833
| | Posted on Tuesday, July 29, 2003 - 9:00 pm: |
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Jeff,
I'm glad there is no hurry, because I only get to look at the forum once or twice a week lately.
I'll reprint your questions and insert my answers below.
-------
You said that it required 7 filters.
1-How was it determined that 7 were needed?
> One filter was required at the common point to filter the induced current from the nearfield generated by the other AM, the other 6 went to the 6 towers (antenna elements) at their ATU's.
2-Are they all identical or step-up? (if there is such a thing)
> They are identical in components, but not settings. Each tower had a different base impedance and phase, which meant that each filter had to be designed and built and slightly 'tweaked' so as to be 'invisible' at the local frequency, but a deep roll-off at the far AM frequency.
3-Are they paralleled or in series?
> Series. Just like a TVI filter. The internals are series/parallel. For low pass, you use series L and parallel C.
4-What determines coil diameter and # of windings?
> Frequency and impedance.
5-How do you determine the # of stages needed?
> By how sharp the roll off needs to be.
In your line of work, you are playing with thousands of watts of power. It would seem to me that there isn't much room for error which leads me to my two final questions.
> Actually, power means nothing. More power just means bigger components. The math is exactly the same for 1 watt or 1 megawatt.
6-At what stage in the transmitter chain are the filters installed?
> Wherever needed. Usually right after the transmitter and in front of everything else.
7-And how much power is actually going through these 7 filters?
> In this particular installation, the local AM is only 5 KW. The far AM is 10 KW. I have done filters on stations over 50 KW. You do the exact same thing, you just buy bigger parts.
I find your line of work fascinating. The more I read your posts, the more I realize just how complex a Broadcast radio station really is. It seems to me that your responsibilities as a Broadcast Engineer must be tremendous.
> That would be an understatement.
One more question...Are you free-lance or do you work one station?
> I own and operate an engineering firm that does work all over the U.S. and overseas. I am what is called a consulting engineer. Not only do I actually go out in the field and do the work myself, I am also hired to design and instruct others what/how to do the work. Personally, I have been all over, and have worked on over 100 broadcast stations. My guys (and gal) have done several, but I still hold 'the record' for travel. As I age, I am slowing down. I moved out of the bay area and back to 'the sticks' in hopes of slowing my pace a little and preparing for retirement in 12 years. I work out of my home 1 or 2 days a week and out of either of my 2 'city slicker' offices the rest of the week. To answer your question a little better, I am also the Chief Engineer, and solely responsible for all technical operations for 8 stations. I have contracts for 13 others. Then, I do the 'freelance' stuff on top of that. I am busy!
PS: There's no hurry for an answer to this post.
> Good! See above.
Jeff, kc0gxz
> Tech 833 |
Kc0gxz
| | Posted on Wednesday, July 30, 2003 - 3:32 pm: |
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Tech 833
Thank you!
I really appreciate the time and knowledge you share with us on the forum. I know you are busy and I often wonder where you find the time to answer all of our questions.
Oh no, you've been cloned haven't you.
Thank you and 73s.
Jeff, kc0gxz.
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Cornbrown
Member
Username: Cornbrown
Post Number: 50
Registered: 7-2005
| | Posted on Friday, October 14, 2005 - 1:53 pm: |
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Hello Tech.833.....
What do you mean when you asked.....
"You were aware that rolloff filters work both ways didn't you? |
Tech833
Moderator
Username: Tech833
Post Number: 1069
Registered: 8-2002
| | Posted on Monday, October 17, 2005 - 9:57 am: |
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Corn,
A filter works 'both ways' meaning that its rolloff characteristics work no matter which way RF is going through it. In other words, if you install a TVI filter in your CB coax with a rolloff frequency of 30 MHz., it not only rolls off everything over 30 MHz. coming out of your radio, it also rolls off anything over 30 MHz. coming from your antenna to your receiver. |
Cornbrown
Member
Username: Cornbrown
Post Number: 53
Registered: 7-2005
| | Posted on Tuesday, October 18, 2005 - 8:15 am: |
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Thanks Tech833 |
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