band pass filter recommendations

FM does it with frequency!
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TPT
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band pass filter recommendations

Post by TPT » Thu Mar 15, 2018 7:24 am

Here's the picture. I own a tower in an area that has become, over the past few years, the local antenna farm. Presently this tower has two full-power FM's, mine with 3500 watts ERP, plus a tenant with 750 watts ERP. ECO-4 and VS-1 transmitters. Just added a 175 watt translator with a BW 300 watt transmitter. Next door (~350' away) are two more Class A's--1500 watts from an old Harris 5K, and 3800 watts from another ECO-4.

Planned shortly are three more translators on my tower, using two new Gates Air Flexiva 500 watters and a BE STX kilowatt, all running 250 watts ERP.
Now the lease agreement requires those installations to cure any interference problems that may develop. Since I know the engineers involved, I would like to have some suggestions for sources of band-pass cavities. The average power into a cavity will be under a kilowatt Site is a rural area, so far nothing really obnoxious in the way of spurs seems to have appeared very far off the 16 acre site.

Question will arise--yes, RF exposure limits have already been calculated and found acceptable by the consultant for the 750 watt tenant. They moved onto the site just last summer.

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kkiddkkidd
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Re: band pass filter recommendations

Post by kkiddkkidd » Thu Mar 15, 2018 8:06 am

Kintronic Labs is now selling filters and diplexers that are supposed to be pretty good.
Dielectric
RXTX / Bird
Telwave
Microwave Filter Co.
Sinclair (may have dropped the FM line)

And for what it's worth, there is a new Microwave Filter Co. FM filter on ebay right now.

Regards,
Last edited by kkiddkkidd on Thu Mar 15, 2018 8:50 am, edited 1 time in total.
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Lee_Wheeler
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Re: band pass filter recommendations

Post by Lee_Wheeler » Thu Mar 15, 2018 8:44 am

My RF Specialties guy has been selling my clients Shively cavities for the translators where the translator antenna is very close to another FM. They seem to work fine. They can be bought in single, double, or triple cavity versions and that decision is made based on the channel spacing between the two signals.

I have one where the translator is 3rd adjacent to a C2 and the translator antenna is 12 feet below the full power. For that one I used a triple cavity just to keep the full power FM from blowing up the translator transmitter. I really don't worry about the translators causing spurs on the high power FMs so I only install the cavities on the translators.

...Lee

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kkiddkkidd
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Re: band pass filter recommendations

Post by kkiddkkidd » Thu Mar 15, 2018 8:51 am

Lee_Wheeler wrote:
Thu Mar 15, 2018 8:44 am
My RF Specialties guy has been selling my clients Shively cavities for the translators where the translator antenna is very close to another FM. They seem

...Lee
I forgot about Shively...
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Kevin C. Kidd CSRE/AMD
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awsherrill
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Re: band pass filter recommendations

Post by awsherrill » Thu Mar 15, 2018 10:15 am

EMR Corp in Phoenix makes FM broadcast filters...

http://www.emrcorp.com/

TPT
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Re: band pass filter recommendations

Post by TPT » Thu Mar 15, 2018 3:04 pm

One of the translators will be on 103.5--and only a few feet below the antenna for a class A on 103.9. When the lease was signed we indicated a possible relocation of the 103.9 station to this tower--just happened faster than we anticipated (they cancelled their lease when AC failed & transmitter got cooked).

Luckily we are dealing with roughly equal power--750 watts vs. 250 watts. The Shively filters sound like they will do the trick--thanks for the tip!

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Deep Thought
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Re: band pass filter recommendations

Post by Deep Thought » Thu Mar 15, 2018 4:24 pm

Second adjacent co-location? Good luck... :shock:
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

TPT
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Re: band pass filter recommendations

Post by TPT » Thu Mar 15, 2018 4:38 pm

Wasn't my idea....I suggested several other possible channels.

Nathaniel Steele
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Re: band pass filter recommendations

Post by Nathaniel Steele » Tue Mar 20, 2018 12:03 pm

Kathrein/SCALA now makes a line of filters, maybe they always have but I only learned of them last year. the catalog shows 100W, 3KW, and 5KW, but I know they make bigger ones as that was what I was looking for at the time, so there may be a 1KW version available too...never hurts to ask.

Nicom is another source but I'm not a huge fan of their filters.

There was another company a Colleague of mine mentioned, I believe it was american amplifier, or something of that nature, he was very impressed with that filter. Here it is, no fingerstock used (which is the problem with the nicom filters) http://www.americanamptech.com/FM_Bandpass_Filters.html

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Deep Thought
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Re: band pass filter recommendations

Post by Deep Thought » Tue Mar 20, 2018 3:29 pm

I saw the Kathrein/Scala filters at NAB a couple years back. They are made by another company but I was impressed by the quality and price point(s). The major issue here is the 400 KHz spacing. None of the commercially available filters will work at this tight of a channel spacing, so whatever is used here is going to be a custom "special" with a price tag to match.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

Nathaniel Steele
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Re: band pass filter recommendations

Post by Nathaniel Steele » Tue Mar 20, 2018 4:46 pm

I understand that, but OP mentioned 3 more coming soon and wanted info on what was out there. I agree the second adjacent on the same tower is going to be tough...

Would a circulator be of any use for that situation? I'll admit I'm not too well versed on how they work, If someone can explain it to me I'm all ears....

TPT
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Re: band pass filter recommendations

Post by TPT » Tue Mar 20, 2018 5:05 pm

What will help is the relatively low powers of the translator and station--103.9 750 watts into an old Collins 3 bay, 250 watts into whatever antenna the tenant plans to use. The transmitters will be new--VS1 and a 1 kw Gates Air Flexiva.

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Deep Thought
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Re: band pass filter recommendations

Post by Deep Thought » Tue Mar 20, 2018 5:40 pm

TPT wrote:
Tue Mar 20, 2018 5:05 pm
The transmitters will be new--VS1 and a 1 kw Gates Air Flexiva.
Neither of those have any tuned circuits on the output so expect some huge cross products. It doesn't matter what the power levels are with that close of a spacing. You'll have to make -71.8 dB minimum which is going to be tough without a very spendy set of filters. I've done two 250 watt translators 800 KHz apart and that was like pulling teeth with six cavities (pun intended).
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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