need some designs for a MW reject filter

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kc8gpd
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need some designs for a MW reject filter

Post by kc8gpd » Mon Nov 02, 2015 8:02 am

i put the FT767GX i recently acquired recently into service. i am in a restricted community, 1st floor apartment with a covered patio, and i have to run stealth. well short story i have a wilson 2000 trucker (tried to use the downspout first as a RX antenna only, big mistake) with a buried ground radial set on the porch and close to it is my 1630 kHz part 15.2219 AM transmitter, topped off with a 1600 station of unknown power and antenna pattern and a 1690 ND 1kW/10kW and then in close proximity are gutter downspouts. well these 3 AM's are overloading my receiver across HF, i have unplugged my 1630 during HF operation but the other 2 still wipe me out.

i need to make a Medium Wave rejection filter capable of handling 150W forward power.

i looked at the commercial options and they are all RX only and in my opinion grossly overpriced and on my fixed income are beyond my affordability so i am left with the only option of home brewing but the internet seems a little lite on designs for this type of filter.

i am now turning to the brain trust here for help. i do have some scrap circuits out of vending machines, some old scrap PSU's from various sources and some PC PSU's i can scrap toroids out of.

i am not quite sure what else i have as scrap out there. might have some old CB gear as well i can scrap parts from.

thanks.
kc8gpd

"The scientists of today think deeply instead of clearly. One must be sane to think clearly, but one can think deeply and be quite insane."

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Shane
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Re: need some designs for a MW reject filter

Post by Shane » Mon Nov 02, 2015 10:11 am

I'm thinking along the lines of the R. L. Drake Co. low pass filter which was ubiquitous in the old days and maybe still is. But what you need is a high pass filter. In order for something like this to work it would probably need to begin to roll off around, say 2.5 or 3 MHz. I don't know if you could build one sharp enough so you could use 160 meters.

Since you really don't need the filter for transmitting a separate receive antenna with such a filter would eliminate the need to build the filter for high power and perhaps you would be able to make it sharper with smaller components.

An ARRL Handbook might have some ideas. If not in today's Handbook, certainly in an older one.
Mike Shane, CBRE
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jammerdave
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Re: need some designs for a MW reject filter

Post by jammerdave » Mon Nov 02, 2015 3:01 pm


kc8gpd
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Re: need some designs for a MW reject filter

Post by kc8gpd » Mon Nov 02, 2015 4:14 pm

the 402x at that link should fit the bill perfectly and it is much cheaper than many of the receive only models i have seen. $50.00 isn't too bad.
kc8gpd

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Deep Thought
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Re: need some designs for a MW reject filter

Post by Deep Thought » Mon Nov 02, 2015 11:16 pm

I suspect that you are going to find the bigger problem is lack of proper grounding and bonding if your part 15 AM is getting into the receiver, too.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

kc8gpd
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Re: need some designs for a MW reject filter

Post by kc8gpd » Tue Nov 03, 2015 7:28 pm

the thing that concerns me is on both sides of my porch are 3 story tall vertical downspouts for the gutter system and it has been suggested that there might be some kind of diode action (arcing across the poorly fitted joints) going on at the joints causing all the near by medium wave transmitters to replicate across the HF band. the 2 power houses down the street and my part 15.
kc8gpd

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jammerdave
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Re: need some designs for a MW reject filter

Post by jammerdave » Wed Nov 04, 2015 1:00 pm

Very well could be an issue with downspouts or similar. Had the same problem years ago. Had a 10kw 1690 down the street, and a 50kw 1530 5 miles or so away that gave me grief due to my pasture fencing and electric fences... rusty joints can do that...

df

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