guy's, i need a AM Broadcast Band Filter design. i need to block the frequency range of 500 to 1700 khz. i have setup my FT767GX in the apartment. it is capable of seperate recieve and transmit antenna's. i have the transmit side going from radio to HF LPF, into swr power meter then into ATU then off to wilson 2000 trucker antenna with some wire ground radials.
on the seperate RX jack i have it going through RG 58 and i have a breakout connector that sperates ground and hot. the ground goes to my ground rod and the hot to a 3 story rain gutter.
the 3 am stations about a 1/2 mile away as well as my on site part 15 am are wiping out the entire HF band on my FT 767.
i want to take and old 250 watt computer power supply and use the toroids and capacitors to build a AM rejection filter.
i know both of you probably know of a design or could whip me up a design for one.
the stations are di or tri plexed. think 1600, 1650, and 1690. 1600 and 1690 i know for sure. i am unsure if 1650 is there.
I looked at the costs for filters and i just cant afford the prices so i need to build one with what i have on hand.
i will also likely need a notch filter to notch out 1630 from 850 which is my LP-2 for my EAS.
my part 15 overloads my dayton AFC3 reciever deck.
... on the seperate RX jack i have it going through RG 58 and i have a breakout connector that sperates ground and hot. the ground goes to my ground rod and the hot to a 3 story rain gutter. ...
The sections of that rain gutter likely are not well bonded to each other, electrically. Those connections can act as diodes, which can generate r-f mixing products from the strong AM broadcast signals there.
You might get better performance just using a single wire conductor for a receive antenna.
Robert,
Try Rich's suggestion but if there is some diode action nearby this may not help but you should see some change. Your receiver has an attenuator built in and the purpose of this is to reduce overload interference. Do you notice any change if you switch it in and out?
When I was designing a transmitter I needed a 7 pole low pass filter but I don't recall how I designed it. I think I used some sort of program for this but I do remember I simulated it with LTSpice. You will need a high pass filter which is just a matter of exchanging the Ls and Cs and picking the right corner frequency. I'll dig out my notes on this and post back if there is anything that looks to be helpful for you.
It could be that all you need is a simple low Q series LC trap as you mentioned and what I mentioned above could be overkill. The problem with using power supply toroids is the core material may not work at RF. Another problem is not knowing the inductance unless you have some way to measure this but it could be done trial and error and may be worth a try since you have the parts available.
Neil
unfotuneately i believe rich is likely right. i had thought along those line which is why i didn't use it to transmit as well, but it didn't cross my mind about affecting the recieve.
and there are at least 4 downspouts 3 stories high within 20 feet of my antenna's and also the actual horizontal gutters. all are poorly bonded. just held together with sheet metal screws.
this might explain why when i set up my imax 2000 5/8 wave on 10 m and tuned the HF band i did not have any of these effects on it.
it was placed maybe 50 to 100 ft from it's current location at my detached garage i rent.