Can someone recomend a good BC band filter?

[ke7trp]

The disney station in town, listed at 50KW on 1580kc, Is tearing up my little Soft66LC2. Can someone recomend a low cost solution for a recieve only filter?  I dont need an expensive Transmit capable filter.  This is a $100 radio... 

Most I have round only offer 1 to 8 DB at 1580 and I doubt thats going to help me.

C

[WA1GFZ]

Clifton Labs, Jack Smith.
I know someone who has one. Maybe he will sell just the board and parts to save money. He just sold me 4 interface board kits for his e probe antenna.
Saved me a lot of money.

[Gito]

Hi

Maybe this will help,a wavetraps circuit.

C resonant is around 300 ,400 pf resonated with a coil at interfering Frequency.
(parallel resonance)
Maybe using two or three wavetraps in serie ?

Gito.N

[Jeff W9GY]

The previous post shows a parallel tuned cuit tuned (I assume) to the frequency you wish to recieve. I prefer a series resonant circuit tuned to the offending station.  This is basically a notch. This works quite well in a high Z antenna system, placed ahead of the receiver input terminal.

[WQ9E]

I second Jeff's suggestion.  I built two of these notch circuits to use with a pair of Hallicrafters SX-101 receivers to remove a 1650 Khz. station out of Iowa that would make it into the Halli first IF when operating on 160. 

[ke7trp]

Any details? Does this apear in the handbook?  I saw one that uses three caps and two 3.3 chokes that might work.   I cant see spending $200 on a production filter for a $100 SDR.

C

[KB2WIG]

On the cheeep.

If you can find an old radio to  'gut'....  rip out the loopestick ant and tuning cap ... and there's your filter.


klc

[ke7trp]

Thats a great idea..  Hmmm.  Now I need a POS old transistor radio to gut.

C

[vincent]

Expensive but a very good one, if interested; schematic and explanation are below. This filter was designed by Doug DeMaw.

[Gito]

hi

Jeff,You are right using a series resonant circuit.if the circuit is connected between the Areal input(antenna input) and ground.

But if you look at the attachment picture .it used a parallel resonant circuit  between the Antenna and the the areal input ,and made a high resistive  impedance at resonance (high Resistance at the tuned frequency)but not for another frequency.

Vincent ,if the Radio  Reciever  is design with a known input impedance like 50 Ohm,than actually we can make a high pass filter ,passing only the hF frequency,there are many high pass  filter design in the ARRL handbook

Gito.N

[ke7trp]

I plan on reading through the handbook tonight. I am using the little SDR reciever now and it really needs  a BC band filter in front of it. Its fantastic for $100 but lacks those filters. 

I cheated by setting the bandpass filter to 5.5mhz to 10mhz.  This stopped the BC stations cold, however, I lost about 20DB of sensitivity on the 75 meter band.  Even so. I get images across the spectrum.

C

[vincent]

Hi Gito,
of course you are right. I do not know this receiver so I thought it had a 50 ohm Z antenna input, like so many other receivers. I was completely "out of tune"!

[ke7trp]

Here is what I am dealing with.  1580KC Disney radio blasting in over the 75 meter ham band. 

C

[Gito]

Hi

Rereading the Article,it says A 50KW broadcast station in town? usually broadcast station is out off town ,to avoid RF interference /minimize interference to electric apparatus in town (audio amplifier ,telephone ....).

A high power BC station must have harmonics frequency ,even it's very low to the fundamental frequency ,it's high enough  to made it into You  radio reciever.
 
If the cause is the harmonic frequency /or the product of it that comes in Your Radio reciever   and in the  75 meter band ,than nothing You an do,since filtering it,is also filtering the 75 meter band.

Gito.N

[ke7trp]

That picture is of an image.  The BC station stays centered when I change Frequency.  The BC station is mixing with the oscilator? 

The filter will work.  I changed the default setting from 1.2 to 5.5 mhz to 5.5 to 10mhz and the BC station disapeared on the 75 meter band. HOWEVER, 75 meter band performance really suffers!

Today I wound chokes for Audio line, and USB cable.  No change.  Only way to remove the image is to unhook antenna.
C

[Opcom]

possible some suitable parts for the filter may come from an -old- inductively tuned AM car radio. They had 3 slugs IIRC.

[Gito]

HI

When You Changed the bandpass filter to 5,5 mHz to 1o Mhz of course the BC station disapeared , because "it's frequency"/the product frequency" You recieved  is around the 75 meter band ,or around 4 mhz,

and of course  75 meter (3.8 Mhz?) band suffers , because the frequency below 5,5 Mhz is block  by the band pass filter.

Gito.N

[ke7trp]

Yes. You state the obvious.  However, this proves that the BC band filter will work. Maybe tomorrow I will experiment.  I woke up this morning with a damn chest cold.  Canceled my trip to family and am stuck home alone sick.  Ba humbug.



C

[Gito]

Hi

Yes the BC band pass filter works It eliminates the fundamental frequency and it's harmonic below the pass band.
That also mean,that the distrubing frequency is pick up through the antenna

A the transmitter produce  harmonic frequency that is filter out by it's output network,but  not 100% eliminate it. and if some of this harmonic gets into Your Radio ?
 It's a 50 Kw transmitter in town(it means "close" to Your house),if the the harmonics frequency  that falls in the 75 meter band has only 2 watt power,it still can distrub the radio. (50000:2 = 25000 =...DB)

It's like this someone is transmitting in the 75 meter band,and We want to block him by a band pass filter.Yes We can but of course we also blocks all the other transmitter which works in the 75 meter band.

So if it's a harmonic Frequency ,that falls in the 75 meter band ,than we can do nothing about it.

Maybe using  a high Q notch filter?

Of course I can be wrong.


Gito.N

[ke7trp]

I think the problem is the BC station mixing with the SDR radio.  The entire BC band and the 75 meter band is destroyed.  However, If i move the filter up or use a higher band, Then I dont have any interferance.

I understand you are suggesting this can be the second harmonic of the BC station which the BC band filter will not help at all.   


C

[flintstone mop]

Clark,
is this a complete self contained SDR. RF 'front end' / I.F. ?? then the usual computer sound card hook up?
Some SDR's are digitizing the RF and maybe skipping the sound card and going USB to the 'puter.
I'm a little out of touch with any advancements.
Is this an Elektor SDR??

http://www.elektor.com/products/kits-modules/modules-%28-9x%29/software-defined-radio-%28070039-91%29.91475.lynkx?gclid=CK7Gm5Wyna0CFcNo4AoddQEDmA

And Gito, it is very possible that a 50KW AM station would be very close to people living close by. A developer near Washington DC built an apartment building right next to a directional array, 50KW, 1500 AM station. Used to be WTOP, NEWS/TALK radio.

There's a little TV shop near by making lots of money getting rid of RFI to consumer electronics and telephones. There is nothing on the WEB about this. I talked to the chief engineer, when they were having terrible coverage problems with their AM signal. They re-built the ground screen and it helped a little. Their weird directional pattern made it almost impossible to listen locally.
The engineer said booo-hooo on them. The radio station was there first. Sorry 'bout that!!!

[ke7trp]

ITs a self contained Receiver Fred.  It can hook to the IF but I do not use it that way.  Its called a Soft66LC2.  I own a bunch of recievers and almost all of them get some kind of interferance from the Station. My R390 and R390A are the worst.  Sp600 a bit better but I can here it. The Icom 756Pro does not get bothered to much. The FT101 does.  It really depends on where you are on the bands and what radio you are on.

The SDR being the worst of the bunch as it does not have any Hardware filters on the front end. 

The station is right around 8 to 10 miles from me.  The pattern plots show its beaming right at me though.  There are hams that life closer and never hear the station. But being in front of that directional array has caused me trouble for years.
C

[flintstone mop]

OK Clark
Being that you mention several receivers getting overloaded from this station, it MIGHT be better to spend the $$$ on a real BC blocker and then your entire station plus the little guy will be happier without front-end overload.

My loop antenna has an optional BC blocker. Apparently part of their loop antenna options.

http://www.pixelsatradio.com/uploads/RF-PRO-1B-Specifications.pdf

A $100 dollar add-on preamp with BC High pass filter.

I own an I.C.E. model 123B Bandpass Pre-amp.......$48......

http://www.iceradioproducts.com/reconly.html

Might also knock out the BC band for $48.00

On 'The CHEEP" causes frustrations and cursing. I'm tired of both!!

Something to consider
Fred

[ke7trp]

Thanks for the links Fred!

C

[ke7trp]

FYI, Fred, The Ice page you sent seems to be products they no longer make. They only make the products on the main page now:

http://www.iceradioproducts.com/