Can someone recomend a good BC band filter?

[Pete, WA2CWA]

ICE is now owned by Array Solutions. Mike Koss, owner of ICE, passed away in March 2011.

[ke7trp]

I kinda guessed that they where purchased.  They had alot of neat products listed.

C

[flintstone mop]

I was wondering why my I.C.E. front-end protector was always taking months to come back from repair.
Looks like Array solutions is offering something better.

http://arraysolutions.com/Products/bcb_filters_top1.htm

[ke7trp]

That filter has only 10 DB or so at 1580. I doubt it would work.

C

[Jim WB5WPA]

A few years ago, 2002 to be accurate, I endeavored on a filter design that yields a minimum of 40 dB attenuation to all signals below 1702 kHz ... so it passes 1.8 MHz and above through 30 MHz with low insertion loss and better than 20 dB Return Loss:

http://www.scribd.com/doc/34925080/AM-Broadcast-Band-BCB-Brickwall-Filter-160M-10M-pass-Design-and-Performance

If it is constructed with the larger toroids and 500 V Silvered-Mica caps it will take 100 Watts transmit power down to 1.8 MHz too.


A more generic description that demonstrates the attenuation but is light on technical or construction details can be found here:

http://datos.s3.amazonaws.com/usblsb/descargas/AM%20Brick-Wall%20160%20Meter%20Filter.pdf

de Jim WB5WPA  Merry Christmas!

PS. Four or five protos were built, and they worked better than expected! W3DQ near Wash DC and WTOP (at the time) tested a unit as he is a big 160 M op.

[flintstone mop]

A few years ago, 2002 to be accurate, I endeavored on a filter design that yields a minimum of 40 dB attenuation to all signals below 1702 kHz ... so it passes 1.8 MHz and above through 30 MHz with low insertion loss and better than 20 dB Return Loss:

http://www.scribd.com/doc/34925080/AM-Broadcast-Band-BCB-Brickwall-Filter-160M-10M-pass-Design-and-Performance

If it is constructed with the larger toroids and 500 V Silvered-Mica caps it will take 100 Watts transmit power down to 1.8 MHz too.


A more generic description that demonstrates the attenuation but is light on technical or construction details can be found here:

http://datos.s3.amazonaws.com/usblsb/descargas/AM%20Brick-Wall%20160%20Meter%20Filter.pdf

de Jim WB5WPA  Merry Christmas!

PS. Four or five protos were built, and they worked better than expected! W3DQ near Wash DC and WTOP (at the time) tested a unit as he is a big 160 M op.

Great info. And thanks for the connection to WTOP.

[Gito]

Hi


The way we think ,a strong MW transmitter (50 Kw) transmitter is transmitting near us,it goes into our Radio reciever ,and this signal is the cause of the all  distrubing frequencies in the band in our radio.Meaning that the cause of all that is this MW transmitter.

And Clark can get rid or at least weaken the transmitter coming in the radio by a band pass filter,and proof with a 5,5 to 10 Mhz  band pass filter,the band below 5.5 mhz is "clean".

Logically thinking when we get rid of this fundamental frequency ,than the radio must be clean since the interference is produce in the Radio is caused by the fundamental frequency.that gets in the radio.

 The point is if we can ellimate the cause,then the trouble is gone.

Yes a band pass filter or BC filter can get rid for all the BC station  that get into the radio .The purpose is blocking the bc station signal gets into Our reciever.(fundamental frequency)

But what about the harmonic frequency,or frequency by rectification..Remember is a power full transmitter and close. to Your House

Harmonic by rectification (from  ARRL}

Even though the transmitter is completely free from harmonic energy,it is still possible for interference to occur because of harmonics outside the transmitter.These result from rectification of fundamentall-frequency current induced in conductors in the vicinity of the transmitting antenna........
.
And harmonic means a second harmonic ,third harmonics,and all the product all  harmonic  frequency mixing  together. The harmonic frequency can very small power compared the fundamental frequency ,but enough to interfere.

This frequency is higher than the bandpass filter,so it gets into the Radio.

If this harmonics falls in the 75 meter band? it is not filtered out out by the pass band.



Gito.N

[Jim WB5WPA]

Hi


The way we think ,a strong MW transmitter (50 Kw) transmitter is transmitting near us,it goes into our Radio reciever ,and this signal is the cause of the all  distrubing frequencies in the band in our radio.Meaning that the cause of all that is this MW transmitter.

And Clark can get rid or at least weaken the transmitter coming in the radio by a band pass filter,and proof with a 5,5 to 10 Mhz  band pass filter,the band below 5.5 mhz is "clean".

Logically thinking when we get rid of this fundamental frequency ,than the radio must be clean since the interference is produce in the Radio is caused by the fundamental frequency.that gets in the radio.

 The point is if we can ellimate the cause,then the trouble is gone.

Yes a band pass filter or BC filter can get rid for all the BC station  that get into the radio .The purpose is blocking the bc station signal gets into Our reciever.(fundamental frequency)

But what about the harmonic frequency,or frequency by rectification..Remember is a power full transmitter and close. to Your House

Harmonic by rectification (from  ARRL}

Even though the transmitter is completely free from harmonic energy,it is still possible for interference to occur because of harmonics outside the transmitter.These result from rectification of fundamentall-frequency current induced in conductors in the vicinity of the transmitting antenna........
.
And harmonic means a second harmonic ,third harmonics,and all the product all  harmonic  frequency mixing  together. The harmonic frequency can very small power compared the fundamental frequency ,but enough to interfere.

This frequency is higher than the bandpass filter,so it gets into the Radio.

If this harmonics falls in the 75 meter band? it is not filtered out out by the pass band.



Gito.N

My experience in/around Dallas (with several 50 kW stations in the area and host of others at various other power levels and distances including a 1700 kHz night-time transmit location just a few miles away) is that most of them have little in the way of 2nd (or 3rd) harmonics of note; I have, however, encountered in-band 'trash' (in the AM band) by malfunctioning transmitters, about 4 years ago I reported one (with detailed info as to direction, where the 'trash' was observable with a spec an and what station the trash was 'coincident' with) to the FCC and the next week the station was busy remedying the problem (they were off the air for a few days).

There is trash presently, in the area, just below 1800 kHz that I have not attributed to any particular 'source' yet.

Of course, if I was setting 5 miles away in the 'boresight' of a DA 50 kW it might be a different story! As it is, 770 (5 miles to the east) and 1080 (50 kW at 10 miles) and the nighttime 1700 (2 miles) are the ones that hold any potential for inflicting interference my way.


Jim de WB5WPA

[WBear2GCR]

I am far from an expert, but I have an opinion anyhow...

This link's filter: http://www.scribd.com/doc/34925080/AM-Broadcast-Band-BCB-Brickwall-Filter-160M-10M-pass-Design-and-Performance

is essentially a Cauer or elliptical filter. If you take out the cap on the leg to ground you have a ordinary 2nd order HP filter per section, each section adding so two sections, 4th, then 6th, etc. The problem with the usual filter is that the stop band is not down that far AND the slope of the stop band is less than one would want.

The solution is that one makes one of the elements in the filter (series C, L to ground) into a notch filter. In this configuration that would be usually the one to ground. This makes the slope of the transition from stop to passband rather much sharper.

One can simulate these filters rather nicely in one of the free SPICE programs, like LTSpice. You could take an existing filter example and just dork the values and add the extra C to make it into that notch. For things like this, LTSpice is great - of course you need it set up with the operation codes to show the results properly (that's a bit obscure) but as I said you can use a generic example that produces a freq response curve for ANYTHING, and change the parts to be your filter, cut and paste!  

In filters used for "important" applications they care about things like ripple, the depth of the first drop, etc... maybe even phase. For the application of notching out a strong local AM broadcast station this all is probably totally unimportant.

So, what I'd suggest is putting together a two section Cauer or eliptical high pass filter with the first drop set to bottom out just about dead center on the offending broadcast frequency. I'd bet you can get 40-60db of attenuation without getting very precise. Also it will be pretty insensitive to input and output impedance if ur a little clever in the input and output loading... you can always add another section. Even with at two section filter one can spread the center freqs plus and minus the target frequency, this ought cause the filter to still provide good attenuation wrt frequency in the event it sees somewhat significant changes in input Z or output Z.

These filters can be built empirically - what happens as you vary the L and C values around a center frequency is that the shape of the filter changes a bit, and the depth of the stop varies from maximum to about 20dB less, but since max is around 60dB down, that's not too shabby, especially since the attenuation goes up with the number of sections. So, get in the ballpark and dork the C until you get it on frequency, sweep it (if at all possible) and get the best you can, which is probably more than good enough!

The article was for a broadband broadcast band filter, you probably only need one that aims like an arrow for the offending BC frequency. Much easier.

My 2 cents...

                  _-_-bear

[Jim WB5WPA]

"is essentially a Cauer or elliptical filter."

Yes, stated so on pg 4. Thanks.

I also admit to using EESOF ESYN (as stated) to initially synthesize the components values, but, it takes 'skill' in picking certain key indices to hit the design points like IL in the passband, nail the 40 dB goal *at* 1.7 MHz and keep the ultimate attenuation better than 40 dB in the stopband; for some of those 'goals' modeling (I used Touchstone) with multiple iterations (many runs) tweaking and changing seeking all the while to meet goals and, indeed, they were met.

So, you're 'talking' to the designer, here. Any questions I've got answers (although it's been a few years since the design, test and field work was done) ...

de Jim WB5WPA

PS. As to 'SPICE', I would guess by now you've made it to the page where the SPICE simulation results for component currents at critical points were listed ... linear simulators like RFSIM99 are nice for quick analysis of filters, but, when it comes time to evaluate the power handling capability one turns to SPICE simulation runs ...

Jim

[flintstone mop]

Very good info Jim,
How can you help Clark out?? Gotta filter to sell?? Not many people have junque boxes with the components needed to build such a nice filter.

He may not need the ultimate 40dB supression.

And Clark would you be willing to try the Array BP pre-amp on the condition that if it doesn't work for you you get a refund??

I'll do this............EDIT::::
I tested the model 123B and there was very little difference atten. BC band freqs. And the unit is only for 160M. It was essentially a pre-amp for a K9AY loop antenna.
Back to the drawing boards.

[Jim WB5WPA]

Fred, if one can find or wind the four inductors the rest of the components are just a bunch of caps! And a combination of values is acceptable, like I had to do to get close to some particular values.

And for receive only, the requirements for High Q components goes down as one can usually tolerate a little more loss on receive on these low frequencies, and the toroids can be the smaller ones and use more like 20 or 24 ga. wire to wind ...

Just come up with the correct uH values and she should fly ... not as optimum as if using the specified components, but again receive isn't as critical ...

Adjustment should be made to 'hit' the important 'notch' freqs shown on the schematic by adding or removing turns on the toroids to get as close as possible, within a turn, so come up with the values of the SM caps and then tune the toroids on the shunt arms to 'hit' those four notch freqs ... and the filter should fall right into place from there (she should meet RL value specs in the passband beginning at 1800 kHz on up).

I added a compression trimmer for the arm that tunes close to the 1700 kHz notch freq, but this is because we in this area needed to kill the 1700 kHz station and also to meet the 40 dB spec *at* 1702 kHz without having to touch that toroid for tuning, just a quick adjust of the trimmer and bingo!

de Jim WB5WPA

PS Should probably come up with a small PC board using small toroids for a receive-only model ... I'll look into that ...

[WBear2GCR]

Jim,

I wasn't trying to be critical of your filter or article.
What I did was to jump right to the schematic and response curve to see what it was. Then I posted. The original post stated that there was one particular frequency BC station in close proximity. So, he doesn't appear to need a broad, AM BC spectrum, filter at all. And he only needs it on receive.

So, his constraints are greatly reduced.

He can get away with maybe two sections of filter centered around the BC stations frequency - in many ways a much simpler filter to design and build than yours. Different problem, different design goals.

Hope this makes sense?

                    _-_-bear

[Steve - K4HX]

Clark, do you have an attenuator? I wonder how many dB you need for the spurious signals to disappear. This will tell you what sort of filter you'll need.

[aa5wg]

Hi C:
I heard that some guys use the link antenna coupler to help with broad cast interference.  The link coupler is band pass design.
Chuck

[Gito]

Hi

If the transmitter is clean.free from harmonics,than a filter that can make the fundamental frequency low enough not to overload the front end of the Radio ,makes the Radio "clean".

Cause this interference is caused by overloading the input front end of the radio and

The interference is build in/produce in the Radio itself cause the overloading.

So if that's the cause, a simple notch filter ,than can weaken the input signal,can solved the problem

But if it's an harmonic frequency that causes the problem ,that's another story

Gito.N

[flintstone mop]

Hi C:
I heard that some guys use the link antenna coupler to help with broad cast interference.  The link coupler is band pass design.
Chuck

That slipped by my grey matter !!!!!!!! YES an antenna tuner will be kinda like a filter.

But Gito brought up a thought about 2nd harmonics.......Any way to listen for the second harmonic on any of these radios?? 2X the broadcast freq.


It's taking this problem apart and do some troubleshooting. To see if it is the station's fault or just fundamental overload to your station.......
Crappy ground conditions/diode action can make life miserable too, Clark.
Do you own a portable radio, Sangean type of receiver, to listen for the same problem? If the portable radio is not affected, then your station needs a looksee.

Fred

[ke7trp]

Hi guys.  I have been very very sick.  I currently have no voice still and lot really feel bad.  This is twice this year I have been on the verge of the hospital. I have had no energy to do anything with radio. 

Gito:
I think the main problem is the primary frequency.  I can listen to the station the second harmonic, however, Its not blasting in or causing me trouble.

Steve, My brother has a few rack mount attenuators here.  I dont know how to use them and have not really looked at them close up. However, one is push button and one has many rotary dials across the front. I will see if I have the hook up cables here to experiment with them. 

Fred. I would be willing to try anything here.  I have a design that a local ham friend sent me that looks very simple to make.  Its a notch at 1580. I will ask if I can post his schematic. 

C

[Steve - K4HX]

Good luck with the nasty BC band interference.

Hope you feel better.

[flintstone mop]

OK Clark
Not goodness to get the same bug twice geeesh.
Get well first.

Fred

[ke7trp]

Thanks Fred.  I Just cant kick this thing. 

Any thoughts on this unit?  I understand its popular with DXers because they can run two bands and radios will not interfere with each other.  I like the fact that it will switch auto or manual, Has an SWR meter which is nice and has these filters for both in and out. I would place this behind the ICOM PRO/SDR radio switch so when transmitting, the icom would go through the bandpass and when recieving it would go through the bandpass.

I wish I had hard data on DB and design.  I can only go on the fact that I am told by a DX/contester that he can run two radios on two bands at once with out any interference.

http://www.rmitaly.us/index.php?main_page=product_info&products_id=18

[Steve - K4HX]

That box is a lowpass filter. That will not remove your 1580 BC signal. You need a highpass or a notch.

[ke7trp]

I asked that question and I am told it is a band pass.  So each knob is a low and high at those band edges which would imply that it would filter everything below the indicated frequency 2-4-7,5-15-22-30-60 MHz

Let me shoot off an email to the company

C

[Steve - K4HX]

If so, you are set.

[flintstone mop]

Clark you might need an antibiotic regimen to kick it out. Probably a shot and then about 14 days worth of pills.
A teacher at school who handles one of my special needs kids has been dealing with something in her lungs the last two weeks. And another neighbor nearby has a similar ailment, something going on in her lungs. Pneumonia in one lung.

Fred