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CB BANDPASS Filter?

Discussion in 'CB and Export Equipment and Accessories' started by Robb, Jan 9, 2013.

  1. Robb

    Robb Yup

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    Is there a company that makes a CB band-pass filter?



    Not talking about a Low Pass filter; but a true band-pass filter?

    Like to get one if anyone knows of a company that sells one - or even looking for a schematic to build one . . .
     
    #1 Robb, Jan 9, 2013
    Last edited: Jan 9, 2013

  2. Mudfoot

    Mudfoot Sr. Member

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    The guy that made Par End Fedz, also makes specialty filters for communications. I believe his main client is the government. I think he sold the antenna line to concentrate on the filter side.

    Anyways, can't remember his name, but he's a HAM. I've talked to him on the phone several times in the past. He was always friendly and helpful. If he doesn't have what you need, he should have a source for you.

    http://www.parelectronics.com/scanner-bandpass.php
     
    Shadetree Mechanic likes this.
  3. Robb

    Robb Yup

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    Looks like he builds some quality stuff. Uses brass boxes to contain the parts. $$$. Have to find out if he does custom freqs. But that could get too costly for what should be just a ~$40 item.

    Maybe a schematic would be better. Or even a formula for part values that determine the turn-on and shut-off frequencies. Or even both if possible. Would also like to make it a 4th order type of filter so that the usable bandwidth has very steep slopes on either side. As well as a ~1,500 watt handling capacity.

    This band pass filter is really nothing more than a tuned high pass and low pass filter - combined. No one seems to make these for CB radio. I wonder why. CB radio users could really use something like this too. Radios that throw off a lot of spurious signals above and below the CB band could be contained and rendered harmless in the Ham, government, and commercial freqs. Seems logical that someone would have made one commercially by now.
     
    #3 Robb, Jan 9, 2013
    Last edited: Jan 9, 2013
  4. RADIOOMAN

    RADIOOMAN Active Member

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    There is likely to be many places on the internet that would provide you with the information necessary to build your own 'band-pass' filter.
    Since you are interested in a 'band-pass' filter then I will assume that it is for a recieve only application as that is really the only place you would need one unless you are talking about the internal circuits of a radio transciever.
     
  5. Robb

    Robb Yup

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    Naw; for RX and TX applications. Should work to clean up the receive and clean up spurious signals above and below the 11m band. Must admit that I do not know all that much about them . . .

    But what I do understand is that by limiting/masking the receiver to a narrower band of signals that the antenna is catching, you can remove that signal load that is just outside of the selected bandwidth. Which will desensitize a receiver - if allowed to pass. Don't know how well the radio's receiver can discriminate; but having a better external filter should allow for greater removal of unneeded signals.

    OTOH, by limiting/masking the TX bandwidth it can also keep interference out of any other band and limits it to the 11m meter band. Or whatever band the band-pass filter is tuned/designed for.

    A filter that is so constructed to allow TX/RX only between 26.700mhz and 27.700mhz (as an example) would be effective to keep transmitted interference out of the Ham bands above and below those freqs. Allowing TX/RX on the CB band only. It excludes everything else for receive as well.

    Found this:

    http://www.siversima.com/rf-calculator/bandpass-filter-designer/

    Chebyshev 2nd order filter

    [​IMG]
    Order=2 Bandpass Chebyshev Filter
    Pi: 2.233nF 15.56nH 12.35pF 2.813uH
    T :6.225pF 5.582uH 1.125nF 30.88nH

    An 4th or even 6th order filter will have a sharper cutoff slope; this means that even less leakage will occur for TX/RX.

    [​IMG]
     
    #5 Robb, Jan 9, 2013
    Last edited: Jan 9, 2013
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  6. rabbiporkchop

    rabbiporkchop Sr. Member

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    Try using a cable resonant at the frequency you are transmitting on. That's the easiest cheapest solution I can think of assuming your receiver sensitivity is in the
    -135 DB range
     
  7. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Doesn't really surprise me much. Basically it would be catering to a limited and for the most part illegal sector of the communications business. Radios should be able to transmit without having spurs all across the spectrum and in most cases if the golden screwdriver is left in it's case they will. An antenna tuner will provide a good measure of bandpass filtering BTW especially if you use a Series-Parallel Capacitor (SPC) type.

    [​IMG]
     
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    What you really need is a Chebyshev filter. Has sharp filter cutoffs.
     
  9. jazzsinger

    jazzsinger Bullshit Buster

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    Only bandpass filter I ever saw or used was made by Jim Finch of SSE Electronics.

    Don't think they are still in production as last time I was on Jim's website they weren't there, they were 26-30mhz and 300w power handling and very well made.

    http://www.radioworld.co.uk/sse-uk-bpf27-4-27mhz-band-pass-filter

    Might be worthwhile dropping Jim an e mail Robb, might just have old stock lying about or even a schematic.

    http://www.ssejim.co.uk/index.html

    73 Jazz.
     
    Robb likes this.
  10. BBB

    BBB Well-Known Member

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    Use this Bencher YA-1 low pass filter and at least have the upper end covered (although they are out of stock currently) I've had many years of service with this unit and no issues so far.

    https://www.dxengineering.com/parts/bnr-ya-1

    ICE and Array Solutions have some cool band pass filters as well:

    http://www.iceradioproducts.com/

    http://www.arraysolutions.com/filters/bpf-hpf

    I bet Array Solutions could build one for 11 meters as their 10 meter "luxury" units have almost full 11 meter coverage already:

    [​IMG]
     
    #10 BBB, Aug 18, 2016
    Last edited: Aug 18, 2016
    Slowmover likes this.
  11. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Yes Array Solutions will do custom builds...Excellent filters! I ordered and used 80m and 40m -400 Watt PEP versions on Field Day this year. The LUXURY units are 3 Pole filters where most available are only 2 Pole.
    I inquired about a 6m version, and the custom build was $185.00 USD for this version.
    Yes a Little steep, but quality of product was excellent and customer service also excellent.
    I sent an Email on Saturday very late and received an answer on Sunday early afternoon from the President and CEO himself...pretty cool
    Will certainly deal with them again.
    One final note: when used field day with a TS-520S for the 40m station the LUX40 model dropped the noise level 6-10 dB after install of the filter in-line. The other observation ZERO interaction from the 80m or 40m station were noted while operating side by side during Field Day
    All the Best
    Gary
     
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  12. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    What was the power handling of the 6m filter you inquired about Gary? I may be looking for a good LPF or BPF for 6m in the near future but it needs to handle a MINIMUM of 1500 watts pep since it will be on the output of a 1200 watt amp.
     
  13. Robb

    Robb Yup

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    4 pole DIY and put it in a paint can filled with oil?
     
  14. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Oil for a thru-line filter? No thanks. I am trying to get away from oil filled loads etc. I have one left, a Bird 600 watt load. I have a 6m LPF but there has been some controversy about how much power it can handle before the solder begins to melt. The maker claims legal limit (1500 watts) but some users have had issues at that power level.The amp I have is super clean so it may be possible to simply use a LPF between the exciter and the amp to reduce harmonics going into it and use a tuned stub on the output since I operate over a fairly narrow range anyway. Nevertheless curious about a high power LPF or BPF made the proper way ie. not needing to be drowned in a can of oil.
     
  15. Onelasttime

    Onelasttime Well-Known Member

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    Chebyshev filter. One of the old ARRL handbooks I have had over the years had the design in it. I think it might be a free download from them as well. That is about as good as it get's from a passive and practical cost stand point of a hobbyist. I have been considering trying to locate the design I used all those years ago. I have gone through at least 2 laptops and 4 desktops and 6 hard drives since I last built one. I am sure though that I got it either from an ARRL Hand Book or off the internet and that it was between 1995 when I graduated from college and 1998 when my first son was born. After that I have come and gone from the hobby a few times. I hope that helps to track down the information. I assure you that you will not see Chebyshev filter mentioned on any dedicated CB site so you can rule that out.
     

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