Band pass filter recommendations

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  • Updated 2 months ago
Hi all,

I'm looking for some recommendations on good band pass filters for multiple transmitter ops.  Some local hams and I are going to be doing some SOTA and POTA work as well as prepping for next Field Day.

When we ran for last field day which was more of a test run for us than a real effort we did have cross-band transmitter interference.  Basically the 40m station did a very good job of blanking the 20m station and vice-versa on transmit.

I am aware of the W3N?N filter designs but I am afraid I don't have the time to construct my own and I don't have good tuning equipment for that either.

I purchased some russian made filters off ebay but they don't seem to work very well.  I can still significantly see the 40m signal on 20m even at only 50w with the antennas separated about 200 feet.

So I'm wondering what people are using and where to get them?

Thanks in advance
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Mark WS7M

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Posted 4 months ago

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Paul

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Hi Mark, I use a DX Engineering DXE419 100W filter bank between my 6500 and Gemini HF1k linear. You can switch bands manually or automatically. Auto operation needs a 12V active low input for each band. I built an interface to drive it from a bit cable from the 6500. I am pleased with the results. I do augment the cross band attenuation by additional filters on the second radio. Array solutions also sell a range of filters for this purpose.

Purists would say you need high power filters after the linear but I have found this not to be necessary at my station.
(Edited)
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WX7Y

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4O3A has great filters that will work great for what I think your going to be using them
http://www.4o3a.com/products/high-power-filters/series-l/

same guys that designed most of the Power genius FLEX AMP.


73's
Bret
WX7Y

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Marty Ray

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You might also look at LowBand Systems bandpass filters. I don't have any direct experience with them, just providing another option.

http://lowbandsystems.com/collection/filters

73,
N9SE
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SteveM

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I recommend these. My club used the 200W set (160M - 6M) for field day. They have the best specs and it will always be obvious to which band each filter belongs. I think DX Engineering sells them.
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Mark WS7M

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I ordered a 20 and 40m version of these to try out.  Thanks for the link!
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SteveM

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Use the LBS-filters in series with the Russian-filters so that you get out-of-band rejection from both filters. I believe the LBS filters are good for ~60dB and if the Russian filters give ~30dB, you'll have ~90dB rejection overall. That's a good number.
(Edited)
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Steven Linley

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Your 6600 has all the filters you need for the contest bands but if you have a different radio array solutions is sold by DX engineering there very good
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SteveM

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The OP is discussing transmit filters. I believe you are talking about receive filters in the 6600. Receive filters don't help much with multi-op interference.
(Edited)
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Mark WS7M

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Hi All,

Well honestly it has been some time since I did a multi station, multi op field day.  We did a trial run last June with our antennas about 50 feet apart using 100w on Icom 7300, Yaesu FT991A and KX3 and the interference was horrible.  

Basically when the 40m station would transmit.  20m would go deaf.  Same in reverse.

So we are staring to plan our next field day.  Right now our plans are:

1) Separate antennas tuned for each desired band.  Currently planning 80, 40, 20, 15, 10.  80 and 40 will likely be dipoles or end fed shot up into trees.  20 on up we are expecting to use verticals with radials.

Our plan is to spread the antennas around in a star pattern around the op position and run coax back.

For each antenna I plan to have a W3NAN (?) BPF specific to that band.  The op will connect to the filter and transmit/receive through that signal antenna.

We will simply coordinate with each other to rotate antennas so we each can work different bands.

I am hoping that the W3NAN filters will deal with the receiver deafness when one of the other bands transmits.

We plan to do a dry run later this year with 2 or 3 antennas and filters just to see how it looks but right now that is our initial plan.

I'd welcome any and all advice.  We don't have thousands to spend on nice filters so we are hoping the W3NAN filters will do what we need.
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DON

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We used EFHW for FD last year. The trick is to provide lots of physical separation if you can. Ours were about 150+ feet separated and they were generally oriented so that they were kind of end to end as much as possible. In sort of a star arrangement.  I ran a bunch of simulations with 4NEC2 and it showed that the coupling could be minimized when oriented this  way. You could also throw one vertical into the mix and probably hot hurt too much. The rigs were more or less in the center of the star and the feedlines branched out from there. We did not use any filters but would have if available.
I made one test with my 6300 and found a -20dBm signal from one of the other antennas on the 40 meter band. (100 W) Wish I had measured the other bands but that was just before start of FD and everyone was anxious to start making contacts. All in all we did not see much interference between stations. If you do not have filters you need physical separation.
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SteveM

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Mark,

For FD, we placed our vertical (digital station) off one end of our all-band dipole (phone station). Our strategy was to utilize the pattern null at either end of the dipole. The problem with that strategy is that the vertical is at ground level while the dipole is 40' in the air (thus, the null is 40' high, too). For those two antenna types, I believe the best you can do is place them in-line and then maximize the distance. It boils down to coax and real estate and we were shy on real estate :-(

So for our setup, we concentrated on the following:
    1. minimize the number of transmitters (3)
    2. employ the cleanest transmitters possible
    3. filter the hell out of the signals before they hit the antenna
    4. we used a generator for power, so filter the hell out of the AC at both ends

Result - everyone was quite satisfied with our setup this year.


(Edit: Hmm, maybe the best way to arrange a vertical and a dipole in close proximity is to stack the dipole on top of the vertical - i.e., utilize the pattern null of the vertical. It would be interesting to test both arrangements. Does anyone already know?)
(Edited)
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Paul

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Steven, I think DX engineering supply the LBS filters, not the Array Solutions range.
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Neal Pollack, N6YFM

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I might suggest reading the below, which I shamelessly copied/pasted from
an unrelated forum today;

=========

After building two TXBPF filter sets for my station, I put them and 
other filter sets I could borrow from NCCC members on the bench for 
extensive testing. The review that I wrote was published by National 
Contest Journal, and is on my website. It includes the ICE 419B set, the 
Dunestar 600 series, and the Array Solutions FM6 filters. Both the Array 
Solutions filters and the TXBPF set are based on W3NQN designs, and both 
are far superior to the ICE and Dunestar sets. 5B4AGN contributed his 
measured data for some high power 4O3A filters he had on hand.

http://k9yc.com/BandpassFilterSurvey.pdf

73, Jim K9YC

=============


Cheers,

Neal
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Mark WS7M

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Thank you for that Jim!   Great article!
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Varistor

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You may want to look at the Array Solutions’ Bandpasser or the OM Power BPFs.
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Kari Gustafsson SM0HRP, Elmer

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Hi, I am very pleased with 4O3A HP filters. Here are my measurements:
http://remotedxandcontestblog.sm0hrp....
73 Kari
P.S. I added stubs to 80 and 40 m that added some 30 db of harmonics supression.D.S.
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Andy - KU7T

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High Power band pass filters vs. Low power band pass filters. What are the main performance differences?

The low pass versions are smaller, cheaper, are integrated in band-decoded switchers. I have not seen this for the High power versions (4O3A filters).  is there any major benefit to use a band pass filter after the amp vs. between amp and radio?

Andy
KU7T
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Kari Gustafsson SM0HRP, Elmer

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Hi Andy, two major reasons. First much simplified switching matrix with filters after PA in a SO2R set up. You do not need two LP:s for two radios. Secondly having filters after PA allows filtering of wideband noise and harmonics from PA.
Adding then only one set of stubs to the HP BPFs simply get you to band isolation levels of 50-70 (BPF) +25-30 dB (stubs) yielding between 75 - 100 dBs of isolation. And your "home". Doing this with LP BPFs would be quite "messy".
An alternative would be the Filtermax LP BPF:s for each radio followed by 1x2 or 1x3 switches (20-30 dB better isolation than 2 x 6 switches) in a matrix for each radio before Triplexers/Diplexers to antennas. I beleive one of the WRTC2018 teams went for this. Good isolation but lots of switches but they can be cheap on the other hand.
I am experimenting with a combination of the latter with HP BPFs to try to achieve 140 dB of isolation on all bands. Why? Three closeby towers and antennas all within 60 feet of radius...