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Author Topic: LPF/BPF for RF Rx  (Read 375 times)

Brian Bolly

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LPF/BPF for RF Rx
« on: November 06, 2019, 05:16:00 am »

One for the RF gurus...

I had a discussion last night about inserting a BPF or at least LPF on the Rx for some RF mic racks.  While there are nicely packaged BPF that can be found from the usual suspects for ~$200 for the 470-616 band, I came across the Mini-Circuits inline LPF that looked promising at only ~$35 each.  But my question is twofold:

1. Would using a LPF (instead of BPF) offer any significant benefit?

If yes, then:

2. In looking at the insertion loss tables on the Mini-Circuits BLP-600+, it appears that it is a solid, inexpensive solution.  Am I overlooking something in the data? 
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Jens Palm Bacher

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Re: LPF/BPF for RF Rx
« Reply #1 on: November 06, 2019, 07:19:43 am »

One for the RF gurus...

I had a discussion last night about inserting a BPF or at least LPF on the Rx for some RF mic racks.  While there are nicely packaged BPF that can be found from the usual suspects for ~$200 for the 470-616 band, I came across the Mini-Circuits inline LPF that looked promising at only ~$35 each.  But my question is twofold:

1. Would using a LPF (instead of BPF) offer any significant benefit?

If yes, then:

2. In looking at the insertion loss tables on the Mini-Circuits BLP-600+, it appears that it is a solid, inexpensive solution.  Am I overlooking something in the data?

I use the HPF: https://ww2.minicircuits.com/pdfs/BHP-600.pdf to keep UHF walkies etc. away from my Axient Digital receivers. I usually place my UHF mics from 550 Mhz and up. Works nicely, i no longer have the "RF frontend limiter engaged" when someone keys a walkie on stage.
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Jens Palm Bacher

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Re: LPF/BPF for RF Rx
« Reply #2 on: November 06, 2019, 07:20:17 am »

I use the HPF: https://ww2.minicircuits.com/pdfs/BHP-600.pdf to keep UHF walkies etc. away from my Axient Digital receivers. I usually place my UHF mics from 550 Mhz and up. Works nicely, i no longer have the "RF frontend limiter engaged" error when someone keys a walkie on stage.
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Jason Glass

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Re: LPF/BPF for RF Rx
« Reply #3 on: November 06, 2019, 10:54:21 am »

One for the RF gurus...

I had a discussion last night about inserting a BPF or at least LPF on the Rx for some RF mic racks.  While there are nicely packaged BPF that can be found from the usual suspects for ~$200 for the 470-616 band, I came across the Mini-Circuits inline LPF that looked promising at only ~$35 each.  But my question is twofold:

1. Would using a LPF (instead of BPF) offer any significant benefit?

If yes, then:

2. In looking at the insertion loss tables on the Mini-Circuits BLP-600+, it appears that it is a solid, inexpensive solution.  Am I overlooking something in the data?

Minicircuits BLP and BHP units work well but pay attention to their shallow cutoff curves (shown in their online documentation) vs. channel freqs vs. desired rejection.  The RFV and PWS bandpass filters have much steeper cutoffs, which make them a bit more predictable and easy to use.
« Last Edit: November 06, 2019, 11:05:39 am by Jason Glass »
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Scott Holtzman

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Re: LPF/BPF for RF Rx
« Reply #4 on: November 06, 2019, 12:01:26 pm »

Minicircuits BLP and BHP units work well but pay attention to their shallow cutoff curves (shown in their online documentation) vs. channel freqs vs. desired rejection.  The RFV and PWS bandpass filters have much steeper cutoffs, which make them a bit more predictable and easy to use.

A nice steep 2 or 3 cavity notch filter would be excellent.  If you carry the same radios you would not have to retune.  To retune in the field would require a tracking generator and a fast spectrum.  RFS (used to be Celwave) made great cavities "in the day"

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Scott AKA "Skyking" Holtzman

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Gian Luca Cavalliini

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Re: LPF/BPF for RF Rx
« Reply #5 on: November 06, 2019, 02:30:32 pm »

Could be useful to use Mini Circuits (or others) filters in IEM transmission to limit the damage of IMD?
MiniCircuits reports 500mW Max input, could be useful for 8ch combiner out (50mw each) or there is still a compression zone before 500mW?
Are others better from this point of view?
Is there any function in WWB or IAS to "limit" IMD calculation in frequency zones? Maybe the "filter" parameters in the equipment profile of WWB? How is it influencing the calculation? Is it just for receiving, RX/TX, or nothing (as tx power, for example)?

Thanx!
GLuca
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Re: LPF/BPF for RF Rx
« Reply #5 on: November 06, 2019, 02:30:32 pm »


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