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Author Topic: Preselector MFJ 1040C  (Read 102 times)

M0LUX

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Preselector MFJ 1040C
« on: December 04, 2022, 01:17:40 AM »

Hello. For many radio amateurs, interference is a big problem. I was very interested in the preselector MFJ 1040c. I want to ask who had practical experience with this preselector and how effective is it? Thanks. 73! Alex. M0LUX
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W9IQ

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Re: Preselector MFJ 1040C
« Reply #1 on: December 04, 2022, 04:50:32 AM »

I have no experience with the unit, Alex but I wonder if this is even the correct device for your issues. Most modern radios have adequate filtering to reject out of band signals and very good filtering for in-band interference on adjacent frequencies. Perhaps you could describe the type of interference you are experiencing and the model of radio?

If you are experiencing RFI from neighborhood electronics, the toolbox consists of reducing common mode current, increasing antenna distance from the RFI source, improving antenna directivity and changing antenna polarity. Some information about your antenna system would prove helpful in this regard.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

WA3SKN

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Re: Preselector MFJ 1040C
« Reply #2 on: December 04, 2022, 08:15:43 AM »

I haven't used it, but it is a preselector.  It goes between the receive antenna and receiver and is great for "front end overload" problems.  It has a relay bypass so you can transmit through it.
If your noise problems are different, it will less effective.
What kind of noise do you have?

-Mike.
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KD7RDZI2

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Re: Preselector MFJ 1040C
« Reply #3 on: December 04, 2022, 09:29:19 AM »

Depends on your radio. Please specify the model. Check the schematics focusing on the RF bandpass filters close to the antenna connector. In any case it should not have negative effects. If you use a portable receiver with no front end filters it would make a big difference. Also if you want to try to build your own receivers you can use that as a tunable filter. I have some (also homebrew) external preselectors, sometimes I feel the difference if a nearby strong station is on 21mhz and I want to operate on 18mhz (which are on the same BPF). Consider that I often use a Softrock Ensemble SDR receiver which has "only" 4 bandpass filters. For in band interference the only solution is the attenuator which you likely have on the trasceiver. In any case a preselector is a good device that have a huge effect on sensitive but marginally RF filtered receivers such as portables. And to be honest, I found that even very cheap portables, including SDR sticks like the original Funcube with HF converter, with the help of a preselector become good radios.
« Last Edit: December 04, 2022, 09:42:30 AM by KD7RDZI2 »
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M0LUX

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Re: Preselector MFJ 1040C
« Reply #4 on: December 04, 2022, 10:28:19 AM »

Thank You for everyone.
 I use a transceiver IC7000 with IC OPC 1457R DC EMC Filter Box. Antenna Hustler 6BTV. All my equipment feed through home brew mains power supply filter. The type of noise is constant and practically the same on all bands.
Thanks. 73! Alex M0LUX
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KD7RDZI2

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Re: Preselector MFJ 1040C
« Reply #5 on: December 04, 2022, 11:08:27 AM »

Then you need to understand the cause of that noise first. Which level you see on the S-meter on various hf bands with the antenna connected?  And with the antenna disconnected? Check for those little switching power supplies in your house first, TV sets etc. Disconnect everything exept for the power supply of your radio and the radio and see if there is any change. It might be anything. I assume the antenna is properly connected, but a W9IQ ;D type of common mode choke is always a good idea especially close at the antenna feedpont and one close to the radio. If everything fails and you conclude the noise is generated outside of your house you might think to add a QRM Eliminator X Phase you find on ebay. You will need to add a receiving antenna to phase out what seems noise but is a signal.
« Last Edit: December 04, 2022, 11:24:12 AM by KD7RDZI2 »
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KH6AQ

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Re: Preselector MFJ 1040C
« Reply #6 on: December 04, 2022, 12:31:18 PM »

Here is the usual RFI location procedure:

Power transceiver using a 12V battery
Check each band and record RF noise levels
Shut off ALL AC power to your residence
Check each band and record RF noise levels

If the RF noise decreased with AC power off, switch AC power back on one room at a time while monitoring the bands for RF noise. If the dominant noise source(s) are in your residence you will be able to narrow it/them down to the room. It is then a matter of unplugging AC powered devices in particular rooms.

Example:
In my small house I located eight RF noise sources. Two ceiling fan lights, A UV water zapper, and five wall wart power supplies. The "fixes" are to leave the ceiling fan lights off when I'm on the air, an FT240-31 ferrite core on the UV water zapper, and replacement of the wall warts with other brands. External RF sources remain and being in various solar power systems in the neighborhood I live with the noise.
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