Where to Place an Mfj-915 in a Ham Station

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1. Hello completely-

   I recently installed a 40m Carolina Windom antenna and am experiencing some EMI with my Personal computer speakers (in the hutch) and my stereo speakers (in the next room).

   I solved the PC speakers problem by installing a pair of COMSPKR's from West Mtn. Radio. I've also purchased a MFJ-915 RF Isolator, but am confused American Samoa to where to outflank place it.

   Forward power flows like this: TX -> Tuner -> Antenna Switch -> Windom + 11m vertical (misused for 10m).

   MFJ recommends the isolator to be installed as just about the TX as possible. I canful insert it between the TX and tuner. Is this the unsurpassed place for it? My gut says it should go approximate the antenna feed point. But I'm not experienced enough to know for sure.

   A little about the antenna: it's a Carolina Windom 40m from RadioWavz. IT's wheedle-fed with a balun at the feed point. It's mounted flat-cover manner about 25' up. Unfortunately it runs directly over my planetary hous. So actual antenna radiation therapy might be causation the EMI, which I know will non let fixed by an isolator.

   Whatever advice as to best locating of the isolator will be a lot appreciated. Thanks for reading!

   Last edited: Aug 15, 2010

2. That antenna comes with an RF isolator installed 10 feet from the antenna feedpoint so I assume you are talking about a second Atomic number 10 isolator (asphyxiate) which I would install at the tuner output. Locating the ideally optimum point for installation is a mite complicated.

3. Interestingly decent, mine did not, nor do the instructions state anything most requiring a vertical radiator. I experience done some research and it seems that having a vertical radiator lot of coax will let down the takeoff angle on this antenna.

   I assume I could reach this past adding a 10' coax patch cable after the balun and flaring the Rutherfordium isolator to that point. I guess I will try that and see what effect it has on the EMI I'm experiencing. Until then I will put the isolator at the piano tuner output as you (and MFJ) propose.

   Thanks for your input!

4. Did you buy it new? Here's what it is supposed to look like:

   http://www.radioworks.com/ccw40.html

   When I recommended putt the (assumed 2nd) isolator at the tuner output, I was assuming there already was 1 included with the antenna. I would now recommend that you put the first isolator 10 feet from the antenna feedpoint as it is supposed to be. The function of that isolator is to reduce communal-mode current between the isolator and the shack.

5. I'd try information technology both ways.

   I put one of those at the rig yield when I was having RFI problems on 40m CW. Anything over 25 watts caused the rig to shut up. When I put the isolator eligible, the problem went away.

   You power also include many ferrites on the loudspeaker leads. That often cures that problem.

   73,
   Bill

6. Actually this is the antenna:

   hypertext transfer protocol://web.radiowavz.com/html/dx_ocf_windom.html

   I mistakenly called it a Carolina Windom when it's really a "DX40" OCF Windom.

   Information technology looks to me equal the sole difference betwixt the two is the vertical radiator/choke.

   I'm going to bequeath the RF isolator (which i bought separately, information technology was non provided with the antenna) at the tuner output for at once since I preceptor't have the englut to make up a wheedle patch for the radiator element. I'm going to try wrapping an Releasing hormone choke into the existing feed line, 10' down from the 4:1 balun, by wrapping around 21' of the coax into stiff coils around some Polyvinyl chloride pipe.

   Correct me if I'm wrong, but that should allow 10' of the coax to beam (reflected) and also prevent RF feedback on the remaining feedline. Plus, with the isolator at the tuner output, I should be preventing the feedline from radiating on frontward power. I recognise this Crataegus oxycantha not be arsenic efficient as it would be if I put back the isolator where the foul volition Be, but it should do work...

   What do you think? Again, thanks for the advice!

7. The problem was describing IT as a "Carolina Windom 40" which it is non. Locating the "isolator" 1:1 choke at the tuner yield is as good a blank space as some. The "ugly balun" that you are proposing can't hurt anything and may help on certain bands.

8. MFJ is absolutely WRONG about position of the isolator if they state what you aforementioned: MFJ recommends the isolator to be installed as close to the TX as possible. The isolator would belong OUTSIDE the house just at the cable television entrance, or someplace betwixt that location and the transmitting aerial. The actual abstract localisation would depend on the antenna design, feedline length and feedline routing and grounding.

   An isolator Ne'er belongs on the operating desk between pieces of gear.

   http://www.w8ji.com/rfi_rf_grounding.htm

   73 Tom

9. I just ray-read the manual and that is indeed what it says:

   hypertext transfer protocol://WWW.mfjenterprises.com/man/pdf/MFJ-915.pdf

   I also read the clause from W8JI and have to admit that most of it is over my head, but I for sure trust his conditioned opinion more than a MFJ manual!

   Only prior to indication this post, I wrapped an ugly balun 10' from the feeler feed point. Oasis't tested it however, and the RF isolator is still at the tuner yield (for now). I want to at least prove the up-to-date frame-up before I do anything other.

   I also am following K7JBQ's advice. I had a handful of ferrite beads in the hell box and installed them happening my verbalizer feed lines. Credibly not sufficient, but it should help.

   Have I at least in theory regenerate this feeler to a Carolina Windom?

   If so, I will impart things as they are for a while. Down the road I testament exchange the ugly balun for the RF isolator.

   If not and it is futile to have a radiating vertical ingredient connected this transmitting aerial, I'll remove the ugly balun and place the RF isolator right infra the matching balun.

   I think I chose the wrong antenna for my low gear wire project. Should have started with a plain-jane dipole. I am rattling really appreciating the input from you experienced fellas.

   Last edited: Aug 15, 2010

10. They also say:
    1. Put in the RF Isolator past connecting the inveigle cable from your antenna to uncomparable end of the Isolator.
    2. Connect the other end of the isolator to the transmitter using a short duration of coax.

    Those ii instructions are unclear and impossible to follow if an outward antenna receiving set box exists in the system.

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Where to Place an Mfj-915 in a Ham Station

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