Bogus instructions alert..

[Splash1]

Recieved my MFJ - 915 RF ISOLATOR today..the instructs say ''the rf isolater should be placed close to the transmitter'' and also it says '' install the rf isolater by connecting the coax cable from your antenna to one end of the isolater . '' connect the other end of the isolater to the transmitter using a SHORT length of coax ''....BEWARE,,the rf isolater is sapposed to be connected at the antenna feedpoint and not close to the transmitter .

 

[hookedon6]

Recieved my MFJ - 915 RF ISOLATOR today..the instructs say ''the rf isolater should be placed close to the transmitter'' and also it says '' install the rf isolater by connecting the coax cable from your antenna to one end of the isolater . '' connect the other end of the isolater to the transmitter using a SHORT length of coax ''....BEWARE,,the rf isolater is sapposed to be connected at the antenna feedpoint and not close to the transmitter .[/quote

the instruction i see don't say the part about "BEWARE,,the rf isolater is sapposed to be connected at the antenna feedpoint and not close to the transmitter" they do say to use a mfj 5803 cable which is 3 feet long.
http://www.mfjenterprises.com/man/pdf/MFJ-915.pdf

 

[C2]

The document says:

The MFJ-915 RF Isolator is a 1:1 current balun designed to be placed in line with 50-ohm
coaxial cable...

The RF Isolator should be placed close to the transmitter...

I thought these things went close to the antenna feedpoint...

They are weeding out the appliance operators.

 

[W5LZ]

I think it's a typical MFJ mistake with instructions. Give it a few weeks and it will be corrected. 'Weeding out appliance operators'? Do you really think MFJ is going to cut it's potential market at all? Or in any way except by mistake?
- 'Doc

 

[hookedon6]

i only use r.l.drake filters near the xmitter output and baluns (if needed) @ the feedpoint myself

 

[Splash1]

Hookedon6....the instructions dont say beware,,i did..

 

[hookedon6]

Hookedon6....the instructions dont say beware,,i did..

OHHH, now i get it
DUH!!!!!, i 'tink i got 'dain bramage:blush::blush:

 

[SR385]

A current balun like that can be used in a couple ways.

It would depend on what you are trying to do.

If you have RF in the shack because you don't have decent grounding and run an out of balance antenna system you are wide band tuning, you could do

TX output -> short coax run just outside the shack -> current balun -> rest of feed line

That would keep the currents off the coax back into the shack which is a fairly common fix. I would guess that since this is made with coax connections on both ends, this would be the primary reason for it....a band-aid basically. That's likely what the manual is implying.

You could also certainly use that at the feed point of a resonant dipole, but it would be more convenient to get one with terminals on the other end rather than an SO239.

 

[Beetle]

Looks like that's actually an "UNUN" (UNbalanced input/UNbalanced output), and actually designed to be near the transmitter. For a dipole or other balanced antenna, you'd use a "BALUN".

Radio Works and other companies used to make a similar "RF Isolator". Nothing wrong with using it AND a balun at the antenna. Like SR385 says, however, make sure the balun has a coaxial input and two leads for the output.

 

[Splash1]

Beetle ,,i instaled this at the antenna feedpoint using a double male plug..will this still function as a choke balun ?