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MFJ 915 INSTALLED AT THE ANTENNA'S FEED POINT

Stellasstillarat

Stellasstillarat

Active Member
Aug 14, 2014
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If need I'm going to install my MFj 915 at the a99's feed point.
I'm going to make a jumper out of some extra LMR 400 that i have.
How long should I make the jumper?
If i were left to my own devices id Make it 2' long but this is a total assumption. Can someone please advise me? Thanks
 

Exactly as Binrat posted as short as possible.

Ensure you have enough room to mount the line isolator securely to the mast pipe, hose clamps or nylon zip ties
 
Since reciving my 915 in the mail I've searched and read every review.

I was totally surprised to read 100's of people who've purchased and used them with excellent results

I was assuming since it's similar to an air choke it should be placed 2' below the antennas 'll 259.
The reviews I read came from qrz/Hams to cb operators.
Almost every one wrote how great these mfj 915 's worked. I know the air would choke should be 2' below the feed point.

I know this is made out of ferrits and the wound choke is just thst, wound coax there usually placed àt 2' brlow the feed point so I'm thinking 2' eould br good but trust be told I've absolutely no idea of where exactly this should be placed.
they basically do the.ame job they basically serve the same purpose..
That's why I said if it were left up to me id put it 2'. When you say as close as possible do you mean 6" 8" 1'. I want to get it to work as well as it can.
Can you be more specific. I will wait to see if anyone else rings in. It's weird because with so many reviews not one person said how far down from the feed point they installed there 915.

'.wavrider thank for your initial suggestion on the MFJ 915. I haven't began the antenna install or new station setup and won't untill sunday.

I just want to have everything that can prepared before hand ready to go. So as i can take it step by step wihout having to stop and cutting a specific length of LMR 400 to install the 915. Thanks.
binrat said:
Personally, if it was me, as short as possible.
Click to expand...
 
Stella,

Do not over complicate this.

the line isolator is just that an isolator, it isolates the antenna from the coax per say,. or it isolates the ampl;ifer from the radio
or the tuner from the amplifier etc etc.
So no exact science to exactly where you install the isolator but AS CLOSE to the feed point as you can mechanically with stabil mounting so it with stands the weather and winds etc etc.

My RF choke is where ever i black taped it and zip tied it to the mast pipe, I did not measure the distance or even consider it, Just installed the RF choke and let it hang there.

Where ever you install your line isolator it will work as it will help prevent cmc on the coax.
 
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Place it 1" or 1ft or 1yd, the device should do the same thing. As long as it's between the antenna and transceiver it should work. As close as possible means just that just like Wavrider said. You don't need to break out a ruler for this. Just get it as close to the A99's connector as you can with your setup. Someone mentioned a pl259 to pl259 adapter. This will work too but I wouldn't put much power through one. So again to answer the question, place it either directly at the feedpoint with an adapter, or make your own and place it from directly at the feedpoint to 2-3ft down. The shorter the better. If you can make a 6" lmr400 jumper and be able to use it with your setup that will work just fine. Like wavrider said, weather proof the connections very well and make sure it's mounted to the mast in a fashion that it won't come off easily. Use either butyl tape or self amalgamating tape. Then follow up with electrical tape. With the butyl tape you'll need to tape before you place buytl on or you'll never get to the connector again lol. The self amalgamating tape doesn't require this and doesn't stick to the connector, just itself. 3m makes some that I beleive can be bought at Home Depot. If not order some. It's well worth the money!!! Just my 2 pennies. Good day.
 
Excellent! This connector will put the MFj 915 as close to the feed point as it could possibly ever be.
.
I did try your link and that company was forcing me to purches four of the male to male so 239's connectors as they have a $10 minimum ordering policy (not inc. shipping)

. I purchased two off an eBay seller that I actually purchased a barrel connector from in the past and that connector made it to my home in 3 days.
Both male to male were a bit under $7 shipping included.

This is why this site is so important to me.
Thanks to everyone who answers my questions and is helping me get one step closer to getting set up.
I really do appreciate it. Thanks again.
Oldme said:
Why not a Male to Male Coupler at the antenna?
https://www.wiredco.com/UHF_Male_to_Male_Coupler_Gender_Changer_p/uhfmtmcoupler.htm
Click to expand...
 
Stellasstillarat said:
I know the air would choke should be 2' below the feed point.
Click to expand...

That's another myth/urban legend mate. As others have said, as close to the antenna socket as possible. I tend to leave mine about 6 inches as its plenty enough room to get my shovel of a hand in to tighten up the PL259 as well as making it easier to wrap self amalgamating tape around the connection to waterproof it.

When wrapping the tape around remember to start at the end which will be the lowest and work up so each turn overlaps the one below it so it works like roof tiles with the rain. Do it the other way around and you end up with a ridge on each turn the rain can sit on and eventually get into.
 
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As you can see I did go ahead a purchase the suggested pl 239 male to male connector (bought two) but what I didn't mention is had my friend and tec who currently is adding new pl 259's on my main tranciver to antenna LMR 400.

He's also adding a pl 259 to 25' of extra LMR 400 which was cut from the original 125' of LMR 400 as it wasn't needed and was laying about my yard. I may use that extra length of 400 as a feed line to insat an 11 meter coax made ddipole in.my attic (inverted V).
I gave him a call last night and told him to make me two short jumpers. One 6" and the other 10"'s so I'm definitely converted. I will go with the so 239 male to male and if there's any problem with that connector (which I doubt) .
I'll go with the 6" jumper. Either way I'm covered.
Thanks for your input. I appreciate all who answer my sometimes ubsurd questions.
M0GVZ said:
That's another myth/urban legend mate. As others have said, as close to the antenna socket as possible. I tend to leave mine about 6 inches as its plenty enough room to get my shovel of a hand in to tighten up the PL259 as well as making it easier to wrap self amalgamating tape around the connection to waterproof it.

When wrapping the tape around remember to start at the end which will be the lowest and work up so each turn overlaps the one below it so it works like roof tiles with the rain. Do it the other way around and you end up with a ridge on each turn the rain can sit on and eventually get into.
Click to expand...
 
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Thanks for your kind words.
By the way those two so 239 male to male connectors were purchased at
sales@thehamshop.com for what I think was a very fare price of $6.42 including shipping.
I've saved them as a favorite seller. With an exspected delivery date of 7/27.
I will check out all future item's I need on there eBay store and if their prices for communications related item's and shipping costs are as fair as the price was for the connectors were, I'll definitely do future business with them.
fourstringburn said:
The only absurd question is the one that is never asked, good luck!
Click to expand...
 
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