rf line isolator

[KC8FAS]

I just go a MFJ 915 line isolator. It is hooked up to a 72 ft. end fed antenna. After hooking up the line isolator im not able to tune most of the bands swr is all to high. I remove the line isolator and then im able to tune all bands 1.5 or less, with internal tuner. Any ideas why a line isolator would make my swr high.

 

[k8krh]

Where do you have it, I have my isolator hooked into the tuner <antenna connector goes> with a double ended connector, no coax from it to the tuner, just coax to the other end to the radio and it does not effect the swr, flat or close to it on all bands and I am using a invee, but have one on my end fed also same setup and no problem but the length of the end fed is 48 feet.
DOCTOR/795

 

[prcguy]

What kind of end fed antenna do you have?
prcguy

 

[FeedForward]

No matter what you call it, it is a 1:1 current balun designed to be placed at the feedpoint of a dipole. It is better to determine the real reason for RFI in the shack rather than lift the station grounding and blame it on the coax. If you are using a long wire antenna, then you DO need a good station ground and a tuner that will handle that type of antenna.

FF

 

[k8krh]

I have 2 of them
ultimax 100, but I added some extra wire as suggested by the chap who makes them,to 48 feet, it works from 6 to 80 very good.
I also have another one fromsome place in Midwest oak???? it was 100 some feet, but I cut it down to 72 feet, but the ultimax out performs it, both are at 30 feet.
DOCTOR/795

 

[prcguy]

The antennas you mention are basically a 9:1 transformer and your coax is part of the antenna and radiates. Using a common mode choke on the coax before the radio is a really good idea and placement will affect the radiation pattern.

There are other types of end fed antennas like the PAR and multiband variants that you can build for just a few $$. These are resonant half wave at the lowest design freq and work on even harmonics like a 40m version will also work on 20 and 10m. These are far less susceptible to feedline radiation and work a lot better than the 9:1 random wire variants.
prcguy

I have 2 of them
ultimax 100, but I added some extra wire as suggested by the chap who makes them,to 48 feet, it works from 6 to 80 very good.
I also have another one fromsome place in Midwest oak???? it was 100 some feet, but I cut it down to 72 feet, but the ultimax out performs it, both are at 30 feet.
DOCTOR/795

 

[KC8FAS]

I have the Isolator in the shack right behind the radio. Im using the built in tuner. Here is a link to the antenna.

"QSO King" End Fed Antenna All HF Bands 1 9 KW Pep Hoa Friendly Works A | eBay

 

[prcguy]

Yes, I know the antenna and its one of the typical 9;1 transformers feeding a non resonant length of wire. If you were to compare with the transformer project shown in the following link with 66ft of wire, it will work much better on 40, 20 and 10m than the QSO King thing. I suspect the new PAR EF QUAD that covers 40, 20, 15 and 10m will work about the same as the resonant end fed half waves I've built from the link.

PD7MAA HOMEPAGE: Multiband end fed antennas 3.5 - 30mHz This end fed can be built in a 100w version and that core is around $2. A 400w version core is about $9 and an 800w version uses two $9 cores. I've built all three and with 66ft of wire they work the same as a 1/2 wave dipole on 40m plus you get all the even harmonic bands. These cores will work down to 80m and you simply add 1/2 wavelength of wire for the lowest band you want and trim for the best match.

I have a few other links that elaborate on the end fed transformer if anyone wants.
prcguy

I have the Isolator in the shack right behind the radio. Im using the built in tuner. Here is a link to the antenna.

"QSO King" End Fed Antenna All HF Bands 1 9 KW Pep Hoa Friendly Works A | eBay