MFJ-1778M, JUNIOR G5RV

[jazzboypro]

Hello all,

i have bought the MFJ-1778M, JUNIOR G5RV antenna. The antenna comes with 17 feet of 450 Ohm ladder line. I will use about 60 feet of coax (probably LMR400) to connect the antenna to my 7610 thru a polyphaser. MFJ recommends using the MFJ-915 1:1 current balun at the antenna feedpoint. I have a few questions.

1- Is the MFJ-915 a good product ? should i use something else ?
2- Do you think that the built-in antenna tuner in the 7610 will be enough to match the antenna ?
3- The ladder line portion will of course be outside the house and some of it will be close to the exterior wall wich is aluminum siding, what adverse effect can i expect from this ?

Many thanks
73
VA2FCS

 

[prcguy]

The original full size 104ft long G5RV was designed as a 20m antenna with gain and all other bands its just a random length dipole, but with a tuner it works ok on 40 through 10m with some degraded performance on 80m. The G5RV Jr is half size and a 10m antenna with a little gain and a random size on all other bands working ok on 20 through 10 and probably 6m with degraded performance on 40m and 80m is out of the question.

The built in tuner in the 7610 might tune the Jr antenna on 20m and up and with a short run of LMR400 probably not on 40m. I have a 7610 and have used it on a full size G5RV and the radio was not able to tune on several bands, especially 80m, which would be similar to tuning 40m on a Jr model.

The G5RV series needs a good effective ferrite choke balun at the ladder line/coax junction. The MFJ 915 is simply 50 ferrite beads over some coax and at best that gives up to about 20dB of isolation and its not that great. An FT-240-31 ferrite core with about 9 turns of coax through it can reach 30dB isolation at some frequencies and the ferrite core costs under $10. The best ferrite chokes I know of are made by MyAntennas but they cost more than the MFJ at between $79 and $89 depending on the specs you want. These reach upwards of 40dB isolation or 100X more than the MFJ.

 

[jazzboypro]

The original full size 104ft long G5RV was designed as a 20m antenna with gain and all other bands its just a random length dipole, but with a tuner it works ok on 40 through 10m with some degraded performance on 80m. The G5RV Jr is half size and a 10m antenna with a little gain and a random size on all other bands working ok on 20 through 10 and probably 6m with degraded performance on 40m and 80m is out of the question.

The built in tuner in the 7610 might tune the Jr antenna on 20m and up and with a short run of LMR400 probably not on 40m. I have a 7610 and have used it on a full size G5RV and the radio was not able to tune on several bands, especially 80m, which would be similar to tuning 40m on a Jr model.

The G5RV series needs a good effective ferrite choke balun at the ladder line/coax junction. The MFJ 915 is simply 50 ferrite beads over some coax and at best that gives up to about 20dB of isolation and its not that great. An FT-240-31 ferrite core with about 9 turns of coax through it can reach 30dB isolation at some frequencies and the ferrite core costs under $10. The best ferrite chokes I know of are made by MyAntennas but they cost more than the MFJ at between $79 and $89 depending on the specs you want. These reach upwards of 40dB isolation or 100X more than the MFJ.

Thanks for the info. About the ferrite choke are you talking about the MyAntennas CMC-130S-3K 1-30MHz ? This what i use for my W6LP loop (i think it was your recommendation from another thread i started about the loop)

Also since you also have the 7610 do you have a recommendation as of what tuner would work well ?

Many thanks

 

[jazzboypro]

Oups my bad you are probably talking about any of those Balun

 

[prcguy]

I use the Icom specific 100w LDG tuner on my 7100s and on my 7610 I occasionally use the 600w and 1000w rated LDG tuners with various amplifiers. Otherwise my MyAntennas 80-10m OCFD and 80-10m EFHW work all bands without a tuner so I usually just connect the amplifier and go without a tuner.

Thanks for the info. About the ferrite choke are you talking about the MyAntennas CMC-130S-3K 1-30MHz ? This what i use for my W6LP loop (i think it was your recommendation from another thread i started about the loop)

Also since you also have the 7610 do you have a recommendation as of what tuner would work well ?

Many thanks

 

[jazzboypro]

Thanks for the info, i will look into it

 

[K6GBW]

The MFJ915 is a decent choke and will work fine. But then, so will most 1:1 chokes. When I used this type of antenna I used one made by Palomar Engineers. If you keep the window line six inches to a foot away from the siding you'll be okay. You can try using the internal tuner, but it is most likely you will need an external tuner. I used a simple MFJ manual tuner and it tuned up very easily.

 

[jazzboypro]

Thanks for the info i'll do my best to keep the feedline away from the siding. As for the tuner i will probably buy one. I looked at the LDG tuner that @prcguy is using and it looks interesting.

 

[krokus]

For keeping the ladder line away from the siding, here is an option. (Could be installed using the "Command" adhesive strips, to minimize any damage to the siding.)

811C-CQ Stand-Off for "Window" Line on flat surface - The Wireman

Easy to lock in place with UV resistant high strength (120lb) cable tie. Lock the 300-450 ladder line into the […]

thewireman.com

 

[jazzboypro]

For keeping the ladder line away from the siding, here is an option. (Could be installed using the "Command" adhesive strips, to minimize any damage to the siding.)

811C-CQ Stand-Off for "Window" Line on flat surface - The Wireman

Easy to lock in place with UV resistant high strength (120lb) cable tie. Lock the 300-450 ladder line into the […]

thewireman.com

Very interesting, thanks for the info