Multi point question....

[KF0AWL]

I'll try to make it condensed.
Ok quick background running a 891 with a mfj 971 tuner normally on my Alpha Antenna mil 2.0 vertical but want to do demonstrations at fairs and whatnot to get others interested in HAM Radio so want to have a smaller footprint Antenna so I don't have people tripping over wires and can block in (block off) area around the Antenna.

I picked up a Super Antenna MP1 used at a hamfest, hooked up my RG8X coax I normally use for my Alpha and had horrible swr on my NANO VNA switched to a RG8U same result so I put a ferrite bead on then a 6 turn choke and got useable swr.
My setup is in back of my vanshack so I'm wondering
1. What would you recommend for a low loss yet flexible coax and choke or UNUN to pick up for my MP1?
2. Would you suggest I mount said choke/UNUN inside the vehicle and use jumpers or outside?
3. Would I be better off manually bypassing the tuner when I'm on the MP1 since my tuner has no bypass switch or would I be ok with it inline even tho I tune the coil?
3. The MP1 came with a collapsible whip (I hate them especially for POTA work as one good breeze blows things over whip bends now no longer collapsible) so I want to replace it with a SS whip I have. How would I trim the whip to equal the collapsible?
Any and all advice appreciated. Thanks for helping.

 

[prcguy]

A Super Antenna MP1 needs a large counterpoise or ground plane to work against for both low VSWR and radiation performance. If its just one counterpoise wire you have made a dipole with one leg laying on the ground, which is not very efficient. If you use multiple wires making a ground plane that will not radiate but it will be big and have the same problem as your Alpha with wires running everywhere. Its just the way things work, no counterpoise, no workee, big counterpoise, workee ok but lots of wires.

When the counterpoise is inadequate, which is most of the time with these antennas, there will be lots of RF on the feedline and it will radiate because the feedline has become the major part of the counterpoise. In that case you need a really good ferrite choke and not just some coax wound up in a ball or just one or two snap on ferrite cores, that won't do anything.

You can make a reasonable RF choke using an FT-240-31 ferrite core and wrap 9 turns of RG-58 or maybe RG-8X size coax around it. That can give about 30dB of isolation in the center of the HF band and less at the edges. Better yet buy one of these CMC-130-3K 1-30MHz
Or one of these MAXI-CHOKER Coax Line Isolator/Choke, 1-61 MHz, 3KW, up to -48Db Common Mode Rejection - Common Mode Noise Filter - Coax - Palomar Engineers® and that should fix any RF problem on any coax. However it will not make up for an inadequate counterpoise which will reduce performance.

 

[KF0AWL]

I forgot to meantion I'm also trying the window screen counterpoise

But I'll check out the chokes.

 

[prcguy]

I forgot to meantion I'm also trying the window screen counterpoise

But I'll check out the chokes.

That can work better than several random wires. You could roll out a 50ft length of 4ft wide chicken wire, that will work great.