Balun for AIM4170C

[jimworth]

I work with balanced feedlines frequently and would like to put a balun on my analyzer. The MFJ-917 looks like it would fit well since it is small, could connect directly with a double male PL-259, and was designed for the purpose. Has anyone tried this balun? If so, does it seem to work well with custom calibration?

I realize I could build a small balun, but it would be well worth the $30 asking price to forgo the time and trouble of gathering the parts and packaging it to use easily with the AIM4170C.

Jim AD4J

[killy]

JIM,
i'm currently phasing loops for 80m and have been using isolated ps for both the vna2180 and the laptop.
When i am at the loop base itself to do phasing measurements, i use battery power (ATV 12VDC battery).

I just make sure i dont touch (and thus ground) the equipment when it is doing its scans.

VA2GU

[jimworth]

killy: Thanks for your ideas. I have been using my laptop on battery power with only the AIM4170C attached and running the analyzer off a battery pack with a short lead (< 3"). However, my laptop (MacBook Pro) has an aluminum case and I get the impression from some other posts that a balun should be used.

[k6mhe]

Here’s a partial quote form Agilent Application Note AN 346-2 that I posted on this forum a year ago:

“….. A balanced circuit cannot be directly measured with an unbalanced measurement instrument because of the difference in their configuration. When measuring balanced circuits, the unbalanced measuring instrument requires a balun (balanced to unbalanced) transformer….”

You can get a copy of AN 346-2 for yourself here:

cp.literature.agilent.com/litweb/pdf/5091-4480E.pdf

Hope that helps.

Danny, K6MHE

[jimworth]

K6MHE: Thanks, Danny. I read the Agilent note.

I have ordered the MFJ-917 and am wondering if anyone has tried it with one of the W5BIG analyzers.

Jim AD4J

[k9fv]

Jim, I realize this thread is old, How do you like the MFJ-917? Does it really help?

I just got an AIM4170 and use open wire feeders myself.

73 de Ken H>

[jimworth]

After waiting for the MFJ balun on special order for a few weeks, I canceled the order. If anyone has found a small balun that works well for this purpose, I would still be interested in hearing about it.

Jim AD4J

[k6mhe]

Jim,

I was able to get hold of the MFJ analyzer balun and check it out and decided to build my own, which, I fell works pretty good in the HF range. I see that you’ve block your email address otherwise I would have contacted you via email. If you would like me to send you the info on my balun drop me an email.

Danny, K6MHE

[k9fv]

OK, for a bit more info and questions. Danny was able to get the MFJ-917 balun and indicated it was simply a few turns of coax wrapped around a ferrite core - did I understand that correctly Danny?

Do I understand this article correctly? cp.literature.agilent.com/litweb/pdf/5091-4480E.pdf
On page 1 they show an isolation transformer for balanced line testing. This transformer looks like it has dual winding, a few turns on the input side, and a few turns on the output side of the transformer so there is NO direct contact between input and output of transformer.

Is this not what's required for an isolation transformer to testing balanced line with the AIM4170?

Thanks to any and all for the help in understanding.

73 de Ken H>

[n7un]

Dan:K6MHE

Hmmm...so to characterize the feedpoint of a dipole with the VNA, I should use a 1:1 current balun? Am I understanding this thread correctly?

Tnx, Guy/N7UN

[k9fv]

"IF" balanced line (ladder line, window line, etc) is used for the feed line then I understand a 1:1 current balun is required. For coax feedline - not required.

That is "my" understanding, but am very open to correction.

Wouldn't it be great to have a "AIM4170 for dummies" guide about the things it can do and how to understand those things?

73 de Ken H>

[m0yew]

I would like to second the vote for a "4170 for dummies" type of guide. I am sure that my pathetic fumblings are only scratching the surface of the 4170's capabilities, and besides, if I understood ALL the data that is provided (correction - any of the data!) then I am sure that my antenna system would work much better.
Perhaps a wiki type thing might be possible if Bob didn't mind the community of users contributing?

[jayt]

Regarding using the AIM or VNA for ladder line. I suggest you first need a balun that is rated at the frequencies of interest. A small MFJ balun may not work well at below 3 MHz if it is just a few turns of coax around a ferrite core. Your balun can be 1:1 or 4:1. I use one of the Array solutions 4:1 baluns that are rated to go below 1.5 Mhz and up to 60Mhz on a ladder line fed antenna. Calibrate OUT the balun using the custom calibration technique over the frequency range of interest and make sure you put in lots of cal points. If using a 4:1 balun (200 ohm balunced to 50 ohm unbalanced) Set your Zo to 200 ohms and your VSWR plots will be made relative to 200 ohms IE the end of the ladder line hooked to the balun. If you want to see whats on the other end of the balun just set Zo to 50 ohms and its like reading the result of what the 4:1 balun is doing to your transformed impedance. Simple as that, and thats what your tuner will see if you have a ladderline fed dipole or loop. Have fun!