Page 1 of 1

Mag loop feed line

PostPosted: 15th September 2017, 6:01 pm
by M0HSZ
I am now using an MFJ 40 to 15m mag loop with an automatic tuning box on a tripod for portable operating feeding with RG mini 8 for quickness and ease of deployment.

It has been suggested to me that I would be better off using a different spec coax.

Am I correct in thinking that, as only a short run of coax for HF running a radio between 10W and 100W that the difference in using something like RG213, so still reasonably quick and easy to roll up would not make a significant difference to the number of contacts I may get?

Your opinions please gentlemen.

Re: Mag loop feed line

PostPosted: 16th September 2017, 2:27 am
by G4LHT
What's the distance between the TX & Antenna John?


Sent from my iPhone using Tapatalk

Re: Mag loop feed line

PostPosted: 17th September 2017, 2:00 pm
by M0HSZ
I am only running about 19 meters of coax. On the tilting mast, I have that goes under the wheels of the van I was finding that the metalwork of the van was affecting the SWR too much. I got the tripod because it is lighter for me to carry up and down stairs and to move the antenna further away from the van to give more space in the near field before it interreacted with any metalwork. it was just that a G1 suggested changing the coax, so thought it better to ask. At what length in RG mini 8 does it make it worthwhile swapping to a higher spec coax on HF?

Re: Mag loop feed line

PostPosted: 20th September 2017, 12:59 am
by G4LHT
Indeed 213 is better than Rg8, Image

Here is the losses, with loops though there's a drop in efficiency depending on the frequency, if you include so239 insertion losses these should be correct. So use the best coax you can afford look at air-cell 7 if not 213 actually i've got some you can have amphenol 75 ohm equivalent to West-flex 103 you can try.


Sent from my iPhone using Tapatalk

Re: Mag loop feed line

PostPosted: 20th September 2017, 11:06 am
by G3YKB
Yes, RG213 has less loss than RG8 but only 0.25 dB better for 19 metres at 10 MHz. Even at 50 MHz the difference is only O.6 dB ie a TENTH of an S point - about the thickness of the needle on a decent size S-meter. You won't notice the difference.

Brian

Re: Mag loop feed line

PostPosted: 21st September 2017, 12:52 pm
by M0HSZ
Thanks for the info guys much appreciated.
All understood.

Going to have to do a lot of test on the loop using the RG8 first.

Had a contact into Serbia on Sunday at Old Redding only a 5 and 4 report but assume the contact at the other end was using a beam. He said the bands were completely dead with no activity. I took the loop down and put up the Atas120a and the 40m and 20m bands were buzzing, unfortunately I had to call it a day due to other commitments. Either the loop is not preforming that well or the bands only opened up as I was taking the loop down? More test required.

Mag loop feed line

PostPosted: 23rd September 2017, 12:14 pm
by G4LHT
Brian is of course correct, I come from a qrp point of view where every milliwatt is precious as I found on a recent trip to Malta with my 817 and a mag loop, their inefficiency on the lower bands is telling, above 20M they come into they’re own.


Sent from my iPhone using Tapatalk