Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
I've attached the slides I presented tonite.  I converted it to a PDF to reduce the filesize below the forum limit, so all my cute animations are gone.

If you have any questions, please post here & I'll try to get you an answer.

Thanks for your attention.

Dave, VE3WI

Attached Files
.pdf   BALUN_PRES_8JUN.pdf (Size: 879.99 KB / Downloads: 15)
In the presentation I mentioned that the big parts houses probably have better prices for ferrite toroids than the well known ham suppliers like Palomar Engineers & Amidon Associates.

I did a little research for prices on a 2.4" OD Mix 31 toroid (Fair Rite part # 2631803802).  This is the one you'd most likely want to use.  I did the US$-CDN$ conversion on

Vendor            US$       CDN$    $10       $12.51    $10       $12.51    $5.10    $6.38     $7.55    $9.45    $8.31    $10.40
(MFJ doesn't list this item)

Canadian websites:                   $7.09                    $10.42                   $11.82

I was impressed by the US Newark price.  I expected that I would get bounced to their Canadian website when I tried to order, but they actually processed the order.  Can't go wrong at that price!  I ordered 10, so if anyone wants one I'll sell it to you for my cost.

Dave, VE3WI
I found a design chart by Glenn, W9IQ for common mode coax chokes using Mix 31 ferrite toroids, that is simpler than the G3TXQ chart in my presentation.  See attached.  12 turns on a FT240-31 looks like the best compromise over most of the HF bands.  If you need even wider suppression range, put a 14-turn in series with a 10-turn.

W9IQ specifies very expensive RG400 teflon coax.  Good quality RG58 (with solid dielectric & 95% braid) is the same size & should work fine unless you're running a big amp.  The stranded center conductor type would be definitely preferred over solid single conductor, for ease of winding.  Don't use the foam dielectric type.

Solid dielectric stranded conductor RG58C/U is listed for $0.39/ft at Maple Leaf Comm (although Bob is trying to retire & has moved some products to other sellers)

Cheapest RG400 I've found is Chinese stuff from at $43 for 20 ft.  Aircraft Spruce in Chatham has it for $5.40/ft (ouch)

Dave, VE3WI

Attached Files
.pdf   W9IQ_chokes.pdf (Size: 87.56 KB / Downloads: 1)

Forum Jump:

Users browsing this thread: 1 Guest(s)