SLIDE 17:
Assembling the Hybrid Balun
It is NOT necessary to enclose baluns into a sealed enclosure/box. The cool much better when not mounted in a box. This helps prevent "SWR Creep" which occurs when the cores overheat.
In his excellent paper entitled "A New Choke Cookbook for the 160-10M Bands" (2018-19),
Jim Brown (K9YC) wrote on page 10:
"Avoid Putting Transmitting Chokes in Enclosures -
it greatly reduces the transfer of heat to ambient air,
and can easily cause destructive overheating. In
general it is best to leave the choke exposed to air,
weather-proofing connections as needed."
(
LINK to original article:
http://k9yc.com/2018Cookbook.pdf )
HHG2 OCFD: Part-2 COMMENTARY
SLIDE 7: CMC FIELD TEST (2013)
SLIDE 8: BATTLE OF BALUNS (BoB) FIELD TEST (2015-2017)
2013 "CMC FIELD TEST":
(Click on picture to link to the Field Test)
An extensive study of the CMC characteristics on real life 40m dipoles and 40m OCFD antennas in the field.
During this test, a study was made of the amount of CMC on the transmission line when running 100 Watts and CMC was intentionally induced by skewing the coax such that it was physically very close to one leg of the antenna.
In addition, an SWR scan was made across each band so that I could see the effective the CMC had on the antenna's SWR characteristics.
2015 "BoB FIELD TEST":
(Click on picture to link to the Field Test)
In this field test, I compared several different balun technologies to determine which type of balun was best at eliminating the measurable CMC on the antennas feedline.
It was this test where I determined that a Hybrid Balun is superior to a dual-core 4:1 Guanella (current) balun, and that the dual-core 4:1 Guanella balun is insufficient for use (alone) in an 80m or 160m OCFD antenna.
SLIDE 10: A HYBRID BALUN
A Dual-Core 4:1 Guanella (current) balun has only half as much Common Mode Impedance as a 1:1 Guanella (current) balun.
This is explained in detail with links to reference in the Reference-Info for Part-1, Slide 13.
SLIDE 11: The 4:1 Ruthroff (voltage) Balun
DO NOT USE a single-core 4:1 Guanella (current) balun.
This was explained in detail with links to reference in the Reference-Info for Part-1, Slide 18.
SLIDE 12: Build a 4:1 Ruthroff Balun
Using Twisted Pair instead of Bifilar Transmission Lines.
IMO, using twisted pair is easier than keeping parallel wires close-spaced when using bifilar transmission lines.
Here's what Tom Rauch (W8JI) says about using twisted pair:
SLIDE 13: Build a 4:1 Ruthroff Balun - DETAILS
Although Sevick used simple enamel-insulated through his book on building baluns, it is advisable not to use this - except for very low power applications.
REASON: there is a significant difference of quality in the enamel insulation, especially with cheap wire. this scratches easily, creating critical points where voltage breakdown may occur.
The following document is posted on Owen Duffy's (VK1OD) Blog:
SLIDE 17: Assembling the Hybrid Balun
It is NOT necessary to enclose baluns into a sealed enclosure/box. The cool much better when not mounted in a box. This helps prevent "SWR Creep" which occurs when the cores overheat.
In his excellent paper entitled "A New Choke Cookbook for the 160-10M Bands" (2018-19),
Jim Brown (K9YC) wrote on page 10:
"Avoid Putting Transmitting Chokes in Enclosures -
it greatly reduces the transfer of heat to ambient air,
and can easily cause destructive overheating. In
general it is best to leave the choke exposed to air,
weather-proofing connections as needed."
( LINK to original article: http://k9yc.com/2018Cookbook.pdf )
SLIDE 20: Construction Tip: Backplane Balun
Here is a PowerPoint file. It prints 1:1 size for the backplane.
SLIDE 21: EXAMPLE: C5DX DX-pedition Antenna
LINK to INFO: https://www.aerial-51.com/sponsored-dx-peditions/c5dx-2018/
SLIDES 29 & 37: CHARTS FOR SCANNING W. A SCANNING ANALYZER
Measuring with a scanning analyzer greatly simplifies taking measurements. If you do not yet have one and plan to buy one, be sure to buy one with a computer interface, so that you can save your measurements.
The charts below will assist you in making your measurements with a scanning analyzer:
SLIDES 33, 34, & 42: Manual Tuning Charts (no Scanning Analyzer)
It is necessary to record your measurements on 3 bands during the TUNING procedure, and then again when your antenna is finished.
As an aid for recording manual measurements, you may use either an Excel Spreadsheet or a jpeg chart. Downloads are below.
EXCEL SPREADSHEETS No Scanning Analyzer:
JPEG CHARTS No Scanning Analyzer:
SLIDE-44: Tip #2
Sources of good Maxwell Chokes:
Spiderbeam (Germany):
DX-Wire (Germany):
THE WIREMAN (U.S.A.)
And for those of you who wish to d-i-y, I suggest you buy the Spiderbeam Kit or source your own components and follow the instructions for building the Spiderbeam Maxwell Choke:
Those of you interested in this antenna are invited to join the OCFD Group on groups.io. We have nearly 1300 members of this group and share a wealth of experience with these antennas.
See: The Off-Center-Fed Dipole Group