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Factor Software Boom

Factor Software Boom

Coax Velocity Factor in Baluns, Does it Matter Part 2. Preface to Velocity Factor Experiment. In the Part 1 of this series I discuss various attributes concerning the use of Baluns especially in the VHFUHF bands. Reviewing I point out other web sites with excellent tutorials on why and where to use Baluns in VHF work. Two particular Balun styles come up strong 1 1 Coaxial Cable Balun and the Pawsey Stub otherwise known as 1 1 Folded Balun. Factor Software BoomAccording to the widely recognised authority on the matter, the National Bureau of Economic Research based in Cambridge, Massachusetts, the longest U. S. economic boom. Dell electronics and accessories page has customer reviews, hot dealsoftheday and popular categories to help quickly locate the right products. Why Israels economic boom is driven by dangerous bubbles that are similar to those that caused the Financial Crisis. Learn at your own pace by watching usercontributed online videos. Follow stepbystep lessons to learn basic skills and improve your expertise from skilled. Factor Software BoomEach Baluns topologies are shown in Figures 1 and 2. I highlight the mistaken, I believe, assertion one should adjust the Pawsey Stubs length by the amount of the coaxial cable velocity factor. Figure 3 shows why I think the Pawsey Stub length does not need as drastic a reduction in length as you might do for stubs that contain the electric and magnetic fields within their structure. Finally, I say I will prove my assertion the Pawsey Stub is electrically a 14 wave in free space or close. What follows is the experiment which provides proof Velocity Factor of Coaxial Cables does not apply to cables used simply as a wire in parallel with another wire. Velocity Factor Balun Experiment. The two Baluns are an excellent pair to compare. The Coaxial Cable Balun is just two transmission lines tied together one 14 wavelength long, the other 34 wavelength long. In this case the electric and magnetic fields are entirely within the dielectric material. Thus the velocity factor adjustment should apply. The Pawsey Stub relies entirely on becoming a parallel transmission line with the feedline coax. Its fields are entirely outside the structure of the coax. I built the two baluns using some RG3. Can I cut my energy bills by turning off my fridge freezer at night or will the food spoil Has Barclays given millions of customers antivirus software thats. Factor Software BoomMy target frequency for both is 3. MHz. I cut pieces with no corrections applied to see how the frequency changes. Coaxial Cable Balun Measurement. The Coaxial Cable Balun has the following dimensions based on calculations14 wave section 3. MHz. 2. 5 2. MHz. 7. 5 7. I simply cut two pieces of coax to the above lengths and added a third with an SMA connector for the feed line. Figure 4 shows the Coaxial Cable Balun with a 5. Fig 4 Coaxial Cable Balun with 14 and 34 sections of coax, cut for 3. MHz Freespace, in parallel. With the resistance at the feedpoint, the Balun should show some very obvious frequency dependence on a Return Loss or SWR plot. UK spymasters raise suspicions over Kaspersky softwares Russia links Private equity fights back on US tax reforms Trump backs US. Background Most patients with nonsmallcell lung cancer have no response to the tyrosine kinase inhibitor gefitinib, which targets the epidermal growth factor. Because this is the case where the published coax Velocity factor does apply, the target frequency of 3. MHz should be lowered by. MHz. Given that I flayed the coax shield and center, thereby reducing some of the coaxial cable length, the actual frequency should be a little higher. Figure 5 shows what happens when I connect the Coaxial Cable Balun to the VNAFig 5 Return Loss of Coaxial Cable Balun from 1. MHz. Markers M1 and M2 are at 3. MHz respectively. Wow the 2. 14 MHz pretty much confirms that Velocity Factor is well in play for this style of Balun. Folded Balun Pawsey Stub Measurement. Now lets try the Pawsey Stub. The only critical dimension is the stub length. MHz. 2. 5 2. Once again, my trimming slightly shortens the actual mechanical length to about 2. MHz. Figure 6 shows my test unit with 5. Fig 6 Pawsey Stub Balun with 14 of coax, cut for 3. MHz Freespace, in alongside the feedline. Whats the prediction here If you listen to the web sites which suggest coax cable VF applies, the frequency will be between 2. MHz. If I am right and this is free space, or very close to free space, then the frequency should be something above 3. MHz, or since I made mine a bit short, something above 3. MHz. Lets see the Return Loss plotFig 7 Return Loss of Folded Balun from 1. MHz. Markers M1 and M2 are at 3. MHz respectively. Bulls Eye This strongly suggests the lengths of external stubs, like the Pawsey Stub or any Folded Balun variant, should be calculated using free space wavelengths without corrections for published coax Velocity Factor. The thing is, this has been the case in the ARRL Antenna book for many many years. The later editions never suggest to apply velocity factor to external stub calculations and the 1. VF does not apply. Interference from Nearby Objects an Additional Observation. Testing of the above two Baluns revealed an interesting behavior. The 1 1 Coaxial Cable Balun was immune to effects from handling during the test. The Pawsey Stub was very sensitive to touch or even being close to the stub portion. This evidence correlates well with the measurements suggesting the Pawsey Stubs electric and magnetic fields are, at least some if not entirely, outside the realm of any dielectric material. Conclusion. It is a good thing Amateur Radio Operators know about transmission line Velocity Factor specifications. Without this knowledge you would be cutting stubs incorrectly. However, some Amateurs assume that just because a piece of coax is used for a stub, Velocity Factor applies. The key to understanding when it does and when it doesnt is found by following the electric and magnetic fields. Where are they Are they inside the coax or outside between pieces of coaxIf inside, apply VF. If outside assume freespace with a little loading by the coaxial sheath. Measure, but verifyThis experiment relies on some crude cutting of cable lengths and assumed values of Velocity Factor. Potential sources of error include Cable End Trimming Source for my slight errors above. Coax Velocity Factor not what the manufacturer says When you do need to know VF, it might be a bit off especially with lower quality coax. To date, however, I have not seen coax velocity factor off by more than a couple percent. The Pawsey Stub is certainly not a way to measure VF of coaxial cable. Freespace not quite freespace Even the best air gap transmission line has some dielectric material in the fields VF values of 0. Dont Blame the Coax. A little research into the literature goes a long way towards understanding how a Folded Balun or Pawsey Stub if you like works. A simple hand grab test of the Folded Balun that results in changing SWR or Return Loss instantly reveals external fields outside the realm of the coax dielectric thus, coaxial cable VF rating does not apply. Lacking this understanding, an all too often quick assumption is to blame the manufacturer of the coax for poor control of VF during manufacture. So what does this suggest If you are going to the trouble to make something as critical as a Balun for your Yagi antenna, electrically measure each cable with your SWR meter or VNA to ensure you are spot on the frequency of choice. This was an interesting test. I am now so interested in Baluns, I will focus on posts for each type in the near future. Thanks for reading. John. Enjoy reading these similar articles About John Huggins. John is an electrical engineer working in astronomy and aerospace including 3. RF design with experience modeling, manufacturing and measuring past, present and new antenna concepts. View all posts by John Huggins. Tags Baluns, Pawsey Stub, Split Coax Stub. Copyright 2. 01. John Huggins. This entry was posted. Monday, August 9th, 2. Antennas, Lab Shootouts. You can follow any responses to this entry through the RSS 2. You can skip to the end and leave a response. Pinging is currently not allowed.