Recommended reading…. The sent email with that question remains unanswered. Thank you for sharing this. Ok, this shows attenuation with the ferrite, as expected. Inquiring minds want to know…. The current attenuation for a given common mode circumstance drops by the square-root of power.
Figure 1 – RG-58 coax with and without the choke delivered with N9TAX’s Slim Jim antennas. Learn how your comment data is processed. Since the plain coax was also our calibrator, its transmission in green shows a nice flat line from 10 to 500 MHz. What type of ferrite would be best for VHF (or even UHF) ?
We must keep in mind measuring power through a choke requires knowledge of impedance to calculate current. This means this ferrite’s ability to mitigate common mode current is even worse than the graph suggests. Hence the term “Choke”. Long coax runs can benefit from additional chokes near the shack as it cuts down on receive noise. Ultra-Lightweight antennas for expeditions and stealth applications. Other types of cables benefit in the same ways a coax.
Besides burning your fingers on the key or lips on the mic, it can also cause some Worst case it can cause TVI or BCI, etc. In many of the diagrams you find on this site, I’ve generalized impedance points along antennas, feeds, etc. It is vitally important for the antenna user to understand there are many flavors of ferrite material.
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Puzzling why I’m not measuring coax loss via the center conductor and shield? Put an end to annoying RF related problems with our choke kits. Calibration complete, the coax with ferrite was swapped in place. USB and ethernet easily pick up radiated RF energy and conduct it right into places it does not belong. The ferrite provides almost 90% power attenuation for the 2m band. Fair-Rite offers potentially more pragmatic hope with their Type 61 material….
It appears to have some utility above VHF, but you’re going to need more than one in series or apply other advanced ferrite methods. Indeed if we substitute a #10 copper wire for the coax the results will be the same. The next figure shows the ferrite with its coax along with a similar length of RG-58 for comparison.
Unwanted RF in the shack due to Common Mode Current (CMC) on the coax can be nasty. Besides burning your fingers on the key or lips on the mic, it can also cause some devices to fault. What is the ferrite material used in the N9TAX products? For testing like this we can likely assume for calculations a 50 ohm system impedance. Unwanted RF in the shack due to Common Mode Current (CMC) on the coax can be nasty. Patience please). I used a G-R Admittance Bridge for this, which is pretty old-school, but admittance is the inverse of impedance so it's easy to calculate one from the other.
Paired with how you apply the available ferrite products yields designs benefiting specific frequency ranges and uses. Let me see what I can add. Yeah it brought a tear to my eye, but I cut out the ferrite choke from my MURS/GMRS N9TAX ‘Slim Jim’ J antenna for the purposes of measuring the common mode attenuation it provides. This field attracts the stray RF and chokes it off before it travels down the coax, and it is dissipated within the EM field. The squiggly green line of course shows 100% by definition, but isn’t perfectly straight as a reminder that real data often has real noise and to give the reader some understanding of data uncertainty. Copper wire provides shorter connection between ports than the path through the VNA’s connectors. https://vk1nam.wordpress.com/2018/02/10/portable-2m-144-mhz-coaxial-dipole-antenna/, (You must log in or sign up to reply here. Figure 5 contains the results of the ferrite test with arrows highlighting values at VHF and UHF amateur radio spectrum segments. Form the choke by winding 9 turns of coax, snug against the pipe with no gap between the turns. © 2007-2020 John Scott Huggins and other authors and creators, All Rights Reserved.
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