As annoying as the stranded center conductors of cables like this LL240 are, I really appreciate the flexibility and how it reduces loading on the connectors.
After dealing with so much reactance from "normal" resistors, I finally got a 50Ω thick-film resistor that is advertised as "non-inductive" and rated for 700V. I cherish it. :3 #AmateurRadio #HamRadio
Made my first SMA cables today. It was pretty challenging because they are so small and it was my first time making them. I hope I didn't mess up. :( #AmateurRadio #HamRadio
It was definitely poor cable construction. After practicing with SMA connectors a few more times, I learned that the center conductor's strands really need to either be very_ carefully stuffed into the center pin's "cup", or be cut very short and carefully stuffed under the cup if they don't fit in it. Now I no longer have cables that short between the center conductor and shield when bent. #AmateurRadio #HamRadio
TNC (threaded nut connector) is about the same dimensions as BNC (bayonet nut connector). N connectors are the same thread size as UHF (universal high frequency), but the interior are the same as BNC/TNC.
So, it is possible to remove the nut from a BNC and plug it into an N.
Thinking the Ant/TX port is a N-connector as TNC are similar diameter as BNC, but threaded instead of twist-lock. Looks super-nice! Have fun on on 222!
Although some writers consider the gap in the halo antenna's loop to distinguish it from a small loop antenna – since there is no DC connection between the two ends – that distinction is lost at RF: The close-bent high-voltage ends are connected capacitively, with a RF electrical connection completed through displacement current. Despite the abrupt reversal in voltage across the gap, the RF current bridging the gap is continuous (although possibly momentarily zero).
The gap in the halo is electrically equivalent to the tuning capacitor on a small loop, although its stray capacitance is not nearly as large as needed for a tuned loop: Capacitance is not needed since the halo antenna is already resonant, but since some small capacitive coupling is present anyway, the arms of the dipole are trimmed back from 97% of a quarter-wave each to restore resonance. Moreover, the halo ends are often pressed even closer together, to increase their mutual capacitance and the ends then cut even shorter to compensate, in order to make the radiation pattern even more nearly omnidirectional, and to produce even less wasteful vertical radiation (for a horizontally mounted halo).
How does one determine the spacing between a gamma match and the main antenna conductor? As in, where they're parallel between the two feed point terminals. :/ #AmateurRadio #HamRadio
Without doing any modelling, I would say it's probably not critical and it's likely to be a small fraction of a wavelength at the relevant frequency. I suspect it would just adjust where the gamma match attaches to the driven element, similar to, eg a J Pole feed point.
Of course, the correct way to answer this is to post a picture to QRZ.com and wait for 40 different "you're doing it wrong" posts that reference ARRL handbooks from the '40s
Just landed on my first C4FM repeater net. It's pretty cool! It shows both the call sign and distance from the repeater of the transmitting stations. :O #AmateurRadio #HamRadio
In 2013 Yaesu introduced “System Fusion,” new technology utilizing C4FM 4-level FSK technology for transmitting digital voice data. The System Fusion communication protocol enables devices to analyze an incoming signal and automatically determine if it is using C4FM or conventional FM mode. System Fusion also enables data transfer at full rate with speeds reaching up to 9,600 bits per second.
Finally back on 70cm. The dipole as-is can only cover the upper ~14 MHz of 70cm, but I'm going to see about getting some even smaller brass tubing so I can extend the legs even further. 🤔
And if that doesn't work, I have plenty of variable capacitors in my shack. 👍
After even further experimentation, I discovered that the lower leg can remain fixed at 10.5cm for the upper part of 70cm. Just need to change the upper leg to 15cm almost exactly. 👍
Finally back on 70cm. The dipole as-is can only cover the upper ~14 MHz of 70cm, but I'm going to see about getting some even smaller brass tubing so I can extend the legs even further. 🤔
And if that doesn't work, I have plenty of variable capacitors in my shack. 👍
Did you try varying the center (gap) spacing? Have focused on minimizing this with some dipoles in the past to good success. Did you incorporate a sleeve balun at the feed? Have had unbalanced feed dipoles yield narrower bandwidths. 73
Another thing that makes me think it's the coax is that I was seeing an "extra" resonance when the dipole's self-resonance was at a lower frequency. #AmateurRadio #HamRadio
Got really low radiation resistance (~20Ω) on that 70cm dipole with balanced legs, but an off-center feed raised it to 45Ω with a decent bandwidth. 🤷 #AmateurRadio #HamRadio
Ended up getting longer legs (in aluminum because the hardware store was out of the copper tubing I like) and switching to a proper common mode choke winding pattern…and it just worked. It covers the entire 70cm band with SWR≤2! :O
I do have some more aluminum tubing that fits snugly inside these dipole legs, so I can make the legs telescoping to reduce the resonant frequency.
Bad SWR with this. Wondering if it's the length of the coax, which is pretty close to two wavelengths when accounting for the velocity factor, or if I messed up somewhere.
Anyway, I have some -61 mix ferrite beads on the way. :P
So I think I'm going to do a ½-wavelength metal stick, so 35cm to start, but I'm not sure about how much to space the gamma match rod from the radiating rod. :/
There are many variations of this. If you have separate feedlines, this would be what most contest and mult-operator stations use. There are also e.g. triplexers that allow you to use three radios (10/15/20m) on a common triband antenna. See e.g. https://va6am.com/ for some examples.
Finally got my 6m dipole working with a -43 voltage balun. Since I mistakenly cut it a little too short all those months ago, it resonated at the upper end of the 6m band, so I had to tack on a tiny loading coil to add some inductance and bring the resonant frequency down to where I wanted.
The unfortunate thing is that the loading coil also significantly cut the bandwidth of the antenna + voltage balun. At some point, I'll build a new dipole and not cut it as much. :P
That would work well if I had a wire dipole, but this one is comprised of painted copper pipe.
When I do make the new dipole, I plan on having bolt holes on the outer ends so I can attach stuff like additional length for 10m (probably with a trap) and capacitive hats. :3
The oval 2 bolt bulkhead N connectors are not especially hard to come by, but I would only bother with the 2m & 70cm connector. It's still not much benefit for a fair bit of work.
I tried something like that once, but with an external antenna and 40 watts while running FT8, and my laptop's USB phy would fritz out during transmissions and refuse to recognize my Signallink, let alone my mouse. Had to use clamp-on chokes and find a metal laptop case screw to attach a ground lead before it would resolve itself. RF is crazy.
Neil E. Hodges
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