Good job, nice and simple and they work!! Excellent tutorial for new hams to follow to show how simple things are to construct....
In an absolute sense, that's true. But it seems just a wee-but American-centric. I mean, how much I3 power are you contemplating is coming back along the cable to run through the ferrite? Maybe people should just stop looking at QRO operation as required and desirable, and try something a bit less machoistic. Last week, I made a 8500km QSO on 5W, SSB from a 1/4 wave vertical. It's not about 'winning'. It's about purity and efficiency. But I know these words are largely wasted, particularly here at Cowboy Central.
Continuing the saga here: I recently put up a Gap Titan DX. I've got RF in-the-shack from it; particularly on 40 meters, and I've been playing with chokes before I 'permanently' route the coax. I tried snap-on beads and an air choke wound around a coke bottle (both helped but did not fix the problem), and this morning I added a common-mode choke. This one is 12 turns of RG-8x wound around a circular ferrite core (mix 31) and received some interesting results. If the core is close to the antenna feedpoint, 80 meter background noise gets very quiet and 40 meter resonance moves lower on the band. If I move the choke outside the 'hoop' section of the Gap Titan, 80 meters gets noisier and 40 meters goes back to its resonance point. The choke at either location IS reducing RF in the shack; and appears to be doing a better job at the base of the antenna. I'm going to do more testing this evening, to see what it's doing to 80 meter reception.
That is because the feedline until you installed the toroid choke has been part of your antenna, "loading it" so to speak. With the choke in place the antenna only sees the feedline between it and the choke which now becomes something of a tuning stub. As you move the choke the coax the antenna sees goes up and down in length.
That of course is my first guess. I find it interesting that 80 meters quieted so much with the choke close to the feedpoint, and noise increasing so significantly with the choke moving only 10 feet or so. There's a lot of sleigh of hand going on inside of a Gap (loading, tuning stubs, and a capacitor), to make me curious what's going on internally.
You are absolutely right, but HAM used as a rule one choke balun for antennas from 160 to 10 meters and for it mix 31 better (universal). With regards Viacheslav
I hope no one ignores most of the test data is using RG-58 a poor choice of coax to use for a choke. Its shield is loosely woven wire inviting external coupling and reduces bandwidth. Examine the chart for RG174 and not how wideband it is. RG400 would show considerable improvement. Little expensive but doable with the small quantities needed to make a choke. In the end, there is no perfect material to fully cover the bands from 160 to 10 meters. That is when you use 2 in series splitting the bands in two using both 31 and 43 cores.
I agree, QRP can be magic. Yesterday morning, as always, my first TXwas FT8 at just 5 watts into the atu and antenna to test the propagation. Surprisingly JA8RRP lit up for me on PSK Reporter at -17 dB, 5456 miles away from my London QTH ! I wonder how many of those 5 watts escaped system losses and ground losses and found their way to JA !!! And it occurs to me that if our wanted transmissions at QRP levels can go that far, how many RFI-generating unwanted noisemakers (switch-mode PSUs etc) are out there on the planet sending crap at us from thousands of miles away!!!! ...and it further occurs to me that maybe somewhere out there in the universe there's a planet of highly intelligent radio ham beings who are extremely annoyed with the megawatts of RFI emanating from planet Earth and will shortly be taking the advice on QRZ to kill the RFI at source
if you read the details from G3TXQ and the K9AY choke cookbook, you will see that there are just a few mix recipes available today commercially that are "best" to cover the HF ham bands as common mode chokes and as transformers. The older mixes (others listed) are much less effective across the entire HF spectrum -- yes they work, of course, but if you want to build a new device with modern ferrite, there are but a few "best" choices and the rest of the information is mostly noise. For example, unless you don't have access to the modern ferrite material, you would never bother to wind a coax air-choke again given it's very limited bandwidth. So yes, generalizations that consistently work are a good thing to sift through the noise -- that's the way the human brain works.
One would think (at least me) that over time the inner coax wire would start to migrate to the outer shield. This would change the capassitance as well as the impeadance. (2 cents) KG0BK
That's why RG-400 is used in high quality baluns, It has a solid (not foamed) PTFE (Teflon) dielectric which has a much higher melting point (and therefore, it doesn't "soften" at lower temperatures) than the plastics that are used in RG-58U, RG-8X, etc. This should prevent the migration of the center conductor over time. Preventing migration of the center conductor is one reason why it's important to keep the balun as cool as possible.
RG400 has similar voltage ratings etc as LMR400. It's great for this type of stuff. RG142 is close to it.
Tuning around and working a few stations this evening with the choke close to the feedpoint. The Gap Titan seems to be working. I'll start making some more permanent coax feeds tomorrow.
