We had a brush fire flare up yesterday about 3mi from here. Looked serious but an air tanker arrived soon. Vegetation management is a major problem in California. As a mountain biker I see classic examples on nearly every ride.
Just a large current mode choke. I want to suppress coax shield currents as much as possible. The antenna will be a multi-band ground plane (10-15-20m) plus a 40m dipole in parallel. Later maybe an 80m dipole as well.
The main reason is receive noise. If you do not suppress shield currents well enough the coax becomes a small part of the antenna and picks up all sorts of man-made noise from switch mode supplies.
CW. There could also be digital modes in the future.
Well, the legal limit is 1500W but I won't likely go there because then the neighbor's electronics will likely keel over.
Thanks, that has interesting info in there that I hadn't pondered yet. Resonance with the line, that could really mess things up. So I guess 31 material is better in the end and that is also what he uses.
That only applies if you use a tricorder :-)
I can't go too high. I assume that is what made at least one of my baluns fail in Germany. One went with a muffle POOF. The other went silently. Suddenly I heard a thwock sound and that was my wire antenna smacking to the groud. Luckily there wasn't any car parked underneath when that happened. The balun enclosed had melted, stretched, stretched some more, wanted to become spaghetti and then it was over.
Ouch, that is tough. I better not bother him for now and just trust his judgment that 31 material is the ticket.
I am not a QRP guy but my wild days of full legal power are nearly over. If I can't use 1500W it'll be ok. At least for now. I'll jsut go with a single FT-240-31 and if I ever need more power I'll stack two or three.
If your house is EMI-quiet that may be true. I found that any kind of imbalance in the coax (meaning common mode curents) causes pickup from stuff near the cable ... bzzz ... rat-tat-tat .. phssss. Wood frame building construction doesn't help either.
Yes, it's more suitable for a voltage mode transformer than a CM choke.
Yep, magnetostriction or magneto-elastic resonance:
...an FT50-43 has a mean circumference of 32.04 mm; for a soundwave to travel that distance 190,000 times per second (resonance at 190 kHz), then the speed must be 6088 m/s. And sound speeds of about 6 km/s are indeed normal for such materials, according to literature.
Agreed. #31 was apparently formulated for low frequency RFI suppression as evident by the loss tangent being specified at 100KHz. Mechanical resonance would likely be a problem at those frequencies.
Thanks for the relevant terms.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Probably a Guanella type balun. Plenty of construction articles available online. Also see articles by Walter Maxwell (W2DU), Owen Duffy (VK1OD), and others. For example:
All About the 1:1 Current/Choke Balun
For symmetrical antennas, such as 1/2 wave dipoles and yagi antennas, you don't really need a balun if you feed it with symmetrical ladder line or twin-lead. As long as the currents through each wires is equal and symmetrical, the feed line will not radiate. However, if you follow my mistake, and install your antenna on a hillside, where one half the dipole is closer to the ground than the other half, you'll have some radiation from even the best ladder line. Therefore, it's probably best to install a balun, even if the antenna design appears to not need it.
Note: In my never humble opinion, asymmetrical antennas, such a the G5RV are abominations that should be avoided.
I have a different theory about HF receive noise. Most of what the receiver is hearing as noise is the product of mixes between multiple noise sources in the bandpass of the antenna system (which includes any balun, transmission lines, antenna tuner, and RF power meter). Once the noise gets into the system, no amount of filtering will remove mixes that land on the receive frequency. By my warped logic, the only way to reduce the noise is to narrowband the antenna system so that it doesn't pickup any out of band junk. That's opposite of conventional wisdom which favors broadband systems. The usual result is overloading (and mixing in) the first RF amplifier. The most common fix is to improve the IP3 point of the receive RF amplifier resulting in some rather high power dissipation in the receive RF amplifier and first mixer. If the antenna and front end were not trying to amplify the entire 2-30MHz HF band in one gulp, none of this would be necessary. A really high Q and a very narrow antenna receive bandwidth is how a small magnetic loop antenna works.
Another approach is to simply reduce the antenna gain. That reduces the receive signal by some amount, but also reduces the noise by the same amount. Eventually, the signal levels are small enough so that a fairly simple RF amplifier can handle whatever the tiny antenna picks up. See the various PA0RDT mini-whip variations: There's nothing in the "rules" that require you to use the same antenna for transmit and receive.
True, but the real problem is the antenna, any antenna. No sooner do you install a big ugly antenna farm on your roof or tower, all manner of electronic failure at the neighbors will be instantly attributed to your activities. When I first moved into my house, I installed a 3ft white fiberglass marine antenna on my roof. Within a week, I was being blamed for poor TV and FM reception at two different neighbors houses. This problem is partly responsible for the trend toward smaller HF antennas.
Observation: The uglier the antenna, the better it works.
Notice that most of Jim's assertions are backed by measurements and experimental testing.
Just send him an email at @arrl.net. If he's busy, he'll let you know. I don't think it will be a bother. Just don't remind him that I still have his Mirage VHF power amplifier that I'm suppose to be repairing.
Plug: We have a local company that manufactures excellent ham radio equipment: Not involved with Elecraft in any manner.
You might become involved with QRP by using WSPR for testing your transmit antenna system and checking propagation. See:
A bit more on which material to use: Notice the frequency range graph. If you want to go down to 3MHz, I think you're stuck with #31. Also, notice the effect of more or less turns of coax through the core.
Y'er welcome.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I think this will help with the material selection:
"High Performance Common Mode Chokes" See Fig 10. The author prefers stacking 2 or 3 FT240-xx toroids. There's no ideal material or number of turns that will operate over the entire 3-30MHz. It looks 10 small FB-31-1020 ferrite beads strung over RG213 is the best overall. See the black horizontal line on the graph for the optimum frequency range for each combination.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
We live in very hilly terrain and even the ground conductivity is grossly different from 20ft down the yard.
The easiest test is to tune into a noise from a switcher or similar. If you clamp a 43 clip-on ferrite around the coax and the amplitude drops then you know there's shield current on the coax.
But they look so cool ...
If stuff mixes then either the receiver is lousy or there are corroded contacts in the line and maybe nearby.
I've got good receivers with high IP3. The main one is a JRC NRD-515. The transceiver is a JRC JST-100, also high IP3.
That transceiver has me worried after a hint from a friend. It is controlled by an 8085 MCU (anyone remember those?) which gets its brain contents from a 2732 EPROM. That EPROM is now almost 40 years old. I do not have a programmer and modern TL866-based ones can't program those anyhow. Might have to roach in a 27128. Disappointingly, the manufacturer quit ham radio and could not even send me the code that's in this EPROM.
One day I am going to build myself a magnetic field receive antenna. Not a priority though because the receiver can handle just about anything.
Or they might blame your equipment interference for making their candidate losing in Dancing with the Stars :-)
One of the reasons why keeping an electronic log might be a good idea.
But ... I am married.
Yes, I noted that and promptly ordered a FT-240-31.
[...]
A friend in Germany is a fan of their stuff.
Yeah, all those digital modes did not exist when I was a ham in Germany (DK9JK) and now I had to learn all that for the US exams (now it's AJ6QL). Might as well try using some of it one day.
Yup. One of the reasons I decided to order a 31 core. Not sure if I ever do 1.8MHz, first I'll have to find out if there is anything interesting going on down there. In this area 7MHz seems to be the main band.
To my utter surprise 440MHz is also quite busy so I bought a Diamond X50A dual-band vertical.
It's not just hams. I used a lot of this stuff in medical ultrasound designs. However, those all had to be voltage mode baluns in order to provide a 5kV-rated defibrillator-proof isolation barrier.
Oops. Looks like the author does NOT like the 10 beads over RG213 coax. Quoting: G3TXQ Choke Chart. The chart in Fig 10 shows my recommendations for a range of high-performance ferrite chokes, between them covering all the HF amateur bands. Be warned that the last three are examples that you should not follow! Sorry. I missed that during my first reading.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Not for this type of unun. The 1:64 impedance ratio (more commonly 1:49 or 1:56 is used) is made with a 2 turn primary twisted onto the first two turns of 14, 15 or 16 turns. This creates a very high output impedance suitable for driving very near the end of a dipole. The windings are best when they're spaced close initially, then further and further apart, with a cross-over in the middle. If you crunch them up you get too much distributed capacitance for the >2400 ohm output impedance. It also needs 100pF across the primary to work well on the higher bands.
What's really nice about this type of antenna is when you hang and cut the wire right to resonate on 40m (or 80m), it also resonates in higher modes on 20&10m (or 40&20m with reduced performance on 10m) and that means you can operate three bands without using an antenna tuner. The lowest band chosen tends to resonate a little low (depending on wire height in the middle vs the ends) which some folk fix by adding 50uH about 2m away from the unun.
This is very different from a 9:1 (3:1 turns ratio) antenna, which has a much lower feedpoint impedance and will not resonate on multiple bands; it needs a tuner.
The unun should be grounded with a short path, and far away from E-field noise sources (often away from the shack). Any residual RF current on the coax is rejected with a CMC.
That's my setup anyhow, and a lot of other folk find it works really well, low SWR and great efficiency without needing a tuner.
The signal-to-noise ratio on most groups looks high thanks to moderators who muzzle churls and blarney spewers.
Danke,
--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
A brand spanking new Elecraft K-3 kit was acquired after my decades old Kenwood TS-440S broke down once too often. (The Kenwood-TS440S groups.io mail list is an invaluable resource for TS440S DIY repairs.) The K-3 uses innovative construction techniques to allow assembly of a "top shelf" radio from small pieces of sheet metal:
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snipped-for-privacy@2x.jpg It's a joy to operate. It features an RS-232 interface to allow operators to use software to remotely control about a hundred parameters instead of fiddling with its front panel.
Danke,
--
Don, KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.
He has a CM choke in there (says Mantelwellensperre on the lid) but it's not the big white round toroid, it is the black slot core up top. Surprisingly small.
I mounted five coax connections in the feedthrough box plus there will be 16 control wires for relays and such. That leaves me lots of room for antenna experiments.
Grounding is a major challenge here. Huge rocks everywhere and low soil conductivity.
No tuner is what I like as well. Never had one and not planning on one now. I am ok not having all bands. 15m and 40m will probably be my main roaming places, later maybe 20m and, hoping the sun spots will become more favorable, 10m.
In Europe most local traffic happened on 80m but here on the US West Coast 40m seems busier and more interesting. An 80m dipole will likely follow some day but that requires a small pole on the other side of the driveway and there are ... huge rocks in the ground.
If you run a long enough co-ax to your feedpoint you can probably do without a CMC. As I said, you get better noise performance if the unun is away from the house wiring (unlike mine).
The average soil depth here is perhaps 20cm. The rest is Sydney sandstone. I ran coax through our metal roof (ca 200m^2) and call that "RF ground".
You might need to splay out a dozen ground wires, if possible.
It is as common here to own a jack-hammer as it is to own a shovel. But the alternative is to get a fence-builder in with a core drill and make a nice hole in the rock. I plan to get a "flagpole" aka antenna mast mounted that way, to avoid the need for guy wires.
On a sunny day (Tue, 20 Oct 2020 18:43:24 -0700) it happened Joerg wrote in :
The issue is that not everyone has space for long antennas.
Most local traffic is on 70 cm here in the Netherlands, via repeaters. And now we have access to the QO100 stationary satellite for audio an video SSB and DVB-S2.
2.4 GHz uplink, ~10 GHz downlink, small dish will do for SSB, websdr:
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covers most of Europe and part of South America. Finally I think you perhaps blocked nntp.aioe.org ? the only free Usenet server that is still usable!
As to problems with GPA antennas, last place I lived almost everybody had one for CB... When the across the road neighbor was transmitting I could light a LED with my antenna.
Here I can see an other one from here... But CB is very quiet these days.
With one Baofeng on 70cm I cover the north east of the country via the repeaters.
Of course cellphones work even better, worldwide :-)
In comparison it is an expensive hobby, ham radio. But experimenting is fun:
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digital.
When next WW happens maybe Morse an tubes again...
Oops. You're right. A G5RV is symmetrical. I was thinking of a different OCF (off center fed) antenna, possibly a Windom.
I don't do much with HF antennas. Mostly, I do VHF and up. I've never built, used, measured, or repaired a G5RV antenna.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
If you run a balanced HF antenna system, you don't need a ground. Yeah, I know this is heresy: Some types of antenna are unbalanced and are designed to operate with a ground connection to enable them to operate correctly. Balanced antennas like dipoles do not need an RF ground for their correct operation as long as common-mode currents are kept off the feeder. However, even with a balanced antenna system, you might need a ground to deal with lightning hits, electrical safety, and building/electrical code requirements. If your station is full of RF (everything you touch is RF hot), you did something wrong.
If you have a septic tank, cram some wire down the cleanout for a ground. Fiberglass tanks don't work too well but there's enough capacitance between the sewage and the ground to get some kind of ground. Concrete tanks are better because the concrete is about 50% water. Note that ground conductivity is sometimes used to detect a leaking septic system. If your HF grounding results are too good to be true, your tank is probably leaking or your leach field is flooded. Also, you can get good results if your buried water lines are galvanized steel.
Anyway, think of using symmetrical antennas, avoid asymmetrical or monopole antennas, and don't worry (much) about grounding.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Only if the coax isn't parallel to mains wiring a lot. In Germany that was the case, here not so much and the noise sources have greatly multiplied because almost every power supply is switch-mode now. Plus all those CFL and LED lights.
Of course. Mine will be right at the feed point of ground plane and 40m dipole. They'll be tied together except the "hot" leg of the 40m dipole will have a 21MHz trap in series, so it won't resonate there and steal energy from the ground plane. I am hoping a 1" diameter #6 iron powder core will suffice for the trap inductor because that's the biggest I have and can fit inside the balun box.
That would be very tough here. However, there is a copper water pipe to the pool pump house that starts off about 10ft from where all the coaxes enter the house. This is also where the coaxes are all bonded together.
When they built that pool and some of the trenches around 1970 that work was started before the house (any any other house nearby) because they needed dynamite.
I still need to get a pole for the 2m/70cm stuff. Not my wind load, just a Diamond X50A vertical and a folded 2m dipole horizontal. I was planning on EMT conduit. Unfortunately they only sell 10ft sections,
20ft are nearly unobtanium here. So I'll have to join two, in a way that it won't shake loose so I don't need guy wires. This concoction will ba supported about 6ft up from the ground via connection to a balcony rail.
The flag poles they sell around here are expensive and often tapered. And they often come with a flag :-)
Out here most people do. 40m is probably more practical for the terrain and distances.
Cool. Like the big repeater in the sky.
Blocked? Their web site shows up here. I am using news.individual.de in Berlin, Germany. It's only 10 Euros per year, a very small price for a reliable service. No binaries but most other folks don't have access to those anyhow so sharing schematics that way is no longer practical.
Until one fine day when that network quits. I've experienced it numerous times and then ham radio can become a lifeline. For example, when a neighbor has a stroke and nobody else can call an ambulance because everyone ditched their landlines.
Same on mountain trails which is one reasons why we have the KA6GWY-R High Sierra repeater. One of its purposes is to provide emergency communications when somebody messed up big time on the Rubicon trail (no cell coverage).
I do not find it epensive but I built a lot of stuff myself and except for a litte Baofeng UV-5R I never bought any gear new. All used or even worse, defective and then I repaired it.
Hey, the usual solder spatters on the schematics are missing :-)
I have an old HW100 for "post-EMP communications". Regarding digital modes I am a rookie and may remain that for a while. CW has been more fun so far.
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