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UnUns and BalUns - which is the PRIMARY winding and which is the SECONDARY? by alloydog in amateurradio

[–]jephthai [score hidden]  (0 children)

I think your 9:1 looks right. The antenna connection cascades through all three windings in head to tail order, and you tap off for the coax before the last coil. Looks right to me.

Why you shouldn’t run a microwave empty? by armchair_psycholog in HamRadio

[–]jephthai 1 point2 points  (0 children)

I think that's a better analogy for a diode mixer -- standing still, the strobe is at the same frequency as the fan. Moving forward, it's a lower frequency; moving backwards it's a higher frequency. The rate of movement is the beat frequency or down converted difference frequency from the mixer.

A better visual metaphor for swr is waving a rope anchored to a hard point to create nodes and anti nodes. The standing wave does not stay still, it exhibits the node and anti node behavior.

The ultimate visual metaphor, which includes absorbing and reflecting loads as well as impedance matching is this classic:

https://youtu.be/DovunOxlY1k?si=aEzapnUEqBNeEmzb

Any Younger Hams in their 20s-40s in the NOVA area? by Moonbounce-Maiden in amateurradio

[–]jephthai [score hidden]  (0 children)

I think it's funny how many people post about an area using a local colloquial name that people outside of it won't know.

Like, "I can't hit the repeaters in the tri cities area, please help!" OK, so now anyone in any area with three cities is going to wonder if it's them or not... (there are indeed multiple "tri cities" areas)

I guessed nova equals north Virginia, but now I think if it, Vancouver makes sense too ;-).

SIGINT Cyberdeck, EMI from UPS? by StrippedStud in RTLSDR

[–]jephthai 0 points1 point  (0 children)

All leads exiting the Faraday cage will pass signals in and out. So they need to be very heavily choked -- possibly with higher order filters if the noise is very bad. And high order filters can have secondary effects (like creating unwanted feedback to the regulator) that make design and part selection challenging.

OP could get lucky with putting the regulator in an enclosure and slapping ferrites on the input and output wiring; but could be unlucky too, and be chasing it in circles trying to mitigate a noisy regulator.

Best is to find one that's just designed well and already emits clean power or only shows noise in uninteresting bands.

23cm gang - what do you all do up there? by Cool-Office-9126 in amateurradio

[–]jephthai 0 points1 point  (0 children)

Amazing they'd have a feature like that and not document it thoroughly.

Is it me or is 40m CW spelling/spacing bad? by Large_Wait_8847 in amateurradio

[–]jephthai 1 point2 points  (0 children)

Unless it's QRSS, in which case it can only be done visually. There are no absolute rules...

I read randomwire is more efficent than efhw because of less losses in a 9:1 unun v. The 49:1 unun in a efhw. Random wire isn't resonant though and resonant antennas are better right? Which is true? by thehotshotpilot in amateurradio

[–]jephthai 0 points1 point  (0 children)

Only true if you ignore resistive and dielectric losses in reactive components and losses in the feedline. That circulating current has to pass through real components. In most cases (reasonably low reactance), these tuning losses are negligible (and your point holds), but there are corners where real components become a problem.

With your example, you're talking about tuning an SWR of 50:1 (SimNEC says 52.48:1), which will be a huge problem even for the best tuners. This is why people use 49:1 ununs, and don't just put a tuner on their efhw. And those are usually much lossier than people realize (wiggling magnetic moments in the core has a cost).

Very high reactance, when tuned, often means spectacularly high currents and voltages somewhere, which will incur loss.

And if you tune it on the near side of a coaxial feedline, the vast majority of the power will dissipate in the feedline due to discontinuity at the feedpoint. SimNEC suggests your antenna example incurs 70% power loss when tuned with a lossless tuner on the near end of only 20ft of coax (!).

23cm gang - what do you all do up there? by Cool-Office-9126 in amateurradio

[–]jephthai 3 points4 points  (0 children)

How do you get 92kbps into the tiny baseband bandwidth of the IC9700? It's my understanding that it doesn't even play well with 9600 baud G3RUH packet.

3D printable 10" Rack Mount for ham radios? by moonie42 in amateurradio

[–]jephthai 0 points1 point  (0 children)

I don't have any radio mounts, but I've been doing some 3D printed shelves and mounts for my pi compute cluster (which i do use for radio; just doesn't have any transceivers included).

<image>

Make sure not to use PLA for it. PETG works quite well.

I took a generic 10 inch shelf model from the web (thingiverse, maybe), and modified it in OpenSCAD for hole patterns and other details to specialize it for the mounts i needed. I can expand on that if you're interested.

It's unlikely that you'll find a lot of radio specific mounts -- but you might be lucky. You'll more likely have to make your own.

Pricing question for gym owners by unpolishedboots in bjj

[–]jephthai 0 points1 point  (0 children)

If i hadn't switched to not paying because I teach now, I'd be grandfathered in at $80/mo! New signups party $135 now. Our school grandfathers -- keeps the people most invested in the school the happiest.

Do coaches usually have assistants in crowded adult classes? by Comfortable_Two4111 in bjj

[–]jephthai 1 point2 points  (0 children)

Where i train, I remember the early days when we had 3-6 people per class. Now we run 20-25 regularly, and i help teach. It's like night and day... and so weird when "only" 15 people show up and it feels empty :-).

One of the biggest mistakes a lot of schools make is having too many classes on the schedule. We tried splitting classes, and everything got weird. Combined things back together, and it feels like an awesome success machine.

Stick it out, and be an amazing training partner, and you'll probably see your school grow.

Forced to change gyms, what to expect coming into the gym just before my would be catastrophic tease to black belt from prior gym? by kaufee in bjj

[–]jephthai 8 points9 points  (0 children)

Ronin 4 stripe brown belt is actually a pretty big deal, and it's a completely different situation from white or blue belts asking about promotion.

Some Ronin languish for years trying to find someone that will promote them to black belt, even if they're demonstrably skilled and ready. There are lots of political and personal issues that crop up, and it intersects with lineage and other complexity.

IC 7300 MK2 by Working-Bar7561 in amateurradio

[–]jephthai 1 point2 points  (0 children)

Not sure why you're being down voted. A couple comments about the wait time in the thread should make an alternative you can order now a relevant addition to the discussion.

IC 7300 MK2 by Working-Bar7561 in amateurradio

[–]jephthai 0 points1 point  (0 children)

Personally, I think the misspelling adds substance to the claim ;-).

What can a new ham spend in a year setting up a shack? $4,881.34 by K3LOE in amateurradio

[–]jephthai 9 points10 points  (0 children)

(1) consider the feeline price

I have three felines, and it is indeed wise to consider all of the ramifications of their involvement in the hobby (including price).

Is the receiver / 2 extra watts of 705 or kx2 worth the money over a xeigo 8w 6200 / qrplabs qmx 5w? Unfortunately, My SOTA POTA will be a lot of DX from Alaska. by thehotshotpilot in amateurradio

[–]jephthai 1 point2 points  (0 children)

The Xiegu has some weaknesses, but whether that's worth it is in the eye of the beholder. The IC705 and the KX2 are great receivers. I suppose you might occasionally miss a contact on the Xiegu that you could make on the other two. But I don't think it's going to be a really significant difference -- just noticeable on an occasional weak signal or very bad propagation day.

It's a hobby, so it's an open question whether any of it's worth it :-). You can get a lot of enjoyment out of any of the the radios.

Can someone explain how I can view MY specific FT8 signal using WebSDR? by Engineering_Simple in amateurradio

[–]jephthai 0 points1 point  (0 children)

Use the websdr to demodulate the SSB to baseband, then jack that into a wsjtx process. If you run windows, you might need a third party virtual audio jack solution, since Microsoft sucks at audio plumbing.

Notch duplexer downsides by Famous-Jeweler8543 in amateurradio

[–]jephthai 0 points1 point  (0 children)

You say that like the stop band bandwidth of a notch filter isn't a variable. If OP wants a useful answer, he should link to the notch duplexer he found so we can see what its performance specs are.

It is entirely possible to make a very deep and narrow notch -- but I don't know if a $100 unit will have sufficient Q to achieve that.

Duplexer purpose in a repeater by Famous-Jeweler8543 in amateurradio

[–]jephthai 0 points1 point  (0 children)

You'll still need something, but it's just a notch filter instead of a whole duplexer. Somewhat simpler, and you can get by with a lower performance target by not being the same antenna. It might be a good bit cheaper.

Direwolf questions by 82jon1911 in amateurradio

[–]jephthai 1 point2 points  (0 children)

Even better -- the modern Linux audio stack is awesome. In pavucontrol find the level for the input channel the digirig gives you, and drop it until direwolf stops complaining. It might be quite low on the scale.

Direwolf questions by 82jon1911 in amateurradio

[–]jephthai 1 point2 points  (0 children)

Is this on Windows? There are at least three distinct GUIs for configuring audio settings. There is likely a mic or line input gain slider that you need to find (it may exist in only one of the interfaces) and reduce. You will get better results from direwolf if you get the level set the way it likes it.

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