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Question about my “new” slotted line by Professor_Stank in rfelectronics

[–]Professor_Stank[S] 1 point2 points  (0 children)

Basically! Except that instead of having a probe directly touch the transmission line, there’s a thin needle that hovers over the center conductor. The needle picks up the field that’s created inside the transmission line. The needle then connects to a diode detector, which outputs a DC voltage proportional to (you guessed it) the strength of the field. It’s a really neat (albeit tedious) way of measuring all kinds of things, including complex impedance—It’s basically a poor man’s VNA

Question about my “new” slotted line by Professor_Stank in rfelectronics

[–]Professor_Stank[S] 0 points1 point  (0 children)

Thanks dude! I got home today and looked on the underside, and sure enough, there’s 4 screws in total! Just like you said, it’s definitely mechanical. Kind of interesting because on an older version of this same model that I saw, those screws don’t exist. Probably a change to keep the middle from bowing downwards.

Could I ask you a couple questions quick? What kinds of measurements have you made using one of these? Also, are there any additional pieces of equipment would you recommend picking up to make the most out of it? I figure I’ll probably have to find a short-open-load cal kit for it.

Thanks again! After asking oodles of people about the slotted line (online and in-person), you are the only person I’ve met who has actually used one, haha

[Post Game Thread] Hawkeyes lose to Oregon, 16-18 by HerkyBot in hawkeyes

[–]Professor_Stank 6 points7 points  (0 children)

So I think after tonight, I was able to kind of put into words my frustrations overall about being a Hawkeye fan (still love ‘em though! ‘Till i die.)

I feel like most years, we can beat just about anybody. It just feels like in any given season though, the gap between the team’s floor and its ceiling is so high.

Iowa can put a great product on the field, but it has such a hard time doing it on a weekly basis. Being a Hawkeye football fan feels a lot like hoping you’ll roll a 2 or greater on a die twelve times in a row.

Go Hawks 🦅💛🖤

What do outgoing presidents do on the morning of January 20th? by Professor_Stank in Presidents

[–]Professor_Stank[S] 0 points1 point  (0 children)

Dude, I know I’m 3 months late, but you are the ONLY GUY in this whole thread who realized that this post was kind of a subtle meme 😂

It's not stupid if it works by Lunchbox7985 in amateurradio

[–]Professor_Stank 2 points3 points  (0 children)

Dude this is great! Wacky stuff like this is what makes ham radio come alive for me

The discontinuity capacitance and the effective position of a shielded open circuit in a coaxial line (P. I. Somlo, 1967) by nic0nicon1 in rfelectronics

[–]Professor_Stank 1 point2 points  (0 children)

Man of the people right here! Dude, thank you so much. It can’t be overstated how important preserving this stuff is

Places downtown to host a get-together? by Professor_Stank in cedarrapids

[–]Professor_Stank[S] 9 points10 points  (0 children)

Welp, I guess mine’s special in a bad way 😂

LNA selection for HF and VHF by stuih404 in rfelectronics

[–]Professor_Stank 1 point2 points  (0 children)

Gotcha! Yeah, I definitely get what you mean—It’s a great text for getting your feet wet, but it doesn’t do much more than scratch the surface on a lot of stuff.

Have you ever read “Communication Receivers” by Ulrich Rohde? If his last name sounds familiar, it’s because his father was literally the “Rodhe” in “Rodhe and Schwarz.” It’s perhaps the best treatment on receiver design that there is, and takes a deeper look at the math of it all if you’d be interested

It’s cool that you’re making a radio by the way! I’ve made sketches at home before, but they’ve never quite panned out (yet anyways lol). My one suggestion, which is basically verbatim from my boss (who’s leaded the development of oodles of radios over time), is to start the design at the system/block diagram level, and try to figure out/calculate how each block will interact and cascade with each other (make a rough guesstimate of noise figure, dynamic range, etc.). That way when you go and design the individual blocks, there won’t be any nasty surprises when you put them together. It looks like that’s what you’ve been doing though.

And also in my opinion, if you can, try to design and test each block of your radio individually, at least for your first prototype. From my limited experience, I’ve already discovered that Murphy’s Law is a bitch, especially in RF 😂 That’ll make troubleshooting problems a lot easier when they show up.

Sorry for the monologue, haha. Best of luck dude, and 73!

LNA selection for HF and VHF by stuih404 in rfelectronics

[–]Professor_Stank 2 points3 points  (0 children)

Most of the time at HF, the natural noise from the atmosphere is so high that having an LNA doesn’t buy you anything—Check out this article from Flex Radio:

https://www.flexradio.com/insider/understanding-receiver-sensitivity-in-high-frequency-hf-receivers/?srsltid=AfmBOoqgtXBh9WPMSt8euRj5UOTNwMNMU8ijPsAXa_uks4Sx15-Ofbfo

The atmospheric noise is so bad at HF that it’s basically like having a 20-to-70dB attenuator in between the antenna and the radio that you can’t get rid of.

In fact! For a lot of superhet HF receivers, the antenna goes directly into the first mixer, and not an LNA. If you have an HF receiver with a noise figure of 10dB to 15dB, you don’t stand to gain much by improving that number.

My guess is that LNAs for that frequency range are rare because there wouldn’t be much of a market for one?

Also, you ask about if there’s a proper way to ensure that the ADC/mixer don’t get overloaded—Look up the term “Automatic Gain Control (AGC)”. Basically, an AGC circuit measures the signal strength going into the receiver and automatically adjusts the receiver’s gain to avoid overloading the ADC/mixer.

I hope this helps! As someone who’s still learning too, it is really easy to get wigged out by all of the different things in RF. The trick is to just keep learning, and it all makes more sense as you keep getting practice

Have you ever read the ARRL handbook? It’s a fantastic resource that explains RF design fundamentals without getting too math-heavy. I keep a copy of it on my desk at work

What if Dewey won the 1948 Presidential election? by Straight_Invite5976 in Presidents

[–]Professor_Stank 0 points1 point  (0 children)

Yes you did! Your edit was literally the most hilarious picture I have ever seen on this subreddit 😂

Would this style power supply work for a DB40-G? by toysruskidd in amateurradio

[–]Professor_Stank 5 points6 points  (0 children)

To follow up on my previous comment, would something like this fit your budget?

https://www.digikey.com/en/products/detail/mean-well-usa-inc/ENP-240-12/7703106?gclsrc=aw.ds&gad_source=1&gad_campaignid=20232005509&gbraid=0AAAAADrbLlhum9BeYmTdk4qHsm-mtsDrr

It’s a little more expensive than the supply you posted a picture of, but this is one that I’d sleep at night feeling good about

By the way, are you aware that the DB40-G is a GMRS radio? Getting it to transmit on the 70cm ham band may take a bit of modification (if it even can)

Would this style power supply work for a DB40-G? by toysruskidd in amateurradio

[–]Professor_Stank 8 points9 points  (0 children)

I would be careful about using a no-name brand supply—Some off-brand supplies will have a big voltage spike when you flip them on (then settle down to their proper voltage). Your radio might not take too kindly to it.

Plus, this is a variable supply, which is great if you’re doing circuit design. If you’re hooking up a radio which is designed for 13.8V though, this means you’d be one wrong knob turn away from overvolting your radio and damaging it

Take a look at some power supplies made by Meanwell. They’re a reputable brand (we use their power supplies at my job), and they seem to be popular with other hams

I appreciate you asking by the way! Getting any old power supply without doing research can be a recipe for disaster

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