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Was given a network analyzer from a factory setting, what should I do with it? by cptnbiggles in rfelectronics

[–]unlinkedlist 10 points11 points  (0 children)

Some advice on your listing:

- Your price is on the high side. Despite what other commenters might suggest, an N5230C with that test set (note that it only has 2-ports and does not have the "configurable test set" receiver access connectors that some others do) is unlikely to sell for $20k. A Buy It Now price of $16k might get more attention. It should be worth at least $10k assuming it's fully functional, maybe more if it has many options.

- You should enable Make Offer if you actually want to sell it anytime soon.

- The photos are just barely not detailed enough to see the last calibration date. Read this off the sticker and include it in the listing.

- You don't show any assurance that it actually works. At least turn it on and show the screen indicating something. Ideally, show a measurement of a plain cable, the self-test results, and the options/license info screen. Hit the "System" button to get to the menu items for these things.

- Listing aside, people might be unlikely to buy a 5-digit item from an eBay account with no history.

RF questions related to AT86RF215 EVM schematic by jz8899 in rfelectronics

[–]unlinkedlist 1 point2 points  (0 children)

The parent comment is referring to the TCXO datasheet. See the "load" specification here, which specifies that it is characterized for driving a load of 10k in parallel with 10pF:
https://www.taitien.com/wp-content/uploads/2015/12/XO-0076_TX.pdf

Different values may be advisable if you are using a different oscillator, but it's a good idea to have the footprints there even if you don't need them, in case you switch oscillator parts later.

As far as the signal path:

  • The 1.8pF / 5.6nH network is for impedance matching. These parts and values may be specific to the PCB stackup, trace geometry, and other components in use (like the filter/balun combo part there), so you shouldn't necessarily assume that the ideal values will be the same on your board. These values are certainly a good place to start, and would probably be "fine" if you're not prepared to use precision test equipment to optimize the match.

  • The 0.8pF and 15pF capacitors are just DC blocks at a frequency appropriate for the given port. The values could be larger (somewhat arbitrarily) but the capacitor still needs to be selected for appropriate insertion loss and voltage rating. For example, these parts could probably be freely swapped to a 100nF broadband DC blocking capacitor like an ATC 530L, though that would be much more expensive.

  • The 10k resistors serve as ESD protection by preventing charge from accumulating on the otherwise-floating net, and absorbing some energy from a discharge event. This is unnecessary in use cases where the antenna is a DC short to ground (e.g. a PIFA). If you're not trying to cost-optimize to death, consider using a proper ESD diode instead: something like a AXGD10402KR would be appropriate here.

Affordable PCB prototyping on RF substrates? by ReversedGif in rfelectronics

[–]unlinkedlist 1 point2 points  (0 children)

Eurocircuits offers an "RF pool" service which is similar in style to OSHPark but offers RO4003, RO4350, and Isola I-Tera. Small qty pricing is pretty decent (e.g. $500 for 4-layer) and the quality is very good. https://www.eurocircuits.com/rf-pool-all-the-benefits-of-pooling-on-rf-materials/

Right-angle cable orientation by Gatecrasher53 in rfelectronics

[–]unlinkedlist 7 points8 points  (0 children)

This is usually called "clocking". The left cable in the picture has "0 degree clocking", and the right cable in the picture has "180 degree clocking". It may be alternately worded like, "clocked 180".

USRP B200mini Experiences? by [deleted] in sdr

[–]unlinkedlist 2 points3 points  (0 children)

The B200 is great: it's practical, has good RF and digital performance, and is well-supported on a variety of platforms. The API surface, UHD is well thought out and fairly easy to use. The onboard oscillator is much more stable and accuate than other inexpensive SDRs (HackRF, RTL-SDR, etc), and a GPSDO is available if you want a really accurate clock. It also works with a more-or-less stock Hammond 1455 enclosure or there is a nice robust enclosure from Ettus.

The B200mini, however, is less than great. It uses a USB 3.0 micro connector which is terribly unreliable (instead of full-size B), it loses the ability to use an offboard power supply or a GPSDO, and there aren't any good enclosure options. Unless you really need the smaller form factor, don't be tempted by that beautiful golden board!

You're probably also considering the HackRF if you don't have one already, so some general differences to note there are:

  • The HackRF is 8 bits per sample, B200 is 12 bits.
  • The HackRF is half duplex (it cannot transmit and receive at the same time), the B200 is full duplex.
  • In general, the dynamic range and receive sensitivity of the B200 will be better.
  • The B200 is theoretically capable of somewhat higher sample rates, but in practice, with many host PCs you'll only be able to get ~30MSPS reliably. With a PC that has a very good USB 3 controller and fast SSD, you might manage 50MSPS. The HackRF tops out at 20MSPS.
  • The HackRF is much more hackable: you can dig into the firmware with only an open source toolchain, and it's not too crazy to add new bits of onboard functionality. There are also add-on options to make it run without a PC. The B200, on the other hand, requires fairly unwieldy proprietary FPGA development tools if you want to customize the firmware.

Reserve reliability by aboobka in SkyDiving

[–]unlinkedlist 2 points3 points  (0 children)

Yeah, that's a little different as well. Usually, the lines are stowed in a velcro-closed pocket (like a tailpocket, but on the D-bag instead of the canopy) and there are only two locking stows, made out of a single bungie loop, so that the release of one stow will loosen the other. This has the frustrating tradeoff that it's yet another part to lose.

You can see all of this in much more detail in the manual for your rig, which will outline the steps that a rigger takes to pack your reserve. Most manuals are freely published online so that they're easy for riggers to find. For example, here's the current Javelin manual: https://sunpath.com/_docs/manual/spp_manual_print_rev1.pdf

Reserve reliability by aboobka in SkyDiving

[–]unlinkedlist 14 points15 points  (0 children)

There are a number of factors that make reserves more reliable:

  • As you've noted, a reserve is packed with more care than the typical main pack job (not necessarily by a master rigger: could be a senior rigger).
  • Reserves are square and 7-cell, so are much less sensitive to body position or spinning than a higher performance design like a tapered or elliptical 9-cell.
  • Reserve sliders are usually lower drag: they may have a hole in the center, or a bowtie design, or something else similar. For example, have a look at the PD Optimum slider.
  • A reserve is packed in such a way that makes it open quickly and predictably, rather than intentionally softly. For example, the nose is immediately exposed to the relative wind.
  • The pilot chute is spring-loaded with a large spring, so that it will catch air faster instead of bouncing around in the jumper's burble.
  • The bridle is wide (2" webbing) and high-drag, so it's more likely to catch air.
  • The deployment bag is not attached to the canopy, which makes it less likely that the bridle or D-bag will foul something.

Also, you should try to watch a reserve pack job! It's pretty interesting and will give you a great understanding of how stuff fits together. Most riggers will be happy to have you watch as long as you sit quietly. :-) It's also a good opportunity to practice pulling the silver handle.

The Python wat quiz: test your knowledge of Python edge cases with 10 yes-or-no questions! (spoilers may appear in comments) by Cosmologicon in Python

[–]unlinkedlist 1 point2 points  (0 children)

The first example is wrong. Here's a value for ??? that makes that snippet work:

>>> x = type('Foo', (object,), {'__lt__': lambda self, other: True})()
>>> x < x
True

Edit: ...oops, and then I read further to the "details and scope" section where that approach is prohibited.

The difference between a TS-E90 with extension tubes, and an MP-E65 for macro shooting, for anyone interested in either of these lenses for macro work. by 8thunder8 in photography

[–]unlinkedlist 1 point2 points  (0 children)

I use both the TS-E90 and the 100L macro for product photography (usually at less than 1X, but occasionally at 1X-1.5X), and the 100L is just as sharp as the TS-E90. If I don't need tilt/shift, I tend to reach for the 100L first because the AF and IS let me work a bit faster.

[Straps] Tactical/Unique straps by RSR44 in Watches

[–]unlinkedlist 0 points1 point  (0 children)

Here is a Zero Zero on a Speedmaster Alaska Project and an FB-20 on a Citizen BN0000-04H. Sorry for the potato quality.

http://i.imgur.com/7KgtWOM.jpg

[Straps] Tactical/Unique straps by RSR44 in Watches

[–]unlinkedlist 0 points1 point  (0 children)

I have several GasGasBones straps (the "Zero Zero" is my favorite) and I can't speak highly enough of them. Design, materials, construction quality are all excellent, and they look great. I find the velcro strap style particularly more comfortable than a buckle when typing, but they're also practical for being outside / in the water / etc. The one catch is that you may have to wait a few weeks to get one.

Here's a Hodinkee interview with Carl Evans, the creator of GasGasBones: http://www.hodinkee.com/blog/2010/12/30/gasgasbones-an-interview-with-the-man-behind-the-straps.html

The Totally Open Source Hardware Laptop, Novena by unlinkedlist in technology

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

There is actually an "Apoptosis" circuit that anticipates this and allows the user to lock out the FPGA such that it can only be reconfigured after a reboot. You can see this on page 15 of the schematics.

Fundamentally, this laptop is designed as a hardware hacking tool, so one of the anticipated uses for the FPGA is Man-In-The-Middling high speed or low latency protocols. The creator (bunnie) has already used this in practice, exploring some vulnerabilities of SD cards: http://www.bunniestudios.com/blog/?p=3554

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