PersonFromPorlock posted:

I have a small collection of old TVs and most have no input besides over-the-air VHF. I have an old Ramsey TVC6 kit (three, actually) that's swamped out by WiFi when the transmission antenna is more than a couple feet from the receiving antenna.

How can I magnify its signal the circuit (shown here: http://www.allspectrum.com/ramsey/TV6C/TV6.pdf ) to be stronger than the local WiFi? I've already been told to remove resistor r12 and replace it with nothing but a straight wire and replace the caps with NPO caps. What else? How can I change this circuit to broadcast over the Band III VHF channels, 7-13? It currently only does Band I, channels 2-6.

There's no risk of interfering with anyone else's WiFi -- I can't pick up any at even a weak signal here besides my own.

As asked in the other thread, it's in an unshielded, ungrounded plastic box.

csammis posted:

Also, are you sure that it’s your WiFi swamping the TV broadcast signal? I’m not an RF wizard but the North America VHF TV frequencies (60MHz for channel 3 I think) are nowhere near 2.4GHz or 5GHz that’s used for WiFi. 2.4GHz is like the 40th harmonic of 60MHz. Have you turned off your WiFi to see if that’s the problem?

Forseti posted:

But anyway, I don't doubt the WiFi is affecting you I just think it's affecting the transmitter rather than the TVs. The TV antenna is unlikely to have a good response at 2.4GHz, the whole point of the antenna and tuner is to selectively pick out a narrowish band of frequencies. The antenna and tuner should be greatly reducing (attenuating is the fancy official word) the signal for all other parts of the spectrum than the part you care about, which is the channel you have selected.

Likewise for the sending antenna on the unit. So my suspicion is the the WiFi is being picked up further up the chain in the the circuitry of the Ramsey unit and ending up as noise in its output e.g. it could be adding noise to your power lines.

I did eventually find some pictures of it and it does look like it's in a box, but I couldn't tell if it's a shielded box (metal) or not. If it's not already metal you could try wrapping the box in foil as a crude test shield. It'll work best if the foil also is grounded which could be done by simply making sure it touches the threads on the output coax or whatever.

Ambrose Burnside posted:

just copper tape doubled back on itself with a grounded wire lead wrapped around the midsection, and with a crude hook/loop clasp made from some scrap wire in my brass bin. screwed with the hook geometry to fine-tune the fit and keep it snug and in contact with my skin. looks like rear end but not bad for a 5-minute cobbled-together replacement

PersonFromPorlock posted:

Removing r12 was just something I was told, on Instructables I think. The reason I think it's the WiFi is the picture gets better the further from it I get and is swamped-out entirely within a few feet.

Ambrose Burnside posted:

building a computer but I let someone borrow my ESD bracelet. never fear



just copper tape doubled back on itself with a grounded wire lead wrapped around the midsection, and with a crude hook/loop clasp made from some scrap wire in my brass bin. screwed with the hook geometry to fine-tune the fit and keep it snug and in contact with my skin. looks like rear end but not bad for a 5-minute cobbled-together replacement

Foxfire_ posted:

That's not actually how a (correct) ESD wriststrap is wired. There should be a ~1Mohm resistor between the part connected to you and ground. It provides a path for charge to drain, but makes there not be a low-impedance path through you if you touch something live. Fine for touching computer parts while its off though.

Shame Boy posted:

Shame Boy posted:

Actually, while we're talking about this circuit can I point out how weird it is they used a 7808 with two diodes to get 9V and not just... a 7809? Is there a reason for that or did they just buy a million 7808's by mistake and had nothing to do with them?

Stack Machine posted:

What are you powering this thing with? Does it work better with a 12V battery installed very close to the board instead? I'm wondering if your wi-fi interference is at least partially conducted EMI through your supply.

PersonFromPorlock posted:

The great big transformer that came with it. I don't know why it has to be so large, but it is.

Foxfire_ posted:

That's not actually how a (correct) ESD wriststrap is wired. There should be a ~1Mohm resistor between the part connected to you and ground. It provides a path for charge to drain, but makes there not be a low-impedance path through you if you touch something live. Fine for touching computer parts while its off though.

Ambrose Burnside posted:

whoops, good catch, thanks


in other news, here's the first of two planned 1ohm/5w ballast resistors for my 3d printer resin vat heater, think it came out ok





i used half-round copper jeweller's wire as both electrical buses and thermal bridges, the idea was for the round part of the wire to contact the ceramic resistor casings and for the flat side to act as a nice big pad against the tank side. the resistors don't actually contact the buses well so the thermal aspect probably won't work well, but they're sitting on a thermal pad so it shouldn't matter. if i stick with these long-term I think i'll pot them in metal-filled epoxy with the bus wire flats exposed on the bottom for the best thermal performance.

Shame Boy posted:

Not sure if metal-filled epoxy would short it out or not, I've never actually used it, but might wanna test first to be sure. Also you probably know this but you can get specific thermally conductive / electrically insulating epoxy, I use it to glue small heatsinks to things sometimes.

Ambrose Burnside posted:

whoops, good catch, thanks


in other news, here's the first of two planned 1ohm/5w ballast resistors for my 3d printer resin vat heater, think it came out ok (please do not scrutinize the solder joins they're not my finest work)





i used half-round copper jeweller's wire as both electrical buses and thermal bridges, the idea was for the round part of the wire to contact the ceramic resistor casings and for the flat side to act as a nice big pad against the tank side. the resistors don't actually contact the buses well so the thermal aspect probably won't work well, but they're sitting on a thermal pad so it shouldn't matter. if i stick with these long-term I think i'll pot them in metal-filled epoxy with the bus wire flats exposed on the bottom for the best thermal performance

Cojawfee posted:

Thinking back on the things you've posted, you really have the most appropriate avatar in this thread. Everything you make looks like it should be a museum exhibit of electronics from the 1800s. I don't mean this in a bad way.

Stabby McDamage posted:

Hey, thread. I've got a really weird motor thing and I'm not quite sure what its deal is. I got a few of these from a factory surplus shop a few years ago, and immediately chalked them up to "DC brushed motor with a wheel", but now that I finally get one out for a project, its actually weirder. Two capacitor-like things are soldered to the power wires. One is from motor + and - (decoupling, sure, no problem), but one of them is in series with the ground wire by means of the motor chassis (what??).

Stabby McDamage posted:

EDIT: if anyone cares, the project is this trillion-to-one gearbox I'm building as an art project.

ante posted:

Yeah, that series thing is for sure a PTC

Shame Boy posted:

Oh, going by the picture I figured you were building this thing:

https://www.youtube.com/watch?v=72C_4L8Vu2o

Forseti posted:

Pretty cool, similar idea to this thing that LOOK MUM NO COMPUTER just built

https://www.youtube.com/watch?v=xu9Wid465o8

Stabby McDamage posted:

That makes a lot more sense. Now I gotta figure out why it slowed down. Maybe I overvolted it? Oh well, now I have stuff to go on. Thanks!

Stabby McDamage posted:

It has that effect, just over the course of between 5 minutes to 10000 years, depending on where in the gears you put the thing. It's designed so that continuous input rotation at like 300 rpm for a century yields about a degree turn on the output. I'm going to redesign the faux marble plate on the output side to have a "gear" as part of its geometry that physically can't spin, and yet you'll never get to see it break in your lifetime.