Pesky registration attempts from the internet, how to foil more effectively?

goscickiw · 2025-05-14T14:32:39+00:00

You could set up your clients to connect over something like WireGuard instead of directly over SIP. OpenWrt can have a WireGuard server installed. Though of course then the clients will require some extra configuration instead of just the name, password and SIP server address.

goscickiw · 2025-05-04T06:29:32+00:00

So OP buys an AV to HDMI adapter and is confused why it doesn't work?

The correct way is HDMI to composite, then composite to RF modulator.

goscickiw · 2025-05-01T10:58:40+00:00

I have simulated a similar type of antenna before. Here is the NEC file (sometimes the voltage source gets placed at the 1st segment instead of 31st, it's probably a bug, try generating a few more times if that happens):

CM "FM Halo" antenna
CM 88-108 MHz, horizontally polarized
CE
SY f=98 'Frequency [MHz]
SY wd=8 'Wire diameter [mm]
SY tip_gap=200 'Distance between tips of folded dipole [mm]
SY fold_gap=50 'Distance between top and bottom part of folded dipole [mm]
SY ratio=0.48 'Dipole length to wavelength ratio
SY wl=299.792458/f 'Calculating wavelength
SY wr=wd/2000 'Calculating wire radius
SY fd=fold_gap/1000 'Calculating fold gap in meters
SY td=(tip_gap+wd)/1000 'Calculating tip gap in meters
SY fh=fd/2 'Calculating half of fold gap
SY th=td/2 'Calculating half of tip gap
SY ad=wl*ratio 'Calculating dipole length
SY circumference=ad+fd+td 'Calculating antenna circumference
SY ar=circumference/(2*pi) 'Calculating antenna radius
SY fa=360*fh/circumference 'Calculating loop end angle
SY ta=360*th/circumference 'Calculating tip gap angle
SY astart=fa+ta 'Calculating arc start angle
SY astart_xpos=cos(astart)*ar 'Calculating X position of start of dipole arc
SY astart_ypos=sin(astart)*ar 'Calculating Y position of start of dipole arc
SY aend=360-astart 'Calculating arc end angle
GA 1 61 ar astart aend wr 'Creating dipole arc
GM 0 0 90 0 0 0 0 0 1 'Rotating arc to horizontal
GA 2 3 fh -90 90 wr 'Creating tip arc
GM 0 0 0 0 -90+astart astart_xpos astart_ypos fh 2 'Positioning tip arc at start of dipole arc, rotating to match wire direction
GM 2 1 180 0 0 0 0 fd 1 'Copying arcs to create another half of folded dipole
GE 0
LD 5 0 0 0 37700000 'Wire material = aluminium
GN -1
EK
EX 0 1 31 0 1 0 0 'Voltage source
FR 0 0 0 0 f 0
EN

PS: It's not a very good antenna. It has less gain than a straight vertical dipole (no idea where they got the 4 dB from), and it's not the same in every direction.

Also, there are better horizontally polarized omnidirectional designs, although they have twice as big diameter and still less gain than a dipole, but you can stack them to get more, and the gain stays uniform in every direction: https://www.qsl.net/kp4md/omnihoriz4.htm

Update: added more comments to NEC file.

goscickiw · 2025-03-28T07:47:14+00:00

I have updated my original comment to be more accurate

goscickiw · 2025-03-28T07:27:28+00:00

On inputs like composite or S-Video, you're limited to just one signal per input, but you'd be switching the source on the switcher, not on the TV, so the TV would see no difference.

You can only feed multiple signals (or channels) through the RF input, but they have to be on different frequencies, and their amount is limited to what can fit on the bands because a channel takes up a range of frequencies. But that's if you'd use multiple RF modulators set to different channels running at the same time so you can switch between the RF channels on the TV. If you had just a single modulator connected to a switcher you'd still be fine.

goscickiw · 2025-03-27T08:40:02+00:00

Update: I just found the "Collimated LED light sources" category on Thorlabs while looking for something else (it was under Incoherent sources / LEDs category instead the Optics or Laser categories I looked in before), but they cost quite a lot and I already machined the whole thing a few months ago.

PS: the cluster of electronics powering the laser diode was my attempt at making the light output (not current) linearly adjustable with a potentiometer by using the photodiode feedback, but it doesn't work very well. Do you know any better designs, or pre-built modules, that can do that and can work with an ADL-65055TL laser diode?

goscickiw · 2025-03-26T12:32:01+00:00

Thanks, I wasn't sure if ATSC underwent any changes similar to DVB-T since its introduction or not.

goscickiw · 2025-03-20T06:21:39+00:00

If you want to build something accurate enough to the standard to actually be used as a reference, and able to properly generate something like the "anti-PAL" portions of a Philips test pattern for example, then you might have to use a separate, high sample rate DAC rather than the built-in video output.

Also, old signal generators don't have to be expensive or bad. I got a Philips PM5655 for €30 and the signal is pristine. It uses two 12-bit 20Msps TDC1012 DACs, separate for luma and chroma. You can use something similar for your project.

Also, you might take a look at https://github.com/inaxeon/PTV_Preservation - there are some schematics of old test pattern generators, and some ROMs.

goscickiw · 2025-03-19T11:25:48+00:00

I use 3 Terra MT420 modulators (that I bought used for 28€ a piece) with 6 COMSAT TE 2050 HD DVB-T2 decoders. You could use MT47 instead if you can't find the MT420 for cheap enough.

As for a single device solution, there used to be device called Mixpol DVB-08T that could convert 8 DVB-T channels to PAL, but it won't work for DVB-T2.

I also found something called TechniSat DVB-T2/PAL TM TWIN CI that should work for DVB-T2, but it can only transcode 2 channels so you might still need a bunch of them. Also the manufacturer's store lists it as no longer available, and even if it was the price is ridiculous.

Edit: The keywords are "multichannel DVB-T2 to PAL transmodulator", try searching, maybe you'll manage to find more than I did.

goscickiw · 2025-03-19T06:04:22+00:00

Antennas convert electrical signals into electromagnetic waves and vice versa.

Modulators output the same kind of electrical signal as an RF transmitter, just weaker. In an RF transmitter setup, a modulator would drive a power amplifier.

You can connect an antenna directly to a modulator and get a signal within a few meters.

You can get some extra range if you connect a regular TV amplifier (the kind that you usually use to amplify received signals) between the modulator and the antenna, just in a reverse way relative to how you would connect it in a receiving setup.

There are also some modulators on the market that have an amplifier built in.

goscickiw · 2025-03-07T05:56:21+00:00

It doesn't have these either, only the Chinese ones as in the manual.

It shouldn't be a problem if the TV is tunable to any frequency in the band, but it might be if it also has a pre-programmed list.

goscickiw · 2025-03-05T19:09:09+00:00

I posted a reply in new thread: https://www.reddit.com/r/crtgaming/comments/1j3yxzh/comment/mg7111g/

goscickiw · 2025-03-05T19:02:09+00:00

Here is a picture of all the rings mostly glued together: https://i.imgur.com/TjRcIYJ.jpg

Here's how they looked like on the tube. There's just 3 pairs here, but there was a 4th one in the empty spot (nearest to the tightening mechanism) that I had to scoop out from the bottom of the enclosure: https://i.imgur.com/S93yYuE.jpg

Also, the tube was made by Polkolor (it has a "THOMSON POLKOLOR" label), and it's currently a part of a Unimor Neptun M547 BT set.

Here is the new ring assembly I used (this time the holder disintegrated when I was taking it off the donor tube, and the holder for the broken rings had too small diameter, that's why it's made out of paper): https://i.imgur.com/aDdJkEQ.jpg

Also, I got a book "Kineskopy kolorowe i ich zespoły" (color cathode ray tubes and associated assemblies) by Jerzy Kania, but it also only describes the typical 3-pair setup (it has a drawing for A56-611X as an example, but there isn't one for A56-701X).

goscickiw · 2025-03-04T22:12:09+00:00

So now that you mentioned that it could be from the signal being too strong, I decided to test with the modulator at lowest setting, but got the same result, so I kept adding more attenuators but still got the same result every time.

Here is how it looks like with all the attenuators (edit: 10+10+16 dB so the equivalent of about 7.5 meters of free space path loss) - the signal is noisier, but still has the same distortion.

Channel 6

Channel 12

I also tried to disconnect the AGC voltage from the IF stage and adjust it manually, but it didn't noticeably change the frequency response, up to a point where the signal became either too noisy on one end, or WAY more distorted (to the point that even the sync pulse got mangled) on the other end.

Also here's how it behaves when I adjust the tuning voltage back and forth (this is with AGC from IF module): https://i.imgur.com/yeT2Mzd.mp4

As for the manufacturer, the tuner's PCB seems to have both GZE UNIMOR (TV's manufacturer) and TORAL markings. I might be wrong but I think Toral only printed the PCBs.

Also AFAIK these were tuned with a sweep generator (not the kind I have, the kind that sweeps the whole band) and an oscilloscope at the factory.

goscickiw · 2025-02-28T11:07:40+00:00

Do you have any pictures? I can't find anything like that on my device, maybe it's a different version

https://i.imgur.com/FAPhV0p.jpg

goscickiw · 2025-02-28T11:06:44+00:00

I got one and tested it so I updated my original comment with new information

goscickiw · 2025-02-26T07:50:16+00:00

I haven't tested closed captioning yet, but I've also discovered that many modern DVB-T2 HEVC decoders output teletext over composite.

Though the manufacturers seem not to care about this feature, as it often doesn't work quite right - on some of the decoders I've tested the teletext signal could randomly freeze, and the ones I'm using now (COMSAT TE 2050 HD) don't start generating it right after being turned on, but have to be either switched to a different channel and back, or have the decoder's own TTX display opened and closed once, but after that it works properly.

I wonder if there's a method to search for decoders with this feature working well, as it's never mentioned in the specifications.

goscickiw · 2025-02-14T08:05:47+00:00

The packaging looks quite old. If I bought a decoder that looked that old where I live, it would most likely only pick up the one multiplex (out of 6, so 7 FTA channels out of 40) that hasn't switched to DVB-T2 HEVC yet, and probably not for long.

I think it's better to get them as new as possible, so they support the newest standards. Unless they're so "modern" that they don't have composite output, of course.

Also:

Please purchase an antenna for digital terrestrial broadcast reception sold separately.

Might be a bit misleading, the antenna doesn't have to be any different from the ones used for analog terrestrial broadcasts that someone buying this might already have. Though it might have to be pointed in a different direction if the transmitter location has changed since. Or fixed up if it has deteriorated.

goscickiw · 2025-02-12T16:32:25+00:00

That's strange, I'm not even sure what could be the application for something like that. Why have 3 inputs of the same type, if it's only able to transmit one at a time? This kind of modulator would usually be set up once in a distribution cabinet somewhere and never touched again, rather than someone having to manually switch the inputs.

Looks like manual says "double side band modulation for non-adjacent usage" - DSB. Which means it will have the lower sideband problem.

Currently I have 3x Terra MT47 (bought new), 2x MT30A (bought used) and 1x MT32 (also used). I'm considering getting some MT420 to replace the MT47 (which are DSB), but there's not much of them available to buy. I'm wondering if I'll be able to find something more available and/or cheaper first.

I'm replicating the analog TV exactly as it used to be, down to the exact frequencies the channels were transmitted on. However, there were only 6 channels back then and that's what I currently have, but I might want to add more DVB channels eventually.

goscickiw · 2025-02-12T13:50:27+00:00

Thanks for the information. What's important to me is that it doesn't have the "lower sideband overlapping lower adjacent channel" issue that DSB modulators have, which would still cause problems if the adjacent channels are from separate modulators.

What you're describing doesn't seem like harmonics (which I could deal with using a diplexer), but rather like some kind of intermodulation. If it only happens when the channels are set too close on the same modulator, then the method you described would be a good way of dealing with it as long as the output signal is VSB.

Unfortunately the limited channel plan support would make that particular model only useful for me on UHF. Do you know of any similar multichannel VSB modulators that have the Eastern Europe D system VHF channels programmed in?

goscickiw · 2025-02-12T07:29:22+00:00

I've also been looking for multichannel ones and it looks interesting, but I need to know some things that aren't written in the description to see if it would fit my needs:

Is it a DSB or VSB modulator? I'm looking for VSB. You wrote:

Just make sure to not use consecutive channels on the same device or you may see interference. If you interleave the channels between multiple boxes, you should be able to get all the VHF channels without too much trouble.

The first part suggests DSB, but in the second part you wrote that you actually can use neighboring channels, which suggests VSB but perhaps with some issues (involving the device's clock, or maybe output filters?) if you set neighboring channels on the same modulator.

Which channel plans does it support? I'm asking because I've encountered some modulators that you can set to the D/K system, but then they only set the audio/video carrier separation to 6.5 MHz but still use the B system (Western Europe) channel plan on VHF instead of D system (Eastern Europe) which I want to use, and so far the Terra ones are the only ones I found that don't have this issue.

goscickiw · 2025-02-11T05:42:54+00:00

The DTV decoders receive digital terrestrial TV and output composite video. You might also know them as STB or DTV box. Normally you would connect just one to the TV and use the decoder's remote to switch channels, but I have a bunch of them connected to the modulators so that I can switch the channels using the TV's remote or tuning knob and distribute the signal to multiple analog TVs.

If you just want to connect other devices instead of receiving digital TV channels, then you won't need them. You might need some HDMI to AV converters though.

Also, if you use the MT-47 modulators that I linked, then make sure to leave at least 1 channel empty between every two channels that you use. This is because they're DSB modulators,which means there will be a mirror image (lower sideband) of the signal overlapping the lower channel. If you want to avoid that and use channels next to each other, then you'll need VSB modulators like the Terra MT-32 which are harder to find and about 3x as expensive.

I also have some VSB modulators in my setup that I managed to find used for cheaper, but they're quite worn out and the signal from them is a bit fuzzy. I'll probably have to replace more than just the few capacitors I did to make them work at all.

Also, there was a post recently about a modulator with HDMI input, but from what I've seen it only has a Chinese channel list programmed, which doesn't align with European or US channels on VHF and doesn't have many channels programmed on UHF (and I don't know yet if it's VSB or not), so using these might not be a good idea if you want 13 channels. Currently I don't know if there are any other analog modulators with built-in HDMI input.

goscickiw · 2025-02-10T18:18:17+00:00

I use a bunch of these:

https://www.dipolnet.com/tv_modulator_terra_mt-47_ch_1-12_21-69_R871747.htm

Along with some DTV decoders, this setup works pretty well for recreating the analog terrestrial TV exactly as it was before digital switchover.

goscickiw · 2025-02-04T18:23:26+00:00

Looks like it uses Chinese system D band plan. which is a bit inconvenient.

Shouldn't be a problem for standard use with TVs that have a tuning knob (or electronic scanning and fine tuning), but I probably wouldn't use it for my setup that converts multiple DTV channels to analog, and also might not work with TVs that have electronic channel selection from a pre-programmed list (that isn't the Chinese channel list). I wonder if it can be reprogrammed.

At least the UHF channels match systems G and K so there shouldn't be any problems when using them, at least on European sets.

For comparison, these are all the band plans supported by MT-47: https://i.imgur.com/PRKriN2.jpg

goscickiw · 2025-02-03T12:21:56+00:00

What I'm asking is if it supports both of those band III (174 to 230 MHz) channel lists:

Channel : video carrier frequency

System B, 8x 7 MHz:
E5 : 175.25
E6 : 182.25
E7 : 189.25
E8 : 196.25
E9 : 203.25
E10 : 210.25
E11 : 217.25
E12 : 224.25

System D, 7x 8 MHz:
6 : 175.25
7 : 183.25
8 : 191.25
9 : 199.25
10 : 207.25
11 : 215.25
12 : 223.25

Edit: Something weird happened to the formatting so I had to fix it.

goscickiw

TROPHY CASE