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 Post subject: Chinese RF modulator for TV
PostPosted: Jan Mon 08, 2018 8:50 pm 
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Location: Durham, NC
I saw these things on eBay https://www.ebay.com/itm/High-Performan ... 1468255587 and wondered if anyone has tried one of them? It's hard to beat the price for an "agile" modulator if they work at all.

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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 08, 2018 9:07 pm 
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For $21 it might be worth a try, they are much more compact than the BT modulators.

The Output Level: 80-95dBuV

Is that sufficient?


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 08, 2018 9:34 pm 
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IIRC, 90dBuV is about 30mV, which is typical of analog TV tuners. Tube type tuners might need a skosh more.

But then, I have 100 or so TV signal boosters in my collection, so that signal level should be OK for my purposes!

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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 08, 2018 10:56 pm 
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Joined: May Sun 07, 2017 11:35 am
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That does look very good. Looks like you can set it for any analog standard, including UK and Europe as well as USA.

Someone is obviously flogging these off as demand for analog CATV gear has fallen through the floor.

I hope Gupta's law doesn't apply!


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 12:10 am 
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How's it gonna work in the U.S.?
Quote:
Input: AC230V, 50Hz

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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 12:27 am 
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fifties wrote:
How's it gonna work in the U.S.?
Quote:
Input: AC230V, 50Hz


The US model should work fine.


Attachments:
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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 12:32 am 
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Location: Woodinville, WA USA
Now all we need is a volunteer to buy one and set up a "Pepsi challenge" to compare its performance to one of the popular Blonder-Tongue agile modulators.

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 1:26 am 
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Location: Buffalo, NY
Why not just use a modulator from an old VCR?
Granted, it would only be channel 3 or 4 out, but it is analog.
Could easily be put inside a little project box.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 2:07 am 
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VCR modulators will work but they are not as good as a "professional" modulator for a variety of reasons I have explored in another post.
No modulator is going to strip the VBI content (Macrovision &c) for you.
Don't worry about this one working in the US though, the power supply is universal switched mode. It will quite happily run on 110v volts as well as 220v.

No, I have no connection, it just looks like a good deal to me.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 2:57 am 
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I don't think a VCR puts out enough to use as a transmitter.

I looked up the specs for a BT AM-550 and it's output is 60 dBmV so this $21 modulator is more powerful, at least on paper.

I think I'll get one and see how it works, tough choice between blue and orange though. :lol:


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 3:04 am 
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Hmm, before I buy one what is RHF? (RHF UHF) do you think they meant VHF? and is this thing going to output something an NTSC TV can use?

Edit: never mind, it says VHF in the Specs, must be a translation issue in the description.

Anyway I ordered one, it's $20 so I'm not going to be homeless if it's useless and I toss it in the trash.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Tue 09, 2018 9:35 pm 
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Location: Pewaukee, WI
Eric H wrote:
For $21 it might be worth a try, they are much more compact than the BT modulators.

The Output Level: 80-95dBuV

Is that sufficient?


Eric H wrote:
I don't think a VCR puts out enough to use as a transmitter.

I looked up the specs for a BT AM-550 and it's output is 60 dBmV so this $21 modulator is more powerful, at least on paper.

I think I'll get one and see how it works, tough choice between blue and orange though. :lol:

95dBuV is less than 60dBmV....It should be plenty for a wired connection, but for folks like me that prefer wireless (wireless is cheaper/easier for a large TV collection), it will not be enough to transmit.

One option would be a power amplifier on the output. Some time ago I rigged up an MC44BS373CA based modulator (taken from a junk sat box) that has an 82 dBuA output and feed it into an external power amplifier (Cougar Components AC573)...It was no Blonder Tongue, but it could transmit far enough to be usefull.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Thu 11, 2018 3:12 am 
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Location: Buffalo, NY
something tells me not to consider a $21 device from china as "professional". But hey, knock yourself out if it floats ur boat.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Thu 11, 2018 5:28 am 
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majortom wrote:
something tells me not to consider a $21 device from china as "professional". But hey, knock yourself out if it floats ur boat.



It's probably more likely to catch fire than the Blonder Tongue. :lol:


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Thu 25, 2018 12:37 am 
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Location: Bloomington, IL USA
Did anyone buy one of these? Mine just arrived and i can't figure which settings to use. The instructions are bad and make no reference to US channels.
Has anyone got their's working?
Thanks
Joe


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Thu 25, 2018 4:47 am 
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I suspect it wouldn't talk about US channels, they are not unique and this seems to be aimed at a world market.

Does it tell you how to select vision carrier frequency and sound subcarrier frequency? You just need a list of US channel frequencies, from the net....
Your sound subcarrier is 4.5MHz above the vision carrier. Modulation is FM. Pre-emphasis is 75uS. Vision modulation is negative.

If you see any settings in the sound part like Zweiton or Nicam, don't select them.

That should be enough....

Can you post a copy of the instructions? I'm good at interpreting Chinglish.


Last edited by irob2345 on Jan Thu 25, 2018 10:04 pm, edited 1 time in total.

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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Thu 25, 2018 8:57 pm 
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I thought I ordered one but must have forgot to click the final button because it doesn't show up in my orders, just as well. 8)


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 29, 2018 4:28 pm 
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Joined: Aug Tue 29, 2006 4:09 am
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Location: Racine, Wisconsin
Well....I bought one, and received it within 10 days. Even though I specified the US (120V) plug, it powers up as an EU device, incompatible with anything. (when the unit is first plugged in, it displays EU for about 5 seconds) Scrolling through CH+, CH- indicates channels with an "S", and/or begins with CH21 as shown in the Euro chart in the manual. Dealing with the seller has been annoying at best. They want pictures....I send them pictures, then they tell me that they can't open the attachments. They want an explanation of the "failure" ....I explain that it powers up as an EU device "they" don't understand what I'm talking about. As previously mentioned, the manual only references European channel/frequency assignments, and under the specifications chart....only references 230 VAC.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 29, 2018 4:36 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Bloomington, IL USA
At least you are getting a response. They are ignoring my emails.


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 Post subject: Re: Chinese RF modulator for TV
PostPosted: Jan Mon 29, 2018 4:49 pm 
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Joined: Aug Tue 29, 2006 4:09 am
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Location: Racine, Wisconsin
Can you go through eBay and request a refund?


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