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 Post subject: can i amplify an rf out on a TV box?
PostPosted: May Thu 14, 2020 9:42 pm 
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i have several older TVS and lately i have had to move a bunch of them, i normally have 6 or 7 hooked up at once and all on at the same time...(this may be weird but even though i am not actively watching them i just enjoy having them on), i have a converter box but dont really use it as i have a cable box with an RF out on it which outputs to channel 3, i have had to string splitters and matching transformers around my room and it always ends up having an issue in one cable that makes everything not work. i was wondering if there was an easy way to amplify the analog output to channel 3 from the box... i only need it to work about 50-75 feet. i have seen people who have old transmitters or something anfd have alot of heavy equipment and broadcast stations to the entire neighborhood likely, i dont want to have a bunch of heavy and expensive equipment.

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Thu 14, 2020 11:26 pm 
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Location: Pewaukee, WI
Most cable boxes, consumer RF modulators etc don't have enough power for most amps to get them to adaquate short distance wireless transmission power.

Does your cable box have composite video and audio output? If so all you need is a Blonder Tongue AM40 (weakest output), AM60 (strongest output) or BAVMz(medium output smallest device) series professional RF modulator...they used to be used in analog cable and hotel cable systems, but now are cheap second hand. You will need a transmission antenna too...you can make one with an old RF jack and some lamp cord (shango66 has a good YouTube video on this). If not then get a VCR to tune your cable box RF and use the VCRs composite video and audio output to feed your Blonder Tongue. Another route if your cable box has HDMI is to get a HDMI to composite AV converter and feed that to the Blonder Tongue.

My AM60 with a tuned dipole covers a solid block radius at max power. My AM40 and BAVMz series easily cover my entire house and yard and can approach a block radius under ideal configuration.

The BAVMz is the thickness of 2 VHS tapes about 4" deep and about 17" wide (it's a 1 rack unit device if you are familiar with rack units). The AM series units are both the same as the BAVMz only they are about 16" deep. The AM series are agile modulators meaning you can set them to any VHF channel (some will do cable and UHF if the last 3 digits of the model corresponding to max frequency are high enough). The BAVMZ are fixed channel and only do the one channel they were built for....so make sure there are not any strong potentially interfering DTV carriers on the channel of any BAVMz modulator you buy and don't buy one set to a lettered channel number (I believe those are cable TV specific channels).

Many Blonder Tongue modulators you find used for $20 on eBay have bad Electrolytic capacitors (despite being newer solid state devices) so sometimes you gotta spend $10 in caps to fix what you get.

I have around 100 pre-1970 TV sets scattered around 3 floors of my house and have found transmitting with the Blonder Tongues is easier and often performs better than wired RF from VCRs and the like.

There's lots of threads here and on videokarma.org about using Blonder Tongue modulators to transmit. Phill's old radios website has a good page explaining this too.


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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Fri 15, 2020 1:32 am 
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Location: Ann Arbor, MI
If you want to use the wired approach, channelmaster makes distribution amplifiers with multiple outputs. They have them with as many as 8 outputs. The outputs are isolated from each other so you can mess up the wiring on one without affecting the others.
There are also signal splitters available that provide some isolation between outputs. But with each split you get less signal. If you split the output of an amplifier you can afford to loose some signal strength.
Go to http://www.channelmaster.com and look around and see what is available. You may be able to find used equipment for sale once you have an idea what you want.

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Fri 15, 2020 4:40 am 
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Location: Norfolk, VA
If you do go with an Agile Modulator, make sure you don't get one of the upstream BT models with fixed ("T") sub-band channels. These were typically used to send a signal upstream to a cable company, for a local cable production, school channel, or some other purpose. They were plentiful on eBay after 2009, when localities dumped them by the dozens.

I had several friends get these from eBay or Public Surplus, only to find they don't work for consumer use. It says agile right on the unit, but is fixed frequency, and unusable.

Here's one example: https://www.ebay.com/itm/362638831774

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"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Fri 15, 2020 10:08 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Woodinville, WA USA
This article explains how to use a Blonder-Tongue agile modulator to transmit TV signals within your house:

https://antiqueradio.org/HomeTVTransmitter.htm

Regards,

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


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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 4:15 am 
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thanks, i will probably get one soon as right now none of my TVs are hooked up and i am batteling the cable company because they only want to give me a box with HDMI, and i know they have older ones with coax out because my friendwho signed up for the same company less than 2 weeks ago got one of their older boxes, but that is another story. thanks for the info

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 7:40 am 
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At one point, I wanted to use one of those Blonder Tongue for over-air use, and Amplify it (30dB), but the good ole' FC of C would probably get wind of it. Maybe not, since analog is not a 'Useful' thing anymore.

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 8:16 am 
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Location: Belrose, NSW, Australia
You wpuld probably have radiated some harmonics that interfered with some essential service mobile service and it would be THAT that would get you into trouble.

Band 1 in Sydney just has noise now, no-one is using it. But if you radiated in that band in the way you suggest, you'd likely generate a 1st harmonic that would fall in the aeronautical VHF band. THEN there would be trouble!!

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 8:32 am 
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True, the only way the FCC is going to know if your broadcasting it and is interfering with Mobile Cell Service (unless they are constantly scanning the waves, which they probably are not Maybe).

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Electronics are filled with smoke. It’s my job to put the smoke back in when they fail.


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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 8:43 am 
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Joined: May Sun 07, 2017 11:35 am
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Location: Belrose, NSW, Australia
I guess it depends on how far from civilisation you live. If you lived on a farm, in a river valley, miles from anywhere, I doubt anyone would know or care.

You DO need to be careful about the air band though. Every pilot is a potential snitch because they monitor the band for EPIRBs! And you'd better believe me, they get very snaky about ANYONE impinging on THEIR frequencies. It's a safety issue.

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 5:51 pm 
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One thing to keep in mind is that there could be a TV station broadcasting on channel 3. For quite awhile there was nothing on channels 2-6. But now that stations are being repacked, some stations are being shoved down there. And there is one station in the Detroit area that was moved to channel 3. Now if you have an agile modulator you can set it to output on any channel you want.
Note that with digital broadcasting the channel that a TV station shows up as is hardly ever the RF channel that they are broadcasting on. To find out what is what, go to www.rabbitears.info. Chose the 'Signal Search Map' and enter your zip code. You will get a list showing both the advertised and RF channel numbers.

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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sat 16, 2020 8:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Phoenix, Arizona
Look for a Drake VMM860AS modulator. We were using these to feed Analog TV translators before the digital transition.

It is a small self contained module that will transmit on any TV channel broadcast and cable bands. Takes audio and NTSC video in, puts RF out. Has LED's for level adjust.

They run on 12 volts and Drake had a matching power supply.

Drake also had a matching DTV receiver we paired up with the modulator to convert our Digital Companion signal to NTSC and feed the translator PA directly.

I have seen these on ebay, not sure Drake still makes them.

Jim


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 Post subject: Re: can i amplify an rf out on a TV box?
PostPosted: May Sun 17, 2020 9:11 pm 
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Location: Pewaukee, WI
In the US there are a few different laws allowing low power analog TV transmission for consumer use. If you limit your range to 200' radius you're not really doing anything you'll get in trouble for. Blonder Tongue modulators have an RF output level adjustment and it is fairly easy to take a battery powered 90s portable TV for a walk to find your range and dial it back to only cover your property.
Also worth doing is using a Zenith DTV box or any other that has menu settings that allow you to manually check the RF level of any carrier manually on each RF channel (as opposed to virutal channel where a station may claim it is CBS ch3.1 despite it's RF carrier being say RF ch21). There are websites that will give you a list of carriers you might be able to receive too. When you know what channels are occupied it makes it easier to transmit on one that isn't and prevents trying to outshout another station while trying to transmit....with ATSC3.0 changing channel packing I'm about due to recheck where all the stations are...

I have been transmitting with my Blonder Tongue modulators for around 8 years now and never been bothered. If I were interfering with aircraft the Waukesha airport across lake Pewaukee from me would have bothered me ages ago.

BTW if worse comes to worst you can get HDMI to composite video adapters relatively cheap some need a HDMI splitter between them and the box to strip out the HDCP copy protection...View HD splitters seem to work well for that.


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