Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Television Broadcast Gear

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 02-17-2015, 11:35 PM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
modulator

What would be a good modulator/transmitter, that would transmit in both VHF/UHF for TVs inside my house?
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..
Reply With Quote
  #2  
Old 02-18-2015, 12:06 AM
wa2ise's Avatar
wa2ise wa2ise is offline
VideoKarma Member
 
Join Date: Dec 2002
Location: USA
Posts: 3,106
Look on that auction site for "Blonder Tongue" modulators. Many cable companies are going all digital, and unloading their analog equipment.
__________________
Reply With Quote
  #3  
Old 02-18-2015, 12:12 AM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
Ya, I've been thinking of the Blonder Tongue AM-60-550B AM Series..
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..
Reply With Quote
  #4  
Old 02-18-2015, 12:34 AM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,683
Those are not bad units unless you get a damaged one.

What I recommend is to use a DTV box or a decent web search to find which RF channels are occupied with DTV carriers in your area, and avoid using those channels.

If you want more than one modulator get an agile modulator (one where you can pick any given channel) first, and test different frequencies, and antennas*. I would recommend getting blonder tongue BAVM-z modulators once you have found which channels work good. BAVM-z modulators come with the channel permanently fixed, but are cheaper, and come in a variety channel options. *I've had DTV adjacent channel interference prevent me from using some channels I wanted.

Shango66 has a good video on youtube on making a custom tuned TV transmitting antenna out of lamp cord that you may want to watch.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #5  
Old 02-19-2015, 04:42 PM
Findm-Keepm's Avatar
Findm-Keepm Findm-Keepm is offline
Followin' the Rules...
 
Join Date: Jun 2007
Posts: 2,826
...and stay away from any "T" channel modulators - they are upstream modulators and not what you are looking for. I mistakenly bought two at an auction and was disappointed tof ind out what they were.

Cheers,
__________________
Brian
USN RET (Avionics / Cal)
CET- Consumer Repair and Avionics ('88)
"Capacitor Cosmetologist since '79"

When fuses go to work, they quit!
Reply With Quote
Audiokarma
  #6  
Old 02-20-2015, 12:54 PM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
I received my Blonder Tongue AM-60-550B today, it was preset to 16 on the dip switches.. I'm trying to go into the UHF channels and can't get anything out of UHF.. and have the same antenna set up with the loop antenna as he has in this video.. I don't have a manual or dip switch card but I did download the card from here http://antiqueradio.org/HomeTVTransmitter.htm.. I'm able set presents for the single digit channels, but on the UHF channels I can't get anything out of it, I think with the UHF the left side is used to add up for first digit and right side is used for the second.. Anyways I tried different combinations, and nothing.. This guy in the video is able to get strong signal with just a loop antenna and not even any antennas on his sets..

https://www.youtube.com/watch?v=V3k4e-0_Wy8
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..

Last edited by tvcollector; 02-20-2015 at 02:22 PM.
Reply With Quote
  #7  
Old 02-20-2015, 01:56 PM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,683
I'd go with a UHF bowtie dipole. Those loops are shorts. 75ohm cable is transmission line. if you short transmission line and it is at the wrong fraction (or multiple of) the wave length of the transmitted signal then some or ALL of the transmitter signal power will not be transmitted but instead reflected back to the transmitter (which can damage some transmitters).

Also I'm leery of using matching transformers/baluns designed for receiving antennas...The transmitter power may be sufficient to damage them, and cause poor or NO performance.

I'm VHF exclusive right now, and this video has been my guide.
https://www.youtube.com/watch?v=z4dhRt7tmd4
I'd give it a try on VHF this way first, then start trying UHF if I were you....That video you posted is the first talk of using a BT mod for UHF that I've seen.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #8  
Old 02-20-2015, 07:07 PM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
I'm using VHF and made an antenna similar to the video you posted and signal is very weak, doesn't even come in good 3 feet away from it.. And can't get anything from it outside the room that's viewable.... 7 8 and 9 seem to be the better channels.. All other VHF channels seem to either not be anything or something very weak.. I had it hook directly at one time and still could not get a UHF signal to the TV.. While hooked directly with using a VHF channel still pic is not 100% clear, still slight noticeable fuzz and noise pattern on screen.. If I adjust to channel 10, 11 or 12 the green light starts blinking.. I don't think this thing is working right at all..
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..

Last edited by tvcollector; 02-20-2015 at 07:55 PM.
Reply With Quote
  #9  
Old 02-20-2015, 08:12 PM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,683
First off make sure your antenna is TUNED TO (ie cut to the proper wavelength for) the channel you wish to transmit on.
I first tried my modulator on a pair of all band rabbit ears, and could hardly get 30' of range at max transmitter output, but with a tuned dipole I could could get the same range with MINIMUM transmitter output, and several times that distance with the output maxed.......

...Which reminds me, do you know what all the pots with flat head screw driver adjustment on the unit do? If not here is a run down on how to set them: Output level should be maxed (until you know the max transmit range, then back it off a bit if the signal travels farther than you are comfortable with). The audio and video level controls are also important to set. Tune in a TV to the signal and increase the video level until you see fine bars/noise in the picture and the synch gets messed up, then back off until the picture is normal. The audio and aural carrier should be tweaked the same way up until distortion, then back off until good again. Some models have over-modulation indicator LEDs....You don't want them to light more than the faintest amount...Back off controls till they JUST go out.

Channel 7 seems to work best on my BT agile modulator too. Channel 2 gives me about 2-300' radius, channel 7 gives me about 1 block radius, and 9 gives me about 3/4 block radius. 3 and 4 are not used to protect VCRs being used with their RF out, 5 is DTV occupied here, 6 has too much interference from 5 to be used, 8 is also DTV, and I don't have enough modulators to bother with channels over 9 presently.

BTW I don't recommend using wire thinner than lamp cord strands for the dipole antenna leads....Thickness of the dipole wires is directly related to antenna bandwidth and a 6MHz NTSC TV signal has a whole lotta bandwidth....They did not make roof top TV antenna wires finger thickness just for resistance to wind damage, they wanted the entire bandwidth of the signal to be strong, clear and flat.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.

Last edited by Electronic M; 02-20-2015 at 08:20 PM.
Reply With Quote
  #10  
Old 02-20-2015, 08:58 PM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
output level is maxed, all other levels are adjusted and were backed off until indicators went out for both audio and video.. But I would think to have a clear pic with this thing hooked directly to the TV right? I'm getting a bit of fuzz and a slight barley visible line pattern on the screen.. I'm not aware of those pots.. Probably under the cover where the little screw is..

Was using 18 gauge stranded wire.. I didn't cut them to the proper range though.. I also have lamp cord if that would make a difference.. I don't have a VHF/UHF Antenna Analyzer like Shango has, they are in the $300 range on eBay..

I have the model AM-60-550B I know there is a model AM60-550 without the "B", not sure what the difference is...

That spatsbear guy on Youtube just has that loop antenna, and TVs with no antennas hooked up and he get a perfect raster with UHF, even in a next room over.. I can't get nothing to come up with UHF, nor even a perfect raster hard wired.. I do have a UHF bowtie dipole antenna in storage that's connected to a 85" GE portable that I can take off and use.. But this thing is not giving me any UHF..
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..

Last edited by tvcollector; 02-20-2015 at 09:22 PM.
Reply With Quote
Audiokarma
  #11  
Old 02-20-2015, 10:12 PM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,683
Hooked directly to a TV you may have TOO MUCH signal power for the tuner to handle. With a direct connection start with minimum output power and slowly increase it until it is decent, if it even needs any increase (which it should not). The pots I mentioned and named are on the front and back panels and can be adjusted without opening the unit....

Try again with lamp cord and cut to the appropriate length for the channel you are going to use.
I do NOT have an antenna analyzer either....The math process Shango uses was sufficient for me to cut antennas that work well. Cutting them to proper length is rather important...You will get VERY little transmission range if you use an antenna that is not tuned to the station you wish to transmit on (case in point the crappy results I got with an off the shelf UHF/VHF all band antenna). Also make sure your dipole is high up in the room you are using it in, the two ends of the dipole are pointed away from each other, the dipole leads are taught, and the antenna does not sway, vibrate or move in any noticable way.

Lets not worry too much about UHF for the moment. UHF is much more finicky to transmit and receive on, so lets first get good results with simple VHF frequencies and methods to prove your modulator is working before working with UHF.

By the way do you know what RF channels (as opposed to those stupid, fake 'virtual channel numbers') your regions DTV stations are transmitting on? That is important to know. If you transmit on the same channel as a regional DTV carrier your modulator will likely be drowned out by the DTV station, or at least severely interfered with by it (or if you look at it another way you may be jamming your neighbor's attempts to receive that DTV station, which could bring the FCC to your door). If you can, also avoid channels next to DTV stations (at least until you confirm your modulator is good) as adjacent channel interference may result.

Also the test TV is important. I'd test the antenna with a newer solid state TV (preferably a portable that you can walk outside with to check the signal range once you get it right) if I were you. It is hard to be certain of the calibration and performance of the receiver sections of older TVs. If it works with a newer set, but your old one is not liking it then that old set will need some work.

Remember over modulation and under modulation can cause many strange effects just as too much signal or too little signal can cause undesirable effects.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.

Last edited by Electronic M; 02-20-2015 at 10:21 PM.
Reply With Quote
  #12  
Old 02-20-2015, 11:27 PM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
I'd rather trouble shoot this wired directly to the TVs first, it will better determine there is a problem much easier.... Comes to find out that it's only channel 3 that has a slight line pattern.. Hard wired with it set to channel 7.. I adjusted the audio/video peak controls and the level and aural control, and still there is a bit of noise in the pic like the station isn't coming in at 100%... I notice there is 3 or 4 holes on the top front of the unit, they seem to be pot controls. 2 of them are adjustable, I adjusted those two, and they didn't do anything, and they don't have any kind of label on them either.. No pots on the front and back panels, other than the front what everyone already knows (Audio/Video Aural and Level Controls)..

On the other forum, someone mentioned that this unit may have a power supply problem, which results in weak signals.. They said they have a bunch of these units and one with power supply problem..

Looks like I'm going to have to return this.. Just my luck I received a unit with problems.. Seems like this always happens to me when I get a new item I learn about..

Here's a short video of what I'm talking about.. That's as clear as It can get:
https://www.youtube.com/watch?v=8-OH...ature=youtu.be
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..

Last edited by tvcollector; 02-21-2015 at 12:09 AM.
Reply With Quote
  #13  
Old 02-21-2015, 12:00 AM
Electronic M's Avatar
Electronic M Electronic M is online now
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,683
Don't tweak the ones other than already mentioned unless they are labeled, you know they need adjustment, and you know how to properly set them.....A modulator is essentially the opposite operation of a TV tuner/IF system, and just like a tuner IF system if the adjustments don't look like user controls then they should not be casually messed with.

Try lowering the Video, audio, and aural carrier levels, and see if the interference goes away.

Also there should be a short IF patch cable on the back connecting 2 75ohm jacks together...Try another cable in it's place (the one it came with may be damaged).
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #14  
Old 02-21-2015, 12:09 AM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
I've done all that, and more than once.. And just tried replacing the cable.. Now I notice the audio and video over modulation light stays lit, even with it all the way down as the unit gets warm..


Here's a video of what the issue is:

https://www.youtube.com/watch?v=8-OH...ature=youtu.be
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..

Last edited by tvcollector; 02-21-2015 at 12:30 AM.
Reply With Quote
  #15  
Old 02-21-2015, 12:45 AM
tvcollector's Avatar
tvcollector tvcollector is offline
VideoKarma Member
 
Join Date: Sep 2010
Location: So. Florida
Posts: 1,566
The over modulation light issues were the pot controls on the top I had adjusted.. I got them to where they should illuminate.. That was a whole problem in it's self that I created and fixed..
__________________
Looking for an all tube or hybrid color TV set from the late 1960s, early 1970s that's in a steal cabinet..
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:13 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.