Another modulator option- Drake VMM860AG

[VintagePC]

(Apologies if this is not suited for this forum... Technically it's broadcast gear but it doesn't really fall into the same class as the types of things discussed there and I figured the restoration crowd that hangs out here would have a bigger benefit)

Just thought I'd share this PSA with the folks here who are interested. I got a hold of two Drake VMM860AGs (http://www.rldrake.com/product-vmm860ag.php) and am pleased to report that they make serviceable modulators for our vintage sets.

I can't comment versus the commonly used blonder-tongue and drake ones bandersen has mentioned but since prices on those are increasing (and these don't take up nearly as much space!!) they might be a nice alternative.

They're made to be rack-mounted en-masse, but they don't use any special backplane connectors or anything - they have standard input connectors and can be powered with any supply that provides +5 and +12V.

I'm also happy to answer questions about them if you have any; it gave a clear, sharp picture on my Fleetwood TV set when directly connected and worked okay with some old rabbit ears. I don't doubt it would function much better with a proper antenna attached to it.

I don't see many on a certain auction site at the moment... and those are exorbitantly priced. I've asked person I got mine from whether they have more and if I can pass on their contact info to the folks here that would like one for a far more reasonable price. Will update post with info when I get it.

[Jon A.]

I'm in! I was just checking those out last night.

[zeno]

Same Drake as the ham radio Drake ? R.L. Drake IIRC.

73 Zeno

[VintagePC]

Originally Posted by zeno

Same Drake as the ham radio Drake ? R.L. Drake IIRC.

73 Zeno

That's correct.

[Jon A.]

This may sound silly, but it's the name of the more popular modulator that puts me off getting any of them. I know that they were made in Taiwan; what about the Drake units?

[VintagePC]

Originally Posted by Jon A.

This may sound silly, but it's the name of the more popular modulator that puts me off getting any of them. I know that they were made in Taiwan; what about the Drake units?

You probably already know but that name comes from the two founders, Isaac(?) Blonder and Ben Tongue (who has actually been seen around these parts and is a pretty cool guy to talk to)

AFAICT, Drake is USA-made in NJ, or so they claim on their site. I have a Drake high-pass TV filter which states "Assembled in Barbados with USA components").

Been looking at some more of their products... am tempted to try to get a DMM806 demodulator as well but they seem pretty scarce and pricey.

[Electronic M]

The most important thing about an agile modulator IMHO is it's wireless range. Unless a set was built for the Japanese market (NTSC standard, but with different low VHF channel frequency assignments that are in our FM radio band), has a mostly bad tuner (although if you still have analog cable like me you don't need a modulator to check/deal with that), or is a lousy design that can't take dual sideband video like the predicta, you are wasting your money buying anything more than a cheap consumer RF modulator if you are direct connecting the modulator to the set.

[VintagePC]

Originally Posted by Electronic M

The most important thing about an agile modulator IMHO is it's wireless range. Unless a set was built for the Japanese market (NTSC standard, but with different low VHF channel frequency assignments that are in our FM radio band), has a mostly bad tuner (although if you still have analog cable like me you don't need a modulator to check/deal with that), or is a lousy design that can't take dual sideband video like the predicta, you are wasting your money buying anything more than a cheap consumer RF modulator if you are direct connecting the modulator to the set.

Agreed. I need to get my hands on some wire to build a proper dipole and see how it performs at range. I wouldn't have bothered trying these out if the price wasn't attractive enough vs. a dime-a-dozen cheapie.

[VintagePC]

Took some time today to tinker. I calculated the length for a proper dipole, set my rabbit ear transmitter antenna to that length, and was able to get a good watchable picture with audio and sound over a distance of about 7m, the furthest I can get from my console while still having a power source and video to transmit (my room is in the middle of the house, unfortunately). The neighbours might get suspicious if I go outside with a long extension cord and a box with an antenna on it...

This was with the output on the modulator at about 1/3 of the way up (adjustment goes from 35 to 45dBmV, the B-T ones go up to 60), the TV's internal wire loop antenna, and an unadjusted/aligned set.

I do get some noise in the picture with output at minimum, but that's not really conclusive as I am in a very messy/noisy area as far as RF goes... the AM band sounds like a chainsaw no matter where you tune it, and even some cable channels aren't immune)

So as you can guess... it's serviceable with lots of room for potential improvement (dipole & alignment on the TV, proper antenna orientation) and could perform pretty well in a permanent setup. Might not cover the entirety of ones country mansion, but will work well for most folks' needs.

[Jon A.]

Originally Posted by VintagePC

The neighbours might get suspicious if I go outside with a long extension cord and a box with an antenna on it...

I just try to steal myself against what others might think of stuff like that. It becomes necessary when you're pushing console TVs home on a dolly. Fortunately I got delivery with both of my Zenith consoles. If I lived in a house or even an apartment building with more relaxed management, I'd be right up a big tree with at least something like you described.

[VintagePC]

Originally Posted by Jon A.

I just try to steal myself against what others might think of stuff like that. It becomes necessary when you're pushing console TVs home on a dolly. Fortunately I got delivery with both of my Zenith consoles. If I lived in a house or even an apartment building with more relaxed management, I'd be right up a big tree with at least something like you described.

I definitely don't have an issue with that... Couldn't care less what people think if they see me wheeling a TV. Maybe I'm just paranoid but I don't fancy having to explain to a police officer exactly what I'm doing with a laptop, an antenna, a bunch of wires and a TV transmitter... I'd be harder than "Well officer, I just bought this and I don't have a car..."

[Jon A.]

Yeah, I was never questioned about what I was doing with the dolly, whether it was bringing home console TVs or my mattress. One TV was a Thomson set that I considered only good for its cabinet, the other a rotten mid-70s Hitachi I saved the boards and jug from and leveled the cabinet. Good thing said mattress was covered in plastic; the day was very windy and eventually snapped the hold-down string, taking it out into the entrance of a side street. It came in handy even when my latest Zenith was delivered, and I don't know what I would have done without it when moving.

As for climbing trees with transmitters, I guess I should do that under the cover of darkness.

[VintagePC]

Originally Posted by Jon A.

Yeah, I was never questioned about what I was doing with the dolly, whether it was bringing home console TVs or my mattress. One TV was a Thomson set that I considered only good for its cabinet, the other a rotten mid-70s Hitachi I saved the boards and jug from and leveled the cabinet. Good thing said mattress was covered in plastic; the day was very windy and eventually snapped the hold-down string, taking it out into the entrance of a side street. It came in handy even when my latest Zenith was delivered, and I don't know what I would have done without it when moving.

As for climbing trees with transmitters, I guess I should do that under the cover of darkness.

That or you have to master the ability to look like you belong. Perhaps a clipboard, official looking name badge, and a lab coat should do the trick...

The other caveat being that most of the trees here are very near power lines and I don't particularly fancy holding a big metal rod near those... The few kv at mA range in TVs isn't so bad in comparison to 5+KV on the order of a few hundred amps... Once played golf on a course which was spanned by some EHT lines (the ones on the BIIIIG metal towers, I think those are a few hundred KV for distribution...) You could most definitely hear it, just about feel it in the air, and man, was I nervous swinging a big metal rod around... Just imagine the sound of taking off your sweater on a dry winter day, but then on a much louder and more menacing sounding scale... at about 60hz.

[Electronic M]

A good low key mobile TV signal strength meter is a old SS battery powered 3-5" TV. They have their own antennas, and if someone happens to be smart enough to know what DTV is and that your set is older than it, and wants to know how you are getting signal you can just tell them 'Don't know, it must be some low power repeater'.

Half the trick of successfully doing stuff you might somehow get in trouble for is knowing how to look like you belong/are perfectly innocent/ignorant of anything suspicious.

[jshorva65]

Is anyone familiar with this modulator, the Jerrold C6M aka "Commander 6" model? I got this one as a "free to good home" deal from Don at the 2015 ETF Convention along with some other unsold retired CATV / Satellite items he'd brought to the ETF looking for a buyer and/or new home for them. The only literature I'm able to find through search engines is for the Jerrold C6M II, apparently the next generation of this model with an LED readout in place of the mechanical Channel dials. Hopefully, I can get this working as an addition to a fleet of a few of the more common Blonder-Tongue AM60-550A's that I've picked up on eBay for varying prices. The idea I have is to program the three Blonder-Tongue units for Channels 7, 10, & 13 respectively, set a cheap modulator up with a DVD player on Channel 3, program an ATSC set-top converter box for Channel 4, and set up the Jerrold C6M with its pushbutton channel selector to switch as needed to any of the other channels, simulating medium signal strength OTA reception to achieve the best possible performance on the professional Vintage TV Restoration work done here.

To prevent running afoul of FCC regulations, each source will be limited to no more than about 20mW and one of these little battery portable TV sets will be carried around the property line to make sure that the signal attenuates abruptly beyond the edges of a standard 50'x150' residential lot so there's just enough signal strength to produce a decent picture on receivers anywhere inside the house or out in the garage where final assembly and packaging of large console sets for shipment or customer pickup is done.

Returning to the topic of this Jerrold C6M specifically, none of the internal DIP switches seem to be effective in extinguishing the "REF OFF" LED on the front panel and the only output it seems to produce is an unmodulated carrier corresponding to the selected output channel, no audio or video. I've tested it with antenna "rabbit ears" and with a direct wired connection to the Antenna input of a known working 70's-era 13" Color portable TV, with and without the white coaxial cable "jumper" between its IF OUT & IF IN connections. I've also tried picking off the IF OUT to feed to the IF IN of a known working Blonder-Tongue AM60-550A and reversed the test by sending IF OUT from the same Blonder-Tongue AM60-550A to the IF IN of this Jerrold C6M. Is anyone familiar enough with these to provide some insight into what I might be "missing" here? Operator error, circuit fault(s) in the unit, maybe both? Does anyone have a manual for it? The one for the C6M II is *totally* different.

Here are some photos of the unit (front, rear, & the DIP switches and Settings chart inside the sliding top cover) and the little AM/FM/TV receiver that I use along with a handheld field strength meter to verify compliance with FCC range limits.