Canadian TV, Computing and Home Theatre Forums banner
1 - 20 of 67 Posts

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #1 ·
With all of the antennas up on the tower (four or more at any point in time), how do we combine them for watching television?

Well, the big dual PR-8800 UHF array is combined with a longish VHF dipole through a diplexer, and the result is then split out and distributed to several tuners, a (defunct) VCR, and the TV itself.

But for the specially antennas described above, for specific channels 24 and 11, we use an antenna switch. A good old fashioned slider, with > 60dB isolation between inputs.

It works really well, and doesn't noticeably degrade the signals. But the problem is remembering to switch it when the PVR is going to be recording shows that require a specific antenna.

See, we don't "watch TV". We watch pre-recorded shows, with commercials all stripped away before we see them. This is done using a dedicated computer, configured with MythTV software, as a PVR -- it has two digital TV tuners, and two analog TV tuners. Three of those just take the main feed from the dual PR-8800 + dipole setup.

But the fourth, an analog tuner, is where the switch comes into play. Normally, the switch gives this tuner the same feed as the others see. But when the PVR wants to access programming from channels 24 or 11, it needs the switch in the other position.

So, we motorized it, and gave the PVR control over the geared motor via two bits from the computer's parallel port.



The motor direction, forward or reverse, is controlled by relays, which in turn are controlled by the parallel port. Very Rube-Goldberg style. I'm working on a solid-state update of this, using a USB controller (modern PCs don't have parallel ports anymore), but for now, this *works*!
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
A great, cheap source for movement mechanisms: old VCRs!

For those of you looking for mechanisms that are electronic, reliable, and even can use a timer, time to dig out that old VCR that you were going to send to the dump. Heck, go find 2 or 3 before they disappear.

With some thought and some light fabricating you can come up with excellent electromechanical timer devices. ;)
 

·
Registered
Joined
·
7,360 Posts
I'm working on a solid-state update of this, using a USB controller (modern PCs don't have parallel ports anymore), but for now, this *works*!
Computer interfacing the $20 Radio Shack remote controlled A-B switch may be an easier route.
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #4 ·
Computer interfacing the $20 Radio Shack remote controlled A-B switch may be an easier route.
That could work, if the signals were clear enough to tolerate the much worse isolation figures that those devices usually quote. Any idea what the RS one specs at?

Not that it matters much -- a $1.50 for >60dB isolation, plus motor and relays (about $15 or so) is considerably less outlay than $43/switch *before* S&H and interfacing costs.

Oh.. and no RS in Canada, so that's a non-starter anyway.

-ml
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #5 ·
Now, the satellite people have really got this stuff sewn up, with 4:2 and 4:4 multiswitches readily available in the $20-$50 range.

But they look to be a bit of a nightmare to actually try and repurpose for OTA television -- lots of weird voltages need to be inserted/blocked again on various connectors.

And that's assuming one could even find units that didn't filter away everything below 1GHz on the "satellite" inputs.

I'm also looking into having a commercial OTA unit (from the CATV industry) made up for me: 4-inputs, 2-outputs (or maybe vice-versa..), but these all seem to be made to order, at $300 and up.

Cheers
 

·
Registered
Joined
·
7,360 Posts
I would be perfectly happy if I could find a cheap, well built, 4 input, one output A-B-C-D manual switch, heh.
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
mlord said:
they look to be a bit of a nightmare to actually try and repurpose for OTA television -- lots of weird voltages need to be inserted/blocked again on various connectors.
Yep, the ones that operate by voltage differential would be killers for anyone running a preamp, but if they could operate on audio tones sorta like old POTS switching gear that would probably work.
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #8 ·
300ohm said:
I would be perfectly happy if I could find a cheap, well built, 4 input, one output A-B-C-D manual switch, heh.
Yeah, that would be nice -- if it used a rotary knob, then a stepper motor could be used for automatic control of it.

Our local electronics chain has 3:1 switchboxes with individual push-buttons. The travel on each button is only about 1/8", so I'm thinking that solenoids could be used to push the buttons.. Going to go shopping for those next time I'm in Toronto.

Cheers
 

·
Registered
Joined
·
7,360 Posts
Our local electronics chain has 3:1 switchboxes with individual push-buttons. The travel on each button is only about 1/8", so I'm thinking that solenoids could be used to push the buttons..
The push-button A-B switch I currently use (Channel Master I think) has a travel of about 1/4", and is rather stiff to push in and makes a definate lock when pushed in. It is nice and heavy duty though.

Any idea what the RS one specs at?
Nope, but (forgetting the infra-red remote part) the base unit has to have some kind of a relay or electonic switch built into it. Radio Shack isnt cheap, and I do recall seeing some cheaper similiar units on the market, but I dont have the links, so Ill have to search.
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
mlord said:
3:1 switchboxes with individual push-buttons
The 3:1 push button units I've used in the past (I still have some in my shed) were really dirty signal-wise (poor isolation and shielding) so I vowed never to use them again. I hope you can view the switching taking place on a signal analyzer to see if its clean enough.
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #11 ·
Mmm.. The commonly available 3-way pushbutton coax switch in the USA is the Steren 200-315, available at many places for about US$3 - $4.

In the photo of it (everybody has exactly the same photo), it doesn't look exactly the same as what our local "The Source" store (was Radio Shack years ago) carries for CAD$18 (yes, expensive).

Both claim 60dB isolation on the inputs. Whether that's true or not, I dunno. But the real question is, how much force is required to push the buttons on the Steren?

I've found some cheapish solenoids ($2.49/each, item #G16939 from Electronic Goldmine), and ordered six of them (to drive a pair of 3-way switches).

But I still have to decide upon the switches themselves.. might just use the locally available ones unless somebody can say anything about the Steren ones.

This will be a fun project!

Cheers
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #12 ·
stampeder said:
The 3:1 push button units I've used in the past (I still have some in my shed) were really dirty signal-wise (poor isolation and shielding)
The Steren ones claim to be fully shielded. Could you dig out one of yours from the shed, and see what brand/model it is, if marked?

And also see if you can measure the force required to push a button (use the kitchen scale for this)?

Thanks
 

·
Registered
Joined
·
325 Posts
mlord:

"lots of weird voltages need to be inserted/blocked "

Yup the satellite switches are controlled by the DC voltage on the coax which is either 13 volts for vertical or 18 volts for horizontal polarity, I believe (or RHC or LHCircular if its a circ polarity). And they have - I think - a 20 kHz tone up the line to change the LNB. Which of course means you need more than just an RF path up the coax.


Nice work on that box by the way. Very cool that you can get a PVR to talk binary to a remote terminal like that.


Damn - i have some of those solenoids from Goldmine. Id have given you a few had I read this earlier before you ordered them - or I can just speed up the shipping and give you a few now (ground takes about a month from them in Arizona)
 

·
Registered
Joined
·
597 Posts
A lot of the satellite switches claim -3db insertion in the specs.
I've seen some electo-machanical coax switches with bnc connectors on fleabay recently 115vac coil buy it now of $16 US.
 

·
Registered
Joined
·
1,543 Posts
Discussion Starter · #17 ·
GerryB said:
Damn - i have some of those solenoids from Goldmine.
Heh! You and I have simply got to get together someday! It does sound like we have more than a few things in common! :)

The solenoids are apparently due by air-mail, which from most places on this planet means a week or so, but double that when from the USA. :)

No hurry, I'm still pondering switches and building yagis; We plan to explore Queen St.W and College St. in Toronto this weekend, in search of useful parts (need anything?)..

Cheers!
 

·
Registered
Joined
·
325 Posts
mlord:

when you are back in Ottawa let me know. I'm not a big fan of the outdoors in the winter but if there's an antenna mast involved Id make an exception
 

·
OTA Forum Moderator
Joined
·
24,867 Posts
Archer 15-1256

Without doing an archaeological dig in my shed I found a bunch of cheapie A-B sliders but also an Archer (Radio Shack) 15-1256 3:1 RF switch. A quick Google shows them available from a few sites. Actuation force (as tested after I'd pushed the buttons several times to work them in after many years of storage) averages about 450g. If I remember correctly, and I'm not saying I do, this is the unit that didn't have very good isolation or shielding.

I wish I could find the heavy duty A-B slider I once had - the required force was very high such that a kid would have trouble with it, but the isolation and shielding were superb. I think its either deep in my shed or I installed it for someone in years past.
 
1 - 20 of 67 Posts
Top