[mythtv-users] OT: Addressable Antenna Switch

[Richard Woelk]

bhaskins at chartermi.net wrote:
> ---- Dennis Cartier <dennis.cartier at gmail.com> wrote: 
>   
>> On Sun, Sep 6, 2009 at 11:15 PM, drew einhorn <drew.einhorn at gmail.com>wrote:
>>
>>     
>>> Hmm, I wonder if the diseq switches that are typically used to select which
>>> LNB signal is fed from the satellite dish to the satellite receiver
>>> could be adapted
>>> for this purpose.
>>>
>>>       
>> I had thought of this. I even have some switches laying around from days
>> past. I am a bit worried that I would not be able to safely inject the
>> supply voltage and not to mention the DiSEqC control signals onto the coax
>> and have it not interfere ... fry or otherwise hamper the ATSC
>> signal/tuners/etc. I am fairly analog challenged.
>>
>> Going back over the plan, I realized that the HDHR interface in Myth does
>> not have the ability to run a script on channel change. Doh! Then it hit me,
>> I had a similar problem while trying to orient the second antenna this
>> weekend. Rather than climbing up and down the tower to check the signal
>> output from the HDHR after every adjustment, I created a script that mailed
>> the output to my Blackberry every 30 seconds. That way I could stay on the
>> tower and get instant feedback. Well almost instant. I could use a similar
>> method of having a script watching the status output of the HDHR devices and
>> then switch the required antenna in depending on the channel it was tuned
>> to.
>>
>> The next hurdle is how to communicate to the location where the HDHR devices
>> are located. I have them installed in a workshop at the base of the tower
>> and I would like the signals to use the existing ethernet network to control
>> the switching. Hmm,I would rather not require a PC for this function so ....
>> I need a print server. I know what you are thinking, a print server??? For
>> what? Simple, to be the network interface for the antenna switch. An older
>> style parallel print server should be perfect to interface a micro
>> controller to. Sending the the commands will be as easy as echoing to lpr.
>> You may even be able to do it without the micro controller just by creating
>> a simple latch from discrete components but why pass up the opportunity to
>> do something neat with a MCU.
>>
>> All that is left to work out is how to actually switch the signal. I was
>> thinking perhaps a lobotomized DiSEqC switch might work, but I had better
>> consult the OTA DigitalHome forums where the real antenna geeks hang out.
>> They will know how to accomplish this.
>>
>> Dennis
>>     
> All of the old VCRs had a antenna switch to enable a pass-through when the 
> unit was turned off and of course these things are being junked by the ton now.
> Maybe someone on the list could identify this switch and it coud be used for this.
I work with RF in two-way radios. Often, the older radios had a relay to 
switch the transmitter or receiver to the antenna.
A simple single-pole-double-throw relay will work, tie all the grounds 
together and hook the centers to the relay.
You can then control this with an output of the parallel port.
you'll want to make sure the project box is metal, and keep the stripped 
coax as short as possible.

Another way to connect two antennas, is if their freuqency is far enough 
apart (3 channels, I assume) is to use a splitter backwards as a mixer.
My Dad has this on his analog OTA, with channel 5 and 12, and it works 
fine. (We're in Canada, we haven't switched tot digital yet)

- Richard




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