[amsat-bb] Re: Mirage preamps

[Floyd Rodgers]

Look carefully at the power consumption on the preamp. If it is less 
than the max for the 847 (which I forget the maximum current), you could 
use it powered from the radio. BUT pay careful attention that anything 
between the radio and the preamp does not provide a dead short from 
center conductor to shield. In my case a lightning protection part shows 
as a dead short. This would of course zap the internal power supply 
parts in the 847. In my case, I just provide external power and hard key 
the preamp from the radio. (The preamp is actually in the shack not on 
the tower.)
Another problem in my install is I am using a pair of duplexers to 
combine the 2m and 70cm to run in a section of 7/8 hardline. The 2m 
ports pass voltage. The 70cm ports do not and present yet another short 
circuit on the coax. I do this arrangement to gain the low loss for a 
150 foot run to the tower base. I also benefit using this technique to 
avoid interference problems between 70cm and 2m. This gets me about 
120db of isolation between the two ports.
There is also another possible issue to consider in that the 847 when 
first powered up sends a full power transmit for a very short time. Also 
another stupid pet trick is never plug into the data port when the radio 
is on. Seems simple, but when the tip/sleeve/ring cross the right 
contacts, a full power transmit occurs. Yup, cost me my best preamp 
while playing the Arecibo EME fun a while back.


On 8/9/2011 7:07 PM, Tim Goodrich wrote:
> On this, would it be possible to power preamps for 70cm and 2m through coax
> if the antennas are split using a diplexer? Or would 12v go to both on TX
> and fry one of them?
>
> Tim
> K6TW
>
> -----Original Message-----
> From: Sebastian, W4AS [mailto:w4as at bellsouth.net]
> Sent: Tuesday, August 09, 2011 4:41 PM
> To: AMSAT-BB
> Subject: [amsat-bb] Re: Mirage preamps
>
> My thanks to everyone who has responded.  4 out of 4 say it's ok to use the
> 847 to power the preamp.
>
> I put up the 432 one today, but with the KP2 control box, just in case.  But
> I will go ahead and remove the box, and let the 847 power it.
>
> One interesting response was to be careful if there is anything inline
> between the rig and preamp.  Lightning protection, or even an SWR power
> meter, could affect the sending of voltage.
>
> 73 de Sebastian, W4AS
>
>
>
> On Aug 9, 2011, at 3:16 PM, Lowell White wrote:
>
>> Hi Sebastian,
>>
>> I'll be interested in knowing that also... thanks for asking.
>> I also have an FT-847 in my stable and have the KP2/2m on my "soon to
> acquire"
>> list.
>>
>> 73,
>>
>> Lowell
>> K9LDW
>>
>>
>> ------ Original Message ------
>> Received: Tue, 09 Aug 2011 11:34:22 AM CDT
>> From: "Sebastian, W4AS"<w4as at bellsouth.net>
>> To: AMSAT-BB<amsat-bb at amsat.org>
>> Subject: [amsat-bb]  Mirage preamps
>>
>>> Before I destroy these, is anyone using Mirage KP-2 mast mounted preamps
>> with a Yaesu FT-847?
>>> I picked up a couple of them recently, and they came with the control box
>> (which appears to be a bias tee) that supplies 12 volts via the coax line,
> in
>> order to power them.
>>> The FT-847 can already supply 12 volts up the coax to mast mounted
> preamps;
>> but I wonder if these Mirage preamps require the use of the control box
> for
>> some reason.  I would prefer to use the rig to power the preamps, but the
>> manual doesn't mention that option.
>>> 73 de Sebastian, W4AS
>>>
>>>
>>>
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>
>
>
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