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@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@bellsouth.net To: AMSAT-BBamsat-bb@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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