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Re: [TowerTalk] Metal Roof

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Metal Roof
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Thu, 11 Jan 2018 20:30:57 -0800
List-post: <mailto:towertalk@contesting.com>
On 1/11/2018 5:31 PM, Grant Saviers wrote:
How well the seam capacitance suppresses diode rectification RFI is a good question as is what is the likely power output of such a diode.  Unsoldered copper seams sound like the devil's playground.

The pros who have chimed in certainly know this, but I'm emphasizing this point for Gilbert. BECAUSE this is a repeater, suppression of any intermod must be REALLY REALLY good to keep it below the level of the very weak mobiles you want the system to hear. AND, because we're talking VHF or UHF, the spacing between bonds must be pretty close.

Another point. IM follows the square of the signal strength that excites it, so reducing TX power by 3 dB reduces the IM by 6 dB. I'd keep the TX power up while diagnosing and evaluating your fixes, but I'd reduce power for general operation until you've declared victory on the fix.

Also, consider moving the RX antenna, even making it a split site system.

73, Jim K9YC


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