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Re: AM antenna switch for 5kW ?
To: CRTech <crtech@crtech.org>
Subject: Re: AM antenna switch for 5kW ?
From: Lamar Owen <lowen@pari.edu>
Date: Tue, 15 May 2018 00:45:35 -0400
Content-language: en-US
In-reply-to: <alpine.WNT.2.10.1805111649050.3300@Lyle-Dell-D630>
References: <alpine.WNT.2.10.1805111649050.3300@Lyle-Dell-D630>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0
On 05/11/2018 08:20 PM, RADIO DOCTOR wrote:
What remote control switches are being used for AM nowadays?  Shielded for coax or open relay(s) on a panel/board?  Controllers? Automatic?

Kintronic's RF contactors have been the standard for years, both at the ATU/LTU and in phasors, and you've already gotten a pointer to those.  Kintronics has a wide variety of controllers and can custom build pretty much anything related to AM antenna systems, including dummy loads.

The transmission line is a 1/2" late 1980's version of the current 1/2" CableWave (RFS) LCF12-50J.

1/2 inch at 5kW?  Well, CableWave does rate the 2013 version of this cable for 38kW average at 1MHz and 38kW peak; with AM you have to take into account the peak, not average, power, which for 5kW at 100% positive modulation is 20kW (peak voltage at 100% 1kV; the cable is rated 1.95kV) .  Should be ok, although I have always recommended 7/8's for 5 and 10kW.

What's best for jumpers?  Should I bother with connectors or just wire it up?  Transmitter will probably be 7/8" EIA output, but DIN connectors might be nice for hooking everything together.  Is there a 7/8" EIA to appropriate size DIN adapter.  I've never used DIN connectors anywhere.

At 5kW I'd use 7/8's flanges everywhere.  They're easy enough to work with, and it's just a few bolts to decouple when you need to do so.  In this case it's not the voltage but the current that becomes the primary concernt; your connector needs to handle 10 amps with dead carrier and 20 amps at 100% modulation (and 1kV at 100% positive peaks).  This is hard to do with connectors smaller than 7/8's flanges, although the 7/16 DIN is a really good and rugged connector.

Being an FM Guy, I've rarely dealt with real AM.  Always tried to keep AM at least 50 dB down :)

AM is a completely different beast in many ways.  You're solidly down in lumped constant territory, but distributed constant stuff keeps showing up.....  AM directionals are my favorite; love negative resistance towers..... :-)  You're also into real loudness-war territory, since with an AM your effective maximum listenable distance is directly related to positive modulation percentage.

Follow-Ups: Re: AM antenna switch for 5kW ?
(RADIO DOCTOR <lylehenry@fastmail.fm>, 16 May 2018 03:09:47 -0000)
References: AM antenna switch for 5kW ?
(RADIO DOCTOR <lylehenry@fastmail.fm>, 12 May 2018 00:20:15 -0000)
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