KPA3 / KAT500 Remote Question

[WB9JPH]

Question . . . .

My station is in a 2nd floor loft.

The antenna coax cables come into the basement utility room and then up behind the plasterboard walls to my shack.

Will I be able to put the KAT 500 and KPA 3 in the basement utility room and control them by snaking an RS232 cable from the shack to the utility room through the PVC pipe that contains my coax?

If this will work are there any special considerations I need to be aware of?

73
John



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[Dick Dievendorff]

John:

I still think that the ATU and amplifier are things that you'd normally want to keep nearby and in view in the radio room.  It's more convenient there, you can easily observe what's going on, you can turn them on and off easily.  The losses contributed by an extra 25' of quality coaxial cable are arguably insignificant. If something goes wrong, you won't have to run back and forth between the radio and amplifier, or bring a radio to the amp and ATU to try to figure out what the problem might be.  It's easier if everything is in the same area. Warning lights and buzzers in the amplifier won't get your attention if the amp is in an uninhabited room.

If you really want to move the ATU and amp, the cable between the K3 to KAT500 to KPA500 will need to include the key line, and you'll also want a wire to bring to ground to initiate tune.  That, and band change lines that facilitate band change without transmitting and automatic adjustment of K3 power are easy if the amp and ATU are within a few feet of each other.

How much feedline will you have overall?  What additional power will be lost in the 25 foot or so of extra coax you'd add by keeping the amp and ATU with the operator?  What sort of coax are you using, and what's your estimated range of SWRs?

I did a quick check with N6BV's "Transmission Line for Windows" program (TLW, offered on the CD accompanying the Antenna Book in recent years).

If you have, for example, a relatively awful 5:1 SWR and the tuner in the shack (I used a 250 +j0 impedance for 5:1 SWR), you'd expect to lose about 1.12 dB in 100 feet of quality RG-8 like coax (TMS LMR400) on 14.150 MHz.  Changing the line length to 125 feet results in a 1.35 dB loss; you'd save 0.23 dB for that 25 feet by putting the ATU (and the amp) on your ground floor.  They won't be able to hear 0.23 dB at the DX end.  Yes, the loss would be higher on 10 meters. And it would be a lot less if you used hardline.

I have a non-resonant dipole that I have fed with about 25' of quality coax to a balun outside and then low-loss (and high SWR) ladder line to the feedpoint of the dipole.  Works great (or as great as a simple dipole ever works).  The loss in the coax, which runs at high SWR, isn't much, as there isn't that much of it.  What hurts you is relatively long runs of low quality coax at high SWR at high frequencies.  This is usually solved by some combination of shorter distances, higher quality feedline (sometimes hardline), more power, or better matching at the antenna (or some combination of these).  TLW can help you understand these tradeoffs.

I understand the appeal of a remote antenna tuner (I want one too), but moving it just a little down the wire where it's inconvenient to reach but not really near the antenna feed point doesn't seem to me to make that much difference.  Might as well keep it nearby.

My education on this topic is from Walt Maxwell's book "Reflections III".

By the way, my new station (we're in the midst of a building a house) will also on the 2nd floor. The amp and ATU will be in view in the radio room when I operate. I don't normally need to touch them during operation except to turn them on and off, but I want to be able to see them.  I have a 100 foot run to one tower (plus 25' or so to get to the 2nd floor) and a 200 foot run to another.  The 200 foot run, to a HyTower that can sometimes benefit from an ATU, will be fed with surplus CATV hardline.

73 de Dick, K6KR



>> My station is in a 2nd floor loft.
>>
>> The antenna coax cables come into the basement utility room and then up behind the plasterboard walls to my shack.
>>
>> Will I be able to put the KAT 500 and KPA 3 in the basement utility room and control them by snaking an RS232 cable from the shack to the utility room through the PVC pipe that contains my coax?
>>

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[Joel Black-2]

John,

RS232 has a reliability issue past 50'.  I have seen it work up to 60'
with DDS circuits using CAT5 as the conductor and RJ45-to-DB9 / DB25
connectors.  After that, all bets are off.

BTW, this is not anecdotal, this is my experience in the real world.

73,
Joel - W4JBB


On 5/26/2012 2:55 PM, WB9JPH wrote:

> Question . . . .
>
> My station is in a 2nd floor loft.
>
> The antenna coax cables come into the basement utility room and then up behind the plasterboard walls to my shack.
>
> Will I be able to put the KAT 500 and KPA 3 in the basement utility room and control them by snaking an RS232 cable from the shack to the utility room through the PVC pipe that contains my coax?
>
> If this will work are there any special considerations I need to be aware of?
>
> 73
> John
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[Peter-64]

Or you can use an RS232 to RS442 level convertor to a distance up 1.200
meters

Peter
http://www.axxessid.com/Pguide/102-603.html
Joel Black schreef:

> John,
>
> RS232 has a reliability issue past 50'.  I have seen it work up to 60'
> with DDS circuits using CAT5 as the conductor and RJ45-to-DB9 / DB25
> connectors.  After that, all bets are off.
>
> BTW, this is not anecdotal, this is my experience in the real world.
>
> 73,
> Joel - W4JBB
>
>
> On 5/26/2012 2:55 PM, WB9JPH wrote:
>  
>> Question . . . .
>>
>> My station is in a 2nd floor loft.
>>
>> The antenna coax cables come into the basement utility room and then up behind the plasterboard walls to my shack.
>>
>> Will I be able to put the KAT 500 and KPA 3 in the basement utility room and control them by snaking an RS232 cable from the shack to the utility room through the PVC pipe that contains my coax?
>>
>> If this will work are there any special considerations I need to be aware of?
>>
>> 73
>> John
>>
>>
>>    

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[Jim Brown-10]

On 5/27/2012 5:20 AM, Joel Black wrote:
> RS232 has a reliability issue past 50'.

Not if you use low capacitance cable, like CAT5.  At some point, the
RS232 specification for distance was redefined on the basis of total
cable capacitance.

73, Jim K9YC
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