tx/rx isolation and safe tx input power for K3

[pendulous]

Good morning. I have a K3 with a P3 and all the fixins. I have had the radio since before Christmas. Love it. Great product and great company. I recently installed the DX engineering bidirectional Beverage systems. I have been using them in conjunction with the K3 and a Hustler 6BTV and a couple of Dipoles-seperate TX and RX. SeemS to work well. I have a question concerning the minimum safe TX RX antenna separation to protect the front end of the K3. I have not heard the COR kick in, at least I don't think so. Anyway, the separation between the TX antennas and the beverages ranges anywhere from 50 feet to 90 feet, with the Beverages for the most part broadside to the TX antennas. Transmit power is never more than 800 watts on CW. Is this a safe distance for 160 to 20 meters? Is there a formula or model that allows one to easily calculate the required isolation in terms of distance? Thanks in advance for your help.

Mike
AB4KJ

[Jim Brown-10]

On 3/1/2011 6:17 AM, pendulous wrote:
>   I recently
> installed the DX engineering bidirectional Beverage systems.

Are you also using the DX Engineering preamp?  It's got a lot of gain,
more than is needed to bring your Beverages up to match other antennas,
and that could be contributing to a high signal level from your TX
signal.   Consider putting a simple passive attenuator between the
preamp and the K3.  You can build the attenuator from a few resistors.  
Another name for such an attenuator is  "pad." I suspect that there are
some formulas in the ARRL Handbook to calculate the resistor values.

Just working off the top of my head, I'd start with a 68 ohm resistor in
parallel with the line at the input of the pad, a series resistor of
about 270 ohms, and a second 68 ohm resistor in parallel at the output
of the pad.   This will be good for something on the order of 14 dB, and
will be close enough to a decent match for either 50 ohm or 75 ohm coax.
In this application, that's plenty close enough. If you want more
attenuation, increase the 270 ohm to 560 or 680 ohms, which will get you
a bit more than 20 dB.

73, Jim K9YC.


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[Tony Estep]

On Tue, Mar 1, 2011 at 11:25 AM, Jim Brown <[hidden email]>wrote:

> ...Consider putting a simple passive attenuator between the
> preamp...

======
Or alternatively, the DXE preamp manual outlines a number of simple mods to
reduce gain.

Tony KT0NY
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[gm3sek]

Jim Brown wrote:

>On 3/1/2011 6:17 AM, pendulous wrote:
>>   I recently
>> installed the DX engineering bidirectional Beverage systems.
>
>Are you also using the DX Engineering preamp?  It's got a lot of gain,
>more than is needed to bring your Beverages up to match other antennas,
>and that could be contributing to a high signal level from your TX
>signal.   Consider putting a simple passive attenuator between the
>preamp and the K3.  You can build the attenuator from a few resistors.
>Another name for such an attenuator is  "pad." I suspect that there are
>some formulas in the ARRL Handbook to calculate the resistor values.
>
>Just working off the top of my head, I'd start with a 68 ohm resistor in
>parallel with the line at the input of the pad, a series resistor of
>about 270 ohms, and a second 68 ohm resistor in parallel at the output
>of the pad.   This will be good for something on the order of 14 dB, and
>will be close enough to a decent match for either 50 ohm or 75 ohm coax.
>In this application, that's plenty close enough. If you want more
>attenuation, increase the 270 ohm to 560 or 680 ohms, which will get you
>a bit more than 20 dB.
>
>73, Jim K9YC.
>

WinATT by GM4PMK is a nice little Windows program that designs Pi and T
attenuators in a snap. As well as calculating theoretical values for the
attenuation you require, it also finds the closest standard resistor
values in the E6, E12 or E24 series and calculates the attenuation and
VSWR for those values too.

The 64KB stand-alone exe file is at:
<http://www.ifwtech.co.uk/g3sek/in-prac/winatt.exe>


--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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