[Elecraft] Fwd: FT5000 PIN Diodes

[Wayne Burdick]

Hi Karl,

I think there are a few issues to clear up here.

The K3 uses PIN diodes that are rated down to around 500 kHz, so they  
won't cause any IMD due to broadcast band signals. Such PIN diodes are  
readily available, but more expensive, so I can see why a manufacturer  
might want to use relay switching instead. That wasn't an option in  
the K3 -- it had to have solid-state T/R switching.

In addition to using the right PIN diodes, we took two extra  
precautions.

First, we incorporated a high-pass filter into the T/R switch. It  
rolls off signals below 1 MHz to ensure that extremely strong signals  
in the 500 kHz range or below are attenuated. The attenuation at 500  
kHz is about 20-25 dB. This is not a problem for casual broadcast band  
DXing.

However, we also provide a way around the T/R switch: the RX ANT IN  
jack on the KXV3 or KXV3A module. Most broadcast-band enthusiasts  
connect their low-band receiving antenna directly to RX ANT IN,  
bypassing the high-pass filter. If you still have a particular station  
that's a problem, you could use an external notch filter in line with  
RX ANT IN.

73,
Wayne
N6KR


On Nov 15, 2010, at 3:33 PM, Karl Marderian wrote:

>
>
> Sent from my iPhone
>
> Begin forwarded message:
>
>> From: Karl Marderian <karlmar at sbcglobal.net>
>> Date: November 15, 2010 3:23:33 PM PST
>> To: "elecraft at mailman.gth.net" <elecraft at mailman.gth.net>
>> Subject: FT5000 PIN Diodes
>>
>
>> As I remember, when I bought my K3. I want to receive AM, even down  
>> to the low broadcast band. I was told that I needed the optional  
>> receive plug. This was to bypass the PIN Diodes.
>> Maybe this is why Yeasu did not use them.
>> N6XVT. Karl