[Elecraft] KX3 Receive Performance Below 1500 kHz

[Wayne Burdick]

Mike,

My explanation stands, but "not really usable" isn't a fair  
assessment. I frequently use the KX3 in the BC band. I can clearly  
copy all the same stations with the KX3 that I can hear using other AM- 
capable radios at my QTH.

The KX3's receive sensitivity does fall off by design below about 1.5  
MHz (as described below), but in many cases you don't need a lot of  
sensitivity here due to high atmospheric noise. The exception, of  
course, is if you're a serious BC-band SWL. In that case you might  
want to consider a simple broadcast-band receiving converter using an  
IF of say 7 MHz. The KX3 provides up to 9 built-in transverter bands,  
one of which could be programmed for this purpose so the VFO would  
still display the actual target frequencies.

73,
Wayne
N6KR


On Jul 7, 2012, at 6:15 AM, Mike Morrow wrote:

> A discussion of KX3 MF lack of sensitivity recently took place
> on the KX3 list.  The KX3 should not be considered really
> usable below about 1500 kHz, as Wayne explsined:
>
> ---- Original Message (from KX3 list)
>
>> I thought there was some advantage to AM BCB reception
>> to be had with the KXAT3.
>
> If a KXAT3 is installed, harmonic images are attenuated,
> but this has little effect on signal strength.
>
>> Why wouldn't the T/R PIN diodes be as well protected by
>> high pass filtering that rolled off below 400 kHz rather
>> than 1500 kHz
>
> The carrier lifetime of the diodes is roughly 1.5 microseconds.
> This means that strong signals at the low end of the broadcast band  
> could cause IMD (IP2) if not attenuated. The HPF provides
> about  20-30 dB of rolloff by this frequency, ensuring that
> this isn't a problem. The KX3 is optimized for ham-band use
> so this is entirely appropriate.
>
> Wayne
>
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