KX3 Receive Performance Below 1500 kHz

[Mike Morrow-3]

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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[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
>
> ______________________________________________________________
> 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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