Re: [Elecraft_K3] filters


jbollit@ymail.com
 

“nuf said”

 

Jim

WA9ZBV

 

 

 

 

 

From: Elecraft_K3@... [mailto:Elecraft_K3@...] On Behalf Of Rob Sherwood.
Sent: Wednesday, April 30, 2014 9:43 PM
To:
Subject: Re: [Elecraft_K3] filters

 

 

Comments on my K3 data vs. the three quoted roofing filter bandwidths. 

 

Once the dynamic range values are up in the mid 90s or higher, several factors affect the results. Passive intermodulation in the roofing filter is often a issue, and there is sample variation if one tests several different filters with the same filter bandwidth. The variation in dynamic range due to the slight intermodulation in the filter itself can scatter the results a few dB.  It is hard to know whether the Intermod in the measurement is the result of distortion in the filter or the mixer, not that it really matters. 

 

Also the K3 receiver with the 200-Hz filter (and 200-Hz DSP bandwidth) has a lower noise floor than with the 500-Hz filter and it integrates less phase noise. Thus the dynamic range is modestly higher with the narrower filter.  In the case of the data with the 200-Hz filter, there was no Intermod in the filter or the mixer compared to the level of phase noise.  The League now calls that Reciprocal Mixing Dynamic Range (RMDR).  

 

Nit picking between a 95 dB number and a 101 dB number is rather pointless.  If one is really trying to work weak DX in a pileup, keying sidebands of the undesired stations will often be the limiting factor if they are within 1 to 2 kHz of the DX. 

 

On SSB the problem of the intermodulation sidebands of an interfering signal is even worse. Most rigs with a 13.8 volt power amp are not very clean compared to a tube rig like a Collins 32S-3.  Let's say the DX is S3 and there is QRM 3 to 5 kHz away that is S9 +30 dB, a 60 dB difference. The splatter from the adjacent signal will likely make copy of the DX difficult. The dynamic range of the radio at 90+ dB is way better than the splatter problem.  

 

A 2.1-kHz roofing filter (or a 1.8-kHz) and a 1.8 DSP bandwidth will eliminate the offending signal, but it cannot get rid of the in-band splatter. The Intermod products are on frequency. 

 

It is unfortunate that while receivers have improved dramatically in the last 10 years, transmitters (particularly on SSB) have not.

 

73, Rob Sherwood, NC0B.




On Apr 30, 2014, at 9:37 PM, "Joe Subich, W4TV" <lists@...> wrote:

 


> And if you have the time just look a Sherwood's receiver chart. The
> K3 with a stock filter is really just slightly an above average
> receiver. It's with the optional filters that's when it gets into
> the top receivers on his list.

Sherwood's tests of the K3 were all CW. The wide spaced (20 KHz) test
results were independent of the roofing filter at 104 dB which was the
second highest value registered on the wide spaced IMD test. Your
statement lacks validity and is not supported by the facts. However,
5 KHz spaced dynamic range with the standard 2.7 or optional 2.8 KHz
filters would have been essentially equivalent to the 2 KHz spaced
dynamic range with the 200 Hz as the test tones would be at roughly
the same place on the roofing filter skirts.

Sherwood's narrow spaced tests only measure receiver performance to the
narrow filters. With <500 Hz roofing filters the test tones never get
past the filters (the tones are reduced by at least 20 dB) so the rest
of the receiver including the final mixer is not stressed.

73,

... Joe, W4TV

On 4/30/2014 9:50 PM, Keith Ennis wrote:
> I just don't get the reasoning with the narrow filters and great sounding audio. If I'm contesting and running rates of 150+ per hour. The last thing I am trying to do is make everyone sound good. I use my 1.8 kHz all the time while contesting. I am using it to help block the signals next to where I'm running. I don't have time to worry about how someone sounds.
> And if you have the time just look a Sherwood's receiver chart. The K3 with a stock filter is really just slightly an above average receiver. It's with the optional filters that's when it gets into the top receivers on his list.
>
>
> Keith, XE3/K5ENS
> On Wednesday, April 30, 2014 8:39 PM, "mikerodgerske5gbc@..." <mikerodgerske5gbc@...> wrote:
>
>
> Sorry Ed, see I misspelled you last name.
>
> 73
> Mike R
>
> Check out the QRZ app
>
> On Apr 30, 2014, at 8:34 PM, mikerodgerske5gbc@... wrote:
>
>
>
>> I too agree use lo/hi cut on ssb. You don't touch lo cut much and get a better sounding experience.
>>
>>
>> I've got a 1.8 but in casual operating rarely get that narrow, get close say 2.0 or 1.9 so my 1.8 is rarely engaged. Some day I'll get a 2.1. Also some say contesting and "running" a frequency the 2.1 is preferred.
>>
>>
>> You may not need any for ssb. If you've got ham neighbors or intend on field day or multi multi contest use then they might help.
>>
>>
>> I'd probably want something more tight for cw. Some of the cw filters are a little different from the label.
>>
>>
>> You should take a look at Ed Mouns wonderful presentation, google " demystifying the k3".
>>
>>
>> 73
>> Mike R
>>
>> Check out the QRZ app
>>
>> On Apr 29, 2014, at 2:48 PM, <rosswilcox2002@...> wrote:
>>
>>
>>
>>> hi
>>> i have just got a k3/100w
>>> whack is fitted with 2.7 5 pole
>>> and was wondering what would be the best filters for sub work
>>> and which of the filter locations would be the best positions to fit then in
>>>
>>> thx
>>> ross
>>> m0gtt
>>>
>>>
>>>
>
>

 


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