[Elecraft] K-3 Contest agc settings

Tue Sep 9 00:33:46 EDT 2008

Get Elecraft to fix ur radio so that the AGC works

better, early versions out of the box necessitated

turning off AGC and riding RF Gain, like the first

DXpeditioners did.  Those who say K3 AGC is ok

either got a good one or got it fixed later.

73

Charles Harpole

k4vud at hotmail.com

> Date: Mon, 8 Sep 2008 09:35:39 -0400
> From: dave.wilburn at verizon.net
> Subject: Re: [Elecraft] K-3 Contest agc settings
> To: elecraft at mailman.qth.net
>
> I have found that I tailor the AGC to the types of signals I am
> working with. Jacks articles were a big help with understanding what
> is going on ( cliffton labs ).
>
> If I am play with weak DX signals, I tend to keep the AGC levels a bit
> hard, meaning louder. Low signals low, high signals high. I have
> also used this, and RF gain together in a contest, to dig weaker
> signals out between the big guns.
>
> When in the midst of lots of big guns, I have to flatten the signals
> out so that my ears are not shorted out by the big signals coming in.
>
> David Wilburn
> K4DGW
>
>
>
>
> H Kohl wrote:
>> Ed ....
>>
>> If I understand what I think you said, the agc settings are
>> dependant on:
>> Pre-amp on/off and / or Attenuator on/off
>> The DSP filter width
>> Which 1st IF filter is active
>>
>> and .....
>> the AGC SLP and THR settings are, for the most part a
>> well kept secret and not to be shared.
>>
>> However mine are SLP= 8 and THR= 4 and, to me, it
>> sounds pretty close to the K2. I don't use NR much on
>> CW because of what it appears to do to the received CW
>> signals.
>> This is with MCU 2.34 and DSP 1.81, which may affect
>> how those two settings are set.
>>
>> If SLP= 8 and THR= 4 are bad settings, please tell me
>> why.
>>
>> 73 Hank K8DD
>>
>>
>>
>> ----- Original Message ----- From: "Ed Muns" 
>> To: "'Mike Kasrich'" 
>> Cc: "'Elecraft'" 
>> Sent: Sunday, September 07, 2008 11:51 AM
>> Subject: RE: [Elecraft] K-3 Contest agc settings
>>
>>
>>>> If you are a contester please respond off list.
>>>
>>> I chose to reply to the list because this is a topic of interest to many,
>>> whether contesting or not.
>>>
>>>> What AGC
>>>> settings are you using? In sprint last night I used the K-3
>>>> (first real contest) and I was less than thrilled with rx
>>>> performance. Close by stations seemed to overload the rx.
>>>> Something I didnt have with my MKV with the inrad mods and
>>>> filters. Been fiddling with the settings but obviously dont
>>>> have it right.
>>>
>>> All my operating is contesting and I've used two K3s for a year now. At
>>> home, there are several local contesters just a few miles
>>> line-of-sight off
>>> the back lobes of my Yagis. At 1.5 KW they saturate my S-meters. Still,
>>> they are unnoticeable when outside my filters and I'm usually run the
>>> default AGC settings. Most people have reported just the opposite
>>> comparison between the MKV and K3, i.e., they prefer the K3 RX in
>>> contest or
>>> crowded band conditions with strong signals nearby.
>>>
>>> The PREamp has more impact on RX overload than the AGC in most cases. On
>>> the low bands, you may even need to engage the ATTenuator. Don't make
>>> the
>>> AGC do all the work by slamming it with too much signal strength.
>>> Certainly, you can optimize the AGC for different conditions by
>>> changing the
>>> threshold and slope. For many it is a matter of personal preference more
>>> than an absolute "correct" setting. You will probably want higher
>>> thresholds on the lower bands due to the noise level. The slope is a
>>> trade-off between reducing gain for strong signals and still having
>>> discrimination between different signal strengths. If you keep the
>>> front-end tamed down with appropriate PRE and ATT engagements, then
>>> you will
>>> find the AGC gives you fine control over the range of signal strengths
>>> rather than relying on it alone for dealing with the very strong signals.
>>>
>>>> filters in rig 2.8, 1.8 and 250
>>>
>>> Remember your "250" filter is really 370 Hz at the -6 dB points, so you
>>> might have it engage at DSP bandwidth of 350 or 300 Hz. But even at 350,
>>> the cascade effect will produce an overall bandwidth of less than 300 Hz,
>>> which is a bit narrow for CW contesting, IMO. At DSP WIDTHs of
>>> 400-500 Hz,
>>> your roofing filter will be the 1.8 kHz, if you have it configured
>>> "normally", so that doesn't give you IMD protection for the DSP with very
>>> strong signals located between your DSP and crystal filter widths.
>>>
>>> (I should point out that some K3 ops don't subscribe to the K3 design
>>> that
>>> deploys the crystal filters as roofing filters that are set wider than
>>> the
>>> DSP WIDTHs to protect the DSP. Instead they prefer the passband shape of
>>> the crystal filter and effectively eliminate the DSP filter by
>>> configuring
>>> their K3 filtering to have the crystal filter engage at DSP bandwidths
>>> GREATER than the crystal filter. Until the DSP WIDTH is reduced to well
>>> within the crystal filter bandwidth, the crystal filter is dominating the
>>> passband shape and filtering. Of course, the DSP will still provide
>>> steeper
>>> skirts at a point well below the passband.)
>>>
>>> 73,
>>> Ed - W0YK
>>>
>>> P.S. Thanks for the Sprint Qs!
>>>
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>>
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