[Elecraft] [K3] RE: K3 S-Meter and Noise
Don Wilhelm
w3fpr at embarqmail.com
Sun Oct 4 19:43:06 EDT 2009
Jim,
There are 2 reasons I can think of to make that condition 'normal'.
First is if you have the preamp on for a band where it is not needed -
that would amplify the atmospheric noise when the receiver has no signal
present and no AGC is active. If your preamp is on, try tuning it off
and see if it makes a difference. A good test for whether the preamp is
needed or not is to disconnect the antenna and reconnect it. If the
noise level increases when you connect the antenna, there is more than
enough gain in the receiver - turn off the preamp and try the same thing
again - if the noise level still increases when the antenna is
connected, try again but use the attenuator this time.
If you can just barely hear the band noise, that is the proper gain
setting for that band at that time and your antennas. The noise level
on a particular band will vary, perhaps even on an hourly basis (i.e. 80
meters is noisy during the day, but will quiet down some at night).
The second reason is that you may have the AGC threshold (the point
where the AGC starts to take action) set too high. The K3 has a broad
range of settings that allow one to customize the AGC action so it meets
your personal preferences, but because of this 'liberty', it may take
some experimentation to discover which settings will work best for you
and your particular situation.
In part, what I am saying is that a more sensitive receiver will hear
more band noise than a less sensitive receiver. Yes, there is no reason
to be bothered by that band noise - try reducing the gain of the
receiver front end, even if you have to reduce the RF gain a bit and see
if that helps. A typical K3 is not noisy in itself, and the MDS
measurements will tell you how weak a signal can be heard above the
internal receiver noise floor. Something can be done about the internal
receiver noise if it is too high, but if you are simply hearing the band
noise louder on the K3 than the other receivers, it may simply be due
the the fact that the K3 is more sensitive to signals of any kind - and
band noise coming in on your antenna feedline is a "signal" even though
it may be broadband and undesirable.
As several have pointed out, the S-meter reading can be misleading - the
S1 or S2 level on the K3 may be the same level as an S0 level on other
receivers.
Give a try at reducing the front end gain of the K3 or experimenting
with the AGC settings.
73,
Don W3FPR
Jim HaRRIS wrote:
> Don,
>
> I did not say nor hopefully imply that my "procedure" was intended to be scientific. I was simply doing a layman's side-by-side comparison. Obviously, my K3 has a higher noise level than my other four radio's and it is represented on the S-meter. QSO's that are something like S7 and above are a real problem as during pauses by the person on the other side as the AGC drops I'm hit with this rush of noise as the S-meter settles around S2+. I don't hear this on my other radio's as the noise level is usually settles closer to S0. After 20-30 minutes it becomes mostly unbearable. Maybe this is one of the reasons so many people complain about K3 audio.
>
> Thank you for the reminder about the MDS procedure in the XG1 manual. I'll work on that in the next day or so as I get a chance.
>
> One thing most interesting about this whole discussion on the email forum is that no one has said what I am experiencing is normal for a typical K3. I've been in communication with support and Wayne and none have said it's normal. I've had comments from I don't understand what I'm talking about to in-depth discussions on noise but no one has said what I'm experiencing is normal and it's not a problem.
>
> Wayne has offered a beta software with a revised RF gain procedure that may be of some benefit. I'm going to ask him to send it and see how it works.
>
> Thank you for your reply.
>
> Have a good day and 73.
>
> Jim, W0EM
>
>
>
>
> Date: Sat, 3 Oct 2009 20:50:36 -0700
> From: ml-user+39068-1894282159 at n2.nabble.com
> To: w0em at q.com
> Subject: Re: K3 S-Meter and Noise
>
>
>
> Jim,
>
>
> I know perception is 99% of reality, but your measurement technique is
>
> not entirely valid.
>
> The proper way to make the determination of sensitivity is to measure
>
> the MDS of each of the receivers.
>
> Use your XG1 signal generator to determine the MDS of each reciever
>
> using the technique outlined in the XG1 manual.
>
>
> A more sensitive receiver will create more "antenna noise" than one that
>
> is less sensitive. Say that the K3 can hear a -138 dBm signal, and the
>
> atmospheric noise is -136 dBm, then the K3 will hear all signals on that
>
> band that are greater than that -136 dBm noise level. If the MDS of the
>
> other receivers is at -132 dBm, they will not be able to hear the
>
> atmospheric noise, and will also not be able to hear a signal of -133
>
> dBm either.
>
>
> A receiver that hears more 'antenna noise' is usually the more sensitive
>
> one.
>
> The noise floor - the noise level with the antenna disconnected - is the
>
> limit where the receiver will mask weak signals. OTOH, atmospheric
>
> noise (antenna noise) will mask signals on all receivers.
>
>
> 73,
>
> Don W3FPR
>
>
> Jim HaRRIS wrote:
>
>
>> Tom,
>>
>
>
>
>
>> I have three radio's in my shack besides the K3. I've checked their
>>
>
>
>> S-meters with the recommended XG1 and all have comparable readings. All
>>
>
>
>> four are equally quiet without an antenna connected and with a dummy load
>>
>
>
>> connected. When connected to an antenna the K3 has about 2 S units more
>>
>
>
>> noise indicated than the other radios connected to the same antenna (A/B
>>
>
>
>> switch) and the noise level sounds about that much louder. All volume
>>
>
>
>> controls are at about 9 o'clock. This applies to most bands. Strangely,
>>
>
>
>> WARC bands seem to be mostly excepted.
>>
>
>
>
>
>> This afternoon I took the my K3, K2 and FT-857D mobile using a 54" Li'l
>>
>
>
>> Tarheel II screwdriver antenna tuned to 20 meters. I operated the K3 & K2
>>
>
>
>> from a SLA battery with the van turned off. I was in a park with nothing
>>
>
>
>> electrical for at least a half mile. Volume was again set at 9 0'clock on
>>
>
>
>> all three. The K3 have a steady S1 with peaks to S3. The other radios had
>>
>
>
>> S0 with no peaks. Volumes sounded appropriate for indicated S-meter
>>
>
>
>> reading.
>>
>
>
>
>
>> I've almost completely disassembled the radio and reassembled it and done
>>
>
>
>> the EE INIT reset with no change.
>>
>
>
>
>
>> It's apparent this K3 is more sensitive to antenna noise than the other four
>>
>
>
>> radio's which are all about equal. This leads me to believe this particular
>>
>
>
>> radio is going to bury weak signals in noise making them harder to dig out
>>
>
>
>> than the other radios.
>>
>
>
>
>
>> I've exchanged several emails with support and next week I'm supposed to
>>
>
>
>> talk with someone higher up at Aptos. I'm trying to be patient with this
>>
>
>
>> but it has been over a month since I placed the initial order. During
>>
>
>
>> assembly I had to replace the DSP board for an unrelated problem. If the
>>
>
>
>> radio has to go back to Aptos it will be close to two months since ordering
>>
>
>
>> before I have a fully functional radio.
>>
>
>
>
>
>> Have a good day and 73,
>>
>
>
>
>
>> Jim, W0EM
>>
>
>
>>
>>
>
>
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