[Elecraft] Comparing the K2 to other rigs: background noise

[Eddy Avila]

To All....I find it absolutely fascinating that we're comparing a rig that 
sells for way less than $1,000 to those selling for around $3,000 (and 
that's without additional accessories, ie: the necessary additional 
filters!!!) .....and..... the rig for less than a grand keeps beating 
them!!!

Who's getting their money's worth here, eh?

73's all....k6sdw


>From: Wayne Burdick <n6kr@elecraft.com>
>To: Christoph Rheker <dl4yao@web.de>

>Christoph Rheker wrote:
>
> > ... My TS870 sounds in most cases like
> > there is some kind of life on the bands. For example, during
> > evenings on 15/20m there is always some kind of background noise.
> > When I switch to my K2, there is no such thing!
>
>Chris, the K2 is quieter than the TS870 because it has a single I.F. and 
>less
>overall gain. Because of this, really low-level band noise won't activate 
>the
>K2's AGC. (The TS870 is probably "in the AGC" with normal band noise, even 
>on 10
>meters, because of all of the excess gain.)
>
>But I want to make sure I understand what you mean by "no such thing" in
>reference to band noise. When you connect a resonant antenna to your K2 on 
>any
>band, including the higest bands, you should hear an increase in background
>noise. This should be true even when there's no unusual atmospheric noise 
>on the
>band. Of course the effect will be much more dramatic if you're using a 
>wide
>filter bandwidth.
>
>I'll give you an example, using a test I just did on two different K2s:
>
>1. Switch to one of the highest bands (15 m up), USB (FL1 = OP1 = about 2.1 
>kHz bandwidth).
>
>2. Disconnect the antenna.
>
>3. Connect an AC voltmeter (DMM set to lowest AC volts scale) across the
>headphone jack (use a plug only, no headphones)
>
>4. Turn AF GAIN and RF GAIN all the way up, and turn the preamp ON.
>
>5. The AC voltmeter should indicate around 20-30 mV RMS or higher. This is 
>the
>baseline (no antenna) noise, generated within the K2 itself. It will be on 
>the
>low end of this range if you have a KAF2 audio filter installed, or if you 
>use
>the CW filter rather than the filter on the KSB2. The narrower the filter
>setting, the lower the voltmeter reading will be.
>
>6. Connect a resonant antenna, preferably the lowest-noise antenna 
>available for
>the selected band.
>
>7. The AC RMS voltage should go up by a factor of two (6 dB) or more. (If 
>it
>goes up a lot more than this, it could be because there's a signal on the
>frequency you're tuned to, or because there's a lot of atmospheric noise.)
>
>
>I did this test on two different K2s. On the one with a KAF2 installed, the
>noise on 10 meters went from 20 mV to 50 mV RMS when the antenna was 
>connected.
>On another K2 with no KAF2, and using the CW filter set for 2.20, the noise 
>went
>from 35 mV to 70 mV RMS.
>
>If you do this test and discover, for example, that both the antenna off 
>and
>antenna on conditions show much lower AC voltages at the headphone jack, 
>you
>could have a problem with your K2. Try turning AGC off (hold PRE/ATTN and 
>AGC
>together) and see if the results differ significantly. If it turns out that 
>the
>AGC threshold is set too low, you can cure this by reducing the value of R1 
>on
>the Control board. If the signal amplitudes are too low even with the AGC
>threshold set correctly, it could be due to excess loss in the band-pass or
>crystal filters.
>
>If you do the same test on the TS870 you'll no doubt see larger antenna 
>off/on
>figures due to the much greater gain in the receive path. But this is to be
>expected; the K2 design aims for both good sensitivity and low current 
>drain, so
>low-current devices are used at every stage, and there are far fewer 
>stages.
>
>
> > One problem with I don't like is the S-Meter activation issue. With my
> > antennas I often get S7 S-Meter readings without any "real" signal
> > present. Yes, I have done the RFC11 mod. No, I have not done the mod
> > to the front-end band pass filters. Another item on my list.
>
>The narrower filters should help quite a bit.
>
>73,
>Wayne
>N6KR


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