[Elecraft] RF gain, preamp and attenuator

[Bill W4ZV]

I am a new owner of a K3 and also run an Orion 2 which is IMHO a fine rig.
I like its larger size and remote pod for use in contests.   Put this aside
I need to know how to drive the K3 but am influenced by the O2.   For the O2
I keep attenuation off, preamp on and ride the rf gain and I do this for all
bands on CW including 160 M.   Sometimes for contest work I throw in some
attenuation though it does not seem to be required.   Is it the consensus
that for the K3 a similar approach is used or am I right in gathering that
many of you disable the preamp and introduce attenuation as well as
throttling rf gain?


EI2CN is a very familiar call on 160...most recently in the ARRL DX CW!  I was an original Orion owner for 4 years before getting the K3 so here are some comments which apply to both.

First, it's important to carefully place any receiver's noise floor just below the band noise being presented by your antenna.  There is no hard and fast rule for this because it will depend on the band (low bands being noisier), your antenna's gain and the gain of your receiver.  If you do this properly, you will be maximizing the dynamic range of your receiver above the noise floor and not wasting part of it by being below the noise floor.  Here's a graphic example, where A is the antenna noise, and 1 = ATT, 2 = neither ATT/PRE, 3 = PRE:

1:      0000000000
2:    0000000000
3:  0000000000
A:    N

In case 1, you have too much attenuation so you will miss the weak signal N.
In case 2, the receiver is maximizing its dynamic range above N.
In case 3, You have too much gain (i.e. noise floor is below N) and are wasting some of your RX's potential dynamic range above N.

The simplest way to properly set ATT/OFF/PRE is to apply your antenna (with no signals except band noise) to your RX with RF GAIN max CW, and listen to see if you can hear any band noise increase in the following order:  first with ATT on, then both ATT/PRE off, then with PRE on.  You should stop when you can just detect an increase in band noise when the antenna is applied.  Normally this will mean ATT on for the low bands because the atmospheric noise floor is much higher than higher bands **but** it will also depend on the antenna you are using.  If you have a very lossy RX antenna like a Flag/Pennant, you very well may need PRE on.  If you have a large vertical, you will probably need ATT on.  So the best setting will depend both on the level of band noise and your antenna gain.

Once you have ATT/PRE set properly, then you should back off RF GAIN (CCW direction) until you see band noise stop flickering the S-Meter.  That is, set RF GAIN so it is just at the ambient noise level being shown on the meter.

For the K3, I usually have AF GAIN set at about 9 o'clock and RF GAIN will vary from 3 o-clock to noon...depending on the ambient noise level.  I also often use diversity with two very different antennas.  My 160 TX antenna is a 3-element parasitic vertical with approximately +5 dBi gain and my RX Beverages have approximately -10 dBi gain.  I want to normalize the signals into the K3 so I set ATT on for the TX antenna path on Main and PRE on for the RX antenna path on Sub.  Then I can keep both RF GAIN knobs at approximately the same settings.  I also use the SUB RX Audio Gain fader control so both channels are controlled by the inside AG Gain knob.

I hope this helps and that my little graphic is not too distorted to get the general idea.

73,  Bill  W4ZV



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