[Elecraft] (no subject)

[Warren & Barbara Reese]

Tom & Don,

Tom,

When the antenna is connected and disconnected the noise floor moves 
just barely.  You can tell, but it requires a critical ear.

>No, I'm not talking about "antenna noise."  I'm talking about 
>signals, in particular at 21.150.  Using the pre-amp makes signals 
>that are unreadable jump out clearly  above the K2's noise floor and 
>turns them into arm chair copy.

>A note about my antenna.  It is a HyGain 5BDQ trap dipole and the 
>SWR on it is 1.2:1 into about 200' of LMR240.
_____________________________
Don,

3dB does NOT explain the improvement in the copy of signals received, 
it is more like 7 or 8 S units, signal to noise.  A quantum improvement !

Warren
________
OK, that helps explain a bit - 200 feet of LMR240 has more loss at 15 
meters and above than what I find is acceptable for me.  At the shack 
end, on 10 meters, the RF voltage is only about half that which is at 
the antenna base - approximately 3 dB loss.  Your preamp is making up 
for that feedline loss.

LMR240 is good feedline, but at higher frequencies and long lengths, 
I prefer to use something with less loss - I usually use LMR400.

>>However, the sensitivity of a properly working K2 on 15, 12 and 10 
>>meters is sufficient to make a -136 dBm or lower level signal stand 
>>out well above (greater than 3 dB) the internal noise of the K2.  I 
>>have measured many, including yours.
>>
>>Normally the atmospheric noise on those bands is low, especially 
>>during the current (and extended) sunspot low period, and that 
>>allows a preamplifier to be of value.
>>
>>The other thing to consider is the antenna (and feedline loss).  If 
>>there is not an increase in noise (due to the presence of 
>>atmospheric noise) when you connect the antenna to the K2 (or any 
>>other radio), then a preamp will help.
>>If there *is* a noise increase when the antenna is connected, then 
>>*usually* a preamp will not help - it will make the atmospheric 
>>noise heard in the audio output greater, but that is not a signal - 
>>we normally do not copy signals buried in the atmospheric noise - 
>>although a few ops have excellent ears for doing just that.
>>Warren & Barbara Reese wrote:
>>>Dear fellow Elecrafters,
>>>
>>>I want to report the stunning success the PT-3 has had on the 
>>>upper bands.  Especially 15 and 10 meters.  I have long held the 
>>>suspicion that the K2 is deficient in sensitivity on these bands 
>>>and the PT-3 confirms it in spades.  Stations that are 
>>>indecipherable now stand out clearly in arm chair copy.
>>>
>>>Let me recommend to others to try the PT-3 !
>>>
>>>BTW, my K2 has been back to both Gary and Don and has been checked 
>>>on the higher bands for sensitivity.  It has returned both times 
>>>with a testimonial as to it's being OK.
>>>
>>>TR, K6GC, the Great Circle Station
>>>in the State of Jefferson.
>>>http://www.ijpr.org/Page.asp?NavID=1033
>>>
>>>K2/100/KAT S/N 838, Updated with all the new mods.