Topband: We need better preamps for 160 because FT8 activity

[GEORGE WALLNER]

I have built, for DXpedition use,  a very selective RX front-end for 160 m 
for simultaneously operating CW and FT8 on shared TX and RX antennas with 
800 feet of separation. The LC filter had 8 dB loss at 1825 kHz and it was 
about 10 dB down from that at 1840 kHz (-8dB at 1825 and -18dB at 1840). 
That is a 10 dB difference, which should be enough to prevent a good preamp 
from saturating.


(I also built a XTAL filter that was 40 dB down, but only had a 2.5 kHz 
bandwidth -- OK for a DXpedition that can nominate its RX frequency.)

73,
George,
AA7JV

On Tue, 23 May 2023 20:04:24 -0600  wrote:
>"Any new ideas on high performance preamps for 160m?? "
>
>The only thing I can suggest is to build the front end of the
>preamp as if it were a JW Miller style crystal radio, followed by the
>amp itself.  Yep, crystal radio.  Those sets had a bandwidth of ~10khz.
>Super selective and, yes, on 160m the user would have to retune often
>when browsing the band.  Of course, a nice feature could be automatic
>tracking.
>
>73,
>Charlie, N0TT  On Tue, 23 May 2023 12:55:36 -0400 <n4is at comcast.net> writes:
>
>>Hi Folks
>> 
>>I am following the conversation about LOG RX antennas, I understand the painfrom a noise city lot on 160m. it is hard. I am using Waller Flag'svertical, since 2006, and horizontal since 2010, however vertical noise isso bad with new solar panels and EV charges , on top of LED lights, that Ino longer have my Vertical WF, it is inefficient  for a city lot. My HWF isworking very well.
>> 
>>The reason I started a new tread is what I noticed during the last DXseason. The number of KW station on 1840 is growing exponentially. If youhave 100 station with 1kW on a small portion of the band, it is equivalent a100 KW single station. Imagine 500 station, 500KW, My HWF preamp is in usesince 2010, my first QSO with my 6xBF981 preamp was XU7ACY, long path (160mCW), from the same city lot, not so noise as it is today. However now withthe number of FT8 KW's, and most of them very bad linearity, with phasenoise several KHz on each side,  my old preamp IP3 is not strong enough asit used to be.
>> 
>>I will be back to old NORTON's preamp on my station with new high Q frontend. With all the power of 100's FT8 station at the same time, theconsideration for a new RX antenna and new preamplifier is raising the baron overall performance.
>> 
>>Any new ideas on high performance preamps for 160m?? We will need it.
>> 
>>73's
>>JC
>>N4IS
>> 
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