TopBand: Rx noise figure

[km1h @ juno.com]

On Thu, 09 Apr 1998 19:39:03 -0500 Larry Higgins <n9dx@michiana.org>
writes:
>Something I've wondered about for some time: if daytime 160 beverages
>require only an amp having a 5 db noise figure or better, and 
>nighttime 20
>db or better, why do we need preamps at all?

Good question Larry. A properly transformered Beverage should not require
a preamp. I really do not understand why some insist on using them.
Loops, EWE's and other low efficiency antennas do require a preamp.
What could be very helpful is a hi Q passive and tuneable preselector. 

Several years ago I measured the NF of several receivers; R4C, TS-830,
930, 940, IC-735, 761, 765, Paragon and a few others. At 14 and 28 MHz
the NF on all were in the 9 to 13dB range.

I can not speak for the latest crop of rigs with switchable preamps, etc.
but a part of that NF is in the front end filters and switching diodes.
Perhaps someone has run tests on the TS-870, FT-1000D and MP, etc.


 I would have thought 
>that
>even the worst receiver out there would do better than a 5 db noise 
>figure,
>let alone 20 db.  

With the popularity of 6M to 160M rigs maybe the new generation of radios
can offer 5dB or less.

73  Carl  KM1H

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