Hi Mike,
Yeah, when the off-air noise floor is a lot higher than the thermal
noise floor from the JFET pre-amps, the imbalance I was alluding to
wouldn't typically impact the overall noise floor since that is still
limited by off-air noise. In Steve's particular case, aside from one
S3-to-S4 source of QRN, it sounds like has an extremely quiet QTH. Under
those circumstances (especially since we are talking about the higher HF
bands), the thermal noise from the receiver can start to dominate over
the off-air noise. That is when getting the off-air QRN levels balanced
between the two channels (as measured going into the MFJ unit) can matter.
FWIW, I've had the same experience as you nulling out local QRN. In my
case it is noise picked-up on my 160 meter transmit antenna that I null
with the MFJ-1026 using a 20ft top-loaded vertical as a sense antenna
(it's what's left of a 160M RX 4 square that got shredded by the wind
after some varmints chewed through the guy ropes). I should be so lucky
as to have a QTH so quiet that the hiss from those JFET preamps is the
dominate source of noise (that's quiet!).
73, Mike W4EF...............
On 3/14/2020 11:57 AM, Mike Waters wrote:
Steve,
I have an MFJ-1025, and I have never experienced your issues. I was going
to ask some of these questions myself.
I have had very good results indeed with mine for eliminating a single
source of RFI. Something at your end is not right.
Mike,
There have been cases where my 580' Beverage antennas have made a superb
sense antenna. I usually use the W7IUV preamp with the output somewhat
attenuated. Mostly, with the signal antenna being my 75m dipole (with
severe RFI) and a amplified Beverage being the sense antenna.
Every QTH and noise is different, of course. What works for someone else
might not work for you.
73, Mike
W0BTU
On Sat, Mar 14, 2020, 12:46 PM Michael Tope <W4EF@dellroy.com> wrote:
2) Is your sense antenna intrinsically inefficient like a beverage or
K9AY loop or is it something efficient like a tribander up reasonably high?
3) Is your sense antenna intrinsically efficient when you include the
feed line loss (I assume the feedline loss on your main TX antenna is
very low)?
73, Mike W4EF............
On 3/14/2020 9:40 AM, n2icarrl@gmail.com wrote:
I have an MFJ-1025/1026 noise canceler. I like to use it on the higher
HF bands to cancel power line QRN. The noise is typically S3-S4, but I
want it down to S0 to hear the bottom layer of stations. My sense
antenna works fine, and the QRN is canceled. However, the MFJ-1025
amplifier noise is quite significant, often negating the QRN
cancellation. The MFJ amplifiers are J310's. Any recommendations for
something quieter ?
73,
Steve, N2IC
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