So John-- if a mismatch can't cause the receiver front end to oscillate,
why when I completely disconnect antenna leads from the SO-239
connectors in the back of my Flex 5K, totally open connection, I get
wild broadband oscillations and spurs across the spectrum on most bands
averaging -95dbm, but if I hook up a dummy load, it all goes away
instantly, and I get a nice flat baseline at abt -138dbm or so?
And why when I plug in a matched antenna, those wild oscillations and
spurs go away, and I just have normal band noise and signals? A closer
match doesn't increase the oscillations, it makes them go away. It's
not power supply noise.
On 11/30/2012 7:02 AM, John Sweeney wrote:
This could be from a noisy switching power supply. I had the kind of noise as
described and changing power supplies cleared it up. A good linear type power
supply may help. No such noise as described now, so not characteristic of a
Flex Radio.
Could even be noise from a close by wall wort supply, even picked up with the
dummy load.
A mismatched antenna will not cause noise on receive. By using a closer
matched antenna you are increasing the atmospheric noise and general signals to
cover up the possible power supply hash noise.
73. John. N3WT.
On Nov 30, 2012, at 8:46 AM, Drax Felton <draxfel...@gmail.com> wrote:
I see this all the time too. Especially pronounced on 6 meters where I can
chase these but not tune them in as they move.
I assumed that all radios have glitches the Flex just lets you see them at
-130db
Sent from my iPhone
On Nov 29, 2012, at 5:23 PM, Steve Sterling <f...@sgsterling.com> wrote:
My Flex 5000 receivers do not like off-normal (50 ohm) antenna loads. Unplug
the antenna, or put an unmatched antenna on them and they create all kinds of
weird oscillations, big wide humps across the spectrum.
Examples:
* short the receiver inputs, all OK, baseline down there below
-135dbm, all bands
* put the inputs on 50 ohm dummy load, all OK, all bands
* open the antenna input (pull the line) and it goes nuts,
* hook my SteppIR up, but tuned to a different band, many times (not
all) the receivers go nuts; same with mistuned G5RV
* tune any of the antennas anywhere close to 50 ohms-- receivers
behave well, best I can tell (noise may be covering up any
oscillations that are well below my local noise floor).
I just figured this is the way these receivers worked, and they don't effect my
operations. Is the antenna you are using a good match?
Steve WA7DUH
On 11/29/2012 1:22 PM, py...@terra.com.br wrote:
Been playing with JT65HF which on 15m is confined to the 2KHz in USB
on 21.076. I-ve noticed a broad noise covering just about all of that
segment and imagined it to be one more of the many noises generated by
a big city, but the other day I left the antenna disconnected and the
noise is still there! Wonder if anyone else has noticed this and if
there is a way to make it go away or move frequency! I´m using PSDR
2.3.5 / Windows 7 on a Flex3000 and have tried other buffer and
scanning rate settings, but nothing seemed to make a difference. It is
-126dB without an antenna and has a cyclic sound to it.73 Rolf, PY1RO
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