Will...
A small nit... perhaps my ignorance... but, I think that the roofing
filter [by whatever name] comes after the first mixer, at the so-called
IF frequency. Your points are well made. I think the far out SDR's speak
more to what can conceivably be done versus what's the design approach
that best meets a broad range of desirable receiver parameters. Elecraft
seems to have found the sweet spot in the battle of trade offs.
...robert
On 6/12/2018 15:49, WILLIE BABER wrote:
More then one so2r operator has noted that the 7300 will overload in an so2r
situation so that you cannot clearly hear on 7300 when the other radio is
transmitting (yes, on a different band). Since the 7610 doesn't have a
front-end either, I imagine that it will do the same. Sherwood himself notes
that using the SDR radio (i.e, without a superhet front-end) means reducing
gain to limit ADC overload, but he has also suggested that blocking dynamic
range is over-rated. Generally this is true, dynamic range is over-rated if
you are using one radio. However, blocking isn't over-rated in a field day
situation (more than one radio) or if you have a neighboring op running high
power, or in legal-limit multi-op situations (with antennas relatively close to
each other), or in legal-limit so2r.
Reducing sensitivity works to prevent ADC overload on the lower bands where
sensitivity is not needed in the first place but on 15m through 6m one can use
the sensitivity. While SDR radios have their advantages, some of the
advantages of superhet radios still exist today, namely, that a so-called
roofing filter front-end (which is just a mode-specific filter ahead of the
first mixer) will deliver outstanding blocking AND as much sensitivity as
required (compared to SDR).
I don't see any way around this fact (at least not yet) and you can see the
difference in the Sherwood numbers.
73, Will, wj9b
CWops #1085
CWA Advisor levels II and III
http://cwops.org/
--------------------------------------------
On Sat, 6/9/18, Wayne Burdick <n...@elecraft.com> wrote:
Subject: Re: [Elecraft] Field Day rig experience
To: "Bill" <billcla...@nycap.rr.com>
Cc: "Elecraft Reflector" <elecraft@mailman.qth.net>
Date: Saturday, June 9, 2018, 10:34 AM
> On Jun 9,
2018, at 5:24 AM, Bill <billcla...@nycap.rr.com>
wrote:
>
> Along the
line (lightly discussed under "K3- AF Knob") of
what rigs are used for dxpeditions and Field Day...... How
do the new technology ICOMs (7300 and 7610) do under the
"several rigs on the same band" conditions? The
size, weight, and cost factor is inviting for the 7300 -
BUT!!! Is it up to the job? Close to up to the job? Or,
better left home during these events?
Hi Bill,
Hopefully you’ll get some responses to this
question from those with direct experience. But looking at
it theoretically: both the 7300 and 7610 are direct-sampling
radios with about 25-30 dB less blocking dynamic range than
the K3 or K3S. On Field Day this could have a definite
impact when using multiple transmitters on the same band, or
even on different bands, depending on antenna spacing and
power level used.
Dynamic
range of all of these radios is quantified in the receiver
performance table at www.sherweng.com, specifically the
fifth column (“100 kHz Blocking”).
Wayne
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