[R-390] Heretical comparison: R-390A vs WJ-8716

[Tim Shoppa]

Yeah, I know. I'm bad. I got a WJ-8716 from that E-place last month.

This is Watkins-Johnson's HF receiver from the early/mid-80's. Mine has the
preseelctor (PRE), ISB, and GPIB options. The last means that (gasp!) it has
a microprocessor in it.

So how does it stack up against the R-390A? First opinions, after a few
weeks of use:

1. The WJ-8716's shielding is way better than the R-390A's. If I unplug the
antenna from the WJ-8716, I get nothing. At all. Anywhere. Not even the
blowtorch AM transmitter in my backyard shows up. Compare this to the
R-390A, where even with the covers on several of the local AM broadcasters
show up pretty well and even the powerhouse SW broadcasters can come in
on the 6MHz band.

I've been told that the WJ-8716 is supposed to be Tempest Compliant, and
if so they sure did it good. There are about 8 trillion screws holding the
top and bottom covers on. (OK, really like sixty some) and everything
on the back comes out on BNC's. Internal modules are on little PCB cards
that go pretty securely into a backplane. Built-in extenders etc.

2. Sensitivity-wise, both have plenty through at least the low HF. With the
low sunspot count there's not much to listen to above 20MHz right now.

3. Selectivity-wise, WOW. The WJ-8716's filters (a crystal filter at 10.7MHz,
plus mechanical filters at 455 kHz) are incredibly flat in the middle and
steep on the sides. It has 300Hz, 3.2kHz, 6kHz, and 16kHz bandwidths.
This is where this receiver really shines. If the signal is not in the passband,
it's gone.

4. For AM reception without any awful hetrodynes, they both do about
as well as each other. For SSB (keep in mind I have no SSB mods nor
an outboard SSB unit for my R-390A) the WJ is a clear winner. It blows
away all my modernish (well, 70's and 80's vintage) ham receivers too.
It also has ISB, which is a unique experience to get different sidebands
in different ears via headphones. Not sure how much good it is other
than "hey wow" (although it does tell you from which side of the
carrier that stupid hetrodyne is coming from without having to lift
a finger! And it's trivial to select the sideband with the least QRM.)

The WJ-8716 only has two AGC time settings: "Slow" (fast attack, slow
decay) and "Fast" (fast on both). The asymmetrical timing on "slow" is
obviously good if you're setting on one frequency but it's a pain when
scanning through the bands because the hang is so long. I'm still not
really used to it.

5. Control-wise, my only complaint is the stupid thumbwheels for BFO
frequency on the WJ. The WJ seems to have a
TCXO master oscillator and it is spot-on from the instant it's turned on.
4 buttons select 4 different tuning rates. The BFO setting is only effective
in the CW mode. Those used to modern digital radios will think that the
WJ's user interface is hopelessly simplistic (no memories, no automatic
scanning, etc.) but it's fine by me (although all the buttons are identical,
I would prefer good old knobs!)

6. Images: I have the previously-mentioned blowtorch AM transmitter in 
my backyard. On consumer-type radios, images of this show up everywhere
up and down every band. On both my R-390A and WJ-8716, these
Images are not a problem. I haven't gone persnickity looking for birdies
or anything.

All that said, I am back to doing listening and tinkering with my R-390A
as well, so I'm not hoplelessly modern yet!

Tim.