Hi, Guy,
Thanks for your post and the accompanying email. It is appreciated.
Ironically, one of the reasons I went for the '340 was a very similar
problem to what you describe. However, in my case, it was front-end
overload on a level that the R-75 could not handle. My R-8500s,
generally considered "inferior" to the '75, had no problems at all. A
later test with a Drake R8B showed it had similar problems but handled
them more gracefully.
The situation was a 1000 foot Beverage, boresighted on a 50 kW
flamethrower 85 miles away. Even at my home location, with a 400 foot
wire oriented 120 degrees from the aforementioned Beverage, shows the
antenna voltage in millivolts from that station.
The '340 handles it with aplomb, but this isn't a close-in IP3
problem. The '75 did okay at home, but my WinRadio G303i can't cope
with it. The WR is a great radio at many things, but it has trouble
with close-in IP3 *and* front-end overload. A crowded band it can
handle, but only if you aren't overwhelming the front end or the 22
kHz passband that goes into the sound card.
Back to the '340: The two beefs I think of are the poor dynamic range
and the relative harshness of white noise (static) when run through
the I.F. I was wondering what you were finding. While your message
doesn't suggest that the signals were *that* close in, they probably
made it through the same pass band filter as your tropical stations.
I've been aware of Carl's mod -- I just can't bring myself to cut
traces on my '340 just yet. It would also be a cleaner mod if the
narrow filter switched out when the bandwidth chosen by the front
panel was wider than its skirt, but that would take a fair amount of
reverse engineering of the code in the processor(s).
As for your MP3s... I'd be very interested in hearing them! Perhaps,
for others following this discussion, you can put them on a web page?
If not, with your permission (and size permitting), I can do so.
Regards,
Eric
"4nradio" wrote:
"Eric F. Richards" wrote in message
...
"Brian Denley" wrote:
Guy Atkins wrote:
I've had a Ten-Tec RX340 in the shack for a month, and it
performed significantly worse on tough DX than my modded R-75 and the
RA6790GM I used to have.
-------------------------------------------
Any RX-340 that gets outperformed by a R75 needs to be taken to the shop.
I would tend to agree, unless his definition of "tough DX" is
extremely narrow.
Hi Eric, I should clarify that I had TWO RX-340s on loan, and both
performed equally sub-par at home. On DXpeditions away from strong RF
sources, they are fine receivers.
I'll quote from my reply today to Larry Magne, who heard through the
grapevine that I'd done some A-B-C receiver comparisons involving a RX-340
and wanted more information before IBS plunks down $4,000 for another sample
to test. Sorry for the length of this post, but it addresses the questions
brought up:
-----------------------------------------------------------------------
"Thanks for the note and questions about the RX-340.
I do not own a RX-340, but have DXed occasionally with two different ones at
coastal DXpeditions, and this fall I had a close friend's RX-340 on loan for
an entire month. I also had another friend's RX-340 here for a couple of
weeks.
I used both RX-340s extensively in October and November, along side my
modified R-75 and also a Racal RA6790GM (with narrower, 10-kHz roofing
filters). Each radio was fed with signals from my Beverage antennas through
a Mini-Circuits splitter. Note that I didn't have both RX-340s here at the
same time; one followed the other.
My impression of the Ten-Tecs at DXpeditions has always been very good.
However, at our group's usual DXpedition site of Grayland, WA, there are no
nearby strong RF sources to cause problems. At home it's a different matter,
unfortunately. My permanent Beverages are aimed at my favorite Asian and
subcontinental targets, but the wires are pointed "down the barrel" toward
Seattle/Tacoma area powerhouses on mediumwave (I live to the east of Tacoma,
and my targets--and pests--are generally to the west). I have a number of
locals that are in the S-9 + 50db range on my receivers and a few at S-9 +
65db. Despite the RF alley I manage to log trans-Pacific MW DX from home;
Japan, Korea, and China stations were in abundance this past fall! On the
tropical bands I switch in a Kiwa BCB filter + Extension Filter to ease the
load on the front ends of receivers.
Despite the two highpass filters inline, the RX-340s struggled to hear weak
DX on the tropical bands and above. Both my R-75 and RA6790GM performed well
and practically identical under the same conditions. I initially believed
the problem was RF blocking of the RX-340s' front end, but Dallas Lankford
told me he thinks it's a matter of the RX-340 circuitry reducing the gain in
order to "protect" the DSP AGC loop.
When the DX was audible on the RX-340s, it was always weaker and with poorer
intelligibility than the R-75 and RA6790GM. I did numerous tests throughout
the month, and never did the Ten-Tec equal the performance of the other
receivers. They were also the worst performers when the trans-Pacific MW DX
was coming in. I'm not aware of any production changes that would affect the
RX-340 in this way.
Attached are two short MP3 recordings from my files, demonstrating the audio
from an RX-340 and my R-75. The station is AIR Bangalore on 9425, shortly
after it rose above threshold level and began to be slightly readable. The
antenna was my 700 ft. Northwest Beverage, fed equally through the
Mini-Circuits splitter. As you'll note, there's just noise from the
Ten-Tec's MP3 recording. I have another set of recordings from 3320 kHz
(RX-340, R-75 and RA6790GM), and the results are similar.
By the way, Ten-Tec "guru" Carl Moreschi, N4PY, developed a mod for the
front end of the radio that I installed in my friends' RX-340s. It's a 4 kHz
Kiwa filter module that can be switched in and out of the 2nd Mixer/IF Board
via a relay. He claims it provides over 100 db dynamic range for signals
between 5 and 10 kHz removed from a strong signal. I installed the mod in
the two RX-340s that I had on loan. It worked very well--at times-- on
mediumwave to restore sensitivity close to a powerhouse. Unfortunately there
was an overall attenuation that N4PY and I could never figure out, and after
much head-scratching and experimenting, my friends and I gave up on the mod.
They didn't want to sacrifice any performance of their RX-340s in the
low-noise, low-RF DXpedition environments we enjoy so much.
I was as surprised as anyone by the lackluster showing of these $4K
receivers! My R-75 has numerous mods including a narrower roofing filter,
but I didn't think it could surpass (or equal) a RX-340 under equal, but
difficult RF alley conditions. I thought the Racal with its twin roofing
filters mod *might* give the RX-340 a challenge, but I never expected it to
consistently better the Ten-Tec.
I'll note that every "serious" communications receiver used by the Grayland
participants has performed very similar to the others, time and time again.
Our core group of DXers has travelled to the WA coast since 1989 for 2-3
times per year, and we've had ample opportunity to compare our receivers.
Particularly on the foreign mediumwave stations, you'd be hard pressed to
tell any differences in weak DX readability between a $500 R-75, a $1500
R8B, or a $4000 RX-340! It wasn't until I had a chance to use the RX-340s in
my suburban area that I discovered the surprising differences.
As a side note, I recently sold my Racal and bought an ICOM IC-756Pro
transceiver through Ebay for $1500 and I am extremely pleased with it. I
wanted to have an all-DSP communications receiver at a more modest price
than the RX-340, but didn't like IP3 & close-in dynamic range numbers I'd
been reading for the Winradio G3 series (which I otherwise liked a lot). The
756Pro *consistently* outperforms my modded R-75 at home, and I look forward
to getting them to Grayland for comparisons in that optimum environment. The
24-bit DSP and AGC within the DSP loop evidently contributes higly to the
performance of ICOM's 756Pro series. I know of three other DXers who have
now bought 756ProII and 756ProIII models based largely on my findings and
posted reviews. They are also tropical band and foreign mediumwave DXers. At
a price of ~$1700 used, or $2100 new, the IC-756ProII is quite a receiver,
even for receive-only DX. You gotta love that spectrum display, too!
My apologies for the lengthy reply, Larry, but I felt it best to give you a
full backgrounder to my disappointing experience with the two RX-340s I had
on loan. "
---------------------------------------------------------------------------
If anyone wants to listen to the MP3 samples referred to above, email me at
(remove the NOSPAM) and I'll send you the MP3's as
attachments. I'm not out to bash the RX-340, as I better things to do, such
as DXing! If anyone's interested in a bit of my background that briefly
describes my hobby qualifications (ie., I'm not a newcomer at DXing or
evaluating receivers through hands-on use), please see this bio at
dxing.info: http://www.dxing.info/about/dxers/atkins.dx
Guy Atkins
Puyallup, WA USA
--
Eric F. Richards,
"Nature abhors a vacuum tube." -- Myron Glass,
often attributed to J. R. Pierce, Bell Labs, c. 1940