N9EWO Reviews :
Ten Tec RX-320
Ten Tec RX-321
LW / MW / SW DSP Receivers
HUGE "Thank You" to Jim H. KJ7SKB as without his help, the RX-321 review would NOT be here.

The Ten Tec RX-320 LW / MW / SW "Black Box" computer controlled DSP receiver.
In it's day (2000) it was quite advanced and affordable for a real DSP based set and 1 hz tuning.
(N9EWO Photo)

Can actually still be in use with the computer off once tuned and volume adjusted.
Computer communications are via a 9 pin serial port connection.
These receivers use a Windows computer for control / tuning.
DSP is located in the receivers cabinet so uses very light computer resources.

We also test the extremely rare RX-321 variant below that offered many improvements including
front end filtering and TWO TCXO's (filters).

Country of Origin  : USA
Approximate "Test Sample" Serial Number :
DSP Firmware Version Tested : 1.06

N9EWO's Review on the Ten Tec RX-320 Receiver (from 1999 notes)

- Excellent dynamic range
- Excellent DSP bandwidth filtering and totally independent of mode (see Con).
- Tunes in and displays in 1 Hz increments (early Ten Tec software was only 10 hz).
- Superb audio quality along with ultra low distortion (see con).
- Excellent sensitivity (outdoor antenna's using coax feedline).
- Excellent ECSS reception.
- IF shift (see Con).
- Excellent all mode squelch.
- Spectrum display with wide variety of useful sweep widths (see Con and software section).
- Adjustable AGC decay.
- Unlimited memory channels
- Maintains last tuned frequency / settings when PC is turned off.
- Decent owner’s manual.

- No synchronous detection.
- No RF gain control.
- No attenuator.
- Some synthesizer noises.
- Stability OK (improved with RX-321 variant, see below)
- Audio lacks high end frequency response in AM mode.
- Spectrum display scanning poky going.
- Antenna input uses RCA phone jack.
- Some tuning ergonomics only fair (both software tested, see below).
- No notch filter, manual or automatic.
- Lacks IF shift in AM mode.
- S-Meter poorly calibrated and under or over reads (all software).
- Lacks any REAL front end filtering which can allow strong local MW station breakthrough into SW bands.
- Requires external speaker (not included).
- Cabinet make use of self-tapping screws.

LW / MW and SW Coverage Only

Back in 1999 Ten-Tec released a DSP PC controlled set that only tunes the SW/HF spectrum instead of the norm to produce a wide open receiver from DC to daylight. In most respects this set had the edge in it's day, if all you wish to receive is 150 kHz to 30 MHz that is.

We are going to cover the 2 different software packages later, one that come with the set and another from a amateur radio operator.

Nice Owners Manual / Solid Case Construction but Self Tapping Screws

Excellent manual with information for the beginner in this Short Wave game.

A very sturdy steel metal case with a very good looking black paint job is what hits you as you pull out the unit from it’s box. Ten Tec has chosen to use self tapping screws, which takes away the charm a bit .

Ten Tec includes the correct 9 pin to 9 pin serial cable with very  nice flexible cable. No surprises and no adapters needed for a standard home computer. Was good to see.

The on-off switch is of a high quality type and is found on the back of the set. No front panel indicator light is found, not a real drawback . I found if you shut down the computer the set still receives the last frequency tuned to and all other settings (volume setting etc.).

You have a whip antenna that screws on top of the set, and works for VERY STRONG SWBC signals, not very useful and a decent outdoor antenna is near required.

RCA Antenna Jack

Well the first item that hits you as you peek at the rear of the set, is that we have a RCA Jack (phone)  being used for the “Antenna input”. This is almost unacceptable to me, I guess Ten Tec is trying to keep the old Drake Tradition alive ? At least a BNC to be used here, but the performance should not suffer at these frequencies with the RCA. The rare RX-321 variant uses a SO-239 antenna jack (see below).

The cabinet runs only Luke warm which is always a good thing with any electronics.

The unit lacks any internal speaker, and either a external speaker or connection to a sound card needs to be used. My Alpha Delta VRC-2 speaker worked very nice indeed, I would have liked to see even a little small speaker for start up tests, but is not a drawback.

We do of course see a external 1/8 inch phone jack on the rear, as well as another 1/8 inch phone jack for the “Line” jack. So overall was well thought out here. The Line jack is also is the connection to the sound card on the computer. Tec Tec again includes a cable to connect the Line output to the computer, good news again.

Unbalanced Line Audio Output - But watch the Level

A note on the “Line” level. I noticed that you need to be careful how far you adjust the “line” level control. Distortion sets in pretty fast, but provided you go up no further than what is needed, it is quite clean. The levels seem to be at standard levels and work well.

Sensitivity is about average. You are not going to use this set to pull many signals out of the mud, even with DSP. I found myself understanding weaker Station ID’s better with other receivers than with the RX320. But for most moderate-stronger signals and for extended listening period's, the TenTec is more desirable.

A few spurious signals can be found, some signals are awash with a very strong internally generated heterodyne. But overall is pretty clean. I can actually increase the noise floor of this set in certain areas by placing my hand on the top of the cabinet, this is with a external antenna of course.

Decent Dynamic Range / Excellent DSP Filters

I was only able to hear a slight amount of overloading on one occasion. The down side is it seems to be lacking any MW rejection front end filtering. In the evening my local MW (under 1kw) station can easily heard across the entire coverage of  the radio when receiving any another signal, and you have no attenuation to help fight this. The worst flaw in the set that I can see. Can be very annoying.

The RX-320 lacks any real front end filtering (the RX-321 variant model added this (see below).

With the DSP the bandwidth filters are very sharp, excellent skirts. With the right software, many choices are available. A limited range of bandwidths are included on Ten Tec software, but decreases the sets possible capabilities.

Audio Quality While Good is Muffled Sounding AM Mode  / Improved RX-321 variant

I find the overall audio quality is be very acceptable. However, it is on the muffled side when in AM mode. Even when its widest 8 KHz filter is used. It just lacks the crispness and clarity that I’m used of hearing. ECSS helps and gives for much improved audio recovery.

But this is not all bad, the audio has a mellow sound to it, fading and general distortion is very low , or at least where I do not hear it in any large amounts . No hiss either to speak of so overall this receiver can be used for many hours on end.

SSB signals were a pleasure to listen to and worked with no weird sounds of AGC clipping issues or other nasties. See "Sherwood Enginering" test data below.

A professional variant of the RX-320, the RX-321 was designed for Globe Wireless in Florida USA (ship GMDSS use). It was never meant to be sold to the general public. The RX-321 improved the front end filtering, added 2 TCXO (Temperature Compensated Oscillators). Rumors are that only about 100 were manufactured The same RX-320 software applications may be used to control the RX-321. More on the RX-321 can be seen below.

Dave N9EWO
N9EWO, all rights reserved
ver 1.7

**************** RX-320 / RX-321 TESTED SOFTWARE **************
(using Windows 7 64 bit)

We are going to cover 2 software packages here. The included Ten Tec disaster version that comes with the set, and one written by a (now SK) amateur radio operator Clifton Turner KF5OJ. With the Ten Tec included version (2.06 was NOT usable with Windows 7 in the testing period, 2.04 worked fine using a real serial port).

******* RX-320 Controller - Clifton Turner KF5OJ (now SK) ****

Versions Tested :
- 1.10b
- 1.17e (last version)

Clifton done a excellent job with this software package, and is freeware.

- Many operations that totally lack on the included Ten-Tec software (covered below).
- Pass Band Tuning (lacking on Ten Tec software)
- Large tuning meter . However it under reads OR over reads. Pins on most strong signals, but I still find it useful. A peak indicator on this meter has also been added..a nice touch (this can be turned off).
- Two VFO's.
- Separate Line and Speaker controls right on the screen. Makes adjustments a snap.
- You are able to use +/- keys on computer keyboard to adjust frequency (slewing), in whatever step you wish. Excellent.
- Many more IF bandwidths available than with Ten Tec software.
- Tunes in exacting 1 Hz steps as well as 1k, 5k.
- Useful Band scope (scan) operation with later tested version 1.17e. However it's slow going sweeping the up to a 200 kHz swath.
- If the display is set to kHz (selectable between kHz and MHz), then no extra DOT is required for direct frequency entry.
- TIP : For punchier volume control set the "Speaker Minimum" to 35 or 40 in options.

******** Ten Tec RX-320 Control Software *********

(this software originally came on two 3.5 inch floppy discs with the receiver, (click here for later software)

Versions Tested :
- 2.04 (worked fine with Windows 7 provided one uses a real Serial Port on host computer, no USB converter cables)
- 2.06 (did NOT work properly with Windows 7)

- Nice big “Volume” control bar. We found this trait to be actually better over Clifton's program "round" control.
- Line output can be adjusted in properties section.
- Direct entry of frequencies without any other button pushing, always hot.
- Direct entry can only be entered in MHz (extra DOT required).
- Useful Bandscope / Spectrum Display (up to 1.5 Mhz sweep range, better over Clifiton's program).
- Will tune proper larger tuning steps but is a bit quirky (left click of mouse over tuning knob and then arrows on knob for up or down).
- Weird S-Meter with unstandardized markings (thank goodness it can be turned OFF).
- Uses up/down arrows on keyboard for frequency slewing (still too poky slow).
- Keyboard : U = USB, L = LSB, A = AM etc. Great Idea.
- Only 5 bandwidths are available (8.5, 2.5, 1.8, .5 kHz). All are still independent of mode.

Ten Tec RX-320 LINKS (All Subject To Change Without Notice)

eham RX-320 Reviews

Ten Tec's RX-320/D Web Page (includes documents and downloads)

Ten-Tec RX-320 and RX-321 LW/HF receiver radio technical notes

Groups.io Ten Tec forum (Public Archives)

Sherwood Engineering Ten Tec RX-320 Test Report (1999)

N9EWO Review (notes) :
  Ten Tec RX-321
LW / MW / SW DSP Receiver
HUGE "Thank You" to Jim H. KJ7SKB as without his help, the RX-321 review would NOT be here.

The Ten Tec RX-321 LW / MW / SW "Black Box" computer controlled DSP receiver.
This extremely rare improved variant of the RX-320 was manufactured for Global Wireless
and has been reported that only 100 samples were manufactured.
(Frank Gentges K0BRA Photo)

Country of Origin  : USA
Approximate "Test Sample" Serial Number : 01C10xxO (all production was manufactured in January 2000)
DSP Firmware Version Tested : 1.00 (Note : All 100 manufactured samples are 1.00)

N9EWO's Review on the Ten Tec RX-321 Receiver

(as compared to the RX320 above)

- Seven front end bandpass filters for much improved out of band interference rejection including MW bleed into the SW spectrum.
- First mixer has improved double-balanced quad FET mixer for higher IP.
- 2 TCXO's (Temperature Compensated Crystal Oscillators) for improved stability.
- SO-239 antenna connector.
- Spurious signal issues pretty much fixed.
- Barrier strip (screw) connections for power and speaker.
- Green LED power on indicator.
- Professional balanced and transformer isolated 600 ohm line output via DB-9 connector.
- AGC defeat function for use with a transmitter (via same DB-9 connector).
- Uses tapped cabinet screws (not self tapping as with RX-320(D) model.
- Added regulator board for operation between 12 to to 28 volts DC.

- Nonstandard consumer connections for power, speaker and line out connections.
- Larger size case.
- No whip antenna preamp / whip antenna. 
- Slightly increased power consumption.
- Reported that only 100 samples were manufactured (so is extremely RARE !).
NOTE : Some web postings / information indicate that 300 were manufactured. We have received emails from a number of readers that say this is INCORRECT INFORMATION (and 100 is the accurate number) !

Major circuit upgrades over the RX-320 gives much improved performance. The added TWO TCXOs (Temperature Compensated Crystal Oscillators) provides greater stability. Audio line output is now balanced with a isolation transformer and DB-9 connector (see below). The seven front end band filters completely squashes the medium wave breakthrough issue with the RX-320 !

Bandwidths in AM mode sound wider than marked (for example the maximum 8 kHz filter appears more like 10 kHz +). In SSB modes is what you see. Yes you can select the 8 kHz filter in SSB modes for stellar ECSS use. Just as with the RX-320 model, AM mode high end audio frequency is cut off (just like with Drake receivers). Good news is that in ECSS mode this muffled trait is all but eliminated. 

In any event audio quality is simply breathtaking with ultra LOW distortion. Even with the RX-321 lacking Synchronous Detection it is not missed as even virgin AM mode the fading distortion is near nil. See Sherwood Engineering comparison chart below.

Spurious signals that were a problem for the RX-320 have also been completely cleared up.

Dave N9EWO
N9EWO, all rights reserved
ver 1.9

Ten Tec RX-321
**** N9EWO Current Consumption Testing ***
Tested Current Consumption at 12.0 Volts   Meter: Fluke 77 IV   f: 7400 kHz
(volume control set at normal level)

***** ALL MODES *****
405 ma

Ten Tec RX-321 LINKS (All Subject To Change Without Notice)

RX-321 Technical Manual

Groups.io Ten Tec forum (Public Archives)

The RX-321 Web Page / Information

"RX-321 Manual That Never Was"

eham RX-321 Reviews

 Engineering Data

 LOWE HF-250
 AOR AR-7030  Eton / Grundig E1
 Ten Tec RX-320 / RX-321
 * In Band Noise Floor  - 60db

 AM 100 hz Narrow Bandwidth : 1%
Wide Bandwidth :    1%
5 kHz Bandwidth : 3%
 AM 200 hz
Narrow Bandwidth : 1%
Wide Bandwidth :  0.7%
5 kHz Bandwidth : 2%
 AM 400 hz
Narrow Bandwidth : 1%
Wide Bandwidth :  0.5%
5 kHz Bandwidth : 1%
 AM 1000 hz
Narrow Bandwidth : 2%
Wide Bandwidth :  1.0%
5 kHz Bandwidth : 1%
 AM 2000 hz
Narrow Bandwidth : 5%
Wide Bandwidth : 1.5%
5 kHz Bandwidth : 1%
 AM Sync 100 hz
Narrow Bandwidth : 2%
Wide Bandwidth :    2%
5 kHz Bandwidth : 3%
 Not Available
 AM Sync 200 hz
Narrow Bandwidth : 1%
Wide Bandwidth :    1%
5 kHz Bandwidth : 1.5%
 Not Available
 AM Sync 400 hz
Narrow Bandwidth : 0.5%
Wide Bandwidth :    0.5%
5 kHz Bandwidth : 1% 2.7%
 Not Available
 AM Sync 1000 hz
Narrow Bandwidth : 0.5%
Wide Bandwidth :    0.5%
5 kHz Bandwidth : 1%
 Not Available
 AM Sync 2000 hz
Narrow Bandwidth :   ?
Wide Bandwidth :    0.3%
5 kHz Bandwidth : 1%
 Not Available
 SSB 100 hz
(noise) 1%
* < 0.3 %
 SSB 200 hz
(noise) 1%
* < 0.3%
 SSB 400 hz
* < 0.1%
 SSB 1000 hz
* < 0.1%
 SSB 2000 hz
* 0.1%
notes : AM tests - 60% modulation
Sherwood Engineering "Audio Distortion" Test Data
with the Lowe HF-250, AOR AR7030 , Eton/Grundig E1, Ten Tec RX-320 / RX-321.
The Lowe HF-250's overall audio distortion is one of the lowest to be found on a SW receiver
(portable or tabletop). Best SW receiver ever tested for overall audio quality.
Lab numbers courtesy Sherwood Engineering. (N9EWO Chart) 

I will NOT be held responsible for any info that is listed here

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