The WJ-8711 / HF1000 series DSP HF Receiver

Above is a picture of the HF-1000 "A", which is no longer sold new.

It can still be purchased "brand new" under it's WJ-8711A professional version in the $ 6000.00 USD area. The "PRE" preselector option is in the $ 4000.00 USD area. NOTE: For some reason the "PRE" option took the HUGE price jump in 2008. So that makes the combo around the $ 10,000.00 USD mark these days for a brand new sample (ouch !!). IMPORTANT NOTE : The general prices that I give here were proper in 2008 and may no longer be valid ??

Prices for sales outside the USA are usually more.

This old "Watkins Johnson Telecommunications Group" is now owned by the Italian firm "Finmeccania" (October 2008).

Previous owners (since 1999) include Watkins Johnson , Marconi , BAE Systems , Signia - IDT and DRS Technologies-(DRS Signal Solutions) (whew !!).

Either version has been proven for performance. See text below.

Dave N9EWO

N9EWO's review on the HF-1000A / WJ-8711A

What you read below are my own personal views.
One of the HF-1000A ,and Two of the WJ8711A's were tested for this report.

*** A Very Expensive Receiver ***

The first hurdle to overcome with any premium receiver like the WJ-8711A is the excessively high cost. We are not talking about a consumer product here.

** Very Light box and no proper feet included ***

The first observation that hits you about the WJ-8711A is it's weight. This is the lightest "Premium" tabletop receiver I have ever picked up , near 10 lbs. Both 8711A's tested did not have the internal speaker option, which would have added a couple of pounds.

The entire set is made of very thin sheet aluminum. It seems the top being a bit thinner than the bottom and sides. Overall we are talking about some very thin metal here. I would not set any other item on top of this receiver. Not a very robust case here.

The front panel is one very thick piece of aluminum. All is of a bear nature, no part is painted or anodized, except for the very front panel (front side only, rear is bear) which has a light gray painted surface. Watchout for the corners of this front panel. They have very sharp edges and one could very easy get injured.

Reports have indicated that the WJ-8711A's case and or front metal was of a anodized nature. If this was true, we have seen this go by the wayside, more than likely to save costs ?

Another small observance is if you shake the set a bit, you will hear the "loose" internal mounting nuts that are set up to use speed screws for a rack shelf mounting brackets. If you don't plan on mounting the set using these 6 screws and the "jiggly" loose speed nuts bug you (as they did me), just insert six 10-32 x 5/16 pan head screws to tighten these up. Of course another way would be to just open the case and remove these 6 nuts and the little mounting clips.

Were all used in a table top configuration. I did not prefer the included hard pop-on plastic feet. For one they were not high enough for my liking and second were the hard variety so the set would slide around in use.

One would NOT be advised to use any self tapping screws (or ANY screws for that matter) into it's raw cabinet, say using older style rubber feet. In one mounting hole especially, this could easily contact and or penetrate the PC board/wiring and damage the receiver, let alone the metal filings that could enter the set using self tapping screws.

Best way around this would be to purchase a tabletop cabinet. "Hammond Mfg." makes very well made high quality "STEEL" tabletop cabinets that work great with these receivers and usually sell for around $ 150. USD. These normally come with rubber feet , but you will want to order the optional rack screws for mounting as none were included from Hammond in the box (at least with with my sample). These cabinets are made in Canada. I found other ones that can be purchased elsewhere are NOT made of steel and lack strength and are more expensive to boot. I used the "Hammond" Cabinet Model Number (black) : RCBS1900517BK1, plus add the. "Hammond" Package of 4 Mounting Screws and Cup Washers (Cup Washers are Black Plastic) : 1421A

*** 2 Inch thick "Chubby Manual" for WJ 8711A *** Latest Samples Include a CD-ROM Manual as Well ***

I must say this is one of the most comprehensive and well written manuals that I have ever seen. At around 2 inches thick it goes over every control, function, operation and option. The manual for the HF1000A was about 1/3 thinner.

Schematics for all circuits and options are shown with an exception for the SEU Speech Enhancement. It is missing as well as a "Real" parts list for it .

A downside is that it is hard to page through with it's old style "webbed" binding. One should be careful not to bend the pages in the plastic binding as you go through it as it could damage them in time. Also this manual lacks pictorials of the 3 main PC boards, in fact the only one that is shown is for the "PRE" option. One other major omission is ANY schematic for the power supply.

The 2003 sample also included a copy (of the same printed manual) in a CD-ROM (PDF format).

*** Excellent - Cool Running Power Supply ***

Both the WJ-8711(A) and it's old very close cousin HF-1000(A) both use a INTERNAL switching power supply that provides voltage to all circuits. But do not confuse this supply with switching types that are used in consumer/computer or even amateur radio equipment. These are low cost and noisy supplies .

This excellent "custom" commercial supply is built for "DRS" by "Condor" in Mexico (model number SP1348A). It runs extremely clean and with very little heat. It has to be the coolest running supply I have ever run across. Overkill for sure but this is a place where you want to go overboard.

We see a small surge protection device (an MOV) mounted near the power switch, but one would be advised to use a additional plug in device (non-MOV) to protect the set even more from power surges and spikes. A "zero-surge" (http://www.zerosurge.com/) or a "Brick Wall" (http://www.brickwall.com) surge protection product would be a excellent idea here. Switching supplies are more subject to surge and spike damage.

But over the years I have only heard of two folks with any power supply failure issues in these receivers (a capacitor failure and both were being used at 220/240 volts). See "user input" near the bottom of this page for more information on this topic.

*** S-Meter Markings ***

The "Signal Meter" is only calibrated in dBm. So you have to do a bit of conversion over to standard s-units. Beter yet just use my free conversion chart below. The later versions of the HF-1000 did indicate a few "S-Unit points" (along with dBm as well). It works excellent with it's "true" readings and have yet to see it pin .

WJ-8711 / HF-1000 Meter Conversion Chart (from dBm to S-Units).
(chart via N9EWO)

*** Displays and Lights ***

Green "LED" displays and indicators are used throughout, and as anyone knows in this department, as long as they are properly fed with the right voltage, LED's will easily outlast any liquid or gas type display. I find LED displays to be easier on the eyes as well.

You do not need any type of "dimmer" with this display, it is good at any light level.

We have only one light bulb to have to deal with, and that is of course behind the signal meter. This is in a socket and easy to change. Bulb number is a 86 (6 volt). It burns on the dim side so should not need replacing too often. But thank goodness for a socket here. Early samples of Ten Tec's RX-340 meter light is another story, good luck on a easy job here.

*** Memories and Tuning A Real Treat / Excellent 1 hz Tuning and Display ***

We have 100 memories. Some would say that this is a bit light and perhaps another 200 or so would be desirable ? I find the 100 works good for my uses. Having anymore would make it more of a chore of "going around the loop". The memories are used for hard to find channels and having too many would be bad.

Selecting , entering and scanning memories / frequencies is simply a first rate affair with this set. The separate display for memory channels are perfect to my operation. As you rotate this knob and select memory channels...you can have it activate as you rotate, or just display them in the "sub" display.

I like the tuning step arrangement. You can program any step you want. You may tune using this step, or select the digit of the display to tune (it flashes in this mode to indicate the selected digit). Excelllent indeed.

We have a super fine 1 hz min. tuning step with of course a digit to show this. It is "dead on" across the entire tuning range as well. Here is an area where most consumer receivers/amateur transceivers are left in the dust. This makes manual ECSS tuning is simply a dream. There is even a external reference adjustment to keep this dead on too (see text located below on this same web page).

*** SAM ***

SAM (Synchronous AM) operates in double sideband. It's is still very useful, reduces fading distortion by leaps and bounds.

Only once in a awhile does the SAM loose lock (for split second) and usually this is because one is slightly a bit off of the center of the signal. Or if you are using too wide of a filter selection and adjacent channel interference creeps in (even a slight amount can do it). But overall it does hold lock very well (more times than not) and is very useful.

Ten Tec's RX-340 is a truly poor performer with it's SAM (yes, I have run "side by side" test's). It looses lock on a STRONG signal totally in the clear....ARF !! Also see my "Miscellaneous Page" for a display bug with the Ten-Tec RX-340.

*** Passband Tuning in CW mode / Excellent Notch Filter ***

We have Pass Band Tuning in the CW mode with the either the HF1000 or 8711. But there is a "sometimes" useful trick that most owners may already know about to use this in other modes. If you wish to "try" PBT for say an AM signal (quazi-manual ECSS) , select CW mode. Set BFO window (offset) to 0000, and then select the PBT mode and tune.

Does not always do the trick, but worth a try.

The adjustable "DSP" Notch is a huge winner. Extremely deep and sharp. Works in the AM, FM, USB, LSB, ISB, SAM modes.

*** Audio Recovery simply the best ever used but more noise too / Punchy Audio ***

In my view where the WJ-8711 receiver shines is in the "Audio Recovery" area. With the right external speaker, this set just can make sense out of the spoken word on a very weak and even muffled station where as on a lesser set is in the noise . While not being a miracle set either..if you cannot make it out with this set..forget it !!!

We do hear a bit more of a harsher sound overall with this set. Static, interference etc, can sound slightly painful to the ears. However this could be the reason why it does so well with audio recovery as well ?? SSB signals tend to have a bit of clipping distortion (even with the slowest AGC setting was used), but this was not detected at all with manual ECSS (brodadcast stations).

The audio amplifer from the speaker output has way above average punch and loudness. It works very well indeed. However, this may be questionable for any current (new) samples ?

Note : The "before" 2003 data sheet indicated the SPEAKER output level as up to 1 W and the JAN 2003 one gave the output of only 500 mW.

I do know for a fact that the 1.5 watt LM388 audio amplifier IC has been discontinued for a very long while now, and I'm wondering if they ran out and finally had to substitute a different "audio amp" IC in later samples ?

This is for "FYI" only ! Let me say here that I have no solid information on this and may mean nothing at all. However it does suggest that the audio is not as high now having a specification of only 500 mW for output? Folks that's 50% decrease in specification here vs the eariler data sheet.

My sample was purchased in Jan 2003, and still has the very punchy 1.5 Watt LM388 IC.

*** No Local Antenna's / Some will detect Audio "Buzzies" / More noise as you grab the tuning knob / Top Sensitivity ***

The 8711/HF1000's must have a antenna always away from the set using GOOD shielded antenna cable. It emits a nasty amount of noise that WILL be picked up by itself if not done. Even with a remote external antenna, there is sometimes a bit left above 15 MHz.

In certain situations on higher frequencies, touching the tuning knob increases this background "buzz" a bit. I have noticed this on both WJ8711A's and the single HF-1000 that I used.

Weirdly this does not seem to take away from the DX side of receiving weak signals. Unless I grab the knob on higher frequencies (above 15 mhz). This could very well be a trait of my antenna's and at different locations could be much different ??

The speaker output can emit a weird digital noise, but this is one of those subjective gremlins. To me is sounds like a hive of disturbed bees. Turning the speaker volume control down to min (speaker on and connected) shows this. When turned up in normal operation, I don't hear it at all. It does not emit from either rear line output, these are totally clean. Again many users may not be able to detect this at all, so it depends on your hearing. However, for some reason the Jan 2003 sample, has less of this noise.

A on/off switch on the back of an external speaker to totally shut off it's output when saying using headphones would be one idea. If you channel one of the "line" audio outputs to another external amplifer (don't use the speaker audio amplifer in the set), this should cure the speaker buzzies totally if it bothers you. Early versions of the HF1000 that use the rear DB15 connector, this "line output" idea still may not cure it.

Let me say once you do get whatever antenna PROPERLY made and placed , look out for some awesome sensitivity. It really struts it's stuff once the self-generated gremlins are taken care of with a GOOD antenna ! It will blow you away !!

*** Both Audio Line Outputs Have "Hot" Levels ***

Connection for the audio line outputs are found on the rear mounted barrier strip block, shown below (as it is for many of the receiver outputs). Again eariler versions of the HF1000 will course have the dreaded DB-15 connector. In either case the line outputs are a bit too "hot" (loud), and appear distorted when connected to any consumer tape deck, audio mixer, mini disc etc. Level adjustment on the external equipment not helping the cause.

The simple cure of course is to just add a bit of attenuation (one circuit for each if you use them both) in the line outputs. At first I used a 47K trim pot, mounted in a small metal box. And of course this control adjusted to proper level. I tried to use a couple of fixed resistors to replace this, but after some extensive testing it "cut" off the high end using the fixed resistors (values I choose may have been the gremlin here, not sure ??). Anyway, I have since gone back to using a 47K trimmer variable resistor. Actually using 2 (one for each output) and have these mounted inside of a modified "3 audio line selector" switch box.

The rear "TB1" connector as seen in a late model WJ-8711A. To achive a proper audio "line level" output with the WJ-8711 or HF-1000, some attenuation is required. I use a 47K trim pot (one for each output) to get the job done. The two resistor "fixed" pad I tried wired within the cord proved to cut off the high end a bit.
(photo via N9EWO)

*** Audio Connections - Do Not Tin the Wires !! ***

The later versions of HF1000's and all WJ8711's use a rear mounted thirteen-terminal audio "terminal block" marked in the manual as "TB1", as shown above . The dreaded noisy DB-15 connectors were used in early versions of the HF1000's (see picture below). This is indeed a bit strange looking when compared to consumer / amateur equipment. The TB15 is a removable terminal block that allows you to pull it out to connect your wires into the holes, clamping these wires in this plug using screws. This system works fine, but I found in my testing that one should not tin the wires with solder. It will not make the proper "crunch" when the screw is tightned down on the wires. You will make MUCH better connections using untinned stranded wire and to be sure not to get too thick of a wire as well. I used 18 gauge for the speaker connections and thinner shielded wire for the "line out".

Who actually makes this plug / socket combo is hard infomation to locate. The manual states the mfg. of this thirteen-terminal audio terminal block socket on the receiver as "Precision Converter Design". After a bit of research here on the internet, it is now called "Precision Connector Design, Inc" in Peabody,MA USA (PCD). The mfg. part number is ELFP13210 (DRS part number: 645518), the manual misses this PLUG part number totally.

Information sent to me from an anonymous contributor, he found a another source for the rear accessory connector (at time of writing, subject to change). They do have a minimum order but is still going to be at a much lower cost vs. going through Finmeccanica-DRS Signal Solutions. part number : ELFP13210 (put this part # in the search line on the web site). "HEILIND ELECTRONICS INC." http://www.heilind.com/

*** Watch that AGC ***

As indicated elsewhere, no matter how I adjust the AGC, SSB signals can have a bit of clipping distortion with certain signals. Was not always heard.

Switching over to the AGC threshold mode and dropping back the "manual gain" can help in this area, but again this could be another reason why we have superior audio recovery ??

*** 66 Bandwidths on WJ8711A also has Wider Bandwidths up to 16 Khz (stock version) ***

Well this may mean a lesser importance to some, but one reason I did not like the HF1000A was the fact that it stopped at 8 Khz. I like the additional wider bandwidth filters that the WJ8711A has that allows filtering up to 16 Khz. It really makes it for me here. I found myself using the wider filters more (above 8 Khz) than not. This really helps with audio recovery.

The WJ8711A has 66 bandwidth selections from .056 Khz to 16 Khz. USB and LSB modes have a range between .900 to 4 Khz and ISB from 1.8 to 3.2 Khz. All other modes have the entire 66 selectable bandwidths. The HF1000's is the same except it stops at 8 Khz for SSB, CW, FM, AM and AMS modes.

*** "PRE" Pre selector Option / RF Overload Circuit as a Bonus ***

With the HF1000A and the Jan 2003 WJ-8711A sample tested, the "PRE" preselector option was installed.

The manual states, the optional suboctave preselector will degrade sensitivity/noise figures between 1.5 to 2.5 db, depending on frequency. The test report that came with the set (tested for the actual sample) indicated the insertion loss at 1.2 db at 15 Mhz and this appears to be correct. So a very slight loss with it in line and if you need every bit of sensitivity for a weak signal it can be bypassed.

Also if you have the "PRE" preselector option installed, it will give you the bonus of a "RF Input overload circuit" along with some static protection. Another very important reason to have the PRE option installed. The RF overload circuit will shut the RF parts of the set down if it detects an excessive RF input. Will also display that the fact on one of the smaller LED displays when engaged.

*** A Solid Proven Performer ***

This receiver has been around in one form or another since the early 1990's and has seen many updates and improvements over the years (DSP IC change etc). It has been tweaked to a pure DX machine that works fantasic for pulling very weak broadcast signals out of the noisy HF bands. Warts and all, we may never see another set like this one in our lifetime ?

Even now being a bit "Long in the Tooth", (in my view) it's still the BEST DSP "stand alone" HF receiver for super weak broadcast listening I have ever used. But again, this is NOT a consumer device (and so for the very high price).

Dave N9EWO
© N9EWO
ver 10.5

Internal Picture
(with preselector option which is installed on the top of the main receiver board)
(Photo : N9EWO)

Photo edited by N9EWO

Rear view of a "eariler non-A version" HF-1000 (no preselector-option installed) .
As the red circle indicates, a DB-15 was used for external connections on early versions of the HF1000. The WJ8711's never used the DB-15 connector that I'm aware of. This was not a good thing as the digital buzzies were more of a problem using this DB connector. This is why for the switch in later HF1000 versions to the "barrier strip"and was a night and day improvement for the "line" outputs (cleaner). This does not help the digital buzzies for the speaker output which can be another "minor" internal gremlin.

WJ-8711 (A) and WJ HF-1000 (A) user notes

Repair of a WJ-8711 - HF1000 Power Supply

Rick Warnett from downunder has made a successful repair on his Watkins Johnson HF1000's power supply. The Condor SP1348(A) "Custom" power supply is used in the WJ-8711 series receivers as well.

The part failure was a capacitor (C31) that shorted right near the (U3) 7912 12 volt negative IC regulator. It's a 10 uf @ 63V rating, electrolytic type.

Anyone who owns a WJ HF-1000 or WJ-8711 series receiver already knows a schematic of this Condor SP1348(A) power supply is missing in the manual for these sets.

Thank You Rick for this most useful information (see photo below, sent via a anonymous contributor).

IMPORTANT NOTE : I have NOT experenced this problem myself with any of the 3 samples I have owned/used .

The Condor SP1348A power supply as found in the WJ8711 and HF1000 receivers (with covers removed).
Lower part of this picture shows the "C31" 10 uf 63 volt electrolytic capacitor "close up" as coved in the above text by Rick Warnett.
(photo edit : N9EWO , photo source : unknown)

More on the WJ8711 - HF1000's Power Supply

(Ben Bijmans from Holland with the HF1000 power supply issues......many thanks Ben).

I hope the headache here will be not be for reading my bad English.

First you have to know in all cases mentioned here, the HF1000 was further working normal, except for the messages.

After I got for the very first time the message "PS ERROR 1" in the most left display, I sent an email to DRS on what the meaning of it was. They told me that there may be a bad electrolytic capacitor in the power supply. So I did remember the story from the man down under who changed with good result the C31 capacitor (10uf 63v) in the PS (as shown/listed above..N9EWO).  And so I did, and after that the HF1000 was working for long time (about 9 months) properly. But then the message "PS ERROR 1" appears again.

For the second time I removed the old C31 and put a new, now a special type 10u 100v electrolytic capacitor. And so again, after repair , the HF1000 worked good but now for shorter time , namely 2 months .

For the third time I put a new another new C31 capacitor, and again the HF1000 worked well without giving any message.

And then after about 4 weeks working well, not only "PS ERROR 1" appears , but also a new message was there, namely "LO ERROR ". I sent another email to DRS and they told me the meaning is the Lower PLL is not locking then. They advised me to make a cold start and so I did , but the problem was still there .

When I turned ther receiver on the radio the first came the message "PS ERROR 1" going into "LO ERROR" and you can hear the receiver was not locking for a few seconds , but after about 10 seconds the radio locked and played well , but the message "LO ERROR" remains.

Having for the 4th time a bad capacitor was almost impossible in my thoughts. When I change the capacitor, the radio worked fine for a time. What more do I touch when I repair the capacitor ??? Well , simple: disconnecting the three connectors from the power supply to make it possible taking it out the receiver for repair.

With contact spray I cleaned the three connectors, WITHOUT doing ANYTHING further inside the supply. Without changing that capacitor again, the HF1000 worked well ! And now for one week the HF1000 doesn't give any error message anymore. I put the RX on and off after long and after short time working. I left it on for 24 hours . No matter what I do , it stays working well . So slowly my trust in the HF1000 is coming back.

I'm thinking that there probably was nothing wrong with the power supply at all ? The only thing from the very beginning on, was bad connections from the power supply to the PC boards. And when DRS was telling me there should be a bad capacitor, and give me more wisdom than I have normal about a receiver , I would have start with cleaning the connectors.

Ben Bijmans , Holland

(I would say that the C31 capacitor should still be the "first" part to be replaced with the SP1348A Condor power supply. See text and picture above. Dave N9EWO)

Dallas Lankford

Just finished measuring the AM sensitivity at 1.6 MHz (usual parameters). 1.0 uV with the preamp on and 1.3 uV with the preamp off. They may as well have left the preamp out. Of course, a little thing like that…

Do I like the WJ-8711A? You bet. It has the best frequency display I have seen. And the other LED displays are excellent too. The tuning knob is identical to the Racal RA6778C knob, but finished differently (black abodized or powder coated). It has a nice heavy feel to it, and an attached dimple (quite large) for spinning with your finger. The 8711A seems very intuitive and easy to use. The frequency entry, step change, and other features are simply the best of any receiver I have used. I suppose you can customize the BW’s for each mode, but I probably won’t bother because it is so easy to select a BW different from the factory default with the push button selected rotary knob (which, with other push buttons, is also used to select mode, AGC release time, noise blanker setting, and so on).

It appears to have 100 memories, but I haven’t used that feature yet. There are separate audio level knobs for the headphones and speaker. Very nice. The manual specifies 2 Vrms into 8 ohms (1/2 watt) for the speaker output, but I measured 3.5 Vrms (1.5 watts into 8 ohms), and an audio BW of at least 100 Hz to 13,000 Hz at less than 3% harmonic distortion. Connected to a good speaker, it sounds excellent to me. Headphone output through a ¼ inch stereo headphone jack (stereo for ISB, L and R common in all other modes) is specified as 10 mW (presumably rms) into 600 ohms, no BW given. Low impedanced headphones seem to work fine.

Pressing the special function key repeatedly toggles you through various user selectable parameters. In particular, it allows you to choose the release (decay) times for fast, medium, and slow AGC. You don’t have complete freedom to choose, but 10 – 100 mS for fast, 100 to 1000 mS for medium, and 1 – 5 S for slow. I reset mine to 100, 1000, and 3. I haven’t had any hets yet, but the (presumably manual) notch filter is there if you need it. And yes, there is AM synchronous detection if you want it. It is the only feature of the 8711A that is not well implemented. A good AMSD should be transparent to the user, i.e., never lose lock, and lock instantly to the strongest carrier in the passband. The AMSD of the 8711A does not meet these requirements. However, since most people can’t tell the difference between a good slow AGC release time and a good AMSD, it doesn’t really matter. The 3 second release time I chose for my slow release takes care of strongly fading SW and MW graveyarders. And in the rare event that it won’t, the 8711A manual gain control is excellent for those occasions.

Tuning around in CW mode with no antenna connected, I did not find any internally generated spurs from 150 kHz to 10 MHz where I got tired of spinning the knob. I did find one at 125 kHz or thereabouts. This WJ-8711A is the most spur-free receiver I have ever tested, bar none. I wish I could say the same about the LO’s, or perhaps it is the DSP circuits. I don’t really know. But tuning around near a carrier produces all sorts of weak birdies. Most of these are within about +/- 20 kHz of the carrier. But there were additional (presumably 1^st LO) spurs at about +32.5, +72.5, … and -47.5, -87.5, …kHz from the carrier, decreasing slowly in level. These correspond to phase noise of about -127 dBc/Hz when using a 6 kHz BW. So they are not really a serious issue, though I would like to see better LO performance in a receiver of this caliber. It is possible that they are spurs of the internal frequency standard. I’ll check this later. I have been running the 8711A head to head against one of my R-390A’s on some weak signals, and it is a dead heat. I am very pleased with it.

Below via the Premium Receiver List :

For weak signal reception, the 340 often keeps up with the WJ8712p/WJ8711a/HF1000a, but never exceeds (the WJ circuits do a better job with weak circuits). Both TT and WJ weak signal improved with use of SE-3.

The Ten Tec RX-340 does a poor job compared to WJ on trans-pacific mw dxing where the AM stations are on 9khz spacing while US on 10 (which means that you often have a weak TP station just 1, 2 or 3 kHz from a strong USA station, even with phasing). The skirts on the DSP filters of the Ten Tec just don't hold up well in this situation.

 SAM on Ten Tec does not work well -- I don't use it. Instead you'll see that I use a SE-3 (and also for the WJ).

Don AC7ZG

PS: The WJ8712p's, WJ8711a's and HF-1000a's are far superior to the other premium receivers I own. Each has its own SE-3, DSP599zx, and Sony E10. 

My icom7800 does not hold a candle to the WJ8712p/WJ8711a/HF1000a for TP medium wave dxing, nor weak signal recovery on the shortwave bands.

Like the ICOM756pro2 and 3, the 7800 has an attenuator in circuit below 1700kHz to prevent overload by AM stations. Guy Atkins has made some circuit changes to his pro3 to bring it into play as a weak signal MW receiver, including removing the attenuation circuit and replacing the roofing filter with one of the 6kHz versions from the 7800. (I've not similarly butchered my IC-7800)

Don AC7ZG

PS:  I've used one of my WJ8711A's for receive (disabled during transmit) along with the IC-7800 to do some very weak signal ham radio qso’s -- the 7800 could not keep up.

I have had my WJ HF-1000A for many years and for the last few years used it with a Sherwood SE-3 synchronous detector. It has been my top receiver, and I have tried many other high-end receivers that have not been able to match it. Then - enter the RA6790/GM .

But first a few word of what "DX" means for me.

a) I am only DX-ing mediumwave, so all my experience with these receivers are based on frequencies below 1700 kHz - no exception ;-)

b) I only target overseas radio stations, primarily North America, Far East and Pacific.

It useful to know that I am located in a "quiet" location - approx 63 degrees north, 10 degrees east, with good "protection" (mountains) to the south. There are no local AM stations, and the strongest AM-signal on the S-meter would be S9+50 dB. I often go on DX-peditions to even more quiet locations. This means that receiver sensitivity is very important, maybe the most important property of the receiver.

Last fall I got a RA6790/GM "in transit" and tested it for a while. It's not the world's most user-friendly receiver, but I was impressed by the ability of the receiver to pick up signals and make them legible. I would say that it matched the HF1000A in most situations where there was little or no interference from nearby channels. This unit was equipped with the standard Racal filters. I used the receiver mostly with the SE-3.

I now have a RA6790/GM with (the hard-to-get) preamplifier + Rob Sherwood's filters and it's dedicated SE-3. This unit was in excellent condition and had been serviced by Gary Wingerd. This one works even better, and I find it as an excellent second receiver. Second because it's not very fast to work with when checking frequencies for carriers etc. like I often do when looking for DX. It's still not as good as the HF-1000A on weak signals close to European stations - this probably both due to the filters and the missing
notch.

To me the biggest disadvantage with the RA6790/GM is the missing notch. When using the SE-3 I get 1/2/3/4 kHz tones (dependent on the filter width) when I am too close to European stations. On the HF-1000A and a few other receivers I have, there is an IF-notch that actually nulls the carrier of the interfering stations. This is much more effective than the audio notch. I do of course use an audio notch on the RA6790/GM now, but I believe this could be better if I had an IF-notch (with have tried with and without on the HF-1000A and there is significant difference).

So compared with the HF-1000A I will say it's the closest I have tried so far. Regarding the RX-340 I have not worked a lot with it, but from what I have seen I am not impressed by its performance. It's very user-friendly (like the HF-1000A) but it does not fit my needs very well. I'd rather have a (or two) RA6790/GM than the RX-340.

73 de OJS
Trondheim, Norway

I have the 8712P - I use them extensively, along with 8711A and HF1000A variants, dxing MW and SW on the WCNA.  I don't have the 8712A's so cannot comment on these directly.

8712P are electrically identical with the WJ8711, but physically 2/3 the height (2U) and 1/2 the width of the WJ8711A( but just a little deeper). The price point is a big higher than a standard 8711A, but not by much. I have yet to see one on Ebay.

You might see an occasional 8712A variant on ebay as a bunch of 8712A boards were let go to the employees at reduced cost due to a QA mistake - - the boards were overcooked in the QA ovens during reliability tests - nothing major, the buyer didn't want them.  These are invariably the older rev of the board that won't permit the upgrade to the most recent 4.1.10 microcode.  (They are the older 4.1.2 and 4.1.3 microcode, and older motherboard).

Orders new from BAE Systems (now DRS...N9EWO) take about 4-6 months. Almost all the features of the WJ8711A are available -- excepting the change in the roofing filter to 8kHz (I've never noted any difference in adjacent channel dxing between the 16 and 8kHz roofing filters, but there are those that feel this does make a difference).

Regards
Don

One of the bets tips I can pass along regarding the WJ HF-1000 (and most every receiver with an adjustable RF gain control) is to learn to use this control to optimise the recovered audio. With the 1000, you can select AGC Threshold mode (described in the manual); in this mode, the RF Gain control will set the AGC threshold when any of the AGC modes are selected. Using the RF Gain control in this mode is a real plus...by backing off the RF Gain to the point that the AGC stops pumping (especially in Synch AM mode), nearly all effects of fading and the like can be either eliminated or greatly minimised.

Due to the position in the circuit where the S Meter signal is derived (it is more an RF signal strength meter than an S-meter as most other receivers do it), the use of the RF Gain control will not be seen on the meter. On receivers where the S Meter signal is derived from the AGC line, you will see the meter reading rise when the RF Gain is reduced; when the meter has stopped fluctuating with fading (i.e., it is higher than with full RF gain but is stable), you've hit the optimum setting. Just sit back and enjoy consistent audio level.

This method of using the RF Gain control has the added benefit (usually) of reducing distortion in the recovered audion due to possible overloading of the detector.

Walt Novinger

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