The AM Forum

OK
I spent two days on my scanner.
Here is the link for the .pdf's
http://www.criticaltowers.com/General%20Web%20Pages/Ham%20Stuff%20Page.htm
Enjoy
Keith
WA1HZK

Damn, Keith, thanks a million for this!!  **Greatly** appreciated!

Where did you get the manual?? I purchased a copy from Fair Radio 7-8 years ago. I haven't had time to download yours yet but I really appreciate the effort. I am going to pick up another one on Friday--or at least look at it. It was recently purchased from BAE (they bought WJ a few years back) for big $. It will be an opportunity to see what is available. The main thing I want to find is info on the pre-selector, as well as data on the 8716A (I have an A & -)
Skip

Keith,
FYI Guys there is a void in the center of each schematic page. When you scan you can usually overlap and lose some of the margin or they should be done in 3 scan pages to make sure everything is in the picture. I spent over a week scanning the 6830 manual and learned the hard way. I have not looked at this RX in a long time and still think it was well done.
The AM detector is no big deal so they must have set the operating point right. the RX uses a lot of 2N5109s making it a good one.

Man I could hot rod this radio.
I would start with stronger mixers and the tight filters in the first and second IF. The first post amp something stronger. This radio was plus 20 dBM IP3 but I bet it would be easy to push it to plus 30 dBM.

It's a copy of a copy supplied by a good guy, Larry Strong. He had mercy on us and loaned it to me. Fair Radio sales wants $99.00 for a copy.
Keith

The post mixer amp in my 8716 is different than the one in the skizmatic, the latter being one of those mini TO-5 WJ three legged amps.  Mine has a grounded gate FET post amp similar to the grounded gate amp right after the roofing filter.

I think you need to find one, Frank, and go to town  ;)

Hi John,
I saw the CP643 after the second mixer. Also saw that mmic amp after the first mixer but have not looked it up yet. I bet the real performers are the ones with thght filters in the first two IFs. I would tend to use the CP640 or CP666 in each stage. The thing I don't like about WJ is the mechanical design. It does have a nice synthesizer though.
The RF590 has the coolest IF and the RA6830 DF and R3030 are also very good.
Racal has the best first mixer.

I'm kind of yellified to see that the forward bias current of 3 PIN diodes will flow through the 1st LO VCO tank inductors.  One varactor diode, instead of 2 in series.  Is the 8716 supposed to be good with respect to phase noise?

Tom,
I measured the phase noise on the WJ and was quite surprised with it.
Yup a pair of diodes would have been better in the VCO.  fc

What did you come up with in the phase noise dept? I had the Harris, Racal, and WJ lined up for comparison--The Racal drove me nuts to listen too it (hisssss), the Harris was "just OK", -- the only one I kept was the WJ--quiet. The only gripe I have is with the agc. What really baffled me is the Harris RF 350K tranceiver (I still have it) actually seems to have a receiver that hears better than the Harris 2368/550A that I sold. These are all seat of the pants comparisons and I certainly would welcome the views of the more technically savvy. I am going to pick up another WJ--8716B? that goes from .1mhz--1.1ghz and has the built in scope--actually a spectrum analyzer. Does anyone have experience with this rx?

The 8716 goes from 20-1000 MHz but there may have been expander boards to extend the range.  It's intended more for VHF/UHF than HF listening.  A very nice receiver indeed.

After printing out the schematics that are in the signal path I have come up with the following.  If you see any corrections are needed let me know.

Some feature that the 8718 does not have, that a ham would want:
No Muting
No IF noise blanker
No Audio Noise Limiter
no PassBand Tuning
no squelch
no Notch filter.

The receiver does have BFO offset tuning, I believe, so the passband can then be tuned, just not as nicely as the ham receivers.

Muting can be worked around.

I'll stick with my Drake R-7.

So as part of a communications receiver collection, o.k. fine.  But as the only receiver in the hamshack, it doesn't look attractive to me.

The reason the Racal makes so much noise is the way the levels are set around the demodulator and audio section. Dallas Lankford did some nice audio mods to fix these problems. The RA6830 has a better synthesizer but had the same audio level problem. I have my own way of setting audio levels that gets rid of the noise and still passes bite. The problem is driving the output amp into compression with too much drive. This is an easy fix that makes a big difference. This is just settings on two 10 turn pots in the case of the 6830. The 6790 needs a couple resistor changes.
Yes the 8716 is ugly but I don't like the mechanical design. Also triple conversion is a bit yesterday but it does work quite well. I guess it has the 10.7 MHz IF to handle extended ranges. Mark WA1QHQ is an expert on fixing WJs and has done a few of them. we ran some phase noise tests once and I was surprised how well it plays.
Tom, When you have a real RX you don't need bandaide functions. My SDR interface only works slightly better than a stock RA6830 in high noise conditions.
I don't bother with muting because the radio doesn't crash or overload into distortion. All you would need to do is open the speaker anyway. I usually monitor myself with the RX radio.
The all time noisy radio is the Cubic R3030 due to one stage in the demodulator module. Someday I'll fix my two if they ever bother me enough. The R3030 is also a very sensitive RX having an RF stage and preselector. It looks like it will take removing a MC1350 and replacing it with a lower gain amp that handles the same or a bit more power. Then changing the gain of the AGC amp to make up for the quiet. These receivers weren't built for us hams but are easily modified to turn them into fine receivers.  The cubic R3030 has the mechanical BAs of a R390A
BTW the HF350 RX is pretty well done. It has 13 KHz roofing filters so pretty tight.
Dallas Lankford did a number of modifications on the RA6790 transforming it into a very good RX. Most of them were little things that made a big difference. He also got the synthesizer pretty clean.
Well back to building my HPSDR motherboard....the next generation of performance

I think you guys are a little confused with your WJ model numbers. The 8716 and 8718 are HF only receivers the 8617 and 8618 are the ones with built in spectrum analyzer option and a coverage of 20-500MHz with frequency range extender options that allow range extension down thru the HF range and up to 1100MHz. The problem with these receivers is lack of really narrow filters when using them on HF. I have been considering picking one up for a few years now just havn't come across the right deal yet. These can be found on eBay with the frequency extender options for about $1500. A basic 8716 or 8718 is going for about $500 in good shape. I trully believe that the WJ 8716/8718 is one of the best HF receiver bargains out there. I currently own two 8718s and an 8716 and have repaired several others for various people, they are very easy to work on and parts are easy to get. The human interface (front panel) is one of the best I have used however like Frank mentioned the mechanical construction, in particular the backplane and the quality of the PC boards should be better for what the government originally paid for these.

Mark WA1QHQ

^^  Yup.  Listen to what I mean, not what I say ;D

I've found noise blankers and other ham radio toy options to be of limited usefulness,.  Passband tuning might be one exception; the Cubic R-3030 has this (in CW mode only).  The 8716, despite its simplicity and lack of hammy hambone gingerbread, is one stout performer with absolutely fantastic receive audio.

One thing about the 8616, if the pitcher tube is shot, good luck finding a replacement!

Frank,

What is "bandaide functions"?

Please quantify a "real receiver".

John,

I live out in the country and still find the i.f. noise blanker quite important.  My receivers that have i.f. blankers work quite well.  I wouldn't want to be without an i.f. blanker on my main listening receiver.  HF Mobile would be almost impossible without one.  Are you in a noise-free environment or are your blankers not so good?

Years ago I built up a minibox with a 555 timer running at about 100 Hz. powered by a 9 V battery.  The output is coupled through a few pf. to a 51 Ohm resistor on a BNC jack.  One of the handiest things I have ever built.  Sounds just like engine ignition interference.  It gives the receiver about an S-9 level. 

I couple a wire from an r.f. signal generator by the box and crank up the level until I hear a weak carrier in the receiver.  Turn on the 9 V battery and then the blanker, the receiver should again recover the weak carrier.  All receivers I have tested, do well in this test, or eventually do well in this test after repair and i.f. tuning.

What happens when listening to a strong AM signal with the blanker on?

Amazingly Steve, I have never noticed a problem with this.  I use a Drake R-7 and Kenwood TS-430 and leave the blankers on all the time. 

No doubt there are receivers out there with blanker problems, especially the ones with the Russian woodpecker type of blanker that greatly increases the blanking time.  They would sometimes trip on SSB signals and add distortion, and inspite of having an adjustable level too.  In that case you would have to resort to having the blanker turned off and bear with the impulse noise.  The Signal One CX-11 is a great example here.  Is that a real transceiver?

To be fair to the surveillance/point-to-point military receivers in their original market:
1.     the environment they are usually in is presumed to be an isolated site which helps get rid of the impulse noise, a very locally generated noise. 
2.     the stations being listened to are operating outside of the hambands on allocated frequencies free of the lids and interfering carriers.
3.     Aren’t being used in local transmit/receive.

So perhaps they can get way without the blankers, ANL, muting, notch filter and passband tuning.  But listening to NBFM, I would want a squelch.

Tom, I have NBs in the FT-1000MP mk V, the TR-7, Drake DSR-2, and Collins HF-380.  All I notice is more distortion with no corresponding reduction in noise.  I really have little/no impulse noise here.   ANLs are a bit more useful as they clip the peaks of static crashes.  No modern radio I'm aware of has this feature.

You nailed it Tom. Different applications, different requirements, different receivers. That's the way it goes.

The admittedly few receivers I've used with blankers, have always distorted stronger signals, especially AM, and/or produced splatter-like distortion from strong but off frequency signals. I have found them effective in radically reducing impulsive type AC powerline noise, especially when in the SSB (gasp) reception mode.

Unlike JN, I've found very little use for ANL or similarly named circuits on most receivers, for AM use. They seem to be nothing but distortion generators. If static is a problem, I turn down the RF gain or sign off. The NC-303 noise limiter was nice because it was adjustable. You could back it off so it wouldn't distort the audio, but still get some useful limiting out of it.

If we all had 50 acres in a rural location we would have it made. At least that's what Ashtabula Bill says. ;D

http://amfone.net/index.php?ind=media&op=file_view&iden=83

Tom,
I spent the better part of a year trying to build the world's best noise blanker in my homebrew RX. I was never very happy with it. Taking my stock RA6830 compared to the SDR set up the SDR software has a very slight advantage over no noise blanker.
I have found many noise blankers replace noise with the control signal pulse increasing distortion. I have tried many different RF switches and the result was the same. Even if you came close to blanking the noise the silence also caused a transient. The best I ever did was reduce it a bit....and still I wasn't happy. I even had a dealay line in the signal path to give me time to process the blanking pulse. Range gating trick.
 

Keith,

Long overdue – Thanks for copying the manual.  Obviously it’s a great learning experience for us technical types – the opportunity to see what the leaders in premium receiver design did 30 years ago.  Sparks a lot of discussion.

Tom all you need to do with the 8716 to bring it to an IP3 of plus 30 is increase the LO to the first mixer and replace it with one that will handle 1/2 watt of LO and put a better post amp after it and you are there.
The next step is an H mode or FET ring with better roofer.
Networks internation built many of the roofers and all performed about the same. The power limit of a crystal is plus 10 dBM. The  next step is to run a pair off quad hybrids.
This was a very well designed RX that will be around for a long time.
It was one of the best for 1970s design.
The AM detector is pretty simple so operating level must be good.
 

Frank, all you need to do with the 8716 to bring it to an IP3 of plus 30 is put a 10 dB. pad on the input.  A hell of a lot easier and quicker.

If I had one here and put a 10 dB. pad on it, it wouldn't make a bit of difference anyway.  No BC or SW sites near here.

That's fine if you can handle the MDS 10 dB higher.

Unless that receiver is deaf, then a 10 dB pad will mean no difference in reception capability on the lower bands (unless you have an exceptionally quiet location). Average noise at those freqs allows for something like a 20dB noise figure without affecting MDS.

No problem on the low bands I run a 1:4 splitter most of the time but up on 15 and 10 it will hurt you. The RX doesn't have an RF stage so can't handle any more attenuation.

I've been studying the W-J section in Fred Osterman's Shortwave Receivers book.  I see that the WJ8711 followed the 8718.  Any comments on the 8711 and 11A?

8711 and the later 8711A are DSP rigs. the 8712 is the same stuff in a 1/2 rack. the 8712P has a front panel with controls.
I don't know the front end but uses a DSP for demodulation. I seem to remember last IF was 16 KHz into the DSP.
They sell for big money. I've seen them over $4K.
I've never operated one but saw an 8711 once.

8711 is OK, lotsa bandwidths to play with but I prefer the 8716/8718 for simplicity.  At least the 8711 has a real front panel and tuning knob, vs the Collins 95S which relies upon a mouse and crummy proprietary computer program for control.  The 95S is a pretty decent performer though.

Frank and all,

In the early 1980’s I used to do A LOT of short wave listening with my R-7.  In that time period, a local ham was selling a switchable 25 dB attenuator at a hamfest so I bought it.  I kept it on my R-7 input and would switch it in when I listened to strong SW stations, not that I needed to, but because I could, I guess.  I did this mainly with Radio Moscow, the strongest signal I ever heard.  They came in at 60 dB over S-9, yes 10 dB stronger than Ken W2DTC. 

When I switched in the pad I would think wow, my 3rd order input intercept is now +50 dBm., not a station in the world can touch Radio Moscow. 

Then I would sit back and listen to the butt-sucking BS of Vladimir Posner and the grind of the 50 Hertz 3-phase ripple.  STRAPsky.

Back in the 70s I built a hot rod SB303 with three filters cascaded in the IF and a tracking first IF with double balanced mixers. I used to park myself as close to commie radio as I could and operate on 40 meters. back then I took the dynamic range from 67 db to the mid 80s. I dreamed of 90 dB dynamic range.  I then bought a TR7A that ran about 95 dB but the filter blowby limited the performance.....and I dreamed of 100 dB of dynamic range.  Now I have 100 dB and dream or more....
or I could sit on the beach and dream of wild life.

Just looked up the post mixer amplifier and it would support a mixer ahead of it rated for plus 30 dBM IP3. So all you need to do is jack the LO up and change to a better mixer and you have a RX as good as most of the best made today. not bad for a 30 year old radio.