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Reviews Categories | Receivers: General Coverage | Racal RA6790/GM Help

Reviews Summary for Racal RA6790/GM
Racal  RA6790/GM Reviews: 9 Average rating: 4.9/5 MSRP: $900.00
Description: .500 to 30 MHz AM,CW,USB,LSB,FM,ISB knob tuned Mil-Sp receiver.
Product is in production.
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STEVEQ Rating: 5/5 Jun 8, 2011 06:52 Send this review to a friend
Excellent  Time owned: 0 to 3 months
I am a tube radio person with a shack of Drake and Collins including the great R390A. But I took the dive and acquire the RACAL, my first solid state rig ........ the only negative I can say, and it is really not a negative is the audio is not on par with the Collin rigs.

My RACAL is in near mint condition, I can only guess while in military service it was a spare or sat on one freq all the time, I should know I was in Naval Intelligence when the R390A rule the signal intercept world.

My RACAL has the VLF eproms which are nice... the radio is sensitive, very sensitive and I could not resist putting it up again the R390A... well a couple hours into the comparison I concluded both radios are great and a comparison is not fair. The RACAL followed the Collins R390A and its easy of use shines, now on the other hand my wrists are getting stronger as I work the R390A (ha,ha) Since I worked the R390A for CW and DF in the Navy the sound/audio of this radio is music to my ears

Which is better, both are what they are, one generation of receivers apart .... I can bring in SSB on the R390A, it takes a little work but that is the fun of it.

One down side to the RACAL and it is not its fault is it is microprocessed hence I can not play too many tricks on it and make it do something it was not programmed to do. Know what I mean? The R390A well there are a number of things one can "trick" it do to..... but in the end both the RACAL and the R390A are the best I have

Do not hesitate to acquire this RACAL you will not be disappointed ...... the other reviews speak of the techno stuff and the good points so I will not repeat them ........

Well my first solid state radio is a winner that is what I have learned
N1KPR Rating: 5/5 May 25, 2009 08:03 Send this review to a friend
It's a Rock  Time owned: more than 12 months
Stable -- like a big, huge rock!
All the high marks go to the Racal RA6790/GM. Everyone knows that Racal celebrates a great history and reputation for commercial radios. This radio also has its formative roots in some National Agency, but that is of little consequence now. Again, the 6790, like so many of its friends who share free room and board with me, required quite a bit of medical attention. It was mostly therapy for me, but I think the radio got the best of the deal. The traditional design “ooops” with this receiver is the grain-of-wheat display light bulbs. Like anything tungsten, in time they fail. Thanks to Gary Wingerd, I installed his LED lighting kit and finished up the restoration. I’m not a big fan of LCD displays or bargraph S-meters, or membrane push buttons, but those minor annoyances aside, the 6790 has become the de facto, all-time favorite surveillance monitor in my life. I have never, and I stress “never,” have seen or used a radio as stable as this Racal. It reads to 1Hz. When you dial up a frequency to one-millionth of a megahertz, that’s where it goes … and that’s where it stays … period.
I filter-configured this radio primarily for AM work, 5k and 7k positions and usually listen through a Kiwa MAP unit for that little extra weak signal help. I retained one good CW/Data filter, and also use the wide open 16k position for clear signal, armchair work. The standard SSB filters remain as built.
The ergos are basic and without frills. It’s easy and intuitive to operate, built like something from a tractor factory, and has the control feel of a precision lathe. I’m trying to think of some other virtues of this fine radio, but all that
comes to mind is, “dial and listen.” If you can’t hear it on the RA6790/GM, then you need a better antenna or location.
K5YY Rating: 5/5 Feb 23, 2009 13:02 Send this review to a friend
Great GC radio  Time owned: more than 12 months
I have an excellent, completely refurbed 6790GM by Gary Wingerd and it performs flawlessly. I have had many receivers over the years and this Racal Milspec receiver is just a joy to operate. To borrow another reviewer's post.."There are no memory channels, scanning options, notch filters, passband tuning controls, or the like in this receiver. The simple reason is that they're JUST NOT NEEDED to do the job"...
Most 6790s you will find will have 5-6 IF filters. They are sharp with steep skirts and work well. No need for DSP filtering in this radio. The AVC levels work great. Have never had a fault on the B.I.T.E. built in test feature. I only wish I could find a cabinet and the original Racal speaker that was mated with this receiver. Gary Wingerd is the guru of Racals and if you buy a used 6790GM, allow him to go thru it and bring it up to specs.
KK7B Rating: 5/5 May 11, 2006 00:00 Send this review to a friend
This is my lab receiver. A very good choice.  Time owned: 0 to 3 months
I have been using the Racal 6790/gm as my lab receiver for more than a month, and it's a good time to record some early impressions. First, it's nice to own a real receiver again, after a few dacades of making do with a capable but inexpensive amateur transceiver in the lab.

The receivers I actually use on the air are either quirky old boat-anchors (see my review of the HQ-150) or radios I've designed and built for a particular purpose--usually over a narrow frequency range. But the most basic tool in my lab is the best general coverage receiver I can afford. I use it to listen to local oscillator drift and noise, check tuning ranges, listen to the opposite sideband suppression in homebrew ssb exciters, check band conditions by listening to shortwave broadcast stations and WWV and a hundred other little daily tasks. The Racal was a good choice for that application, and I expect I will end up using it on the air as well, if I get around to homebrewing a companion transmitter. All of my previous lab receivers have served in that capacity.

The only other serious candidate I considered in the $1000 price range was an R-390a, and for that price I could have acquired one in decent shape with a recent alignment. I used both the R-390a and R-1051 for years professionally. I chose the Racal for several reasons. Most of the gear I design and build is for SSB and CW, and the R-390a requires external accessories to meet my standards for SSB. The R-390a is still a good tool--but big and heavy and old and it needs more preventative and corrective maintainence than the Racal--I hope. Mostly I chose the Racal because I hadn't used one and after a little study it looked like it would be an interesting radio that would serve the lab function well.

The Racal does everything well except for the audio stages. The "communications quality" audio may be just my particular radio, and it may involve some flaky inexpensive capacitors in the audio stages, but the schematic of the audio amplifier and the particular audio amplifier ICs are similar to circuits I briefly used in my own designs and discarded in favor of more serious discrete output stages and low-noise op-amps. After the first few weeks of listening I wired up an external graphic equalizer and audio amplifier in the rack above the receiver. The gain/filtering distribution in the Racal is also not what one would choose for a "quiet" receiver, so there is a lot of wideband noise on the output. I don't need great audio in a lab radio--and the Racal is considerably better than the amateur transceiver it replaced. I should note that I am more critical of receive audio than anyone I know.

This Racal 6790/gm does a few things very well--it easily tunes to precisely the frequency you want and then stays there. It demodulates CW, USB, LSB, AM and FM at the push of a button. The synchronous AM detector is completely transparent. The five filter bandwidths and all the AGC (or not) modes are easily selectable. Adjusting the BFO is a little more involved than just tuning a knob on an R-390a--but the BFO frequency is locked to the same reference as the synthesizer. The frequency stability of the Racal is better than any previous commercial receiver I've owned, and can be improved still further with an external reference. The skirt selectivity of the SSB filter is noticeably better than the other filters and ideal for my application as a lab radio.

There are no whistles and bells. There are no birdies. There is no drift. The Racal 6790 will tune to within 30 kHz of a rats nest of very strong signals with no ill effects--but once strong signals are inside the 20 kHz roofing filter passband the intermod dynamic range is only average. I would not use it in a CW Sweepstakes. -100 dBm signals at 600 kHz, 4 MHz, 8.2 MHz, 23 MHz, and 29 MHz are all exactly the same volume on the speaker with the AGC turned off.

There are missing features that some users may need: a noise blanker; squelch on FM; memories. But many of the extra knobs on other receivers are needed to overcome limitations that the RA 6790 does not have. The simple front panel is right at home in the lab.

The bottom line is that I need a good general coverage receiver in the lab, and with the Racal 6790/gm in the rack, I don't have to waste any time shopping for a better one or sketching general coverage receivers in the design notebooks.
W9LBB Rating: 5/5 Oct 26, 2003 01:07 Send this review to a friend
An update, and an upgrade...  Time owned: more than 12 months
After a long, difficult search, I've been able to upgrade my "pet" RA-6790/GM with the most elusive of all of the options for the rig, the ISB (Independent Side Band) board. It's been in place and played with for a few months now, so it's time to talk about it.

Where did I find it? Why, in the world's electronics junk box, EBAY!!!

What did i pay for it? I'll never tell!!! However, suffice it to say that the board's appearance on the system triggered a bidding war, and I wound up paying MUCH more for it than I'd have liked!

Having experienced ISB reception capability with my RA-1772, I already knew what to expect in the way of performance and usefullness. Tho scarce these days, occasionally on HF you'll find military ISB transmissions, usually two RTTY signals, one on each sideband or more than that piled up in FDM multiplex stacks. Occasionally, you'll run into an RTTY signal on one sideband, and something else (scrambled voice, some other digital mode, etc.) on the other one.

This isn't the main reason I want ISB in the rig tho... that military stuff is only the frosting on the cake.

If you read my earlier review on this radio you know that I consider it to be the BEST long wave / VLF rig to ever grace my shack. I do a lot of "beacon hunting" for aviation NDBs on long wave, and my RA-1772 showed me that ISB reception is a handy feature to have.

Most aviation beacons generate thier Morse code IDs by keying a second carrier, about 1050 Hz away from the main frequency, that's injected into the PA. The PA stage acts as a mixer, and the resulting output is a modulated CW signal that's receivable on an AM receiver.

The problem tho is that the sidebands of the signal can be sort of lopsided; frequently, only ONE sideband is there. During a band opening when you're digging for a weak signal under 3 or 4 other signals on adjacent frequencies (beacons are allocated 1 KHz apart), ISB can be VERY handy in digging out an ID from an otherwise QRMed beacon. Oddly, it isn't the ISB itself that helps you out; it's the deep, narrow signal null BETWEEN the sideband channels that's deliberately designed into ISB receivers that helps. That null is there to help reduce intermod between sidebands in the detector stages (there are TWO detectors in an ISB rig!) of the receiver.

Anyway... getting the ISB board for is RA-6790/GM is only half of the battle. The board WON'T WORK unless the rig is fitted with SEPERATE filters for LSB and USB. I'd venture to say that the vast majority of RA-6790s in amateur hands have the specialized single LSB / USB filter installed; it was just cheaper that way.

Checking around, I quickly discovered that there are two commonly found dual filter pairs around.

One is a pair of Collins mechanical filters, most commonly seen in the RA-6793 for some reason. The bandpass of these didn't please me; they're a tad too narrow for good SSB rendering, IMHO. These sets are fairly easy to find.

The other pair is a set of matched crystal lattice filters. The "paper" figures for SSB recovery are MUCH better than those for the mech filters. I was informed by several sources that these are RARE beasts indeed... almost equivalent to sighting a unicorn! Chances of finding this set range from "Not Bloody Likely", to "Forget it, Charlie"! Several common Racal parts supply sources said they'd never even SEEN a pair of the crystal beasties.

Imagine my utter shock when a month later a set of the crystal lattice filters suddenly showed up on EBAY!!!

Once again... I went much deeper than I wanted to. The BUY IT NOW button was much too tempting!

Anyway... I had it all now, and I lost no time putting it all together.

Installation is straightforward and simple; you mount the board on four pillars cast into the main chassis, using four machine screws. You then attach a ribbon cable that lives on the IF / AF main board, and add two SMB jumpers to the designated spots. After that, you move one jumper on the IF board to the ISB position, and you're done. Takes about 15 minutes.

A quick BITE test told the radio that something new had been added, and the processor board configured it accordingly.

If SSB is your thing, frankly, you'd be better off with the single USB / LSB filter; the seperate filters are OK, but the single sounds MUCH better.

My first ISB test was to tune in CHU (time signals from Dominion Observatory in Canada). A lot of people don't realize it, but CHU uses vestigial sideband AM; the lower sideband is suppressed.

As expected, the ISB U (upper) button gave CHU loud & clear. ISB L (lower) resulted in dead silence.

I won't go into detail about how it worked out in LF beacon hunting... suffice it to say that my RA-6790 is even MORE deadly a hunter than it was before!

To summarize...

A lot of folks WANT the ISB option for their RA-6790s, but I would advise them to ask themselves one question... WHY do you want it?

The hassle of finding this option, not to mention the probable cost once (or IF) you actually DO find it, should tell you that this is one bells & whistles feature that you'd damned well better have a clearly defined use for before you even get involved.

I don't regret having gone on this unicorn hunt... but I doubt that I'd do so again. The rig is more useful to me because of it all, but it was more trouble than it's worth.


Tom, W9LBB

W9LBB Rating: 5/5 Apr 25, 2002 16:31 Send this review to a friend
A truly GREAT receiver, but it's not for everyone...  Time owned: 0 to 3 months
I've played with my newest toy for long enough now that I feel I can make a few observations on it.

I've owned an used a LOT of communications receivers in my time, but this is my first extended experience with one of the new generation of state of the art, professional grade "super recievers". And, I must say it's indeed an impressive performer.

Let me warn you up front tho... this rig, even as fine as it is, will definitely NOT be everyone's cup of tea! In fact, some folks will downright HATE it.

If you're looking for a receiver with a lot of bells and whistles, try looking someplace else. This is a PROFESSIONAL communications receiver, NOT a ham's or SWL's toy!

There are no memory channels, scanning options, notch filters, passband tuning controls, or the like in this receiver. The simple reason is that they're JUST NOT NEEDED to do the job. The Racal's front panel is downright austere when compared to current high end SWL receivers... besides two liquid crystal displays and a FAULT LED, there's just two knobs (AF GAIN an IF GAIN), two single function keypads, and an AC power switch.

The REAL technological excellence in a Racal is in PERFORMANCE... low noise figure / high sensitivity, selectivity options that can be custom tailored for any purpose, EXCELLENT front end overload characteristics, and optional packages (when you can find them... it can be hard) that will satisfy most requirements. The design of the reciever can only be described as pure technical elegance.

The result is a radio which, in experienced hands, blows most anything else out of the water, but which is uncluttered enough that it's operation is almost intuitive; there's no steep learning curves here. After my R71A, Drake R8, and NR-525, I found the Racal to be a refreshing change; the OTHER radios now remind me of the infant toy known as a "Busy Box".

My "new" RA-6790/GM has a few optional items in it; the RS-232 interface, the elusive RF preamplifier, and the LF / VLF / ELF frequency extension package.

A word of caution to prospective buyers re. this package. The basic frequency coverage is 500 KHz to 29,999.999 KHz. A LOT of radios out there have been "upgraded" by thier owners with the addition ofcopies of the frequency extension EPROMS; this is particularly true of the ex- military R-2174 versions that you're most likely to see on the market.

While the swap DOES work to the extent of allowing the synthesizer to tune the radio below 500 KHz, the EPROMs are only PART of the package. Sensitivity below about 200 KHz takes a serious nosedive, because the package ALSO includes a different 1st mixer and 1st conversion oscillator, optimized for low frequency operation.

With the LF / VLF package, the radio meets performance specs down to 10 KHz. With the LF / VLF / ELF package, it goes down to 1 KHz... and I can tell you that it's the finest VLF receiver I've ever had in my shack. It offers a SERIOUS challenge to the Collins R-389, in many ways.

Other options available (theoretically, at least) include an RS-488 interface board, an an ISB (independent side band) board; like I said, we're talking a PROFESSIONAL receiver here!

Like thier high end consumer counterparts, the biggie on the option scene is IF filters. The Racal will take seven of them (the first one at least, but preferably the first TWO, is / are SSB filter[s]). In my radio the SSB filter is the special single SSB filter rather than the LSB and USB stand-alones. The rest currently installed are 400 Hz, 1.2 KHz, 3.24 KHz, 7.8 KHz, and 16 KHz. This filter set seems to be pretty much standard, but buyers beware; some dealers sell the radios with NO filters installed!

I'm looking to make some filter changes in my rig, and once you've actually got 'em the whole thing is a snap. Racal designed for plug-in crystal lattice filters, but there are a few mechanical filters shown in the manual as available options. Thanks to the internal BITE test (Built In Test Equipment), you just addd the new filters, run BITE, and a built in sweep generator actually sweeps the filters and tells the microprocessor (and you) what the bandwidth of any new filter is! It doesn't just work with Racal filters; a friend of mine made up an IF filter adapter card that fits into the Racal sockets, and he now has his radio stacked up with Collins mechanical filters. He doesn't have the Collins rig anymore and the filters are too expensive to toss out, so he's put 'em back to work!

For chasing RTTY, ARQ, and other digital "utility DXing" modes, this rig is, IMHO, without peer. Even with the rotton conditions the past few days due to magnetic storms, performance has been outstanding.

For SWLing on the broadcast bands, the rig is tops. Very good audio quality, and hard to overload.

My only two gripes with the rig...

The main tuning dial speeds provided in the software. You can select 1 Hz, 30 Hz, and 1 KHz tuning steps. I sincerely wish that Racal had dropped the 30 Hz step and replaced it with a 10 Hz step. While it's very minor really, I would LOVE either this mod or adding a 10 Hz tuning step to firmware.

Second, I really MISS not having a REAL S-meter! For me, an LCD displayed facsimile just doesn't cut it.

If you're looking for the very BEST in receiver engineering and can live without having the clutter of the latest and greatest gizmos in your rig, DEFINITELY take a LONG, HARD LOOK at the Racal RA-6790/GM. I think you'll be VERY glad you did!


KA9P Rating: 4/5 Apr 5, 2002 20:43 Send this review to a friend
Good Value  Time owned: more than 12 months
After using mine for about a year, I find myself coming back to it often. As with most of the professional radios, the full size keypad and otherwise good ergonomics make it easy and pleasant to operate. The ultimate rejection isn't great, but adequate for most purposes.

Near as I can tell, it doesn't mute without resorting to heroic measures, so it's not easily integrated into a ham station. I'm using mine mostly for SSB monitoring, and find it mates up well with a DSP-9 for additional audio flexibility. If you buy one, make sure you've checked out the filter options and know what you're getting, and check out the display illumination to see if all (or enough) of the bulbs (good) or LEDS (better) light up, and try hard to get a full copy of the manual.
W9WIS Rating: 5/5 Dec 21, 2001 11:32 Send this review to a friend
Great High End Receiver  Time owned: 0 to 3 months
The Racal 6790/GM was made from about 1978 to 1996 (the last versions sold for nearly $21,000) and they were provided to US Goverment agencies, the US military and some commercial users like ATT in many variants. I recently purchased my receiver from Gary Wingerd in Hagerstown,MD. Gary was employed by Racal and was the designated service technician for these receivers for 20 years. He maintains a business now in retirement (he's a young guy... I envy him <grin>) repairing, restoring and providing advice to users of these fine receivers. The receiver I purchased was totaly serviced, restored and aligned by Gary prior to my purchase. It was rebuilt as a RA6790/GM-3 which is one of the receiver types the USAF specified and has all the latest software etc.. It has a built in preamp and lightening protection which elevates it's already excellent sensitivity by another 10 dBm. It also has dedicated sideband filters and 4 other filters. Mine was made with Collins mechanical filters although it could take crystal filters as well. The filters are amazing and really steep. There are no memories or scan features on the 6790's.... it was made for single signal monitoring. This doesn't bother me.... it's three tuning rates allow for pretty rapid band excursions. The stock AGC levels are short (<30 msec), medium ( abt 200 msec) and long (4 sec). The short AGC is way too fast for normal cw type signals and results in distortion, pumping and popping.... medium is pretty fast but works well with little popping or distortion (comparison: Drake R-8 AGC is fast (300 msec) and slow (2 sec)). The three AGC time constants are set by three resistors and are easily changed by resistor value changes or the addition of a small internal pot instead of a resistor. AGC was version dependant and not all 6790's were the same... The manual AGC is infinitly variable and works great. The real test for these receivers is their great stability.... set to a station or even WWV and leave on for weeks.... won't matter, return and they will still be smack on frequency. This is exactly what they were meant for. One can now find these receivers for under $1000 which is quite a buy based on what they sold for new. They have their quirks and aren't for everyone but I sure love mine !
N4YTL Rating: 5/5 Jun 29, 2001 23:24 Send this review to a friend
Excellent buy if you can find one!  Time owned: more than 12 months
Here is a chance to get a $5,000+, Mil-Spec receiver for a bargain price! This rock-solid stable receiver includes continuous knob tuning in addition to direct keyboard entry. After a 3 minute warm-up, the frequency displayed is accurate to WWV and stable over days and days. Features include RS422/232 interface (some have IEEE-488 parallel interfaces, but mine did not), adjustable AGC, 5 crystal filters of 500Hz, 1.2KHz, 3.4Khz, 8Khz, and 16Khz, automated built-in test, lighted LCD display, adjustable BFO, and frequency settings to 1 Hz. Although not a lightweight (it is designed for a 19 inch instrument rack), it makes an excellent fixed station receiver. It is powered by 110vac and contains an "N" connector for the antenna. My last receiver was an R-390A, which was good in its day, but this new one is much easier to use, has more features, and as I said, much more stable. Sound quality is excellent and the filters work great with CW and AM. With mil-spec components, this set should last a lifetime. I use mine daily to listen to shortwave broadcasts and monitor my favorite ham band while working in the garage.

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