The RACAL RA17 receiver.

Recently I had the good fortune to acquire a RACAL RA17 for myself. This particular set seems to have had several owners and I've been told it originally started it's life at Radio Australia. Along the way it has suffered it's share of distress and modifications that required a little work to resolve.

What's so good about them?

For me, the key to their appeal is three-fold.

The first lies in their application of the Wadley Loop. This effectively means they have incredible frequency stability and tuning accuracy for a receiver of it's time. The overall frequency stability of this set is governed by one single crystal. Something unheard of at that time. The RA17 was the first mass produced set to use the Wadley Loop.

The tuning mechanism is another attraction. The design of the dial allows for easy setting to within  1 KHz. This was amazing for a time where frequency counters were not normal on receivers. 

Finally, their construction. There's something about a radio that's built like a tank that really appeals.

These sets saw extensive use in the armed forces in many parts of the world. They were also used by government agencies, embassies, coast watch stations, shortwave broadcasters and frequency regulatory agencies around the world. Many, like mine, remained in service until the 1980's and will continue to provide great service into the new century for their lucky owners. Not bad for a set that ceased production in 1962.

The first thing to remember about sets like this is that they are probably vastly different from anything you have ever seen or used before. If you're any younger than forty it is highly unlikely that your radio experience would include something like this. Your experience with radios possibly amounts to tuning in the shortwave or ham bands on a dual conversions radio (tube or semi) by tuning up and down a tiny little dial and selecting the appropriate mode (am, cw ssb). Or, it could be as simple as punching in a frequency on a digital receiver or spinning the dial until the digital display shows the frequency of interest. Not that there's anything wrong with that. That's progress.

These sets need to be operated with care and finesse to get the best out of them. If you want to flick the set on and hear music and not fiddle about then this may not be the best set for you. If on the other hand you love valve gear and love the technology of it all and tweaking to get the best out of a radio then this is the one for you.

Using the RACAL RA17.

To familiarize myself with the set I followed the operations guide in the service manual. There are a number of major differences between this set and a many of today's more modern sets. Spending a little time thinking about the set and it's functions will pay dividends later on.

Kilocycle tuning.

The KHz tuning dial is flywheel weighted and it takes almost one complete revolution of the dial to travel 100 KHz.  The KHz tuning scale of the RA17 is made from something like 35mm film and is calibrated in major increments of 10KHz along with minor increments of 5KHz and 1 KHz. The 50KHz and 100 KHz points and the 0 KHz and 1000 KHz are also clearly indicated. A mechanical cursor adjustment is built into the dial escutcheon to permit accurate calibration. At a glance it is a simple matter to identify your receive frequency to the nearest KHz within any 1 MHz band. 

Six foot tuning dial?

The manual quotes an effective dial length of 145 feet. What does this mean? The distance between any two 100KHz points on the dial scale is six inches.  If you had a continuous dial scale with the resolution of 6 inches per 100KHz, it would have to be 145 feet long if you were to tune from 1MHz to 30MHz.  Consider that with some general purpose SW receivers you might go from 2MHz to 6MHz when you tune the dial six inches and you can start to see the appeal of a set like this.

What does the RED scale indicate?

The red scale is used in conjunction with the RA37 and RA137 LF Adapters. This allows the RA17 to tune from 10KHz to 980KHz. Unfortunately, due to the frequency conversion scheme used by these adapters the set tunes backwards when tuning below 1MHz.   For this reason, you will find the red scale is a mirror image of the normal tuning scale.

But the scale goes to zero anyway?

True, but according to the manual performance below 1MHz down to 500KHz is possible with "slight degradation of performance". I've tested mine down to around 200KHz listening for non directional beacons (NDB) and found that it works OK but there is a definite drop off in performance at frequencies below 500KHz. I think the reason the manual quotes degraded performance is because there is no facility on the pre-selector for frequencies below 500KHz.

Tuning linearity.

Whilst the film scale is linear it's clear that no analog tuning system could ever hope to match the linearity of a scale that is 5 feet long. RACAL included a 100KHz calibrator to allow for slight tuning variations.  Basically you tune the KHz dial to the 100 KHz point closest to your frequency of interest and zero beat to the internally generated 100KHz calibration signal. Once you have zero beat, manually adjust the KHz cursor on the escutcheon to coincide with the 100 KHz point on the film scale. The kilocycle dial is now calibrated. In this way you minimize tuning errors. I calibrated my receiver at the 500 KHz point on the dial and found that the maximum error at 1000KHz was -1.5 KHz and at 0KHz it was +1 KHz. This means that for most of the tuning range on my receiver the reading error will remain under 1000 cycles. Not bad considering the set was last calibrated in 1986.

Megacycle tuning.

The megacycle dial is simply marked in one MHz increments from 0 to 29 MHz. Select the Mhz band of interest and that's it. Away you go. The tuning system on the racal is amazing. This would have to be the easiest tuning system I have ever used. This is all due to the Wadley loop design. One dial for Mhz and one for KHz. You can't get much simpler than that.

Dial Lock.

Because the tuning is so smooth and easy to turn, RACAL included a dial lock to protect against accidental bumping. It's a simple friction lock that pushes a rubber stopper against the dial mechanism for both the KHz and MHz dials.

Best tuning system ever?

In later years a number of manufacturers incorporated the Wadley Loop into their design. Amongst the more famous sets available to the public were the Barlow/Wadley XCR-30 and the Yaesu FRG-7.  In my opinion the "one dial for Mhz and one dial for KHz" system is clearly the most elegant and simple arrangement ever conceived.

Pre-selector and Attenuator.

The RA17 has a five band pre-selector including a wide-band setting. The pre-selector is not often seen in modern receivers and is used to manually tune the input of the receiver to the desired receive frequency. Frequencies outside the range of the pre-selector are severely attenuated. The wideband setting is used to by-pass the pre-selector when searching over a large range of frequencies. Situated just below the pre-selector is the attenuator. This is a five step attenuator allowing 0 - 40db of attenuation in 10db steps. Careful use of the pre-selector and attenuator will help avoid cross-modulation where strong unwanted signals are present near the frequency of interest.

Signal Meter.

The signal meter can be switched to shows either AF output or RF level. When set to AF, the audio output level for an external 600Ω output is monitored. This output was designed to be connected to a landline in the case where the receiver may have been installed at a remote listening post. The monitored AF level can be controlled via a screwdriver adjustment hidden under the MHz dial. When switched to RF, the meter shows the current passing through the detector diode. In this way the meter can be used as a rudimentary albeit un-calibrated signal strength indicator. RA17's destined for the American market also included and S-meter setting that was calibrated in 4db per s-point increments.

The BFO.

The B.F.O. uses a reduction drive to allow accurate setting of the B.F.O. frequency over a range of ± 8kc/s. The B.F.O. is exactly tuned to a central point on the I.F. amplifier response when B.F.O. NOTE KC/S control is set to zero-beat with the check bfo function on the calibrator.

Having standardized the B.F.O. frequency, the frequency of an incoming signal may be accurately measured by setting the KILOCYCLES control to a zero-beat position. The B.F.O. should be detuned in order to produce an acceptable note for c.w. and ssb reception.

A.V.C. - Automatic Volume Control.

AVC is designed to keep the audio output level regardless of the signal strength of the received signal. It does this by adjusting the receiver gain depending on the strength of the incoming signal. In the RA17, the BFO is injected into the detector, this has the effect of reducing the receiver gain (sensitivity) because the AVC reacts to the BFO signal as it would to any other received signal.  Trying to resolve strong SSB signal under these conditions can be very difficult if not impossible. CW reception is not much better. To get around this problem the designers made it possible to disable the AVC and control the receiver gain manually. With judicious use of the RF/IF gain control and AF level the results for both SSB and CW can be very satisfying.  The AVC has a switchable long and short time constant. The choice of time constants depends largely on conditions.

Using manual gain.

Using a receiver with manual gain control is strange at first but once you've fiddled with it for a while it becomes much easier. The first thing to do is back the RF/IF gain right off and open the AF level right up. You may hear the audio change and become harsh as you do this. Adjust the AF level to just below the point where the harshness sets in. Your AF level is now set correctly. The audio output will now be controlled solely by the RF/IF gain control. Now bring the RF/IF gain up until you can hear signals at a reasonable level. With my set I found the best results were achieved with a detector current of 80 - 100 uA as show on the meter. Tuning around the bands is a bit of an experience. It's quiet compared to tuning with AVC. Remember that AVC controls receiver gain to try and maintain a constant audio output. With manual gain you are in charge and must ensure that the gain control is at it's optimum setting. Have the gain set too low and you might miss a faint signal. Have the gain set too high and you may overload the receiver. Using manual gain requires patience and a light touch but once mastered becomes second nature.

Limiter.

The limiter on this set is particularly effective with impulse noise. Electric fence or gas starter noises are almost completely eliminated. The limiter works by clipping any signal exceeding modulation peaks of 30%. Using the limiter when listening to good quality signals will result in deterioration of the recovered audio. As it says in the manual  "It does not introduce noticeable distortion below a 30% modulation level". Maybe it should read "It will introduce noticeable distortion for signals with greater than 30% modulation level". Still, if you are listening to faint signals this might just make the difference between making the copy or losing it.

Bandwidth Selection.

Six bandwidths are provided as follows:-

13 kc/s, 6.5 kc/s, 3 kc/s and 1.2 kc/s (L-C filter)

300 c/s and 100 c/s (crystal filter)

The two crystal filters determining the narrowest bandwidths are adjusted to ensure that their centre frequencies are within 50 c/s of each other, it follows that any  filter width can be selected without retuning the receiver. The 13 kc/s and 6.5 kc/s settings are great for listening to A.M. signals.

The Speaker.

If there is one thing that disappoints about this set - it has to be the speaker. There is a 2.5 inch speaker on the front panel that could be used to monitor the receiver output. I doubt anyone could bear to listen to that speaker for more than half an hour. The response, understandably, is awful. Clearly in a monitoring situation the line out or headphone output are much preferred. I imagine that the designers felt the speaker would only be used during the initial installation of the set and as such did not need to be anything special. Good idea back then, too bad for us. An external speaker does wonders for this set.

On the air.

On air tests show a great receiver that is quite capable of matching performance with today's modern receiver.

Frequency stability and accuracy is excellent. On initial testing I came across a QSO on 40M and I was able to determine the frequency of the stations as 7085.2 on the RACAL. A quick check on my Kenwood R-2000 and Yaesu FRG-8800 showed the same result. There is no discernable drift over an extended period of listening.

Sensitivity is great and the RACAL can hear everything that my R-2000 and FRG-8800 can hear.

In the selectivity department I think the RACAL is ahead. With careful use of the pre-selector and manual gain I feel the RACAL just edges out the two more modern receivers.

Recovered audio is not as good as the R-2000 but I feel the Kenwood audio is very hard to beat. The audio from the RACAL is certainly of a high enough standard to allow listening over an extended period - as long as you use a decent speaker!

Overall a wonderful receiver that is just as good if not better than many modern receivers.


References

These few links I think will help you gain a greater understanding into the world of the Barlow-Wadley loop and RACAL and it's receivers. There are other sites to visit but these are my best picks.


Last modified Thursday April 05, 2007