aeg telefunken e1800a receiver racal ra-3701 ra-3791 ra-1792 harris RF590 watkins johnson 8711 rohde schwarz ek070 radio

Up

RA3791 CONTROLS

Here is a brief overview of some of the more important and unique feature of this wonderful receiver

For full operational details, see the Operating Manual on the documents page

Front Panel

The more commonly used controls are located to the LHS of the tuning encoder. Numeric entry of freq, channel store and recall, tune rates, BFO/bandpass tuning.

To the RHS are the less commonly used controls; Demod mode, AGC speeds, AGC modes, bandwidth selection, meter, squelch, internal loudspeaker, menus and its multifunction M keys (used to navigate through and choose menu items during setting up/prgramming).

 

100 Memories

The memories store all receiver settings and are very intuitive to use. Each memory can be included or ignored for channel scanning. Scanning can be done at the usual variable dwell speeds.

A really nice feature is the ability to view the contents of each memory channel whilst still listing to the current freq, by rotating the tuning control after pressing the CHAN button. Then pressing ENTER to recall and start listening to the chosen channel. That channel number remains displayed in the freq display on the LHS. In this mode, rotating the tuning control, increments or decrements to the following channel.

IF Filter Bandwidths

Up to 100 IF filters for LSB, USB and symmetrical response characteristic may be manually programmed. Symmetrical response filters are used only in AM, FM, CW and FSK modes. SSB filters are setup with a lower and upper cutoff frequency. So in principle, the lower cutoff freq may be set below zero (crossing over) to the other sideband if necessary.

DSP filter co-efficients are calculated by the receiver as you program each filter. Therefore any bandwidth may be setup, from 12KHz (the roofing filter limit) to 70Hz.  !!!

Pass Band Tuning (IF Shift)

The IF passband can be shifted to remove or minimise interference. Available in SSB modes only. Pressing the BFO whilst in SSB and then rotating the tuning encoder, will shift the passband in 10Hz steps. The alpha display shows the position of the centre of the IF passband filter.

AGC

AGC hold and decay times are programmable for all three speeds, slow, medium and fast. A very flexible feature allowing you to tailor the receivers response to your liking.

The AGC attack time was initially one of my concerns, knowing some of the comments regarding DSP sets such as the WJ8711. However, this model has no issues with this. AGC action is very nice indeed and although the attack time is not programmable, it is <5mS and below an acceptable limit of 10mS.

The RA3791 also has the best AGC control range/AF output level. -107 to +13 dBm (120dB) increases the audio output by <2dB.

Tuning Encoder Rate/Step

Both the number of steps (or increments) per tuning knob rotation and the step size can be set for each of the slow, medium and fast tuning rate settings. The setup sizes offered are in multiples of 1, 2, 5 Hz/KHz and steps per rotation are 1000, 500, 200 or 100.

This is the only professional receiver that I have seen that offers this deal of adjustment.

Variable Tuning Rate

Racal introduced this feature originally onto their RA1792 series. The faster you turn the tuning knob, the fast the receiver tunes. On this model the steps it uses to tune are exactly the same steps as setup above. Each of the (slow, medium and fast) tuning rates increment to the next one up as the tuning knob turns faster.

Under the same menu of Variable tuning, a specific step size (e.g. 9KHz for MW/LW) can be entered. This is again a new feature that Racal added to this model.

FSK Tuning Aid

In FSK mode, the meter switch may be pressed to view two segments, representing the FSK tones. Tuning may then be adjusted to centre these two segments in the middle of the display.

The resolution width of this display changes depending on the IF bandwidth.

It is a shame that this tuning aid is only available in FSK mode.

RF and AF Signal Level Meter

This bar is accurate across the complete range of input levels and is calibrate in dBuV.

RF/IF Gain control

The usual slow and fast AGC modes are available.

Toggling the MAN button sets AGC to auto, auto with threshold or fully manual. Squelch is also set using this control.

Notch filter

Operates in any demod mode and with all bandwidths.

Offers a very deep notch. Able to remove the strongest interfering carrier.

The alpha display also shows the exact notch position relative to the centre of the receive passband.

IF Output

Not a particularly unique feature. However, this output is programmable as a wideband output of 12KHz wide or narrow output of the width of the selected IF filter.

Also the output centre frequency may be set in 5KHz steps over a range of 10 to 455KHz and 1.4MHz.

It can be used to drive a tuning aid such as the DK43 or RA2232 or a panadaptor in wideband mode.

 

Optional Automatic Notch Filter

Quite a unique feature for a professional receiver.

This function requires the fitting of a fourth DSP device. Its socket is visible on the LHS picture and the top RHS quarter of the RHS picture.

I will include further details here if I ever fit this option or more information comes to light.

Some of these options may be dependent upon the firmware installed within the receiver. I have very little information regarding firmware versions at present, although there is some mention of this in the operating manual. See documents

 
 
More will be added to these pages as my time permits
If you have any questions or comments about this website, send me an email. I will read all but I can't guarantee that I'll reply to all. This is just a hobby site and my normal days work takes priority
I am not a trader or professional buyer or seller of these great bits of kit. It's just a hobby of mine to collect, play with, digest technical information and then either keep safe or pass on to another equally dedicated individual who will take care of these wonderfully engineered machines!
This website is not affiliated to any manufacture or model and the information contained is of my own work and as such, measurements and figures quoted are for reference only and are not intended to discriminate any individual product
2018 by Andrew Cygan