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Reviews Categories | Receivers: General Coverage | Racal Ra3702 Help


Reviews Summary for Racal Ra3702
Racal Ra3702 Reviews: 2 Average rating: 5.0/5 MSRP: $(missing—add MSRP)
Description: Professional HF receiver from the 1990's. One of the last analog IF designs from Racal
Product is in production.
More info: http://
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G8MOB Rating: 5/5 Jun 18, 2011 10:03 Send this review to a friend
An excellent non-DSP professional HF receiver  Time owned: more than 12 months
I have the RA3701, the single receiver version, with the optional 100kHz IF output module. I have owned this rig for about 2 years. It came from a reliable professional source and was in excellent condition together with a copy of the user and technical manuals.

I fitted the 100kHz IF output module specifically so that I could use it with the excellent DK-43 bargraph unit made by Tewkesbury Electronics for GCHQ, the UK Government's massive listening station based outside Gloucester.

The 3701/02 is excellently reviewed by EI6IZ and I endorse all he says. I also recommend the site of JA2DJH for a thorough technical description together with numerous photographs and spectrum analyser filter plots, and you will see why knowledgeable owners of the 3700 series hang on to them.

I have always loved top flight HF receivers. I have been fortunate via my military and other connections to have used some of the finest gear from Racal, Plessey, Redifon, Marconi, Eddystone, MEL/Philips, Siemens, R&S and a very nice Icom R71-E, and this RA3701 is one of the best. I like it for the following reasons:-

1. The build quality is superb, particularly the screening. It's a lot better than the RA1792.

2. The panel layout is excellent and logically laid out with big chunky push buttons with a long tactile feel that shout top quality. A long contrast to the tiny poxy buttons on most Oriental ham gear.

3. Although there are many buttons it is dead easy to navigate your way round round the front panel, including delving into 5 layers deep of software. The software designer deserves a gold medal. I could mention certain radios that defy any easy usage without a well tabbed manual in front of you.

4. The tuning feel is magically light, like an Eddystone but even better - real finger tip stuff. There is a heavy flywheel running in decent ball bearings, which, when the knob is flicked continues rotating for about 9 seconds, and longer if the brake is fully unscrewed. The only radios that approach this level of build are the Racal RA1772 and the professional Eddystone 1650.

5. The front end is pretty bomb-proof. I measured the IP3 at 25kHz signal spacings of +24dBm with the RF amp in and +33dBm with the RF amp out.

6. The sensitivity is fine. I will measure the noise figure soon for interest. Sensitivity at HF is not important unless you have a tiny aerial. The limiting factor is the external QRM and QRN.

7. The recovered audio quality is superb (to my ears at any rate, and I am dead fussy). There are no squeaks, bubbles or microprocessor audio hash as on the early versions of the HF-1000. My philosophy is that the sole purpose of a receiver is to deliver good quality audio to the operator. Technical numbers such as frequency stability, IP3, IF rejection etc are valuable but the ultimate test is a pair of trained ears listening on professional quality cans. I go to a great deal of trouble to exclude troublesome sources, particularly hum and distortion, even on my valved golden oldies such as the RA17. The 3701 is one of the best. On a CW input, I measured the total harmonic distortion of the phones output at about 0.8%. A contributing factor is probably the excellent professional quality crystal filters made by STC.

Interestingly, JA2DJH compared the 3701 against the Icom 7800 and preferred the analogue sound of the 3701 to the DSP sound of the 7800. In that regard, I have an early DSP professional receiver on loan, the STC STR8212 which has stunning DSP selectivity that would put most ham DSP transceivers in the shade, yet I prefer the audio from the 3701.

I know of another UK ham who has both the DSP and analogue versions of the very costly Telefunken E1800 (and no doubt a deep pocket too!) and he prefers the analogue version for listening.
No doubt DSP advances will overtake analogue in recovered quality but for the present I will stick to this rig.

8. The AGC is nice and docile with very little popping or spluttering, though that on the RA1792 is marginally better - and the 1792 has the best AGC of any radio I have experienced.

9. The S meter, in the form of a bargraph calibrated in dB over 1 microvolt, is accurate over the whole tuning range. I would, however, prefer a proper meter.

10. The 3701 has two IF outputs at 1.4 MHz. One is straight after the second mixer and the other is at the end of the second IF chain. I connect the first to the STR8212 and crank in 40dB of attenuation on the 8212, tune it to 1.4 MHz and use it as a traditional "Q-fiver" so that I get the benefit of the excellent DSP when things get tough but am able to do the tuning on the 3701. The second IF output used to go to my Racal MA1105 bargraph tuning indicator, but the response is non-linear whereas the DK-43 mentioned earlier is absolutely linear across the whole scale. This magic box is like a one line spectrum analyser, with a row 100 LEDs displaying a width of 1,000Hz (or more if switched). As you tune into a carrier each LED lights up in turn left to right at 10Hz intervals as you tune LF to HF. Tuning AM, CW or FSK is incredibly simple and swift. Just centre the carrier on the 0Hz LED or centralise the mark and space lit LEDs either side of the 0Hz LED. Some new DSP radios have a tuning bargraph built in but they are small whereas the DK-43's occupies a scale of 10 inches. The DK-43, however, requires a 100kHz IF input, hence my having to fit the 100kHz IF conversion module.

11. The frequency stability is excellent from the Racal-Dana 9442 standard fitted - I haven't measured it but the specs suggest a drift of a few Hz/month. Actually most professional (and now some ham) rigs have the facility to "pipe in" an external frequency standard on 1, 5 or 10MHz to reduce drift even more. I have an HP105B crystal standard and two rubidium standards but I don't need them for the 3701.

There are some drawbacks;-

1. There is no noise blanker. noise limiter or notch filter. I believe some of these are fitted to the later DSP version, the RA3791.

2. There is some residual audio hiss but this can be reduced by interposing an attenuator between the audio output and the speaker or headphones and increasing the AF gain.

3. The internal panel speaker sounds very tinny but it's only a quick monitoring device. Operators would use headphones or a decent external speaker. I went rather OTT and connected a nice big Linn hifi speaker but it does give a lovely mellow neutral sound.

4. The set is quite large - 19 inches wide and about 18 inches deep. That for me is as I prefer: I can't be doing with tiny radios that don't fit into a 19 inch rack.

That's it. Please feel free to contact me by email for a further discussion.
 
EI6IZ Rating: 5/5 May 31, 2005 15:15 Send this review to a friend
A star performer  Time owned: 3 to 6 months
The RA3702 is a dual LF/HF receiver from the early 90's. A non-DSP design, It covers from 15 Khz to 30 Mhz although it will tune and receive signals down to below 10 Khz.

The RA3702 comprises of 2 RA3701 receivers with identical configurations on a common chassis and sharing a single front panel so much of this review applies equally to the RA3701

The entire receiver is modular consisting of individually shielded modules linked together on a common backplane. Each receiver consists of a front end module, LO synth module, REF/BFO and an IF/AF module. The processor, power supply and front panel modules are shared with both receivers.

You can read copy of the original racal spec sheet at the following website
http://www.kongsfjord.no/data_sheets/data_sheets.htm#Racal

My receiver(s) have the following IF filter configurations 0.3,1,2.7,3.2, 6 and 12Khz which I believe is a fairly standard configuration.

The front panel layout is clean and logical, very pleasant to use with 3 nice clear displays and moving buttons with lovely tactile feedback.

The display on the left is for the frequency or channel information along with the tuning rate, just below this is the keypad for direct frequency entry and receiver selection.

The center display is for the metering, a Digital bar-graph S-meter that can also be switched over to show Audio output levels
Below this is the weighed tuning knob, this knob is heavy, well balanced and very smooth making tuning a real joy.
The tuning rates are Lock, Slow (1 Hz steps) Medium(200 Hz) and fast (1 KHz) there is also a variable tuning rate that selects a tuning speed based on how fast you are turning the knob, in practice this is the most useful setting. It is somewhat unfortunate that there is not another rate between slow and medium but in practice the variable speed does a pretty good job.

The display on the right shows filter, Mode, AGC and BFO (in CW mode or PBT mode) information. The keypad on the right is used for selecting the mode, selecting the filter bandwidth and altering the AGC settings.

The AGC action is very nice and can be combined with use of the manual IF gain control to set the lower AGC threshold.

There are 4 softkeys at the top of this keypad which are used to access the menu system to alter various radio parameters and default settings. The Menu system is well laid out and easy to use.

The loudspeaker on the front panel is connected to whichever of the 2 receivers that is currently connected to the front panel. This speaker can be disabled with the L/S button. However to get the real deal out of this radio you will need to use the 2 line level output connections on the back, one for each receiver. I have my audio line outs fed to a switching matrix that allows me to feed them to left and right speakers or feed them both to a center mix, Left and right is very useful for diversity.

One of the tricks that the 3702 has up it's sleeve is diversity mode, accessible from the menu system, this locks both receivers together for all settings and allows one to hear the same signal using two separate antennas, this, when fed to separate ears is a formidable weapon for Tropical band and Medium-wave Dxing.

The basic receiver performance is superb, the filters have good shape factors and excellent rejection. The receiver is very quite and has an outstanding front end with no evidence of birdies or CPU hash.
The quality of the recovered audio is excellent.

When running the RA3702 as two separate receivers switching the front panel between receivers is easy and soon becomes second nature, it's also very easy to copy the tuned frequency between receivers.
The RA3702 has 100 memories per receiver and includes a scan mode that works quite well

Passband tuning is possible, it's selected via the menu keys and it is also possible to configure additional filter settings for the installed IF filters to provide for filtering tailored to your needs.

The RA3702 can be computer controlled, mine came with an RS232 interface but IEEE-488 may be more common and I have yet to come across any software that will work with this set.
 


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