[RFI] RE 331 Short review

Fri Oct 1 11:31:43 EDT 2021

Question: Do you know what the effective RF or IF Bandwidth of the
RE331 might be?

Since received 'power' in the IF (or RF domain) is proportional to BW,
a 5 or 6 MHz wide IF/RF will present more 'power' to the detector at the 
end of the IF/RF gain strip than a 5 or 10 kHz wide 'normal' AM receiver.

I have used an HP Spec An before with a wide IF selected to look 
at pulse shapes in zero span (non-sweeping) mode, routing the detected
IF output to an O-scope for observation; a wider IF on a broadband pulse
results a good representation of the pulse, sometimes one can see multiple
'breakdowns' of a source per 1/2 sine wave cycle.

I've also used a TV Field Strength meter to look at pulse RFI noise too,
and that receiver had about a 500 kHz IF BW and seemed responsive
to pulse noise (like NTSC Vert and Horz sync pulses).

de AA5CT Jim

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On Friday, October 1, 2021, 5:14:17 AM CDT, Charlie Delta via RFI <rfi at contesting.com> wrote: 

Through good fortune I managed to pick up a RE331 UHF sparking source detector, at a ham friendly price.  Not cheap, but within my ham budget.
I thought that I would just give a brief  review for those who are considering buying this instrument
1. It covers 320mhz to 340mhz according to the spec. However, the dial is only roughly calibrated and can be off 1 or 2 mhz off from  the marked  dial positions. Its no  big deal. It's in the UHF mil air band and there's nothing  that will cause interference here

2. The manual is very basic and covers common sense technical options to find sparking noise sources and multiple sparking noise sources. The manual clearly states that its optimised for locating sparking noise sources. It does do this very well.
3. It's very well constructed. Good cabinet work alignment and would be easy to maintain. Its easy to open for curiosity, and it would be easy to fabricate or mount your own yagi design onto the receiver unit if you wanted to do  so.  It's very elegantly designed compared to the MFJ unit which just seems wobbly and fiddly at every level even though it does work.(I have one as well)
4. It appears to be a very sophisticated design looking at the well layed out PCB, 2 SAW filters and numerous tiny SMT parts with a very well laid out PCB. It would be easy to repair or work on if you every had to do so if you are skilled in SMT. It has an ARM processor  inside which indicates the design sophistication.
5. The receiver does not have a classic AM receiver sound. It almost sounds like you are listening through  something like a 1 khz or 800 hz CW filter rather than say a 6khz am filter. The audio seems raspy and peaky. 

I can't honestly say what the receiver topology is, but my suspicion is that it's a modern version of a regen circuit filtered through  several SAW filters. Much like the K0DK design that was published in QEX. The meter appears to be calibrated according to the manual however checking it with my Rohde signal generator and its hard to know what the Dbuv scale corresponds too, because it certainly does not track the signal generator DbUv scale(Rohde SML03) Not that it matters.
6. The Dbuv meter has a nice response that seems to have all the ballistic characteristics of  an analogue meter movement. I rate it as excellent for peaking and nulling signals.
7. The 4 element yagi is gamma matched and seems to have a clean pattern.
8. The RF  gain controls and audio high low positions are adequate for the job. The Dbuv meter always remains unaffected in its reading regardless of RF gain  settings. Excellent dynamic range for the DbuV meter and RF gain  level control seems perfect. 

9. The gain distribution of the circuit is well done and sufficient for finding noise. What is interesting is that minimum sensitivity seems to be no more than -102 to 102dbm with a 1khz modulated AM source. I felt that it would have higher sensitivity since it detected sparking poles so well. But I was surprised by this  -102dbm figure. I will explain why in the next point.
10, I did a comparison with several wideband AM receiver HT's,  a range of scanners like the AOR 8200, Icom R20, Icom r10, Yaesu VR500 and the supposedly excellent Yupiteru MVT7100. The RE 331 just blew them all out of the water when finding sparking pole noise sources. Its seems that the AGC's in these radios wash out certain pulse widths and things like sparking noise sources unless they are very strong. I know many ham  radios  are designed with AGC responses that minimise hanging on pulse noise and this may explain why the RE331 is much superior when it comes to detecting spark noise. As an example my cars ignition noise is low to non existent on around 300mhz. The RE331 could easily hear  these pops   despite having a sensitivity figure well below -130dbm when  these other radios could not detect the weak ignition noise despite having less sensitivity  maybe 20 30db less sensitivity. So the RE331 is clearly well-designed with an AGC designed to capture various pulse widths and pulse repetition rates far better than most ham radios and scanners at the same frequency. The point is that  if you tuned the average HAM HT or scanner receiver to the 330mhz frequency you will miss many sparking sources that the RE331 will easily pick up. I may off with my reasoning, but the evidence from my testing is very clear in this regard. I was  able to pick up  minor to very severe sparking noise sources  on many poles just standing in the street and pointing the yagi from one to the next. The fidelity and resolution is superb in this regard.

11. I always questioned the extreme price of the RE331 and their other units but it becomes clear that they  have professionally designed equipment that does what they claim and it does it better than a workaround  like just using any AM receiver with a yagi. I am not affiliated in any way with Radar Engineers. I just managed to get lucky by finding this unit at a reasonable price. I would like to acquire one of the RE242 or RE243 models however I dont think I will be so lucky since they are very rare here in Australia and are almost never sold by the utilities.
12. In short if your club or profession can justify the price  I can  really recommend the RE m331. I fully understand that this piece of equipment is outside of the price range for most hams however you may  be lucky and pick up an affordable second hand unit. If you can hire one to find a sparking noise it would be well worth the price.
Overall I was impressed despite being a ham sceptic that believed that this unit was a simple AM receiver with yagi bolted to it. I hope some will find this information useful. If you have any questions, vk3od at arrl.net

73
VK3OD

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