EEVblog #767 - Super Regenerative Receiver Problems

[vk6zgo]

I've got a couple of commercial super-regen receivers here in actual radios. One is a super-crappy 1970s single channel CB walkie-talkie, which has (if I remember correctly) a whole three transistors - a 27.125 MHz crystal oscillator, one doing AF things, and one being a super-wide super-regen receiver. You can tell when it's on because anything else in the place that's tuned between 26-30 MHz makes a rude hissing noise; it doesn't have that much more range when you actually transmit. But a fine example of what you can do with very little. When conditions were good, I remember hearing Radio South Africa on the 26 MHz band come thundering in...

The other is more interesting, it's the B set in my Wireless Sets 19, the classic British/Allied tank radio from WWII. The A set is a proper superhet transceiver on 2-8 MHz (actually, I think it's the first ever transceiver, in that the RX and TX are tuned by the same circuit) that puts out about 10 watts. The B set, though, is for 230-250 MHz (ish), also tuned by one knob, and I think that produces around 10mW. That was used for tank-to-tank comms. Most people who used the 19 set after the war pulled out the B set gubbins, because it produced enough interference to mess up VHF TV over quite a wide area and thus made a chap unpopular. I think that's around three valves (the A set has ten or so), which was really important in the days when valves were in critically short supply. It was also a very high frequency for the time, which made for a very short range and thus fewer security worries.

I would love to see Dave do a teardown on a 19 Set - but it won't be mine, first because it's a prized piece of my collection, but also it weighs about 40 kilos all-in and I think I could afford a holiday in Oz for the cost of shipping the thing from Blighty.

(odd radio fact: the German tank radios used 27 MHz, much like my little walkie-talkie, which was also short range enough to avoid interception nearby, but which during the excellent propagation of the time of the African desert war meant that receivers in the UK could pick up Radio Rommel just fine for large parts of the day.)

"(actually, I think it's the first ever transceiver, in that the RX and TX are tuned by the same circuit)"
Not so sure of that----the Aussie Number 11 does the same.
I'm pretty sure the 11 set predates the 19,but they may be contemporaries.
They were only a HF radio though!

The 19s were always more expensive in the surplus shops,so I ended up with a Number 11.
Unfortunately they used directly heated valves & were not directly usable from mains supplies.

[vk6zgo]

Just as post script on this...
I paused the video and did a little quick reverse engineering and it looks like the extra lead length on coil L2 may be the actual antenna....
I could be wrong but I don't think so.

Give me an HP-8569 any day over that Rigol SA.
or for that matter my old HP-8551 / 851. (it is almost older than I).

Sue,I bit my tongue!

Just kidding!
73,VK6ZGO

[99tito99]

The scariest thing is you have stuffed your “crawl space” with OneHungLow random/spontaneous deflagration units.

Cheers
Mark
********************

[Muttley Snickers]

As 433 MHz is very popular with alot of RF remotes such as car and home alarms, I was a bit concerned that these things could switch on if the neighbour sneezed which could be a hazard, particularly if someone was to use them on an electric heater or a kettle, anyway I read the online user manual and at least they do warn against using them on such devices as well as cooking equipment and power tools.  I dont trust the Arlec stuff much and never have.
Bloody cheap, $14 for one socket and one remote or $26 for three sockets and one remote, the book says 30 meter range, I'm guessing down hill with a favourable wind perhaps.

Muttley

[rs20]

The scariest thing is you have stuffed your “crawl space” with OneHungLow random/spontaneous deflagration units.

Are crawl spaces flammable? I mean, obviously spontaneous deflagration units are to be avoided, but perhaps a crawlspace is an ideal location for them?

[AF6LJ]

Just as post script on this...
I paused the video and did a little quick reverse engineering and it looks like the extra lead length on coil L2 may be the actual antenna....
I could be wrong but I don't think so.

Give me an HP-8569 any day over that Rigol SA.
or for that matter my old HP-8551 / 851. (it is almost older than I).

Sue,I bit my tongue!

Just kidding!
73,VK6ZGO

I admit I am not much of a fan of the latest low cost test gear from China.
I would rather have something I can repair like the gray and beige iron from around the SF bay aria.

[AF6LJ]

As one who is known for looking down my nose at people who garnish their presentations with profanity, I would agree Dave isn't the worst offender out there, and his content is of great enough value that the occasional use of profanity is tolerable.

More to the subject;
The first issue I really have with the lighting setup is the use of an RF remote in an electronics lab. Just another source of noise, an IR remote would have been better.

Those panels are nice they put out a healthy amount of light, I am even considering something like that here. My only concern is being an AM BCB DX'er I can't help but wonder how much noise those will generate. 

[dr.diesel]

I can't think of a single instance of racist comments (and I'm very sure Dave wouldn't knowing do so), that is one hell of a serious accusation you just made.

[mikerj]

How many people constantly complain about Dave's language on the forum?  By my count, it's one person.

[mikerj]

The scariest thing is you have stuffed your “crawl space” with OneHungLow random/spontaneous deflagration units.

That is the one thing that worries me about this kind of crap, and is why I never use e.g. shoddy Chinese mains chargers/adapters.

[mmagin]

Well, it's a faulty design unless they put a big note in the instructions that you have to have the receivers spaced pretty distant from each other (I assume that's what they were thinking,) but it's kind of elegant in a way, if you're strictly optimizing for simplicity. 

Wonder if it meets the relevant government standards (e.g. Australian equivalent of the FCC). 

[G0HZU]

FWIW I've got experience of using several of the UK equivalent to these things. They are made by Status and have model number RCS K09.

The most significant failure/reliability issue with them is that after a while they can stick in the ON position. I think the relay contacts weld or stick.
So when it fails like this you can turn it off via the remote and the unit responds accordingly (LED goes out) and you can hear it try to click the relay but the relay contacts stay closed. So the mains power is still connected to the output!

So you can't rely on these things to turn off something unless you can actually see the connected equipment lose its standby lights or the neons go out in a power strip.

I've seen three of these devices fail like this. You can free up the relay by tapping the unit fairly hard but it isn't exactly what you want from something like this...

Note that I didn't use them on high current devices. I'm guessing that the relay sticks on surge currents. But I only ever used them for devices that take maybe a total of 2A or 3A continuous. I managed to make one stick ON with just a desktop PC as the load.

[bktemp]

FWIW I've got experience of using several of the UK equivalent to these things. They are made by Status and have model number RCS K09.

The most significant failure/reliability issue with them is that after a while they can stick in the ON position. I think the relay sticks.

Yes, the cheap Chinese relais don't like high inrush currents. I have a similiar problem with one used to switch a TV. If I switch the TV off and back on, the relais sticks. Then I need to hit it hard so switch off. This only happens when the time between off and on is short. The TV probably has a NTC for inrush current limiting that needs some time to cool down. If you switch it back on too quickly, the inrush current ist much higher and the relais sticks in on position.

Another failure mode are the capacitive power supplies: I have seen a lot of X2 capacitors with almost no capacity left (<10nF instead of 100-470nF).

[G0HZU]

FWIW I've got experience of using several of the UK equivalent to these things. They are made by Status and have model number RCS K09.

The most significant failure/reliability issue with them is that after a while they can stick in the ON position. I think the relay sticks.

Yes, the cheap Chinese relais don't like high inrush currents. I have a similiar problem with one used to switch a TV. If I switch the TV off and back on, the relais sticks. Then I need to hit it hard so switch off. This only happens when the time between off and on is short. The TV probably has a NTC for inrush current limiting that needs some time to cool down. If you switch it back on too quickly, the inrush current ist much higher and the relais sticks in on position.

Another failure mode are the capacitive power supplies: I have seen a lot of X2 capacitors with almost no capacity left (<10nF instead of 100-470nF).

I was editing my post as you replied and I agree it must be an inrush current issue. I've got three units here that have been faultless since new but the other three all suffered the stuck relay syndrome.

So I guess you have to be careful what loads you connect to them in case they can generate a sharp surge.

[SNGLinks]

The other is more interesting, it's the B set in my Wireless Sets 19, the classic British/Allied tank radio from WWII. The A set is a proper superhet transceiver on 2-8 MHz (actually, I think it's the first ever transceiver, in that the RX and TX are tuned by the same circuit) that puts out about 10 watts. The B set, though, is for 230-250 MHz (ish), also tuned by one knob, and I think that produces around 10mW. That was used for tank-to-tank comms. Most people who used the 19 set after the war pulled out the B set gubbins, because it produced enough interference to mess up VHF TV over quite a wide area and thus made a chap unpopular. I think that's around three valves (the A set has ten or so), which was really important in the days when valves were in critically short supply. It was also a very high frequency for the time, which made for a very short range and thus fewer security worries.

I would love to see Dave do a teardown on a 19 Set - but it won't be mine, first because it's a prized piece of my collection, but also it weighs about 40 kilos all-in and I think I could afford a holiday in Oz for the cost of shipping the thing from Blighty.

(odd radio fact: the German tank radios used 27 MHz, much like my little walkie-talkie, which was also short range enough to avoid interception nearby, but which during the excellent propagation of the time of the African desert war meant that receivers in the UK could pick up Radio Rommel just fine for large parts of the day.)

My father was a radio operator in a tank in WW2. They could never get the B set to work - even to a tank along side. In the 50s he got his amateur license (G3NXU) and his first set was a 19 set. You could buy the complete kit - radio, headset, whip, ATU and rotary converter (so you could run it off 12v) for, I think. £19 19s.

[andersjm]

I've been trying to figure out how the thing is connected at the mains-side.

Is the relay connected in series with the X-class capacitor? If not, how is it connected? Is the purpose of the capacitor to act as a snubber, or some other purpose?

[rs20]

Capacitative dropper perhaps?

[apis]

Yes, I would also guess on a capacitive power supply, it requires a X2-class safety cap. For details see:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

[Goober_in_CA]

Hi Dave

You might try to extend the range of your receivers by adjusting the frequency of each receiver.
Since they are just a simple LC oscillator, the drift of each receiver is really poor.

Most of these cheap receivers are still simple conversion type using an intermediate frequency (IF) and not regeneration types. So what happens when you have 2 receivers together like this is that the local oscillator (LO) from RX1 will get into the front end of RX2 or the reverse. This explains why 1 receiver has interference problems and not the second.

Follow me here: Lets say both are designed to receive 400MHz and use low side injection of 389.3MHz.

RX1 is tuned properly at 400MHs or the LO is at 389.3MHz giving us a IF freq of 10.7MHz
But RX2 has drifted.
RX2 is at 390MHz and not where it should be at 400MHz. Or the LO is at 380Mhzish. This would let the RX1 LO leak into the front end of RX2 and swamp out the receiver.
This is why 1 receiver works better than the other receiver.

I have seen this same sort of problem with other poorly built receiver similar to your light switch receivers.

So how do you fix it? Just tune the receivers. You don’t need any special RF test equipment.
1.   Plug in RX1 and not RX2, have Dave#2 operate the transmitter at a range that is on the edge of working.
2.   Tune the slug in the receiver until the sensitivity improves. Trial and error.
3.   Have Dave#2 continue to increase his distance from the receiver and repeat step 2. Do this until optimum distance is achieved.
4.   Repeat with RX2.

Things to watch out for! The slugs break easily. DO NOT USES a metal screwdriver. You will break the slug and the metal diver will interfere with the tuning. Ceramic tools are the best but plastic will do the job. Something like Digikey 243-1013-ND
Another got-ya is the plastic case itself.  Everything might tune up great without the case. Then install the case and nothing works. Just drill a hole in the case above the tuning slug and tune the receivers with the case enclosed.

Thanks for the great podcast!
Hope this helps.
Daryl

[vk6zgo]

Just as post script on this...
I paused the video and did a little quick reverse engineering and it looks like the extra lead length on coil L2 may be the actual antenna....
I could be wrong but I don't think so.

Give me an HP-8569 any day over that Rigol SA.
or for that matter my old HP-8551 / 851. (it is almost older than I).

Sue,I bit my tongue!

Just kidding!
73,VK6ZGO

I admit I am not much of a fan of the latest low cost test gear from China.
I would rather have something I can repair like the gray and beige iron from around the SF bay aria.

Sue,my comment was aimed at our mutual maturity--we just get better,like wine!

On the other point,though.
We had a small Atten SA at my last work--not much,but we found a PLL fault with it that the expensive IFR SA couldn't find.
Digital-v-analog again--the IFR saw a rapidly changing frequency as a bunch of discrete carriers,whereas on the Atten you could see the damn thing move!

From the look of it,the Rigol SA is digital,so would probably have the same problem as the IFR.

[vk6zgo]

Some additional comments:

One needs to differentiate between a regular regenerative detector/receiver, and a superregenerative ditto. Their schematic may at first blush look eerily similar, yet their method of operation is completely different.

A classic regenerative RX generates a continuous sinewave oscillation at or very near the intended receiving frequency. The RF input signal from the antenna is mixed with the LO signal and an audio or supersonic low frequency signal is the result. This is where the frequently seen audio transformer comes into play in your MW broadcast regenerative RX. So with a regenerative detector you'd expect to see a single frequency being radiated by the detector.

A superregenerative detector is a completely different beast. In this the oscillator is continuously driven into and out of oscillation, usually at a supersonic rate, called the quench rate. Thus the name. The trick is that when the oscillator is turned on, the gain of the RF transistor is 'slowly' increased up until the onset of oscillation. This is done by using some form of positive ramp on the base current.

When an oscillator starts up, it is the noise in the circuit, which provides the initial 'seed' for the amplifier in the circuit. This is the effect, which is (ab)used in a superregenerative detector. How this works is, that at the point of onset of oscillation, the time it takes for the oscillations to exponentially ramp up from the local noise level hugely depends on whether - by coincidence or design - a (very) low level signal is injected into the oscillator from the outside. This effect is ridiculously sensitive, so a supersonic detector is quite a bit more sensitive than your regular regenerative detector with continuous oscillations.

The oscillator thus converts RF input level from the antenna/ambient into time it spends at full oscillation amplitude. Higher signal level means it ramps up much quicker. IE. the DC power input to the oscillator, averaged over many quench cycles, indicates the ambient RF level around the RX frequency. If, like in this case, the quench rate is several hundred kHz, then you can easily detect data bit rates from the transmitter of several thousands. Just measure the voltage drop across a fixed resistor, or, like what is maybe used here, use a simple diode detector of the RF oscillator signal.

So the oscillator ramp up waveform depends heavily on the ambient RF noise/signal level. Which means the ambient RF noise around the RX frequency modulates the oscillator, which in turn is the main reason for the ridiculously wide noise piedestal you see on the SA.

Your description of a Regenerative Receiver sounds more like a Direct Conversion Rx.

The description I first read back in the 1950s & have seen everywhere else since,goes something like this:-

Positive feedback in a Regenerative Detector compensates for resistive & other losses in the Rx tuned circuit, effectively increasing its Q,& hence,both the sensitivity & selectivity of the receiver.

When receiving full carrier AM,the feedback is set to just below the point of oscillation,to obtain the positive effects efficiency enhancement without hearing a beat note against the carrier.

For CW (Morse Code) & Single Sideband signals,the feedback is advanced until oscillation begins,so as to provide an audible beat note for CW,or to re-insert a carrier for the resolution of SSB.

[abebarker]

[Never mind, I talked myself out of this idea working]
Do they interfere with each other less if the coils are turned 90 degrees from each other? I imagine that you are probably going to be able to get them closer together if one of them is turned on its side.

They are coils and they are going to couple when they are right next to each other especially when the coils are pointed in the same direction. That mean one of them is going to push the other off frequency. I remember discussing that phenomena in this thread; https://www.eevblog.com/forum/chat/coupling-tuned-circuits/ When the axis of one coil is 90 degrees from the axis of the other the magnetic field it generates can not induce any current in the other coil (for the most part).

Although, now that I think about it, the cores may be susceptible to the field in any orientation and induce a current in its coil anyway. Oh well, defeated by a susceptible chunk of ferrite.

[rs20]

Although, now that I think about it, the cores may be susceptible to the field in any orientation and induce a current in its coil anyway. Oh well, defeated by a susceptible chunk of ferrite.

If you flip the device upside down, the phase of the signal received by the other coil will be inverted. Therefore, at some point as you rotate the device around, there must exist a point where the signal received by the other coil is zero.

Hmm, although that assumes that the gain can't be complex.

[TSL]

Wonder if it meets the relevant government standards (e.g. Australian equivalent of the FCC).

The relevant standard says 25mW EIRP, so it probably does.

Australian LIPD standard can be found here.
http://www.acma.gov.au/Industry/Spectrum/Radiocomms-licensing/Class-licences/spectrum-opportunities-for-short-range-devices

regards

Tim

[andersjm]

Yes, I would also guess on a capacitive power supply, it requires a X2-class safety cap. For details see:
http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

Ah, so the capacitor isn't involved in the actual mains switching. It really is just the relay, with no MOV or capacitor or anything to protect the relay from arcing while switching off inductive loads?

Shouldn't there be some sort of snubber? Am I correct in thinking this thing really isn't suitable to power inductive loads? Maybe it is only meant to power resistive loads, but I wonder if that is stated clearly on the box it came in?