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carknue
08-10-2005, 12:47
Hi all,

the chinese company Degen offers a cheap active SW loop antenna DE31. As we all know, that loop antennas are working best for DRM in urban surroundings, I bought one via ebay for just 16,90 USD plus 10 USD for shipping to germany and tested it for more than one week togehter with the Digital World Traveller.

http://home.arcor.de/carsten.knuetter/DE31_schrank.JPG

The frequency range is 3.9 - 22 MHz. The receiving frequency can be adjusted by a wheel in the control unit.

http://home.arcor.de/carsten.knuetter/DE31_control.JPG

This unit also contains the 2 AAA batteries. Power consumption is about 6 mA.

The antenna is ideal for travelling, because it fits in every pocket of your shirt.

The DRM performance is very good, maximum SNR with the DWT is 32 dB. I can receive indoor every DRM transmission for europe in my urban flat. I think that the DE31 is the ideal antenna for the DWT and maybe other portable SW radios. Look at my last log postings and you see, that the results were very good. With the 7m wire antenna that comes with the DWT, DRM reception was hardly possible in my flat, or in my office.

Here is a comparision with the Sony active loop:
http://www.radiointel.com/review-degende31.htm

Here you can find the DE31 in Ebay where I bought it from:
http://search.ebay.de/_W0QQsassZtquchina

dk8cb
08-10-2005, 15:53
Hi Carsten,

can you post close-up pictures of what's inside?

I suspect the triangle at the loop to contain the amplifier and the box just to contain the batteries, a remote tuning potentiometer and a DC supply circuit. Is that correct?
Is the loop tuned via a potentiometer and a varicap diode or by a variable capacitor? Does the cable from battery box to loop contain 3 wires (ground, tuning voltage, RF-signal)? Does the amplifier look like a single-ended or a differential input type? Is it made of discretes or an IC?

Roland

carknue
09-10-2005, 09:39
Hi Roland,

here are some close ups of the inside( 1.7 MB each!)

http://home.arcor.de/carsten.knuetter/DE31_inside.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside1.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside2.JPG

dk8cb
09-10-2005, 12:25
Hi Carsten,

thanks a lot.
As I thought, the antenna seem so be a single-turn, remotely tuned, 1-transistor amplifier antenna.

D1 is the varicap diode. There are three wires from the box to the amplifier namely: ground, tuning voltage and RF+supply voltage (on the same wire).
I don't know yet, what the canned inductor in the box is good for, it should be part of the DC bias circuit. However, if there is an SMD transistor on the other side of the board, then it might also be part of a circuit which generates a large tuning voltage out of the battery voltage in order to achieve a larger tuning range since capacitance diodes usually need a few more volts than what the batteries can supply to achieve their maximum tuning ratio.

EDIT: Can you read what is printed on the transistor located between L1 and D1 in the loop amplifier? From general topology and common sense, this should be a field effect transistor, knowing what is printed on it would confirm this assumption.
BTW: Are the colors on L1 brown-blue-black-silver or something different, perhaps red-violet-black-silver? Is R2 marked "109"? The picture is not quite clear there.

Roland

dk8cb
09-10-2005, 14:23
Here is the reverse-engineered circuit diagram of the amplifier at the base of the loop, as far as I have been able to determine it.
The transistor is most likely an n-channel FET, it could also be a MOSFET.

@ Carsten
Can you measure the range of V-tune and V+ against ground? The amplifier does not have to be connected during this measurement.

Update: I have updated the circuit diagram with a few more details and I have removed it here, see further down below for the new version!

Roland

carknue
09-10-2005, 15:04
Hi Roland,

the range of Vtune is from 0 to +13V. V+ is always +2.47V.

dk8cb
09-10-2005, 15:12
Originally posted by carknue
the range of Vtune is from 0 to +13V. V+ is always +2.47V.

Ah, exactly as I thought. So, the canned inductor is most likely part of a DC/DC voltage converter.

Since V+ is 2.47 V, you are most likely using rechargeable batteries, right?

Roland

dk8cb
09-10-2005, 16:10
Hi all,

here is a basic schematic of what should be in the battery box. No more details are available so far. A picture of the solder side of the board might reveal more details, however the board seems to be double-sided with some traces on the top covered by parts.
The screen of the cable leading to the receiver is of course connected to ground, I just forgot to draw the connection.

Roland

dk8cb
09-10-2005, 18:42
@ Carsten

It would be interesting to know the frequency at which the DC/DC converter is running. It should be possible to find this out by connecting the battery box (with or without its amplifier connected) preferably to a longwave receiver and by looking for harmonics of the switching frequency. It might also work with a mediumwave receiver. It might even work better when the box is brought close to the ferrite antenna of a longwave receiver.
The difference between adjacent harmonics would then be equal to the fundamental switching frequency which I suspect to be quite low in order to avoid interference from it.

Roland

dk8cb
27-10-2005, 00:26
Hi,

here is an update of the Degen loop amplifier schematic.
Thanks Rainer (forum member Funkerberg) for helping with more detailed photos!

The transistor is a 2SK544 MOSFET (Idss group E) with y21 = 11 mS, Idss = 2.5 to 6 mA, very low Crss, get its datasheet here (http://service.semic.sanyo.co.jp/semi/ds_e/ENN1792E.pdf).

The tuning diode is a 1S149 or 1SV149 (equivalent) AM tuning diode, get its datasheet here (http://www.ortodoxism.ro/datasheets/toshiba/1083.pdf).

Latest Update: Latest measurements made by our forum member Funkerberg (thanks!), indicate that L1 = 10 uH and C2 = 10 nF which yields a low-Q series resonant circuit for mediumwave at the drain of the FET, more or less shortening mediumwave signals to ground.
C1 = 10 nF, it acts as an RF short.

Assuming a lossless RF decoupling circuit in the battery box, the RF voltage gain for shortwave signals with a receiver load of 500 Ohms is about 0.9, it falls to about 0.36 if a receiver with an input impedance of 50 Ohms is connected. However, more signal power is transferred in case of the 50 Ohm receiver since the impedance mismatch is smaller.
If maximum sensitivity is desired on a receiver with a 50 Ohm input, a 2:1 impedance transformer could be used to transform the loop amplifier's output impedance (100 Ohms, established by R1) to the receiver's input impedance.
Similarily, a 1:4 impedance transformer could be used to transform the loop amplifier's output impedance to a high impedance receiver input in case maximum sensitivity is desired.

Roland

mitajohn
19-11-2005, 15:43
Hi Roland,

I have sent you a private e-mail, through the forum, but I think it is better to public the problem here, because some other members may have or will have the same problem.
Here it is: The DE-31, which I use sometimes, cannot be tuned down to 3995 kHz. The tuning voltage range is 12.90 - 0.44 V. (Carsten informed me that his DE31 has a voltage range of 13.05 - 0.00V.) When the tuning voltage is at 0.44V, it is close to 3995 kHz and if I short the tuning voltage to ground, then 3995 appears strong. I think that a small mod will fix it, since I suppose this is due to component/s tolorances. Would you please give any guidance? Unfortunately I have no schematic of the circuit.

Regards,
John.

Jos
19-11-2005, 17:25
Hi all,

In his mail of 9.10.05,Roland asked to know the frequecy of the DC/DC converter (3 to13 v for tuning).
I did some measurements and it was 2.855 MHz in my DE31 set.

Newt week I 'll look for John what cann be done for his tunig of 3995.

Kind regards.

Jos.

dk8cb
19-11-2005, 18:11
Hi John,

the fact that your DE-31 does not go down to zero Volts is most likely a tolerance problem of the variable tuning resistor. Since I don't own a DE-31 myself, I have to assume that Carsten has given the lower value of the tuning voltage on his DE-31 correctly. If so, one end of the tuning voltage adjustment resistor should be connected to DC ground. Now, if your particular unit does not deliver 0 volts, it may only be attributed to mechnical tolerances in the variable tuning resistor. The wiper obviously just doesn't cover the full range. To cover the full range, one would have to replace the resistor by a new one.

On the other hand, tuning diodes aren't and shouldn't normally be operated down to zero volts, manufacturers usually specify them down to about 1 V only.
If you want to tune your DE-31 further down without having to change anything in the circuit itself, let me suggest that you attach a high permeability ferrite to the antenna wire at an arbitrary location around the circumference as a non-permanent solution. This will increase inductance and bring down the lower tuning limit. Try one of the cores that come in two halves and close them around your wire or wind the wire through it twice. Might perhaps work. If you still want to retain the high frequency limit, remove the ferrite again.

You could also use more capacitance (not so good) or a second tuning diode (better) with a small capacitance (ie a tuning diode that is intended for VHF band I or FM tuning) in parallel to the original diode but this will also lower the upper tuning limit a little.

BTW, I have some doubts about the frequency of the tuning voltage generator. If it really generates such a high frequency, then one should be able to monitor its harmonics at twice, three times, etc. the fundamental frequency.

Another idea might be to remove the original antenna wire and replace it by a longer one.
Be aware that the upper frequency limit will also be lowered then.

Roland

dk8cb
19-11-2005, 18:45
If the voltage generated by the voltage converter is not stabilized (no idea whether it is or not), then using 2 NiCD or 2 NiMH cells instead of ordinary batteries will bring down the tuning voltage a little as well. This will affect lower and upper tuning limits however.

Roland

mitajohn
19-11-2005, 19:06
Hi Jos and Roland,

I measured the dc/dc converter frequency and it is obviously around 2.860 MHz (mine is 2.8565).
I don't think that the problem is in the pot because between wiper and the one end (which is not ground and measures to ground 15k) reads 1.5 Ohms and to the other end about 500k. I don't know how it is connected to the circuit it is not easy to find.
I have in my box a TOKO KV156 varicap which is a double one (like the old BB212) which has a C ratio more than 17, and I intend to test the antenna with this one.
I will also make tests to your suggestions. But all these need some time.

John.

dk8cb
19-11-2005, 19:14
Originally posted by mitajohn
because between wiper and the one end (which is not ground and measures to ground 15k) reads 1.5 Ohms and to the other end about 500k.

Try to find the 15 k resistor and put 10 k across it. Should lower the voltage at the lower end and shouldn't affect the upper end.

But then, either Carsten's measurement is incorrect or the 15 k resistor in his DE-31 is shorted by a blob of solder...

Roland

dk8cb
19-11-2005, 19:21
Your 15 K resistor is clearly the one that is marked R7. It is connected to the proper end of the pot, see the attached picture, which forum member Funkerberg was so kind to take and send to me. (Thanks!)

From what is now known, it is highly likely that D3 is a Z-Diode that serves to stabilize the upper tuning voltage, so trying to reduce the tuning voltage by using rechargeable cells in place of batteries won't work.

Roland

mitajohn
19-11-2005, 19:34
D3 reads 12.88V to ground.
I will add the 10K resistor soon and inform you the result.Thanks

John.

carknue
19-11-2005, 19:51
I checked with Degen DE1103 close to the DE31. There is a strong signal on 2850 kHz and a weaker one on 5700 kHz which disappear if I switch off the DE31 and comes back when switched on.

The tuning voltage is pretty stable. I only use alkaline batteries and the input voltage varies between 3.2 and below 2 V and the tuning voltage is always between 0 and 13 V. Maybe my Voltmeter has a too low internal resistor to measure low voltages, but I don't think so. 0V is best for 3995 kHz.

There seems to be some more magic into the DE31 that needs to be discovered ;)

mitajohn
19-11-2005, 20:03
The best result is when R7 is shorted, but still I am not sure that I got the maximum in tuning on 3995, of course is much better now.
Thanks again.

John.


PS. The frequency figure I gave before was taken with a High resolution digital counter PHILIPS PM 6667 with TCXO.

dk8cb
19-11-2005, 20:18
Originally posted by carknue
Maybe my Voltmeter has a too low internal resistor to measure low voltages, but I don't think so. 0V is best for 3995 kHz.

There seems to be some more magic into the DE31 that needs to be discovered ;)

If your voltmeter is an analogue one, I do agree, if it's a digital one and it still measures 0 V, R7 will be shorted, perhaps accidentally.

No, no, there's no magic in it, in my view it is just a relatively primitive circuit...

Roland

dk8cb
19-11-2005, 20:24
Originally posted by mitajohn
.. but still I am not sure that I got the maximum in tuning on 3995, of course is much better now.

Then, you should try to put in another (additional) tuning diode. It should not be one which is intended to be used for AM tuning since its relatively large minimum capacitance will lower the upper frequency limit significantly.
Also have a look at the maximum allowed voltage of your extra diode, some types are not specified for more than 9 Volts and may suffer from a breakdown if a larger voltage is applied.

Roland

mitajohn
23-11-2005, 15:30
I added a BB221 VHF tuning diode and now I have a clear maximum on 3995.

John.

dk8cb
23-11-2005, 21:21
Originally posted by mitajohn
I added a BB221 VHF tuning diode and now I have a clear maximum on 3995.

Congratulations!

Have you also measured how much lower the upper end of the tuning range has moved as a result of the modification?

Roland

df9rb
26-11-2005, 14:18
Hi all,

with my Degen I couldn't tune below 8 MHz anymore. The tuning potentiometer didn t have contact on half of the turning range. The potentiometer itself is of lowest quaility (also soldering) and I couldn't find one that fits - so installed a standard potentiometer outside the housing. I will contact the seller in China - perhaps he will help???

Now the tuning range is OK between 25 MHz and 3.5 MHz - even
higher MW-frequencies are received quite good with potentiometer in minimum (i. e. Vatican on 1611 at 3 o clock local time afternoon).

Bernd, DF9RB

Rene Schmitz
26-11-2005, 15:20
Hi all,

What are the physical dimensions of the actual loop?
How deep are the nulls you can archieve with this?

Cheers,
René

df9rb
27-11-2005, 09:44
Hello René,

the loop is quadratic with about 40 cm side dimensions.
I could not find a narrow null turning the antenna around but the noise from the PC is lower than with the built in antenna of my Sangean in the same distance from the PC.

Bernd, DF9RB

mitajohn
27-11-2005, 15:40
Hi Roland,

I have changed the combination of 1SV149//BB221 with a single KV1560NT using only the one diode, since this is a double one. With this diode I can tune now the loop, with a clear maximum, from around 3300 kHz to around 21000 kHz. I think this is good enough.

John.

dk8cb
27-11-2005, 16:07
Originally posted by mitajohn
Hi Roland,

I have changed the combination of 1SV149//BB221 with a single KV1560NT using only the one diode, since this is a double one. With this diode I can tune now the loop, with a clear maximum, from around 3300 kHz to around 21000 kHz. I think this is good enough.


I see, you also seem to have a few parts available in your "junk box" for experiments. :)
It is always good to have such parts even if they are used and soldered out...

But it would be nice if the antenna could also be used for the 13 m-band, at least in summer, so an upper limit of 22 MHz would be better.

Roland

mitajohn
28-11-2005, 06:59
Hi Reni,

The antenna works very well also on MW. The antenna, there, has deep nulls.

@Roland, I will try to increase the tuning voltage to 15V, since the diode used now has a VR up to 16V, in order to extent the upper frequency limit.

John.

dk8cb
28-11-2005, 10:54
@ mitajohn

I doubt a little that increasing the voltage to 15 V will still decrease the capacitance much further or at least sufficiently to reach 22 MHz.

Roland

mitajohn
28-11-2005, 16:15
Hi Roland,

The DC/DC converter circuit does not work with any other 12, 13 or 15V Z-diode (if it is a zener) except the one installed. If we had a schematic would be helpful, but it's not worth trying. Any way the loop amplifier works up to 27 MHz and I checked it that it works very good up to 21475 kHz with some directivity and a lot of noise.

John.

Rene Schmitz
29-11-2005, 19:58
Hi Mitajohn, Bernd and all,

Thanks for the notes.

It would seem that a deep null is better with a balanced loop. Could be interesting to duplicate the FET amplifier, and use a transformer for matching them to coax. Obviously the varicap would need to be made "floating" between the ends of the loop then.

Cheers,
René

dk8cb
30-11-2005, 09:36
Originally posted by Rene Schmitz
... Could be interesting to duplicate the FET amplifier, and use a transformer for matching them to coax. Obviously the varicap would need to be made "floating" between the ends of the loop then.


...and the FETs would have to be matched as well, preferably as two on the same substrate.

Roland

df9rb
22-12-2005, 17:37
Hello,

during my last business trip to Japan I could receive the label of DW from Sines on 15440 with the Degen. With 3 m wire no reception was possible. Listening in AM the signal from the Degen was much less noisy than the 3 m wire, both mounted in the hotels window there in the center of Tokyo.
The potentiometer of my 1st Degen has been broken before the trip. I replaced the broken potentiometer and contacted the seller in China for a fitting potentiometer. He offered me to send a new antenna without returning the defective one if I pay the postage. Now I have 2 Degen antennas and I would sell the repaired one (see attachment) only for the additional postage I payed. Since having repaired the DC-Box I miss a clamp to contact the batteries. Therfore replacing the batteries means to solder a little!

Bernd, DF9RB

jabi
23-01-2012, 08:27
Any have the following pictures:
http://home.arcor.de/carsten.knuetter/DE31_inside.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside1.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside2.JPG
Is impossible download for this page.
73,s de Jabi, EA2ARU.

simone
23-01-2012, 16:03
Hi jabi,

I am not sure if Carsten still reads on the forum regularly, better send him a PM (username: carknue), maybe he still has the photos you are looking for.

Simone

carknue
24-01-2012, 19:13
Any have the following pictures:
http://home.arcor.de/carsten.knuetter/DE31_inside.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside1.JPG
http://home.arcor.de/carsten.knuetter/DE31_inside2.JPG
Is impossible download for this page.
73,s de Jabi, EA2ARU.

The links are working again.

mvs sarma
25-01-2012, 10:15
Many thanks , carsten !! it is much useful for hobbyists. we get the concept. but the intervening telescopic which helps to make proper shape of the antenna, i doubt whether is is connected on any side to the antenna?

jabi
27-01-2012, 18:03
Pictures all ok. But, is possible, please, upload the circuit squeme for work (and play) with it?
Regards de from Bilbao, Spain, de Jabi, EA2ARU.

P.D.: I am looking the more little antenna for RX in the ham 40 mtrs. in my SOTA RX informations. Have aucun experience with the BAZ ferrite antennas for RX on 40 mtrs.?

ianf
31-05-2012, 05:26
I use the Degen all the time with my Newstar, top tip, make sure Degen has really fresh batteries, it makes a big difference

Linux-DRM
12-02-2013, 21:20
Although not normally a fan of active loops the Degen 31MS performs very well on shortwave and medium wave. I picked up VOCM on 590kHz, Sunday morning, not booming but good copy (using the antenna direct, not via the coupler). OK, VOCM is not that hard to pick up in the UK in the grand scheme of MW DX but still not bad for such a simple setup. I was using my trusty Ten-Tec RX320D at the time using an unattended recording setup to my ultra low powered UG802 mini PC running Ubuntu.

Cap

Braccini
28-11-2016, 10:23
Excellent combination! Strong signal from All India Radio, Voice of Nigeria, listening in Brazil. It's amazing!
I listened too:
BBC WS to Cuba;
Vatican Radio to USA;
Radio Romania International to France;
Radio New Zealand International to Pacific.
Clint 73!