DRM Software Radio Forums  

Go Back   DRM Software Radio Forums > DRM Software Radio - User Forums > Antennas
User Name
Password
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-10-2005, 12:47   #1
carknue
Registered User
 
carknue's Avatar
 
Join Date: Dec 2002
Location: Frankfurt, Germany
Posts: 1,321
Thumbs up Degen DE31 active loop

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
__________________
regards, Carsten
AOR 7030 + Wellbrook ALA 1530P & DWT + Degen DE31 + TG33

Free DRM Tools for analysing, controling and automating your DRM reception and logging
carknue is offline   Reply With Quote
Old 08-10-2005, 15:53   #2
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
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
dk8cb is offline   Reply With Quote
Old 09-10-2005, 09:39   #3
carknue
Registered User
 
carknue's Avatar
 
Join Date: Dec 2002
Location: Frankfurt, Germany
Posts: 1,321
inside

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
__________________
regards, Carsten
AOR 7030 + Wellbrook ALA 1530P & DWT + Degen DE31 + TG33

Free DRM Tools for analysing, controling and automating your DRM reception and logging
carknue is offline   Reply With Quote
Old 09-10-2005, 12:25   #4
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Very interesting!

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 is offline   Reply With Quote
Old 09-10-2005, 14:23   #5
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Circuit

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
dk8cb is offline   Reply With Quote
Old 09-10-2005, 15:04   #6
carknue
Registered User
 
carknue's Avatar
 
Join Date: Dec 2002
Location: Frankfurt, Germany
Posts: 1,321
Hi Roland,

the range of Vtune is from 0 to +13V. V+ is always +2.47V.
__________________
regards, Carsten
AOR 7030 + Wellbrook ALA 1530P & DWT + Degen DE31 + TG33

Free DRM Tools for analysing, controling and automating your DRM reception and logging
carknue is offline   Reply With Quote
Old 09-10-2005, 15:12   #7
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Quote:
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 is offline   Reply With Quote
Old 09-10-2005, 16:10   #8
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
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 is offline   Reply With Quote
Old 09-10-2005, 18:42   #9
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Frequency of DC converter?

@ 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 is offline   Reply With Quote
Old 27-10-2005, 00:26   #10
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Update

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.

The tuning diode is a 1S149 or 1SV149 (equivalent) AM tuning diode, get its datasheet here.

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
dk8cb is offline   Reply With Quote
Old 19-11-2005, 15:43   #11
mitajohn
Registered User
 
mitajohn's Avatar
 
Join Date: Nov 2002
Location: Athens - Greece
Posts: 6,477
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.
mitajohn is offline   Reply With Quote
Old 19-11-2005, 17:25   #12
Jos
Registered User
 
Join Date: Mar 2004
Location: Leuven - Belgium
Posts: 383
DE31

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.
__________________
-
Jos is offline   Reply With Quote
Old 19-11-2005, 18:11   #13
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
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 is offline   Reply With Quote
Old 19-11-2005, 18:45   #14
dk8cb
Roland
 
Join Date: Mar 2004
Location: Munich, Germany
Posts: 2,748
Another idea

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
dk8cb is offline   Reply With Quote
Old 19-11-2005, 19:06   #15
mitajohn
Registered User
 
mitajohn's Avatar
 
Join Date: Nov 2002
Location: Athens - Greece
Posts: 6,477
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.

Last edited by mitajohn : 19-11-2005 at 19:09.
mitajohn is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT. The time now is 17:04.


Powered by vBulletin Version 3.5.3
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.