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gccengineering
01-06-2006, 23:52
Group, I have a question about our shortwave antennas. Is it best to use
active antennas or just a longwire antenna cause of less noise meaning less
errors? Or would a active antenna help?

Adam E. :)

richard
03-06-2006, 10:45
A passive longwire antenna is not necessarily going to be less noisy. The wire itself will act as a noise source, increasing in power with length. An active whip with a low noise amplifier may give equally good results. If this is used indoors the main limitation is likely to be from locally generated interference. The best antenna appears to be the loop. This is generally more immune to local noise and can be tuned, increasing SNR and giving better front end selectivity. I have successfully experimented with both ferrite and open air loops made from turns of wire and a tuning capacitor. A simple fet amplifier is normally used to connect the loop to the receiver.

Richard

df9rb
03-06-2006, 15:09
Hello,

I can choose between 5 antennas for DRM reception.
- above 13 MHz my 3 element HAM-yagi is the best
- from 1 Mhz to 8 MHz the EWE-antenna (check Google for "EWE-antenna")
has highes SNR
- below 1 MHz a magnetic loop is the best
- a 30 m long wire has always the strongest signal below 13 MHz but the lowest SNR!!!!! That means a low noise antenna (EWE, Loop) is better than
an antenna delivering high field strength but also high noise
On business trips and holiday I use a Degen Loop or 1 m long whip antenna with a passive 1:9 transformer. Both have similar results with an advantage of the Degen Loop in noisy surroundings

73s de Bernd, DF9RB

FritzWue
03-06-2006, 16:36
Hi Adam,

as long as I need no electronics I use passive antennas, at home in the country without much noise a high wire antenna and a remote rotatable and tuneable shielded loop 4x4ft. under the roof.
On the car the 4 foot whip is too short for the lower frequencies giving me not enough signal into 50 ohm, so I use a preamplifier for mobil reception.

df9rb
04-06-2006, 08:34
Hi all,

on the EWE-antenna (passive) the fieldstrength is below 5 µVRMS from RTL on 1440 kHz during daylight but the DRM-signal can be seen in Input PSD and there is audio - on the 30 m long wire the s-meter displays 25 µVRMS but nearly no DRM-signal observable. One antenna picks up the signal the other noise from my home and the neigbours home which is the second fixing point of the antenna ........ The EWE is at least 10 m away from the next TV, dimmer, switching power supply, .....
The active ALA1530 (magnetic loop) is between the EWE and 30 m wire.
I tried several active antennas on medium/shortwave. My experiences are that a passive vertical antenna 2 m (better 3 m) long with a passive 1:9 transformer mounted over ground in the garden as fare away as possible from other electronic equipment is better than a shorter active antenna mounted on the roof or in the shack.
This is what I would like to show with this attachment.....

Bernd, DF9RB

François
05-07-2006, 10:04
Hallo,
i was in Luxemburg last june. i am receiving the visit from an ingenior from BCE, filial from the RTL Group. We have readed over the antennas. Indoorantennas must be forgotten, why not high quality. I use the DRM receiver ELAD FDM77 with Dream(last version) and the standard software ELAD-FRAUENHOFFER INSTITUT(45 euros). The best reception is over Dream with , if necessary, use any options. I have 2 antennas:
1) double zeppelin 2*18.50m with 25m 250 ohm Twincom cable with 1:4 balun.
2) 25m long-wire with MTFT balun(?) 1:10 ( changing this morning)

I have observed that the location is not same as with analog transmission. The antennas must hanged over 5 meter over ground and not in the near of electric parasite.

The best result since I have this receiver was SNR value 32,5dB( Franco Milan from ELAD have writen me that the theorical maximum SNR value is 50 dB, and my maximum value is very good). I cann't say if both antennas are optimal between 150 Khz and 30 Mhz.

I use now a 10 meter long-wire with the same balun to see the normal listner receive DRM transmissions.

Sorry for my poor english langage. Best dialog in french or german langage.

Locator: JN39KF Town :Petite Rosselle Country France
10 km SW Saarbrücken Germany (border with France)
70 km SE Luxemburg City

mitajohn
14-09-2006, 16:55
Hi all,

Have anybody any idea about this: http://www.radiopassioni.it/pdf/pa0rdt-Mini-Whip.PDF very interesting small active antenna and how it would be perform of receiving DRM ?

John.


PS: Also look at this one http://www.cvni.net/radio/e2k/e2k029/e2k29miniwhip.html

Digger
08-10-2006, 08:54
Have anybody any idea about this: http://www.radiopassioni.it/pdf/pa0rdt-Mini-Whip.PDF#search=%22pa0rdt%22 very interesting small active antenna?
John.


Hi John and all,

I built the PA0RDT Mini-Whip Active Antenna according to the PDF document above and I must agree, it is small. The antenna (or "Probe" as they call it) is a piece of Printed Circuit Board 30 mm wide and 45 mm long. The rest of the 90 mm long board supports the active and passive elements. It is fed with 12-16 Volts at 48-53 mA through the coaxial cable from the receiver. I used Metal Film resistors and all 100 nF capacitors are SMD "chicken feed".

So far I have tried it out comparing it to the 16 m Long Wire on:

1. DW on 3.995 MHz overnight. -26 dB compared to the L.W.
2. RTL on 6.095 MHz, 80 minutes. -18 db compared to the L.W.
3. BBC on 9.470 MHz, 50 minutes. -19 dB compared to the L.W.
4. DW on 13.810 MHz, 80 minutes. -17 dB compared to the L.W.
5. DW on 15.440 MHz, 45 minutes. -19 dB compared to the L.W.

On 13 MHz SNR rose some dB when I switched to the PA0RDT-Mini-Whip Active Antenna.

If you want a small antenna or have absolutely no space to put up larger/longer antennas, then build this one. It works.

Terje


P.S.: Case closed. This antenna is too inefficient (for my expectations).

mitajohn
08-10-2006, 10:42
Hi Terje and all,

Very well done !
I found an Italian version of the PSU but the site seems not working today because the link is not working, so I attached a gif of the schematic and the box. (I have downloaded the pdf in Italian. If you want it send me a PM with your email). They claim better noise reduction with this PSU configuration.

John.

dk8cb
08-10-2006, 11:20
They claim better noise reduction with this PSU configuration.

The additional circuit isolates the antenna's ground system from the receiver ground which more or less consists of the mains wiring. Signal strength can be expected to become lower with this circuit, especially on lower frequencies but due to the lesser influence of interference travelling on the mains wiring, reception may nevertheless be improved.


Roland

mitajohn
08-10-2006, 11:27
Hi all,

Here's the link for the Italian pdf: http://www.radiopassioni.it/pdf/miniwhip.pdf

John.

Digger
24-04-2008, 13:56
Hi John and all,

(Edit 24th April 2008)

I built the PA0RDT Mini-Whip Active Antenna back in October 2006. In the meantime it has just been lying around in a box, and I decided to give it another try when I heard about Sixten's 1.7 meter long active antenna. My antenna (or "probe" as PA0RDT calls it) is a piece of Printed Circuit Board 30 mm wide and 45 mm long. The rest of the 90 mm long board supports the active and passive elements. My antenna is fed with 16 Volts at 55 mA through the coaxial cable from the receiver. I used Metal Film resistors and all 100 nF capacitors are SMD "chicken feed".

To be fair to PA0RDT I have to correct my table of results from October 2006, as one of the "chicken feed" SMD capacitors on the PCB was broken! I noticed this when I did some bench tests and traced the signal from point to point on the printed circuit board when I suddenly lost the signal at the BNC connector. I changed the 0.1 µF SMD output capacitor on the board and got the signal back.


Then I have made three minor changes to the PA0RDT antenna:

1. I changed the J310 FET to a 2SK192 which gave 2 dB better output.
2. I added a 5.6 mH choke in the the 2SK192 source between the source resistor and ground. This increased the output another 2 dB.
3. I increased the 470 uH choke in the DC feed to 5.6 mH. It's internal resistance is about 8 Ohm. This improved the Long Wave reception a great deal (down to 77.5, 75 and 60 kHz).


The active antenna is mounted on top of a 4 m high mast. It was tested again comparing it to the 12 m Long Wire (not 16 meter any more) on different frequencies with great results:

1. DRM RFI on 3.965 MHz, more or less same level compared to the L.W.
2. DRM BR5akt on 6.085 MHz, around 7 db less than the L.W.
3. An AM station on 9.575 MHz, more or less same or some dB lower level compared to the L.W.
4. DRM MOI Kuwait on 13.620 MHz, more or less same level compared to the L.W.
5. DRM MOI Kuwait on 9.880 MHz, more or less same level compared to the L.W.
6. DRM DW on 13.810 MHz, more or less same level compared to the L.W.
7. An AM station on 11.700 MHz, more or less same level compared to the L.W.


Indeed a very interesting little antenna!

mvs sarma
25-04-2008, 17:53
Hi all,

Here's the link for the Italian pdf: http://www.radiopassioni.it/pdf/miniwhip.pdf

John.

I incidentally have few English pages of the same file and followed by Italian script. English pages copy attached, thanks to the designer.

Thanks to Terji for the mod details and results obtained. It is encouraging information.

mitajohn
01-05-2008, 08:04
Hi Terje and all,

Very well, but have you compared the SNR with a LW or a Loop antenna?

Digger
01-05-2008, 09:21
Hi John and all,

Yes, in fact I have. Here are two examples, both a bit short, but you can see the difference. The SNR is roughly the same for the 12 meter wire antenna and the 35 mm active. In the DW screenshot from Dream the SNR is less "wavy" with the 35 mm active antenna.

In the REE the max. SNR, 28.01 dB, was recorded at 08:54 with the 12 meter wire. The 35 mm active topped at 08:39 with 27.54 dB SNR. But the conditions change all the time.

In fact, both antennas have their advantages. At 75 kHz for example, the HBG comes in 15 dB stronger with the 35 mm active antenna. Not to mention 531 kHz which is a real nuisance with its 180 kW AM about 20 km away from here. :mad:

mitajohn
02-05-2008, 18:48
Hi Terje and all,

....531 kHz which is a real nuisance with its 180 kW AM about 20 km away from here.

Doesn't it produce IMD problems to your RX?

Digger
02-05-2008, 19:19
Hi John and all,

531 kHz? Oh yes you bet it causes trouble. From now on I have to find out whether the RX or the antenna is the problem, but I believe it is the RX. Problematic is LW and to some extent MW, at least up to 1200 kHz. Under 100 kHz I experience less problems. It is interesting what I can pick up with the 60 cm whip on top of the modded PA0RDT below 100 kHz with my Yaesu FRG-7700: Time signals on 66.6 kHz from Russia, 60 kHz from Britain and today a time signal from Archangelsk on 25 kHz some 2760 km away.

Sixten (SM5DAJ) stumbled upon some interesting pages with a lot of interesting topics, especially about active antennas, which I would recommend studying:

http://www.kongsfjord.no/dl/dl.htm

A lot of interesting things to study there.

df9rb
08-06-2008, 07:46
Hi all,

I bought an antenna phaser and tested the last two weeks a lot on MW where many (or nearly all!) DRM stations are plagued by co-channel interference. The result is astonishing!
All test were made with my ALA1530 and the EWE-antenna.
On 693 I can choose between RAI in DRM and VoR in AM in the early evening or between RAI and BBC later in the night. RAI has no drop-outs anymore with the phaser except during very deep fadings.
On 1296 I can listen to BBC in DRM or a Spanish station in AM coupling inversely phased or with a few db gain for BBC coupling in-phase.

The two pictures in the screen shoot were taken within a few seconds to avoid influence of fading.

The inversely phased coupling needs a lot of fine tunnig but is quite stable even under skywave conditions (but not so deep as for ground wave signals..)

Bernd, DF9RB

df9rb
17-06-2008, 20:24
Hello,

I bought the Quantum Phaser. It is specified from 500 kHz to 2 MHz. On LW it works also quite good, but on shortwave the notch is not very deep or has very often no effect.

73s Bernd, DF9RB