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Old 2nd Jul 2020, 9:08 am   #1
ORAWA01
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Default ATU vs. Preamp vs. Active Antenna

I understand that they are all for peaking and amplifying for the signals we want hear in the band.

But how are they different in the design principles and functions?
Could they work in conjunction such as ATU and Preamp and Active Antenna for DX hunting for the weak signals in the QRM and QRN for maximising the effectiveness? Or would it be better just using one of them? Then which one would be the best?

What devices do you use when listening the HF bands with your receivers? What are your experiences and thoughts about these devices? Thanks.
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Old 2nd Jul 2020, 10:36 am   #2
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Default Re: ATU vs. Preamp vs. Active Antenna

An ATU transforms the impedance of the receiver presented to the antenna with a view to extracting the maximum available signal power from the antenna and getting as much of it as possible into the receiver. No actual power gain, instead it has some loss.

The ATU may have a side benefit of attenuating unwanted signals on other frequencies.

A preamp is an amplifier. Hopefully of low noise. It may not be a particularly good match to the antenna and might benefit from adding an ATU as well. Can be prone to overload. Good to be able to switch out.

An active antenna is a small antenna... too small for efficiency at the frequency involved, and it tries to make up for this by incorporating a preamplifier. There are two sorts, broadband ones and ones with a tuning function to peak them at the chosen frequency.

There is no best. Different circumstances favour different choices.

Sometimes a small rotatable antenna wins by not peaking your wanted signal but by nulling an unwanted one.

I use an inverted-Vee doublet, open-wire feeder and an ATU for both receive and transmit.

David
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Old 2nd Jul 2020, 1:17 pm   #3
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Default Re: ATU vs. Preamp vs. Active Antenna

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Originally Posted by ORAWA01 View Post
What devices do you use when listening the HF bands with your receivers? What are your experiences and thoughts about these devices?
I’ve built the design by PA0RDT, considering it’s just slightly bigger than an old film canister it works really well from VLF to 30MHz, recommended
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Old 2nd Jul 2020, 6:52 pm   #4
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Default Re: ATU vs. Preamp vs. Active Antenna

What is it that you want to listen to? You mention both QRN and QRM, one active antenna which has proved very popular in recent years is the magnetic loop antenna (magloop), perhaps in part because of the great popularity of the commercial product sold by the Wellbrook company. There are now quite a few commercial makes on the market and a number of homebrew designs, many of which seem to get very good reviews. Their great virtue is helping to cut out "electronic noise", like numerous wall-warts and high-speed internet signals travelling down phone lines. There have been a few threads on the forum about magloops.

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Old 2nd Jul 2020, 9:48 pm   #5
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Default Re: ATU vs. Preamp vs. Active Antenna

Thank you for your info & suggestions.

I have been trying to listen to DX BC stations such as Radio Japan, Radio Korea and some of the far away exotic commercial DX stations. And both Radio Japan and Radio Korea have relaying stations in France and UK, so some of their programs are very strong - I can hear even without antenna connected to the radios when the conditions is favourable.

But there are the programs coming direct from the countries, and then their signals get very weak and faint. It then becomes challenging to copy them. I have been using just a long wire and ATU, but now I am thinking of adding some type of preamp and even trying Active Antenna, if these device will help.

I have read about the Wellbrook Loop antennas and the reviews, and certainly it seems excellent piece of engineering which works. But the price of the loop seems rather high, and I was wondering if it will really satisfactorily for my DX activities giving excellent result.

I have been asking about this to other SWLs, and some of them says that it could be the propagation path of the signals. If the signals don't reach where the receiving antenna and radio set up is, then nothing will make them to be heard?

So, I was trying to learn more about these devices, and their functions and capabilities, which will give me clearer ideas for the improvement.
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Old 2nd Jul 2020, 11:14 pm   #6
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Default Re: ATU vs. Preamp vs. Active Antenna

OK, one way to learn would be to build one.

You now need to search this website. Other people on here have built loop antennae that compare well with the Wellbrook.

Do searches for Wellbrook and for Wellgood. David G4EBT has been a ring leader. I think he'll forgive me for dropping him in it. I provided some rather good transistors for some of these attempts and I still have some left. If you want to have a go I can bung a couple in a jiffy bag. It could go in the post or we may be close. I'm to the west of Dunfermline.

You may have to change your moniker

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Old 2nd Jul 2020, 11:40 pm   #7
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Default Re: ATU vs. Preamp vs. Active Antenna

I think the Wellbrook (WB) was ~£350 when it first came out....but you can build one for ~£10?

One or two people have found themselves with non-working WB loop amplifiers, which are potted and impossible to open and repair, but seeing as they were bust anyway, people have gone to great lengths to un-pot them and discover the secrets of their circuitry. In fact they use just two transistors, originally built on Veroborad. A guy called George Smart has been selling a ready-made PCB for a Wellbrook clone which he calls the Wellgood (WG) which has been built by lots of people, including me and a few other people on this forum. The WG is discussed in detail here https://www.george-smart.co.uk/projects/wellgood_loop/. But don't dash in building it; there are some tweaks to that design which may be useful. Alternative there is another very popular magloop design https://www.lz1aq.signacor.com/docs/...op-antenna.htm Since publishing his first circuit, that guy has gone on to run a business based on magloops.

Magloops are very interesting, but much of the technical info about them on the net is contradictory and inconsistent. But they do work, and I do prefer the £10 versions!

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Old 3rd Jul 2020, 7:17 am   #8
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Default Re: ATU vs. Preamp vs. Active Antenna

Great and interesting info. Thank you ~

Yes, I would like to give a try building WBML. I didn't know Wellbrook company is no longer trading either. Certainly the new price for the Mag Loop was well over my budget.

David, if you are in Dunfermline, then maybe we could even talk on 2m FM. I think 2m FM path is very good to Dunfermline from my QTH. But I must locate my BaoFeong 2m FM Handie somewhere, and put it to recharge for a day.

Or I could call you on the phone, if you prefer. Then please PM me your mobile.
Or I could send you SAE, if you PM me your address, and trying to get the transistors.

I have a couple of restoration projects going right now, but they can wait. This WBML diy project sounds very interesting. And if I get stuck with any problems, I could always ask for some help and support here.

Thank you 73s
Jay
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Old 3rd Jul 2020, 7:23 am   #9
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Default Re: ATU vs. Preamp vs. Active Antenna

Wellbrook is still trading! They have completely ignored the clones of their early design, and come out with new models which are still getting very good reviews.

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Old 3rd Jul 2020, 8:15 am   #10
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Default Re: ATU vs. Preamp vs. Active Antenna

Sorry for my misunderstanding on Wellbrook company. It was too early for me, and I misread it.

They seem getting excellent reviews, but if they could be made by DIY with relative ease and low cost, and perform in par with the real thing, then it would be fantastic.

And thanks David. Got your contact details OK. 73s
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Old 3rd Jul 2020, 9:06 am   #11
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Default Re: ATU vs. Preamp vs. Active Antenna

The Wellbrook ALA1530 was £120 in its early days, I know as I bought one. I think they have roughly doubled in price since then. It came complete with a PSU and interface unit. Andy Ikin of Wellbrook is still producing them although he told me he is reducing his product range.
They work well and mine has reduced my local s8 of 'hash' to S1/s2 and literally saved my hobby.
You can build an active loop antenna with a plastic hula hoop, some kind of enclosure for the electronics and a handful of components. It may not have the ultimate performance of a Wellbrook, but it won't be far off.
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Old 3rd Jul 2020, 1:16 pm   #12
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Default Re: ATU vs. Preamp vs. Active Antenna

Also look at Cross Country Wireless, he builds the preamps and the power feed , you just make the loop. I’ve got one of those and made the loop out of a child’s hula hoop and some coax...
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Old 3rd Jul 2020, 1:29 pm   #13
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Default Re: ATU vs. Preamp vs. Active Antenna

Hi Tim,

They look very good value for money, I have been considering the
lower frequency one, as I like to search for the NDBs on MF in the winter.

Kind regards
Dave
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Old 3rd Jul 2020, 11:41 pm   #14
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Default Re: ATU vs. Preamp vs. Active Antenna

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Also look at Cross Country Wireless, he builds the preamps and the power feed ,
I had not heard of CCW. Don't see any specific reference on his website to his amps being clones of Wellbrook; how certain is that connection? Do you know what transistors he's using?

The one part of building the Wellgood which is "a bit of a chore" is transformer T1; quite a lot of separate windings with bifilar wire - you only need the one, but it takes some concentration! George Smart's PCB is very good, but scaled down to just about the smallest possible size. Replacing the original transistors with the (potentially better) 2N3866 and 2N5109's (physically larger), complete with heat sinks, is a very tight squeeze.

There's an article by Peter Mellet (G3PIJ) (of this Parish) in the Issue 50 (Feb 2019) of VMARS publication "Signal" describing the construction of another variant of the Wellbrook which does not use George Smarts PCB, and looks all together more amenable to those of us of "certain age"!

Playing with my Wellgood on 80m recently, it seems to be just very marginally less good than my 80m Inverted V, but I plan to relocate it and that could make a difference.

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Old 6th Jul 2020, 8:11 am   #15
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Default Re: ATU vs. Preamp vs. Active Antenna

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Playing with my Wellgood on 80m recently, it seems to be just very marginally less good than my 80m Inverted V, but I plan to relocate it and that could make a difference.
Could you please try tune these freq. with your Magnetic Loop antenna and also other receiving antennas you have, and see what sort of signal strength and reception they get? Thanks.

Freq Station ID GMT Start End Days Language
9515  KBS RADIO 15:00 17:00 1234567 English
9570  KBS RADIO 13:00 14:00 1234567 English
9580  KBS RADIO 02:00 03:00 1234567 English
9630  KBS RADIO 14:00 17:00 1234567 English
9640  KBS RADIO 16:00 17:00 1234567 English
9770  KBS RADIO 08:00 10:30 1234567 English
9785  KBS RADIO 14:00 16:00 1234567 English
11810  KBS RADIO 22:00 23:00 1234567 English
15575  KBS RADIO 13:00 14:00 1234567 English
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Old 6th Jul 2020, 10:46 am   #16
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Default Re: ATU vs. Preamp vs. Active Antenna

There is something which generates interference which sounds like white noise that covers large sections of the HF bands and sometimes extends up to 145MHz.

In the Forth valley, Lothians, Fife, it is usually strong enough to blot out reception of normal signals. Don't know about its strength out of this area. It switches on and off and I can see the spectrum display on my HF radio go clear exactly as the noise level drops on my 145MHz set.

For this spectrum coverage, area coverage and signal strength, a very large amount of power is involved.

Speculation is about some form of over-the-horizon radar, or maybe a military jammer being fired up and tested perhaps for a training course?

I don't have a directional antenna or a portable HF radio, but I'm intending sorting something out and doing some direction finding.

To see the scale of over the horizon HF radars, look up DUGA-3 this was a famous Soviet one in Ukraine. The antenna arrays are immense. It needed a small town of people to run and maintain it, and it took a nuclear power station to power the whole show. The power station is more famous than the RADAR itself: Chernobyl!

Radars are normally pulsed, and Duga-3 was the famous 'Russian Woodpecker' bur spread spectrum techniques allow them to be continuous output and to be randomised to look like featureless noise unless you have the key to correlate them against.

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Old 6th Jul 2020, 8:17 pm   #17
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Default Re: ATU vs. Preamp vs. Active Antenna

Yes, that has been another point I was thinking about, and still not sure which is the answer. Is it the propagation path for the QTH and RFI situation in the receiver and antenna surroundings? Or could good high quality antennas overcome the problems, and make the reception possible?

I was thinking that maybe one of the reason that I cannot receive those DX stations is that, I am in the location where the propagation path for the signals don't exist.

In my area, QRM and RFI seems not too much problem. But when I go downstairs with my portable radio, I get a lot of motor boating / woodpecker type QRM. I don't know where it is coming from. In the upstairs rooms, the QRM is less problem. In fact it is quite OK, and it also seems some part of the HF bands are more problem than others. In my QTH, 5-7 Mhz is quite good. But 3-4Mhz is problematic with the band noise. 9-15Mhz seems OK too, but receiving those signals from KBS World Radio, has been always problem. I was receiving them very well during the spring, but now in the middle of summer, it is much struggle to get the reception. I can hear they are there in the freq. but I cannot make out what they are saying most of times. Hence I was thinking of the extra devices such as preamp, active antennas, atu or now Magnectic Loop.


I would have thought good quality Magnetic Loop antenna is able to clear the QRM problems, and also with the powerful RF amp within the Mag Loop, it could bring the weak faint signals to good listenable signals?

The SAE is on the way to you David. Thank you so much for your offer of the Transistors for my possible DIY Mag Loop project. Much appreciated.

Thanks & 73
J.
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Old 6th Jul 2020, 10:24 pm   #18
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Default Re: ATU vs. Preamp vs. Active Antenna

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Originally Posted by ORAWA01 View Post
Could you please try tune these freq. with your Magnetic Loop antenna and also other receiving antennas you have, and see what sort of signal strength and reception they get? Thanks.

Freq Station ID GMT Start End Days Language
9515  KBS RADIO 15:00 17:00 1234567 English
9570  KBS RADIO 13:00 14:00 1234567 English
9580  KBS RADIO 02:00 03:00 1234567 English
9630  KBS RADIO 14:00 17:00 1234567 English
9640  KBS RADIO 16:00 17:00 1234567 English
9770  KBS RADIO 08:00 10:30 1234567 English
9785  KBS RADIO 14:00 16:00 1234567 English
11810  KBS RADIO 22:00 23:00 1234567 English
15575  KBS RADIO 13:00 14:00 1234567 English
At 2225 UK local on 11810 is s9+ carrier some fading

10 MHz rotary dipole at 70ft

Fred
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Old 6th Jul 2020, 10:50 pm   #19
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Default Re: ATU vs. Preamp vs. Active Antenna

UK local time 2225 is 2125 GMT, and it is BBC English service via Wooferton Transmitter according to the SW Schedule site?
The KBS 2200-2300 11810 starts in 12 minutes.
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Old 6th Jul 2020, 10:50 pm   #20
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Default Re: ATU vs. Preamp vs. Active Antenna

22:44 11810kHz carrier fading, female voice. Can't make out what's being said.
S9 signal in S8 noise.

If whatever's making the noise gave up, it should be listenable. I tried the DSP de-noising process. I'm using an Icom IC-7700 transceiver on reciev, it has pretty good facilities for winkling signals out of noise and rejecting adjacent channels.

THings should progressively get better over the next few years with increasing sunspots

David

EDIT blast! forgot GMT, which explains things. It's definitely more distant than Wooferton. Could be direct.
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