Loops Directionality of Wellbrook loop antennas?

FrankO23

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#1
A few days ago I received a Wellbrook ALA1530LNP loop antenna, and have been testing it with an SDRplay RSP2.

In general, the performance appears to be very nice on HF, but I needed to install a high-pass filter to block MW broadcast, as well as a 20 dB attenuator in order to get signals to a manageable level. I'm in the Los Angeles area, and we have lots of strong MW broadcasters.

I'm still trying to get a handle on the directionality of these antennas. I've read that the directionality should be strongest at MW, where the antenna can be turned to null out interfering signals. At HF, I understand that they can be close to omnidirectional for distant radio signals, but can still be turned to null out local noise sources such as electrical from households etc.

After a short amount of experimentation, I'm not seeing any difference in signal levels on the MW broadcast band when I turn the antenna. As noted, though, the MW signals are very strong, and are even good-sized with the MW-blocking filter and 20 dB attenuator in place.

One of my friends who has a Wellbrook says this sounds odd, and I should be seeing decent nulling of MW broadcast signals when I turn the antenna.

Can any other Wellbrook owners tell me, how pronounced is the nulling of MW stations when you turn the antenna? If there are broadcast stations in various directions, do you see them reducing one by one as you turn the antenna?
 

ka3jjz

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#2
This smacks of an extreme overload situation. Did you try dropping the gain on the RSP AND the Wellbrook (if you can)? Are you using the correct filters that I understand are selectable on the RSP?

If you are overdriving either or both, it's entirely possible that you won't see any directional effects, no matter which loop you use....Mike
 
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#3
I don't have a Wellbrook, but I did build my own loop.

I'd agree with ka3jjz, Sounds like sheer overload.
I can imagine that you are absolutely getting pounded with MW signals in the LA basin.

I'm far enough away from any major AM stations that I've not had that issue, but in some locations when I've taken it portable, I have.

I could easily imagine that there's enough signal to make it through weak coax shields, bad connections, missing grounds, etc. to make it a problem.
 
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#4
Agree with the extreme overload diagnosis. Probably nothing wrong with the antenna. The RSP just cannot handle the strong AM signals in your area.

Experiment with the RF gain settings. Review the SDRUno guide for the RSP2 at the SDRPlay site.
Ports A and B have a MW notch filter, Hi Z port does not.

Try the loop with another known good receiver (ideally a communications receiver) if one is available for comparison purposes.
 

Thunderknight

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#5
I think that loop has an amplifier at the loop, if it does, there is a limit to how much filtering at the radio will help. Ideally, you would filter BEFORE the amplifier, but I’m not sure that is possible with the Wellbrook.
 

FrankO23

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Thanks for the comments. Yes, I agree it seems as though it's a major overload. In addition to inserting the filter and attenuator, I've been playing around with RF gain in the SDRplay software I'm using, SDRUno.

I'll try using it with other software for the SDRplay, and also with other receivers, to see if this leads to anything. So far as I know, there are no controls on the Wellbrook antenna itself that can be adjusted. I might also try emailing Wellbrook to see if he has suggestions.

Having said all that, I'm pretty impressed by the performance so far. On the bands I've tried it on so far, it's better than my other antennas (longwire through tuner; EF-SWL end-fed wire; active mini-whip). The only thing that jumps out at me as a problem right now is that LW is super-saturated with ghost signals, which is too bad as I'd like to check out that part of the spectrum more. I may have to cobble together some low-pass filters.
 

ka3jjz

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#7
Did you see ZTZ's comment that ports A and B have a MW notch? Are you feeding into either of those, and making sure the notch is on? The data sheet mentions that there are selectable notch filters available. Are you using this?

Your LW overload issue is undoubtedly related to how much MW RF you are receiving. As was mentioned earlier, ideally you want to put your filter before, not after, the amp. Otherwise you could risk saturating the filter and rendering it useless.

In your case, at least, I wouldn't even think of using an amplified antenna of any kind. A passive loop - there are many plans for these, and we have a few in our wiki - would be my choice. The selectivity of a passive loop would really knock all those overload issues down a great deal, I'm sure.

Mike
 

FrankO23

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Did you see ZTZ's comment that ports A and B have a MW notch? Are you feeding into either of those, and making sure the notch is on? The data sheet mentions that there are selectable notch filters available. Are you using this?
Yes, I've worked with that. Your other points make sense as well.

Going back to my original question, however, I'd still be interested in hearing from any owners of Wellbrook antennas. How much of a drop in MW signals do you see when you rotate the antenna? When AM broadcast stations lie in various directions, do you see them drop one by one as you turn the antenna?
 
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#9
Have not personally used the Wellbrook but it enjoys a good reputation for LW and MW work. However, have used various homemade loops. The true test of a loop is how well it nulls. A properly constructed loop will show sharp balanced nulls even on strong signals.

Therefore, again, my suspicion is that your loop is fine but the receiver is the problem. Recently, the RSP1A has become available. It has some additional filtering at the low end.

btw, IMHO, there are much better receiver choices for serious LW work.

Anyway, there are guys on here with Wellbrooks, hopefully you will hear from them.
 

dlwtrunked

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#10
I think that loop has an amplifier at the loop, if it does, there is a limit to how much filtering at the radio will help. Ideally, you would filter BEFORE the amplifier, but I’m not sure that is possible with the Wellbrook.
Three comments:
1. The amplifier is indeed in the base of the loop (and potted to hide its design). The other piece is only a lower injector and signal separator.
2. It is not possible to insert filters between the loop and amplifier.
3. Keep in mind that with a loop like this, *the amplifier is only trying to make up for the low signals of the loop*. It is unlikely the problem is originating in the Wellbrook as it does not see strong signals at it input. For this reason, the spurious signals are the common old problem of a receiver not being able to withstand AM broadcast band typical strong signals (and undoubtedly has the problem with a good wire antenna) and attenuating them before the receiver is a good (and in this case only) choice.

Putting it before the amplifier is only required if the problem originates in the amplifier with it seeing very strong signals at its input which is likely not the case here. (I have 2 Wellbrook antennas.) Otherwise, your filter rule does hold--low signals originating from loops like this is a special case.
 
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#11
My experience with my RSP1 is rather dismal performance on AM BCB and especially poor on LW.
Some of this may be my fault as the receiver learning curve is a bit steep. It comes with no owner manual. There is online support but to me, a well written owner manual is preferable to having to ferret out information online. (Would gladly pay $20 or whatever for a nice owner manual). The LW and MW range on this radio seems very vulnerable to any kind of interference.
OTOH, without getting too far off topic, just let me say that performance on higher frequencies is quite good. Regularly use it in the evening to copy W1AW and it seems as good as any of my ham radios. Had some nice tropo openings here on VHF last summer and was receiving strong signals on all NOAA WX freqs with some stations out 200 - 300 mi. Performance was as good as or better than my most sensitive scanner.
 

EricCottrell

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#13
Hello,

I have a Wellbrook ALA1530 loop and do see the nulls on LW/MW. Nearby metal objects can affect the nulls, so the loop should be in the clear. Nulls will not be of much help if you have nearby MW stations in different directions. I have several nearby MW stations with one of them causing about S9+70 (0 dBm or 1 milliwatt!) on my WJ-8711A. I can get a decent null on that station but still have strong signals from other stations.

I use an external MW Band Reject filter on some receivers, like the RSP1. Sometimes I have to throw in 10 dB attenuation. I also had problems years ago using dipoles and older tube type radios, mainly MW images up to about 3 MHz.

73 Eric
 
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#14
Thanks. Do any ones in particular come to mind?
For serious LW work you really need a communications receiver with good filtering. You want, for example, to be able to pull a Canadian NDB (with 400 cycle offset) that is co-channel with an American NDB out from between the U.S. 1020 cycle offsets. Some portables have LW capability and can be OK for casual LW work when coupled somehow to a good antenna but most lack the filtering and only tune in 1 kc steps. So, you need a communications receiver with the filtering and PBT is nice to have as well. My first choice in a new tabletop receiver would have been an Icom R-75 but, unfortunately, it has been discontinued. So, settled for an Alinco DX-SR8T transceiver which has general coverage receive capability and have not been disappointed. Very sensitive on LW and good filtering. Some ham transceivers have general coverage receive starting below the AM BCB but their sensitivity is reduced on LW and AM BCB... check the specs. A friend has an Icom R-71A which is a nice RX on LW. If you are interested in SDR, my only experience has been the RSP1 so really can't help much other than to say that the guys with the high-end SDRs get some amazing long haul NDB catches.

Probably would be best to ask your question in a new thread in the receiver forum and see what you get for replies. Be prepared perhaps for some replies extolling exotic, nearly unobtainable but nice stuff. Otherwise, there are a lot of R-75s, R-71As, and such out there that with your Wellbrook in combination with some sort of "longwire" would make a nice set up on LW.
 

Token

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#15
I'm still trying to get a handle on the directionality of these antennas. I've read that the directionality should be strongest at MW, where the antenna can be turned to null out interfering signals. At HF, I understand that they can be close to omnidirectional for distant radio signals, but can still be turned to null out local noise sources such as electrical from households etc.
Arrival angle has a lot to do with how a loop nulls.

On MW stations the arrival angle is often low, this is particularity true for local or semi-local stations where you are receiving via ground wave. And the loop will often null very well. On HF when talking about sky wave signals the loop will not present as sharp or as well defined a null.

I have no close MW stations, there is one 5 kW station 6 or 7 miles away and one lower power one about the same distance in another direction. I can null each of them by 30 dB or more with the Wellbrook.

T!
 
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#16
Arrival angle has a lot to do with how a loop nulls.

On MW stations the arrival angle is often low, this is particularity true for local or semi-local stations where you are receiving via ground wave. And the loop will often null very well. On HF when talking about sky wave signals the loop will not present as sharp or as well defined a null.

I have no close MW stations, there is one 5 kW station 6 or 7 miles away and one lower power one about the same distance in another direction. I can null each of them by 30 dB or more with the Wellbrook.

T!
My Wellbrook, even being up 50' from ground level, behaves the same way. I have very powerful MW transmitters very close. I also have Sutro Tower at 1.5 miles and on that is KFOG FM, which I can hear burbling across certain SW bands despite having an FM notch filter and finer receivers.
One thing I still wonder about speaking of directionality and pardon me if I missed an answer here: does the Wellbrook receive signals strongest at the broadside or the narrow side? I was told in the past that it's the narrow side but sometimes it doesn't behave that way. Sometimes I can get something better pointing the broad side towards it.
 
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#17
A loop antenna will peak on the "narrow side" and null on the "broadside". Two peaks and two nulls per revolution.
 
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#18
I'm old school so I have no insight into SDR, but for longwave NDB DXing I would recommend the Lowe HF-225. Been using the Europa version but either are fine. Nice narrow Murata 2.4 kHz with a 200 herz audio filter in CW mode centered on 800 herz and the tone control makes a difference in pulling out the tone through noise. One of the most sensitive receivers ever made on longwave (many of the most highly acclaimed communication receivers don't have the ears at these frequencies though they're terrific on HF).

For serious LW work you really need a communications receiver with good filtering. You want, for example, to be able to pull a Canadian NDB (with 400 cycle offset) that is co-channel with an American NDB out from between the U.S. 1020 cycle offsets. Some portables have LW capability and can be OK for casual LW work when coupled somehow to a good antenna but most lack the filtering and only tune in 1 kc steps.
Probably would be best to ask your question in a new thread in the receiver forum and see what you get for replies. Be prepared perhaps for some replies extolling exotic, nearly unobtainable but nice stuff.
 
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