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Admin wrote:I think it is triflar.

Three coils done in one winding: one isolated for he primary and the other 2 put in series for the secondary.

I think that this is a little wasteful with signal loss - the 1:4 balun is normally biflar (2 coils in series) centre-tap to coax ground, one end to coax centre, and opposite ends to the balanced load.

The drawing shown relies on magnetic induction (mutual coupling) between the primary and both secondary windings.

But that is just my humble opinion

BR Harry - SM0VPO

That's a transformer, and while it will have higher losses, it offers some advantages for an RX antenna; not only it gives galvanic isolation, but it also helps preserving the antenna pattern

The winding can be made using just two wires, one for the primary and a second one for the secondary, the latter will then have a tap so there's no need for a trifilar winding; also and as I wrote, the balun schematic recalled to me this loop antenna from N4CY

https://www.larches-cottage.co.uk/rx_antenna/loops_rx/Evaluating%20a%20Broadband%20Active%20Loop%20Antenna.pdf

the transformer is wound and connected exactly that way, that is with the tap going to the shield; that antenna is pretty good for lower frequencies, but its performances quickly drop when going up in frequency and that's also why the author decided to replace the coax with homemade "coax", again, that antenna is pretty good, but I still prefer the LoG at least if one has that bit of space to lay it down

Oh and as for the LoG, I tried to put together some informations here https://sm0vpo.forumotion.com/t462-the-log-antenna in case someone is interested

Admin wrote:...I think that this is a little wasteful with signal loss - the 1:4 balun is normally biflar (2 coils in series) centre-tap to coax ground, one end to coax centre, and opposite ends to the balanced load.
...
BR Harry - SM0VPO

Hi Harry,
you are absolutely right about how a 1:4 balun usually looks like. But the galvanic separation may be essential for QRM suppressing. Im this case the coax braid must not be connected to the shielding tube of the loop! The magnetic coupling is the right way.

VBR from Ivan

I think it is triflar.

Three coils done in one winding: one isolated for he primary and the other 2 put in series for the secondary.

I think that this is a little wasteful with signal loss - the 1:4 balun is normally biflar (2 coils in series) centre-tap to coax ground, one end to coax centre, and opposite ends to the balanced load.

The drawing shown relies on magnetic induction (mutual coupling) between the primary and both secondary windings.

But that is just my humble opinion

BR Harry - SM0VPO

Ivan wrote:

Andrew wrote:
Forgive me, but... what kind of BaLun are you talking about ? Asking this since I'd be curious to see the schematic of such a 4:1 BalUn, because as of now, I've mainly used two wires for those; then as for the ratio, I believe that the usual "square rule" applies

Hi Andrew,
I suppose the transformer is an isolating one, probably according to this schematic.

VBR from Ivan

 
that doesn't seem a trifilar winding to me, probably it's bifilar, and I'd wind the above using a binocular core (better flux); also, the connection makes me think to the so-called "moebius loop", a good one for the low bands, although I'd better use a 1:1 tapped transformer followed by either a norton or push-pull preamp

Andrew wrote:
Forgive me, but... what kind of BaLun are you talking about ? Asking this since I'd be curious to see the schematic of such a 4:1 BalUn, because as of now, I've mainly used two wires for those; then as for the ratio, I believe that the usual "square rule" applies

Hi Andrew,
I suppose the transformer is an isolating one, probably according to this schematic.

VBR from Ivan

Ivan wrote:

Glenndk wrote:It was a trifilar om ft240-61 - so 50 ohm unbal. to 200 ohm bal.

(guessimated ratio - I have no theoretical reasons)

Thank you very much. At least it takes me into the ballpark.

VBR from Ivan

Forgive me, but... what kind of BaLun are you talking about ? Asking this since I'd be curious to see the schematic of such a 4:1 BalUn, because as of now, I've mainly used two wires for those; then as for the ratio, I believe that the usual "square rule" applies

Glenndk wrote:It was a trifilar om ft240-61 - so 50 ohm unbal. to 200 ohm bal.

(guessimated ratio - I have no theoretical reasons)

Thank you very much. At least it takes me into the ballpark.

VBR from Ivan

Ivan wrote:
Hi Glenn,
what was the impedance ratio of the balun?

VBR from Ivan

It was a trifilar on ft240-61 - so 50 ohm unbal. to 200 ohm bal.

(guessimated ratio - I have no theoretical reasons)

Admin wrote:I received an e-mail recently from Andrea Z, after he read my antenna article, and the QRM problems. Andrea suggested a really weird form of antenna: a square wire loop, 15' by 15' lying on the ground. Apparently it is supposed to give a very high immunity to local QRM.

See https://www.kk5jy.net/LoG/

I opened a topic here, I think it will be useful to keep the discussion alone and don't mix it with "spam in the inbox"

As for the LoG, see the other discussion, that said if someone here wants to try an active loop antenna, I think that a TUNED one will serve much better than an untuned, wideband one, in a past I tried one of such antennas with good results, I'm referring to the one shown here http://techlib.com/electronics/antennas.html the one I built had separate preamp and control unit and the loop was placed outside, it works quite well, although the tuning isn't as sharp as the one which you may achieve with an air capacitor tuned loop, yet the tuning stage allows to avoid offband signals issues (IMD and so on), the only "pitfall" of that antenna (let me call it so) is that in some cases (strong nearby signals) the control cable used for bandswitching, tuning and power may pick up RF which will in turn modulate the varactor; the way I found to overcome this issue was using a CAT5 (network) cable, such a cable has four twisted pair, I connected one wire of each pair to a given "signal" (e.g. tuning) and the other to ground, and this solved the issue; that being said, I prefer using passive antennas if possible

Glenndk wrote:Hi Ivan

At HF I also used a passive balun.

Hi Glenn,
what was the impedance ratio of the balun?

VBR from Ivan

The amplifier module mentioned in the PA3GZK article is probably this one. There is a series capacitor at the output, so some modification is required.



VBR from Ivan

Glenndk wrote:
Hi admin
It works!
It works better vertically - a half meter to a meter above ground - I presume.
It is just a mag loop antenna :-)

I was wondering about that, but it seems a bit large for a mag-loop. A mag loop with a lower current?

I will definitely give this loop a try sometime over the summer. I really need to do something abut the QRM so if this antenna is immune to the rubbish I have at the moment then it could be a permanent fixture.

My multiband 1/2-wave has guys and feeder only 2m up the mast (from the ground), horisontally, radially from the mast. These I can use to experiment with a loop: on the ground and elevated.

Glenndk wrote:The best RX mag loop antenna? A shielded mag loop antenna! Could be made of "cheap" satellite coax-cable or RG-58. The maximal circumference must be less that the shortest used RX wavelength times 0.3 times the cable shortening factor. But note that (with any antenna) you need a current-balun relatively close to the antenna, to choke noise received or mediated on the outside of your cable (e.g. noise from your building):

One reason I love this forum is that there are so many ideas and so much experience/knowledge out there.

I have made many frame and small loop antennas, but it looks as though there are a few other ideas to try when the weather improves.

Glenndk wrote:PA3GZK's WIDE BAND ACTIVE LOOP RECEIVING ANTENNA:
https://pa0fri.home.xs4all.nl/Ant/Active%20antenna/Active%20receiving%20%20loop%20antenna%20eng.htm
Backup:
https://web.archive.org/web/20180311120837/https://pa0fri.home.xs4all.nl/Ant/Active%20antenna/Active%20receiving%20%20loop%20antenna%20eng.htm

Quote: "...The proposed shielded broadband (~200 MHz) active loop antenna offers more quiet and relatively less interference reception. It is known that an antenna for transmit also works well as a receiver antenna, one only forget that all interference signals are proportional strong. Therefore PA3GZK believe that you actually have to use two antennas, one for transmit and one for receive. The latter is most needed at the lower frequency bands. ..."

http://www.karinya.net/g3txq/chokes/
backup: https://web.archive.org/web/20190208231402/http://karinya.net/g3txq/chokes/

http://karinya.net/g3txq/baluns/baluns.pdf
backup: https://web.archive.org/web/20190211134715/http://karinya.net/g3txq/baluns/baluns.pdf

Thank you for the links,¨
I will have a good look at the links and do a bit of reading. It is always good to have a lot of reading before one starts a new project.

Thank you very much for taking the time and trouble to research and post the links.
I really appreciate it.

Very best regards from Harry - SM0VPO

Ivan wrote:Hi Harry and Glenn,
I have encountered loop RX antennas. I planned to try the PA3GZK loop before I got ill, but the setup with brass and plastic fittings seemed too complicated to me....A passive transformer is all it needs.

Hi Ivan

At HF I also used a passive balun.

Ivan wrote:
I seem not to be QRV soon. I often make big theoretical plans, but do not finish them.

Same here - unfortunately :-)

Ivan wrote:I bought a Malachite clone from China, looks exactly this way.

I wait to buy a SDR - but I have bought components to built my own. Would probably use a PC audio input...

Ivan wrote:
Have a nice evening!
VBR from ivan

Same to you - and I hope you can recover.

_________________
best regards,

Glenn / OZ1HFT

Hi Harry and Glenn,
I have encountered loop RX antennas. I planned to try the PA3GZK loop before I got ill, but the setup with brass and plastic fittings seemed too complicated to me. Using a piece of coax would be more convenient. The loop laid directly on the ground is still easier to build - it does not require
any stand nor DC supply for the LNA. A passive transformer is all it needs. The PA3GZK article has been updated recently, it contains a lot of new experience now. 

I seem not to be QRV soon. I often make big theoretical plans, but do not finish them.

I bought a Malachite clone from China, looks exactly this way. The hardware of Malachite is in public domain, while the "proper" firmware is licensed. The RX came with "demo" version, limited to 200 MHz. Mode switching and frequency setting is a bit clumsy, but it is possible to test the full funcionality of the hardware. Then one can buy a license for the full version and reload the firmware. (It is not very straightforward. One recipe requires hard reset with one knob pressed, the second requires temporary short of J1, the third short of J1 and J3...  ) Or one can buy an original Malachite with full license - for more money of course. I play with the demo version now.

Have a nice evening!
VBR from ivan

Ivan wrote:Hi Harry,
The loop receiving antenna is promising. IMHO it was originally developed for military purposes. It can be built very easily. What a pity it does not work for transmission!  

QRM is a great obstacle in our hobby. It is said to have increased 1000 times (+30dB) on HF during the last 100 years. Where the first hams worked with a single tube, we need a 1 kW PA. That is terrible.

VBR from Ivan

Hi Ivan,

Yes, QRM is a huge problem. I once bought some of those touch-lamps from the Chinese shop in Riyadh.
Forget HF. They radiate DC to light. I ripped out the innards and put in simple switches. Another pint is that when I sent SSB they would switch on and off like disco lights.

Ivan wrote:Hi Harry,

I am inspired by your portable vertical. I think to use a cheap wooden or aluminum easel instead of the box. I bought a 5 m aluminum antenna vertical in an army surplus recently. But the weather is still bad now.

VBR from Ivan

You inspired by me? It is usually the other way around. But I am really leased that I can still inspire someone 

I am also waiting for good weather. Perhaps when we both get inspired and QRV we can arrange a time/freq?

Ivan wrote:Hi Harry,

I also got a Malachite SDR clone recently, so I have another toy.  

VBR from Ivan

That looks like a good HF radio receiver. I googled it and looked at some of the reports.

For a few years now I have been thinking about a Sangean HF receiver with BFO. But I think that my modifying a $2 domestic AM MW radio for 3.5 sort of postponed that idea.

There are loads of reports and reviews of the radio. You wrote "clone"? I also read that the Chinese clones were using older firmware that were missing some features and a couple of nodes. But they did cover AM, FM, USB, LSB and CW.

It looks really rugged. Perhaps I should invest in for work?

Anyway, Saturday evening. Maj-Lis is preparing a nice meal, so I will go and join her. I shall read Glenn's post in detail later on. I am especially interested in the technical information he has to offer, and to follow his links.

BR Harry - SM0VPO

Admin wrote:
...
Andrea suggested a really weird form of antenna: a square wire loop, 15' by 15' lying on the ground. Apparently it is supposed to give a very high immunity to local QRM.

See https://www.kk5jy.net/LoG/
...

Hi admin

It works!

It works better vertically - a half meter to a meter above ground - I presume.

It is just a mag loop antenna :-)

The best RX mag loop antenna? A shielded mag loop antenna! Could be made of "cheap" satellite coax-cable or RG-58. The maximal circumference must be less that the shortest used RX wavelength times 0.3 times the cable shortening factor. But note that (with any antenna) you need a current-balun relatively close to the antenna, to choke noise received or mediated on the outside of your cable (e.g. noise from your building):

PA3GZK's WIDE BAND ACTIVE LOOP RECEIVING ANTENNA:
https://pa0fri.home.xs4all.nl/Ant/Active%20antenna/Active%20receiving%20%20loop%20antenna%20eng.htm
Backup:
https://web.archive.org/web/20180311120837/https://pa0fri.home.xs4all.nl/Ant/Active%20antenna/Active%20receiving%20%20loop%20antenna%20eng.htm
Quote: "...
The proposed shielded broadband (~200 MHz) active loop antenna offers more quiet and relatively less interference reception. It is known that an antenna for transmit also works well as a receiver antenna, one only forget that all interference signals are proportional strong. Therefore PA3GZK believe that you actually have to use two antennas, one for transmit and one for receive. The latter is most needed at the lower frequency bands.
..."

http://www.karinya.net/g3txq/chokes/
backup:
https://web.archive.org/web/20190208231402/http://karinya.net/g3txq/chokes/

http://karinya.net/g3txq/baluns/baluns.pdf
backup:
https://web.archive.org/web/20190211134715/http://karinya.net/g3txq/baluns/baluns.pdf

Hi Harry,
the loop receiving antenna is promising. IMHO it was originally developed for military purposes. It can be built very easily. What a pity it does not work for transmission!  

QRM is a great obstacle in our hobby. It is said to have increased 1000 times (+30dB) on HF during the last 100 years. Where the first hams worked with a single tube, we need a 1 kW PA. That is terrible.

I am inspired by your portable vertical. I think to use a cheap wooden or aluminum easel instead of the box. I bought a 5 m aluminum antenna vertical in an army surplus recently. But the weather is still bad now.

I also got a Malachite SDR clone recently, so I have another toy.  

VBR from Ivan

Hi Ivan,
I am really fine, cannot complain (even though I am English).

Yes, we all have to be very careful with the covid situation, especially if you are not so fit. But I do hope your health issues will improve.

I really do miss operating but I have so little time these days. But I had thought about setting up a portable station on a small hill outside my place of work. Then I can have some prime HF time, during the day when the higher bands are active. At the moment it is not so pleasant because we have minus temperatures every night, and we also had some snow today, that also did not settle.

One of my next priority tasks before new projects is to investigate the S9 QRM I have at home on 80m. Until I do that I cannot operate on 80m and 160m bands. I believe it is a TV, computer PSU, or some other SMPSU that needs to be found. I just hope it is not PLT interference. This weekend I have to turn off the power to the house, just in case it is something in our house.

I received an e-mail recently from Andrea Z, after he read my antenna article, and the QRM problems. Andrea suggested a really weird form of antenna: a square wire loop, 15' by 15' lying on the ground. Apparently it is supposed to give a very high immunity to local QRM.

See https://www.kk5jy.net/LoG/

If it works then there is no reason why I cannot have two antennas, one for TX and one for RX. If I can get QRV on 3.5MHz then some of thgose sleepless nights can be put to good use

Very best regards from Harry - SM0VPO

Hi Harry,
I am quite fine, thank you. My health stays at the same level as before. I am afraid of leaving my home due to covid. I seem to be too young for vaccination, hi. At least I am not obliged to go to work each day.
The weather still quite cold here, +2 to +7 deg.C. It snowed yesterday, but the snow melted at once.
I am not QRV at all. I enjoy solving technical aspects of hamradio more than being on the bands.
And how are you?

VBR from Ivan

Thank you very much Ivan.

Unfortunately I deleted the messages, but if there is a next time I will investigate blocking Guest user from posting PMs.

Anyway, how are you?

The weather here in Sweden is still below freezing every morning so it is not exactly comfortable to trim my antenna array.

I also found out that my FT-840 intended for portable use was heavily distorting at powers above 80 Watts. The cause was the cigarette outlet plug I used to get power from the car. I didn't realise that those connectors were so diabolically poor at higher currents. They are supposed to be rated at over 20A. 2 alligator clips directly on the battery cured the problem.

Another month and it will be nice weather to operate in the open from my works QTH. Are you ever QRV on HF these days?

BR Harry

Hi Harry,
I have had no such problem so far.

VBR from Ivan

Hi all,
Over the past 6 months I have receives some SPAM in my messages inbox.
The SPAM was in Russian, but one translate.Google.com later I saw it was some form of sales spam from a "guest" account.

I will have to see if there is a setting that permits guests sending personal messages, or if I canblock the user "guest" from sending PMs.

Very best regards from Harry - SM0VPO