The LoG antenna

Harry, since we're at it, here's another one which tried the LoG

https://rudys.typepad.com/files/630m-log-notes.pdf

the above one was carefully studied and optimized for the 630m and 2200m bands, since the author is mostly interested in those, but aside from the modifications, the "standard" version described on Matt Roberts site will serve you well on all the bands from 160m (and below) up to 20m, just add the 9:1 transformer (on a #73 binocular core as for Matt design) and, if you can/want a CM choke (18 turns of twisted insulated wire around a #43 toroid), at that point you may either directly connect the coax to the transformer/choke box or add a preamp between the transformer and the choke (to stop CM from reaching the preamp), the preamp I suggest (as I already wrote) is the simple one from W7IUV, the full schematic and notes can be found here https://www.okdxf.eu/files/preamp_r60.pdf - if going for the preamp, feed it using a pair of bias-t and add to the preamp box a small relay, this way when the preamp will be powered the relay will close and include it, when cutting off the power the preamp will be bypassed so allowing you to use the log both with or without the preamp, as need arises; the preamp may be useful in case you'll want to boost signals (even just for listening to some very weak station )

(note the 2N5109 can be replaced 1:1 with an NTE278 which is easily available and pretty cheap !!)

HTH

Andrew wrote:Forgot, willing to keep it permanently in place, it would be a good idea installing it now, the antenna will then be in place next winter and won't have problems to work even if covered by snow

If you want to protect the wire when mowing the lawn, just slide the wire (I use 2.5mm diameter insulated wire) inside four pieces of garden hose (one for each side of the square), you may then disguise the antenna as some kind of irrigation system

Also, if you really want to add a preamp (usually not needed, just turn up the rig gain), use this one

https://www.qsl.net/wa1ion/amp/w7iuv_amp.htm

notice that the BJT will need a small heatsink

Hi Andrew,
I know that it would not be optimal as I have been reading all your links and e-mails But the object was to do something to prove the technique, not to make a permanent installation. As it happened the concept was proven beyond my expectations. When I set it up I spent less than 30 minutes as I had promissed to take Maj-lis out to do some shopping, and I did it while I waited for her to get ready.

The idea of the garden hose and such sounds really clever. I must do something before the winter comes, as you suggest.

I do not need a preamp. With only 100 Watts there is no way I can compete with the "big boys" so there is no point in dragging in stations who cannot hear me. It is best to leave the odd JA station unheard rather than be sorrowful of a missed opportunity.

Having said that, I worked a JH8 station on Monday on 18 MHz when I was operating in my lunch break, in a field, beside lake Oxunda, and using just 100 Watts of power. I had the good fortune to hear the guy's first CQ call, before the pile-up started   I also bought a lottery ticket the same day but that didn't win anything. I really tought it may have been my lucky day.

Thank you very much for the response. As always it is great to hear from you, and I read all messages, eventually, on my mobile telephone. I have been ill and also had loads of other "haftas" to do that seem to occupy my time. I find that I can achieve quite a lot with my "stolen minutes" in the shack and my workshop time at work instead of eating lunch.

Very best regards from Harry - SM0VPO

Forgot, willing to keep it permanently in place, it would be a good idea installing it now, the antenna will then be in place next winter and won't have problems to work even if covered by snow

If you want to protect the wire when mowing the lawn, just slide the wire (I use 2.5mm diameter insulated wire) inside four pieces of garden hose (one for each side of the square), you may then disguise the antenna as some kind of irrigation system

Also, if you really want to add a preamp (usually not needed, just turn up the rig gain), use this one

https://www.qsl.net/wa1ion/amp/w7iuv_amp.htm

notice that the BJT will need a small heatsink

Harry, your setup may be ok for a very quick test, but isn't optimal; start by carefully reading this

http://www.kk5jy.net/LoG/

and digesting the reasoning about the antenna size and the transformer

That said, try connecting the conductors of the phone cable in parallel, so that you will have a single turn, and use a transformer as described at the above link, that WILL make a difference

As for transmitting, no way, the LoG is a receive only antenna

Also, don't focus on signal strength but on S/N ratio, try covering your S-meter with a piece of tape and just sweep the bands

In my opinion, if one has noise issues, the LoG used as an RX-only antenna, and coupled with a good TX antenna is the "weapon" of choice, to switch between the two you may use a relay at the far end of the coax and power it over coax, the "PTT" contact from the back of the rig will then control the switching, is really as easy as 1 2 3

Last night I found the time to try something as a crude experiment - I thought I should try it. I took 10m of 2-pair telephone cable and made a 4-turn loop lying flat on the ground (short grass). This I connected to my radio.

3.5 MHz I had absolutely no noise at all - S-0    All the SMPSU noise disappeared: not just reduced, but I could not detect any. The dipole 7.5m above it has an S-8 of SMPSU-type noise and I could not hear any QSOs strong enough to get over the noise.

With the on-the-ground antenna I could hear many QSOs. Nothing was very strong but the S/N ratio was excellent. I didn't try transmitting as I thought knew that the VSWR would be diabilocal, the object was to try it as a receiving antenna.

For me this is proof-of-concept. The antenna on the ground will make a good receiving antenna. Perhaps it will make a reasonable transmitting antenna if it is properly matched? Switching between antennas for TX/RX is OK for me. I have a good coaxial switch.

Just thought I would add the comment.

Now it is back to the 30m fence, the terrace wooden deck, the cat-door and all the other things that seem to eat all my time in the summer. I love the winters - nothing to do outside and more time for the hobby.

Have a nice weekend, gentlemen.

Best regards from Harry - SM0VPO

Ivan, I'm not saying it won't work; but from first hand experience, the LoG will work MUCH better using a #73 binocular core 9:1 transformer, possibly followed by a good CM choke; keep in mind that the simple LoG needs two things, a good transformer (plus choke) and a careful installation ON ground, NOT raised


my 2 cents

See https://youtu.be/e0WvIxoU0LI

BR from Ivan

Ivan wrote:And if one has a problem to obtain a binocular core for the Xformer, a suitable (of the proper mix and size) toroid should do as well. Toroids cca 35 mm outer dia found in old PC PSUs cover all HF bands, maybe except of 10 m. It may need a bit of tweaking of course.

VBR from Ivan OK1SIP

I won't recommend that; while I tried using different cores, including twin sleeve cores (tied to form a binocular) and toroidal cores, and also different materials, I found that the antenna performance degrades a lot with those and isn't up to par with a transformer built using a binocular #73 core; sure, if one is just trying to arrange it that may work, but don't expect to obtain the same level of performances, in short, if you're going to build the LoG for the first time, it's better doing it "by the book", otherwise you may build something which will NOT work as it's designed to

And if one has a problem to obtain a binocular core for the Xformer, a suitable (of the proper mix and size) toroid should do as well. Toroids cca 35 mm outer dia found in old PC PSUs cover all HF bands, maybe except of 10 m. It may need a bit of tweaking of course.

VBR from Ivan OK1SIP

Andrew wrote:

Ivan wrote:OK an thanks.

VBR Ivan OK1SIP

you are welcome, and if/when you'll decide to try it, let me know, I've a trick or three up my sleeve

forgot, if one doesn't have the coax for the choke, the latter may be wound using vanilla "speaker wire"; just twist the wire before/when winding and it will work, just avoid using a too small toroid like a 50 since that won't offer proper choking

Ivan wrote:OK an thanks.

VBR Ivan OK1SIP

you are welcome, and if/when you'll decide to try it, let me know, I've a trick or three up my sleeve

OK an thanks.

VBR Ivan OK1SIP

Ivan wrote:Hi Andrew,
did you find the choke as an improvement? The insulation transformer itself should stop current flowing on the outer shield of the coax, so the choke seems as unnecessary to me. The link you give does not mention a choke in the transformer box as well - or did I miss anything?.

VBR from Ivan OK1SIP

Hi there, Ivan; you are right, the original design doesn't include a choke, and in some cases it isn't needed, but in others it makes a difference, so I thought to give "generic" instructions to cover all the bases, just in case

Hi Andrew,
did you find the choke as an improvement? The insulation transformer itself should stop current flowing on the outer shield of the coax, so the choke seems as unnecessary to me. The link you give does not mention a choke in the transformer box as well - or did I miss anything?.

VBR from Ivan OK1SIP

Just to add some infos and hints for anyone willing to give the LoG a spin

Bill of materials:



* Spool of 2.5mm insulated wire
* Cable eye terminals
* #73 material binocular core (like this or this)
* #30 AWG (0.2mm) enameled copper wire
* #43 small toroid (like this)
* RG-316 coax (about 1m) or "twin" speaker wire
* IP66 plastic box (to host the transformer and choke)
* Small bag of "silica gel" dessiccant
* BNC panel connector (or other desired connector)
* Brass screws with nuts, washers and wingnuts
* Silicon sealant
* Duct tape
* Heath shrink tubing (like these)
* Plastic stakes (the ones used in gardens like these)



Building (keep the LoG page open for reference):

Prepare the box by drilling holes and applying the BNC panel connector and the two brass screws which will be used to connect the antenna wire, seal the connector and the screws using the silicon

Wind the 9:1 transformer around the binocular #73 core  using the enameled wire (see the website for details)

Wind a choke around the #43 toroidal core using the RG-316 coax; 17 turn, that is 8, the "crossover" and then other 8

Solder the secondary of the transformer to one end of the choke coax

Place the transformer and choke inside the box

Connect/solder the primary of the transformer to the brass screws

Solder the coax from the choke to the BNC connector

Place a bag of silica gel inside the box and close it ensuring it's properly sealed

Measure and cut the desired length of insulated wire for the antenna, the original design uses 60ft (about 18m) to form a square with a 15ft (about 4.5m) side

Slide two pieces of shrink tubing over the two ends of the wire

Remove a bit of insulator from the ends of the wire and crimp/solder the cable eye terminals to them

Slide down the shrink tubings and ... shrink them to protect the crimp/solder ends

Fold the wire in half at middle, mark the point with a piece of duct tape

Fold the wire in half again, mark the corners with duct tape

Installation:

Find a spot to install the LoG, the spot may be everywhere, just ensure it sits on grass/ground and not on concrete or the like, also, avoid placing the antenna over some buried metallic objects like wires, pipes, metallic sewer or water tanks and so on, since such things will badly affect the antenna pattern.

Once found the desired spot, carry out the transformer box, the antenna wire and the stakes; connect the transformer box to the antenna wire ends, then unfold the antenna wire up to the tape marking the top corner (half of wire), place that at the desired spot and use a stone or whatever to keep it in place, done so, widen the antenna side corners (e.g. laying down the antenna so that its two lobes will point SE/NW - more later !) and again, use a stone or whatever you have to temporarily keep them in place, done so, adjust the feedpoint and readjust the wires so that they'll form a square (no need to be precise, but at least try to form a square); once the antenna wire will have the desired shape, it will be time to use the stakes, start from the top corner, remove the stone (or whatever) used to temporarily keep the wire in place and plant the stake so that the wire will run around the "outside" of it, move to the transformer corner and do the same, now plant the side corner stakes and you'll be done

Testing:

Now the antenna is ready to go, just connect your coax feedline to the BNC connector (or whatever connector you decided to use - waterproof RF connectors would be cool, but they aren't cheap) and you'll be ready to start listening; before doing so, please, DO NOT look at your s-meter or, even better, cover it with some post-it or tape; then start sweeping the bands, at first you may think the antenna isn't working, but... well, keep on and if possible, compare it with your TX antenna and you will definitely hear the difference, in particular if you live in a noisy zone (from RF standpoint)

Notes:

As for the antenna orientation, if you followed the directions as described above, the antenna wire should be able to slide around the stakes, this means that, by gently pulling the wire from the transformer box point, you'll be able to let it slide and move the transformer to the nearby corner, this will turn the antenna main lobes by 90°, sure it isn't an automatic antenna "rotator", but will work

In my experience, the LoG doesn't need a preamp, since the RX one will suffice, but if you feel the need for a preamplifier, then use a preamp with good IP3 value and not so high gain (10 to 20 dB will suffice), a good one is described here (PDF file), if you'll decide to go for it, the preamp should be hosted inside the same box containing the transformer/choke (so pick a larger box), and connected between the output of the transformer and the input of the choke, also, my suggestion is to power it using a BIAS-T and to add to the circuit a small relay, that way, if you switch off the preamp power (BIAS-T) the relay will bypass the preamp and connect the choke to the transformer, so that you'll be then able to use the LoG with the preamp or without it just by switching the power; as for the 2N5109 used in the original schematic, it can be replaced by an NTE278 which has the same characteristics and is a drop-in replacement (by the way it will still need a heatsink !)

Ok, that's almost all, I hope you'll decide to give this simple antenna a try, not only because it works well, but because, if you're plagued by RF noise/interference, it may help you picking up signals which would otherwise be lost in noise, and then, using it coupled with a TX antenna will also improve your DX capabilities... which isn't bad, I think

--

Happy DXing !

Admin wrote:
That may not be true. I find exactly the same QRM near any of the buildings on the housing estate. The only way is to switch OFF the power to our house. If the crap is PLT born then even turning off the power may not make any difference.

I took a quick walk and it is strong beside any building, No2, No4, No6 (ours) and No54. I need to add an S-meter to my little transistor radio to get something more meaningful, besides just a loud noise from a 2" speaker. But all the houses are residential, digital cable TV, communal heating, conmmunal water, etc.

Well, that may indicate that all the houses in the zone have the same noise generating "device", that may even be one of those "smart" AC power counters or any common device; and the fact that it's picked up using a portable (battery operated) receiver seems to enforce the point that the noise is radiated (again as opposed to conducted one like common mode currents) and that the E/M field is weak enough that, moving at some distance it weakens/disappears

As for hunting it, you may consider some of the circuits shown here http://techlib.com/electronics/allband.htm (or something along those lines), moving around/inside the house with a device like that may allow to find the source

[edit]

Here's another device from ARRL http://www.arrl.org/files/file/RFI/Thompson%20Noise.pdf while it's much more complex than the simple stuff above, the idea of using a small loop as a noise probe may be of help, the same goes for the description of the steps needed to pinpoint the noise source

Andrew wrote:

One point I found is that 1.8MHz and 3.5MHz are unusable from the house, but if I just put up my vertical telescopic just 200m away from the house (clear grass area) then the band is almost silent. The only QRM I could really complain about is centered on 1.6MHz.

The above seems to indicate that the noise is generated inside the house and also that the noise isn't "conducted" (as for common mode) but "radiated", since moving the antenna away the noise is lowered; I believe that it may be interesting (and useful) going around (in the house) with a handheld receiver (possibly with an adjustable RF attenuator) and hunting for the noise source(s), that could allow to identify the source and hopefully to "cure" the issue

Best

Andrew

That may not be true. I find exactly the same QRM near any of the buildings on the housing estate. The only way is to switch OFF the power to our house. If the crap is PLT born then even turning off the power may not make any difference.

I took a quick walk and it is strong beside any building, No2, No4, No6 (ours) and No54. I need to add an S-meter to my little transistor radio to get something more meaningful, besides just a loud noise from a 2" speaker. But all the houses are residential, digital cable TV, communal heating, conmmunal water, etc.

BR Harry

Admin wrote:
Hi Andrew, Thank you for the additional information.

You're welcome !

I will certainly try something along these lines, starting with a tested design to see how it works.

Yes, I believe that starting with a "by the book" design should be the best way to try it, then there's always room for improvement by the way

One point I found is that 1.8MHz and 3.5MHz are unusable from the house, but if I just put up my vertical telescopic just 200m away from the house (clear grass area) then the band is almost silent. The only QRM I could really complain about is centered on 1.6MHz.

The above seems to indicate that the noise is generated inside the house and also that the noise isn't "conducted" (as for common mode) but "radiated", since moving the antenna away the noise is lowered; I believe that it may be interesting (and useful) going around (in the house) with a handheld receiver (possibly with an adjustable RF attenuator) and hunting for the noise source(s), that could allow to identify the source and hopefully to "cure" the issue

When the weather is a little better I will do something.
BTW, yesterday morning we had a real snow blizzard. What a surprise, and so late in the year!

We had snow here (Italy) two weeks ago, then the temperatures raised to around 30°C, yesterday afternoon they lowered again and this morning we had about 15°C, the forecast says we'll have rain till next Friday but then the temperatures will raise again and hopefully the spring will really start

Best

Andrew

Hi Andrew,
Thank you for the additional information.

I will certainly try something along these lines, starting with a tested design to see how it works.

One point I found is that 1.8MHz and 3.5MHz are unusable from the house, but if I just put up my vertical telescopic just 200m away from the house (clear grass area) then the band is almost silent. The only QRM I could really complain about is centered on 1.6MHz.

When the weather is a little better I will do something.

BTW, yesterday morning we had a real snow blizzard. What a surprise, and so late in the year!

BR Harry - SM0VPO

Just in case, notice that the LoG will work even if submersed by snow, just look here

https://tapr.org/loop-on-ground-log-antenna/

so, Harry, if you'll decide to try it (once the snow will melt), it may then be kept in place year round

[edit]

Oh and here's another LoG test, just in case

https://kg3v.com/2020/01/04/loop-on-ground-the-simplest-receive-antenna-you-will-ever-build-and-it-works/

Admin wrote:Thank you for sharing this post, Andrew. It is better on the forum than in e-mail.

In this post you also mentioned the point about grounding the feeder when it enters the radio/house. That is something I have not done   I totally forgot about that.
Previously I have always had a grounded aluminium patch-panel for feeders that enter the house, but at the moment I have just pulled the cable through an open window.

But I will do something about that over the weekend.

There is an underground network connection to the house beside my shack window and there is a grounding rod beside it, connected to it. I can probably use that.

Back to basics

Hi there, Harry !!

As for grounding, I believe it's usually a good idea, grounding the braid helps with CM currents, then there's people which go a looong way when it comes to grounding, just check out this

https://www.w8ji.com/station_ground.htm

also, and since we're at CM currents (and noise!), the best choke (and 1:1 BalUn) you can build is the following:

Core: FT140-43 (up to about 200W) or FT240-43 (up to about 500W)
Winding: RG213 (up to about 200W) or RG174 (up to about 500W)

Cross wind 8+8 turns plus the "bypass" one over the toroid, just for reference the winding schematic is like this



just use the coax to wind it, it's easy to put together and gives a VERY high CM impedance; as I wrote it may be used as a 1:1 BalUn (e.g. with a dipole) or as a choke, in such a case, just connect it at the output of the impedance transforming balun/unun; for example, winding three of those (1 using coax and 2 using teflon insulated wire - trick: twist the wire and use the twisted pair for the winding) you may use two of them as a 4:1 balun like shown here

http://www.m0pzt.com/blog/4to1-current-balun/

and then connect the third one (coax wound) at the output of the 4:1 to choke CM currents then, to improve high frequency response (in case it is a problem) just add a 68pF (about, may need to experiment, values may range between 10pF and 100pF) across the output of the 4:1 (basically where it connects to the choke), that will flatten the response curve, just ensure that the capacitor has a rating of 3KV or more

Thank you for sharing this post, Andrew. It is better on the forum than in e-mail.

In this post you also mentioned the point about grounding the feeder when it enters the radio/house. That is something I have not done   I totally forgot about that.
Previously I have always had a grounded aluminium patch-panel for feeders that enter the house, but at the moment I have just pulled the cable through an open window.

But I will do something about that over the weekend.

There is an underground network connection to the house beside my shack window and there is a grounding rod beside it, connected to it. I can probably use that.

Back to basics

BR Harry - SM0VPO

Hello all, after some mailing with Harry (our admin) about the LoG antenna, he directed me to these forums and, at that point, I thought to subscribe and post some notes about that antenna

First of all, the antenna I'm referring to, is the one designed by Matt Roberts (KK5JY) and found here

http://www.kk5jy.net/LoG/

it's a receive only antenna and it's a very simple to build and lay out, but despite this, if offers very good performances from the broadcast bands up to around the 20m Ham band and is of great help in case one has noise problems, since for its very design the antenna helps improving the S/N ratio and "pulling out the signals"

The above being said, here are some notes from my personal experience

First of all DO NOT raise the antenna, sure raising it may seem to improve signals strength, but it will WORSEN the S/N ratio, so keep it on the ground; Matt (KK5JY) invested quite some time in experimenting and improving it, so don't waste his efforts !

Second, if you're going to try it, please build it "by the book" that is, wind the transformer using a #73 material binocular core and keep the size and shape as near to the original one as possible, it will also be a good idea grounding the coax braid right before it enters your building/shack (but NOT at the antenna side !!)

Then, while it's easy to lay down, as for all antennas the LoG needs a bit of care, it's important to ensure that there are no buried metal objects (wires, buried water tanks...) under it, since those will have a negative effect on the antenna pattern and performances, in such cases it usually suffices moving the antenna of some meters or reorienting it to obtain full performances.

Remember that the purpose of this antenna is not to "boost signals" but to make them readable, so if you are going to try it (and I recommend it !) my suggestion is to cover your S-meter and just test it "by ear", that way you'll be able to tell the difference (not kidding)

A preamplifier isn't usually needed with the LoG since the builtin RX preamp will suffice, but if after testing the antenna w/o a preamp, you'll decide you want to try a preamplifier, then the one shown in this paper https://www.okdxf.eu/files/preamp_r60.pdf will fit pretty well (again, I don't think it will be needed), just connect it to the output of the impedance transformer and power it over the coax; possibly add a small relay so that switching off the power will bypass the preamp and allow you to use the antenna w/o any preamp

While a choke isn't listed in the original design, it won't hurt, in such a case just build a "guanella" type choke by winding 17 turns of RG174 wire (8+8 plus the "bypass" turn) on a #43 material toroid and place the choke at the output of the transformer (or the preamplifier, if you decided to use it)

With all the above being said, if you're curious to see what the LoG is capable to do, just take the time to watch this video till its end

https://www.youtube.com/watch?v=wMb8i5QajW0

and in particular, notice the difference it makes when they switch to the LoG; having built some of those antennas (for myself and for friends), I believe that the LoG, while not a "magic antenna" (those are made with "unobtainium" ) will help taming the noise and, coupled with a good TX antenna, may help making contacts on the "top bands"

[edit]

Forgot, use bricks or plastic stakes to keep the LoG wire in place, do NOT use metal stakes or the like; also, if you look at the image here



you can see that the antenna has two "main lobes" (see the site for details), now, willing to "aim" the antenna one may use some (e.g.) teflon rings or the like at the corners, those will allow to (gently) slide the antenna wire and move the feedpoint to an adjacent corner so reorienting the lobes with a 90° shift, this way an antenna with the two side corners at (say) NE/SW can be easily be reoriented to NW/SE