LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Useful information regarding antennas for SDR products.
sdrom33
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by sdrom33 » Wed Jul 03, 2019 11:08 am

This "antenna" design contradicts many, if not all, antenna principles anyone however superficially involved with radio communications should be aware of. Just to name a few.
- If it is a ground plane it does not have the ground reflector. If it is not a ground plane, what is it?
_ It is claimed to be "noise reducing", but no scientific or otherwise practical reason why this whip should be a "noise reducing antenna" is given.
- worse, to connect the ground return to an earth stake is just about the worst one can do about noise, according to theory and practice.
- it is claimed to be "wide band", but no principle whereby this whip should provide wideband operation is given. To try and pretend to be wideband, it should at least have a large diameter, but no mention of diameter is given.

Furthermore the FT-114-75 core does not exist: must be FT-140-75, with an Al=5500 uH/100 turns, so 40 turns give an inductance of 8800 uH: reactance could now be calculated, but the low frequency side of the antenna is unknown. The FT-50-75 core does exist, with Al=2725 uH/100 turns. Assuming 50 Ohm at terminals A / G of T2, we have 50 Ohm on the other side, so there should be 5 KOhm across the 40 turns winding of T1. With the relay contacting the tap, the antenna impedance goes down to 312 Ohm. All this, without a well defined frequency plan, does not make any sense to me....An antenna output impedance of 5 KOhm? But there is more: in the original design by doctor Dallas, T1 primary has 80 turns..., so this must be considered an "improvement".

Sorry for these severe comments, but many inexperienced operators could be misled by this publication.

It does not matter if this design seems to be originated by "Dr. Dallas Lankford" (lost in the Arctic regions?) it still looks like something evidently not fit for the purpose and surely not delivering the claimed performance.

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Thu Jul 04, 2019 10:25 am

Forgive me for wading in, no doubt Ian is very well intentioned and trying to be helpful, but as sdrom33 says the article is so problematic that it seems to be useful example of what not to do and anyway I love antennas so much I can't help myself.

It seems (to me anyway) that the concept is flawed from the outset as the "noise" being picked up by the antenna is in fact just RF, the stuff the antenna is designed to receive. The more noise, the more efficient it is and verticals are very good at picking up man made noise because of their low radiation angle.

Any attempt to reduce the noise using any form of phased coupling which seems to be what the aim is will also attenuate any useful signals that may also be present.

It does not seem even remotely possible given the values and configuration it could be made to resonate on a wanted frequency and be of assistance that way.

The only way to reduce the noise via phasing without also killing the wanted signals is to use more than one antenna and combine their output through a phase shifting system, eg. an MFJ 1026

Or even better an SDRplay Duo when the new version of SDRuno arrives :-)

I would add that using MMANA modelling software...

A 15 foot lossless vertical placed against an infinite and perfect ground has a feed point impedance on the 80m ham band (just to pick an example) of 0.175 ohms.

At 150KHz which is the lower frequency cited the feed point impedance is 0.0019 ohms.

The turns ratio on the transformers shows that it is stepping down not up. That is going to make the feed line match even worse as well as actively discriminating against the HF frequencies the lower down the band you go from 30MHz.

--

Commercial or home built small loops can make a very effective antenna on the HF bands including at the very lowest frequencies and there are many users on the Forum who would love to give examples.

Alternatively a cheaper and fun way to fiddle would be to buy a simple ferrite rod similar to those used in the old transistor radios, wind 20 turns of any old hookup wire around it and connect it to the zip cord feed line. That would be very much the superior antenna and could be fastened horizontally on the end of a wooden stick and rotated for best signal to noise.

Sincerely, Phil

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g1hbe
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by g1hbe » Thu Jul 04, 2019 5:47 pm

Ian, in regard of the bonus points. The version of 'Let it All Hang Out' that I remember was by a certain J. King in (about) 1970, although I think it was his version of an earlier hit by someone else. Do I get a small prize? :D
Sorry mods for going off-topic, but any mention of bonus points gets me in a lather....

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Andy

vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Thu Jul 04, 2019 10:47 pm

IMHO articles on forums are posted there in order to be discussed and commented on so that the resulting discussion raises pros and cons and teases out other related issues for the benefit of everyone.

I've learned so much from making so many mistakes that I'm seriously considering making more of them.

Commenting on my own post above

- the reason I mentioned noise phase cancellation was because the words "Noise Reducing Vertical Antenna" in title of the post and the title of the circuit led to the possibility that Ian may have thought that "noise reducing" was what was happening with the switched inductances.

- in practice the antenna illustrated would likely work as an off centre fed vertically polarised doublet with the ground wire and earthing system being the non-obvious second part of the doublet, they would at as an RF source rather than a sink

- the ground losses and impedance of the ground wire earthing system as an aggregate would likely present as something above 15 or 20 ohms impedance in practice, meaning that the matching system as illustrated could well result in a halfway reasonable SWR

- if a person set out to design an antenna with the purpose of maximising its ability to pick up noise he would choose a vertical "ground plane" with a longish wire indirectly connected to a mains earth rod.

- if a person set out to design the least effective antenna possible for listening to medium and international HF he would choose a short end fed vertical, the shorter the better.


Phil

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Mike2459
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by Mike2459 » Fri Jul 05, 2019 3:04 am

Phil:
I think Lankford's 'noise reducing' design refers to the use of a 1) a ground rod at the antenna and 2) a balanced transmission line magnetically coupled at both ends. He uses this in several of his other designs.

Some of his other stuff can be found here: https://www.okdxf.eu/index.php/technika ... -lankforda



Ian:
I thought I might give the zip cord a shot with my mini-whip. I can power the antenna with a battery pack for testing. Lankford doesn't recommend using the transmission line as a DC supply line - says it will introduce noise into the signal path.


Mike

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Fri Jul 05, 2019 6:17 am

Hi Mike, yes I know, I did mention connecting to the zip cord in my first post and yes a parallel feed line is one of the pet things I keep pushing in all my posts and kudos for the inductive coupling Lankford used so as to create a balanced system.

If Lankford had used coax in that circuit I would have included it in the litany of antenna parts that acted as a collector of RF.

I use much the same here, after evolving various options in search of the best low noise solution I decided to home brew something similar using a lightly twisted pair of surplus eBay teflon as per mentioned in other forum posts. Its characteristic impedance is around 120 ohms which is the best compromise for my particular antennas. I was using home brew ladder line but couldn't get the impedance as low as that.

For example
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I've checked out zip cord, really handy for receiving but no good for transmitting. There are many other simple surplus options for receiving including CAT5 that actually work really well over modest distances.

--

I looked deeply into my heart and conscience before posting my criticism of the circuit, I cannot even begin to see how that 15 foot vertical and it's matching system (and earthing system) can in any way at all be touted as a "Noise Reducing Vertical Antenna". I think I could fill a detailed couple of pages setting out the proof of why it isn't and cannot be, I side wholeheartedly with sdrrom33's summary:
This "antenna" design contradicts many, if not all, antenna principles anyone however superficially involved with radio communications should be aware of. Just to name a few.
- If it is a ground plane it does not have the ground reflector. If it is not a ground plane, what is it?
_ It is claimed to be "noise reducing", but no scientific or otherwise practical reason why this whip should be a "noise reducing antenna" is given.
- worse, to connect the ground return to an earth stake is just about the worst one can do about noise, according to theory and practice.
- it is claimed to be "wide band", but no principle whereby this whip should provide wideband operation is given. To try and pretend to be wideband, it should at least have a large diameter, but no mention of diameter is given.
Put bluntly, touting that circuit as a wide band 150KHz to 30MHz "Noise Reducing Vertical Antenna" is getting very close to offensive rubbish.

Cheers, Phil

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Fri Jul 05, 2019 9:15 am

On a positive note, anyone looking to build a genuine wide band vertical can, it is absolutely possible.
TC2M Gain-2.png
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TC2M SWR 30MHz.png
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https://www.tc2m.info/

Phil

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sdrom33
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by sdrom33 » Fri Jul 05, 2019 11:05 am

I have been considering this TCM design and planning to do it with 300 mm dia. PVC water pipes supporting a steel mesh. In this case a self supporting wide band antenna could be made with minimum expense and no external supports. Non resonant ground reflector could be made with conducting cloth cheaply available in China. Phil, what do you think about this scheme? Your advice very important to me!

Cheers,

Thomas

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vk7jj
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by vk7jj » Sat Jul 06, 2019 12:41 am

Hi Thomas, nice little burst of enthusiasm you've got there, the article did the same to me when I first read it :-)

Here's the thing:

On my 20m x 12m Colorbond shed roof there is a 10m long vertical using the roof as a ground plane. It's optimised for 40m and is resonant at 7.1Mhz.

10m is the same length as the TCM and avoiding any minor quibbles we can safely say it's performance on 40m will be equal to or better than the TCM. I've had a chance to evaluate it over the last few months and it's not worth keeping in the air ... it's too noisy on receive.

It's located on the roof such that the largest part of the ground plane is shared between the US and EU so you're looking at the smallest part of the roof in the photo.

Sometime over the next week while swapping my WSPR stuff around I'll take the opportunity to connect it to an RSP1A and do a screen dump of the 40m waterfall and I'll do an exact comparison shot using a 160m long horizontal wire delta loop that's terminated only a few meters away and at the same height, and you'll be blown away.

Mind you it's fine on transmit, good low omnidirectional angle radiation, but in reality a 1/4 wave ground plane even on a 240 square meter perfectly conducting roof has less than unity gain. The wire loop modelling suggests it's omnidirectional gain at the same frequency is better than 8dBi and it's vertical angle of radiation is around 40 degrees which is a little higher but good enough to hold the daily world 40m WSPR title for aggregated distance of unique spots for the last few months.

I'm thoroughly sick of debating the theoretical merits of this or that so I'm speaking up here to prove the point. That delta has taken out the daily world title on 80m, 40m, 20m, 10m and 6m (I can post the screen dumps) which is not bad for a bit of wire in a very ordinary take off point low down on crappy ground and among trees, especially compared with what others out there are using; the facts speak for themselves, res ipsa loquitur.

And lest anyone think the participation rate on WSPR is not high enough to use it as a measure of performance there have been 1,349,891 spots in the last 24 hours and 55,495 in the last hour according to the WSPRnet website. Each WSPR spot carries with it information including the power of the transmitter, the received audio SNR and the distance so performance comparisons are almost trivially easy.

Forgive the crappy winter photo; the vertical is a full 10m and the other tower with the primary wire delta does not lean, that's just perspective distortion from me lying on the shed roof. The second 160m delta I use for general work terminates at a second tower attached to the same shed as per the photo on the previous page.
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Here is today's WSPR Challenge using that loop simultaneously on 40m and then split twice for 30m, a 6dB splitting loss. Not shown in the result highlights is VK7JJ3 using the RSP2.
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Phil

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sdrom33
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Re: LW-MW-SW Relay Tuned 15' Noise Reducing Vertical Antenna

Post by sdrom33 » Sat Jul 06, 2019 6:18 pm

Phil,

You need a lot of real estate for a Delta Loop antenna. The example ground plane you show is tuned to just 7 MHz. The TCM promises wide band coverage, from 160 m to 6 m at least... zero gain is no problem if the location you are in is noisy above a certain level. So these are the plus considerations, unless you have something smarter (and with a small footprint) to propose.

The diameter I mentioned is on the low side, 400 to 500 mm would be more appropriate.

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