From: wassermanr46@... <wassermanr46@...>
Sent: Friday, September 23, 2022 1:17 PM
To: [email protected]
Subject: AirSpy YouLoop-2t with Nooelec Lana HF

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I am interested to hear out technical specialists about using AirSpy YouLoop passive antenna constructed of RG402 coaxial cable limbs with 1:1 balun connecting to Nooelec Lana HF 50 ohms pre-amplifier or directly to 50 ohms SDR.

Many sources advocate that Youloop antenna requires Hi – Z input receiver or pre-amplifier.

Author Martin G8JNJ tested and wrote Moebius passive antennas better perform when loaded with 400 ohms input than with 50 ohms. Saying so, should AirSpy Youloop 1:1 balun be replaced, say with 8:1 or 4:1 balun, to have a better S21 response for frequency range from 1 – 20 MHz ?

Based on my experience using the original AirSpy Youloop with 1:1 balun and Nooelec Lana HF with SDRRSP1A or without LNA the antenna works well in MW only.

Regards,

Raphael

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Based on my experience using the original AirSpy Youloop with 1:1 balun and Nooelec Lana HF with SDRRSP1A or without LNA the antenna works well in MW only.

With Youloop, without any LNA and with Airspy HF+ Discovery the reception is very good from VLF up to the lower VHF range. But I never tried a 4:1 or 8:1 balun instead of the Youloop's built in balun.

On Sat, Sep 24, 2022 at 09:45 AM, Dirk wrote:

Based on my experience using the original AirSpy Youloop with 1:1 balun and Nooelec Lana HF with SDRRSP1A or without LNA the antenna works well in MW only.

With Youloop, without any LNA and with Airspy HF+ Discovery the reception is very good from VLF up to the lower VHF range. But I never tried a 4:1 or 8:1 balun instead of the Youloop's built in balun.

As you are probably aware, I'm not a great fan of the Youloop, but as an experiment you could try a single unscreened loop of wire, with the same circumference as the Youloop, but connected between the inner pins of the balun / loop connectors on the 1:1 balun. You could also try a coaxial loop connected to the 1:1 balun, but ensure you split the outer screen connection at the loop midpoint.

See what differences you observe between the various configurations, and make up your own mind about which works the best for you and the range of frequencies you are interested in.

Regards,

Martin

I have built a 50cm diameter moebius antenna with outer side made by multilayer PeAlPe 20mm diameter and the inner with 1mm diameter wire. The idea was to increase the self resonance frequency decreasing, in this way, the capacity. The calculated impedance of 20 by 1 mm with air dielectric coax is more or less 130 ohms, so I started with a 1:3 Balun (50 -> 150 ohms). It have good performances up to 25 mhz, after a sharp decrease. Changing the balun to a 1:9 one the performances are stil acceptable and becomes acceptable up to 30mhz. My receiver is a hf+ discovery.

I hope it can be useful.
regards.

Hi Gabriele,

The given from your email? data are:

1. Moebius antenna with loop diameter of 50 cm, using PEX tubing of 20 mm in diameter, with 1 mm center conductor and air dielectric for a? design of coaxial cable

My calculations show the impedance is around 180 ohms and the capacitance of 1.52 m cable is 28.18 pF and the inductance about 911 nH.
Thus, the calculated resonance frequency is about 1 MHz.
So, I do not see how significantly you decreased the self resonance frequency when for similar loop but using original 50 ohms RG402 solid cable with the dielectric PTFE constant 2.02 I get self resonance around 1.75 MHz

Regards,

Raphael

Hi Martin,

Thanks for a prompt response.
I have been using the commercial made by Aispy Moebius passive anteenna. As you know, this antenna gets supplied with RG402 1 meter coaxial cable limbs terminated with SMA connectors , crossover device at mid point and T-box that contains 1:1 balun.
The secondary winding of RF transfomer ( balun ) is with a center tap that is grounded to same point as shields of coaxial cables meeting the T-box and the secondary winding is connected to inner conductors of coaxial cable limbs.?
I even tried to calculate the resonance frequency of this loop - 1.75 MHz, based on the inductance of 1 meter cable limbs 144.24 nH and capacitance 57 pF. However, from other source I found the resonance frequency should be around?
3.4 MHz ( I am not sure what cable was used and the circumference of the loop in that example ). I have no plans to built and experiment with different loop antennas like a single? unscreened loop of wire.

Let's for sake of argument better focus on your experimental work related to passive loop antennas described in article - " Moebius Loop Antennas, June 2021".?
Regarding this article with your experimental tests I have a few questions:
1. You presented measurement results S21 parameter vs. frequency for a loop loaded with 50 ohms and additionally the Moebius type when terminated in 400 ohms.
? ? You wrote - overall it looks like Moebius type would benefit from a different transformer impedance ratio.?
? ? That is the reason why I asked earlier for a benefit changing the balun impedance ratio allowing my current antenna to see a higher impedance, say 400 oms instead of 50 ohms,?
2. Your Moebius anteena is differently connected to the balun that does not use center taped secondary winding. Why is that ?

Regards,

Raphael

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Hi Dirk,

Unfortunately, my receiver is RSP1A and I cannot judge how commercial AirSpy Moebius antenna performs with Airspy HF+ Discovery that has a better parameters.
However, I crossed article that states AirSpy passive antenna is designed for Hi-Z receiver input but AirSpy HF+ specifications show 50 ohms input...
My intention is to compare apples with apples.

Regards,?

However, I crossed article that states AirSpy passive antenna is designed for Hi-Z receiver input but AirSpy HF+ specifications show 50 ohms input...
My intention is to compare apples with apples.

Ok, but I think, the RSP1A you mentioned in your starting post also has 50 Ohm input impedance like the Airspy HF+ Discovery.?
So: comparing apples? ;-)

I meant not only having same input impedances of 50 ohms but having as well as different sensitivity, dynamic range in the favore of AirSpy HF+.
So,? AirSpy HF+ Discovery receiver can be connected literally to any antenna...

I meant not only having same input impedances of 50 ohms but having as well as different sensitivity, dynamic range in the favore of AirSpy HF+.

Hi Raphael,

ok, I understand.
I also have the RSP1 (not 1A). I will try it next week with my Youloop again, because I don't remember that this combination was only good for MW.?

John,

Let's not talk about the vendor's Noo Electric service support. Everyone probably has his? own experience with them.
You are not familiar with their Lana HF amplifier and? I am not critisizing? your about a lack of experience with this device.
Starting to use MLA30+ amplifier with a homebrew loop antenna, I am sckeptical? to follow that path because many of readers/responders probably reside in Europe where SW broadcasting stations are relatively close to any recepient there and there is not a great difference what antenna is used with SDR unless they minimize the effect of incoming RF interference.
I am residing in south Florida where for me is a challenge DXing across the pound (Atlantic ocean ) european broadcasting stations unless I build a decent outdoors antenna system not relying on any loop antennae.

Have a nice day,

Raphael

Dirk,

RSP1A is an improved version, it differs from RSP1 performance.
Also, I do not know about your location where you are preparing to test Youloop with? RSP1. If in Europe , you may be lucky with SW bands as well.

Raphael?

Gabriele,

My apology, I made an error in my? calculations for the resonancy frequency because of 1 nH = 10-9 H.
So, in your case the self resonance frequency is 31.4 MHz and in my case using RG402 cables will be 55.54 MHz because the inductance is about 6 times less.

Raphael

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On Sat, Sep 24, 2022 at 06:31 PM, <wassermanr46@...> wrote:

I have no plans to built and experiment with different loop antennas like a single? unscreened loop of wire.

That's a pity. If you are prepared to try different transformer ratios, why are you releyctant to try a singe turn unscreened loop ? You could even use the Youloop hardware, by removing the mid point crossover and just connecting the two coax inners together at that point.

Let's for sake of argument better focus on your experimental work related to passive loop antennas described in article - " Moebius Loop Antennas, June 2021".?
Regarding this article with your experimental tests I have a few questions:
1. You presented measurement results S21 parameter vs. frequency for a loop loaded with 50 ohms and additionally the Moebius type when terminated in 400 ohms.
? ? You wrote - overall it looks like Moebius type would benefit from a different transformer impedance ratio.?
? ? That is the reason why I asked earlier for a benefit changing the balun impedance ratio allowing my current antenna to see a higher impedance, say 400 oms instead of 50 ohms,?

Yes there would be a slight benefit, as Youseff the Youloop designer has himself indicated, that the loop ideally requires a higher impedance load than 50 Ohms. However, a single turn loop with a 50 Ohm load is likely to provide more consistent performance across a wider frequency range. The HF discovery has been optimised (very low noise floor and input impedance) to allow use of the Youloop, but it's really not ideal to use the loop with any other receiver, unless you add a pre-amp of some sort.

2. Your Moebius anteena is differently connected to the balun that does not use center taped secondary winding. Why is that ?

I found that it didn't achieve much in terms of noise suppression, and under some circumstances it made things worse, due to common mode currents on the coaxial feedline being transferred into the loop. It seemed preferable to use the isolation provided by the transformer to provide better common mode suppression, especially on the lower frequency bands where it was more likely to be useful.

If a single turn loop is terminated in a low enough impedance which is properly balanced, then the screen is not required. However the Mobeius loop is not low impedance and the crossover can lead to imbalance. In my experience adding a screen does nothing to reduce noise pickup, but it does increase the capacitive loading, which significantly lowers the self resonant frequency of the loop, which in turn leads to other problems.

However your milage may vary, which is why I would always encourage further experimentation. When comparing antennas it is always useful to have a reference point. This is why I suggested trying a single turn unscreened loop, which is easy to model and predict it's performance.

Incidentally the RSP1 was a disaster, it's one of the few items of radio equipment I've ever sent back for a refund. The main issue (apart from the broadband AGC, which was later much improved) was the pre-amp, which could only be switched on or off. So the receiver was either being consistently overloaded with masses of AGC 'pumping' or incredibly deaf. The RSP1A is a LOT better and I do now own one (but still try to avoid SDR Uno if at all possible).

Regards,

Martin

The HF discovery has been optimised (very low noise floor and input impedance) to allow use of the Youloop, but it's really not ideal to use the loop with any other receiver, unless you add a pre-amp of some sort.

Martin,
my RX-888 MK II gives similar results like the Airspy HF+ Discovery with the Youloop. No preamp required.

On Sun, Sep 25, 2022 at 01:32 PM, Dirk wrote:

my RX-888 MK II gives similar results like the Airspy HF+ Discovery with the Youloop. No preamp required.

I can't find a specification for the RX-888, but it's likely to be using an LTC RF amplifier ahead of the ADC which I don't think can match the Airspy HF+ that has a sensitivity specified as being -140.0 dBm (0.02 ?V / 50 ohms at 15MHz) MDS Typ. at 500Hz bandwidth in HF. This is a very good figure and is probably likely to be about 10dB better than the RX-888.

All small broadband loops have low values of gain and generally require some sort of amplifier, typically +20dB, in order to bring the signal levels up to something like that which would be obtained from a full sized wire antenna. The relatively low gain of the Youloop, is compensated for by the very sensitive RF stage present in the HF +. If you can detect a change in noise floor on your RX-888 between the Youloop being connected in comparison to a screened 50 Ohm terminating load. then the chances are that your noise floor is relatively high (urban areas are typically about 20dB worse than remote rural areas). In an electrically quiet environment, such as out in the countryside, well away from other property and overhead cables, it is difficult to see an increase in the receiver noise floor when a passive broadband loop is connected, even using an HF+

As a result you may obtain similar results with pretty much whatever receiver you use. This is where a lot of antenna A/B comparisons that can be found on the web become flawed. It's not the antenna that is being evaluated, but the level of ambient noise that is present.

I'm not saying that you can't hear stuff with your RX-88 and Youloop, but the chances are that the receiver is not really the limiting factor.

Regards,

Martin

All,

Let me add a few cents to the topic of discussions.
Why should we specify the sensitivity of Airspy HF+ like the vendor? desires doing? in terms of? MDS ? I call that as an advertisement trick.
Majority of users who have any designed and produced receiver listens to audio broadcasts. Saying that, the sensitivity of receiver should be specified for certain frequency band at 12 dB SINAD at 3 KHz bandwidth for AM.
For under schemes of modulation like SSB, CW and FM to use other conditions as well ( for SSB and CW at 1.5 KHz bandwidth and FM at 8 KHz bandwidth ).
My SDRRSP1a is specified, for example, sensitivity 0.48 uV/50 ohms at 15 MHz for 12 dB SINAD at 3 KHz bandwith.In radio
In radio? engineering we use well known equation: P sensitivity= -174 + NF + 10log BW + SNR.

Regards,
Raphael
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Hi Martin,

What's wrong with SDR Uno application ?
You wrote that you try it avoid off.

Regards,
Raphael