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,?

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

?



?

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

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.

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

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.

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

?

?

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

?

?

Attention: Chris Trask, N7ZWY / WDX3HLB

Hello,

I am interested in preamps with saturable-reactor (transducer). In his article "The Forgotten Use of Saturable-Core Inductors (Transducers)", a practical example is shown in Figure 7 as "Remotely-tuned active antenna transducer application". Is it possible to get the schematic of this circuit?

Regards,

Fernando Martin

As probably people? think about this issue. Aluminum tape is available from the heatpump/air conditioning industry. Likewise "airframe tape" this is high? grade foil tape. And then there is ubiquitous aluminum oven trays and food? containers that can be moulded around everything. Please take your preference for spelling aluminum/aluminium/whatever. I use this stuff as a workaround in a EMC lab for grounding/shielding/capacitive coupling etc etc around cables and everything else that needs emc design help.

Henry

Sorry, I misunderstood and deleted my iladvised post.

开云体育

开云体育

Hi Hank,

开云体育

That sure brings back memories of working at TI and being responsible for environmental testing of a few systems. ?Stick it in ’the oven’, freeze it, better work … or you-know-who gets a call.

When I worked in the defense industry, all of the equipment we designed was built to handle -40C to +90C. Conformal coating was done on every board that went into the devices. Even though our standard was -40C to +90C, we tested them to -63C to +125C. Conformal coating made that possible, plus it helped the devices meet salt corrosion tests.

--Hank
KB4MTO / TA5ZC

On Sat, Sep 17, 2022 at 04:35 PM, Dr David Kirkby G8WRB wrote:

Its also corrugated, so I would expect the resistance of it to be higher than straight tube of the same diameter and thickness.?

Not by so much, perhaps 5%, from memory Owen Duffy has some calculations somewhere.

Inductance is slightly higher too.

Aluminium ducting tape is a definite NO from me.

Coper flashing is another option, if you can get hold of it, which doesn't seem to be that easy in the UK.

I tend to use LDF4-50, sometimes connected in parallel, but I think Simon's suggestion of Aircon tubing is a good one.

If your tuned loop transmit is working efficiently, it can be quite hazardous at close distances, fortunately from a compliance / H&S perspective most don't work that well, saving folks from serious harm to themselves and others.

I have a theory about transmit antennas, that folks don't notice how inefficient they are, unless they perform about 10dB worse than the user expected them to be. So losses of just a few dB tend to get ignored.? Most home built, and even a lot of the commercial tuned transmit loops are not that good (as it costs money to properly engineer one that works well), but if the performance is 'good enough', folks don't worry, or bother to try and measure their actual efficiency.

In many cases for amateur builds, 'screwdriver' type tuned whips are easer to construct and tend to be more efficient (especially on the LF bands), because they don't require such heavy engineering to minimise losses.

Just my 2p worth...

Regards,

Martin

I've noticed a bit of a problem with the Wellbrook amplifier potting, which may have been resolved on later models.

Having opened up one or two faulty Wellbrook amplifiers that have been donated to me (in return for a clone). The main issue (apart from folks accidentally transmitting into them) seemed to be that there was only a very thin layer of epoxy over the lower (copper) layer of the circuit board. This didn't provide an effective sealing layer of epoxy around the whole board, and with thermal expansion a cavity forms between the board and the epoxy, and in severe cases the epoxy can split and let water in. In one case when I initially started removing the epoxy, the whole of the bottom section just peeled away from the board, revealing moisture and the oxidised copper tracks.

Just my observation, your experiences may vary...

Regards,

Martin

Water pipe is very impure copper..it does not need to be 99% or even near, just a copper colour will do to sell it..

Copper is copper..it costs x? per ton.. so if it’s cheap there is a reason.

Air con tubing for instance has full spec, which can be downloaded to see purity, can’t do that with b and q water pipe..

And since air con tubing is not that expensive compared to water pipe( 2x?if bought on the reel, and not on ebay) it makes sense to use as spec’s can be seen.

Re heliax..yes its corrigated..so one needs less length to make same loop..
Also it’s typically of good quality due to nature of its requirements..so more R is not true as less Length is needed.( corrigated) ie same r.

However my preferred copper of choice is air con from a uk/ euro source..( as annealed and in a coil..)

Ie my 160-80 mag loop will be again this winter chatting to usa ssb on 160m..proof is in the eating as they say.(might av got that saying wrong.)


Simon g0zen