Hello Alan, Martin et al,

Saturday, January 1, 2022

People must be getting bored with my saga by now, so I will keep it as short as I can. Basically, yesterday lent me the opportunity to do some more tests. Running the injector box off a 12V accumulator made zero noticeable difference. Running the KIwi as well, off my mobile phone 5V power pack made a minute difference to overall noise. Disconnecting the coax to the antenna at the injector box still left some strong signals. Wrapping about 10 turns of the coax out to the loop around a BIG ferrite ring (I have the spec but can't recall it off hand) made a noticeable difference.

Then I had the idea to wrap the short (2 foot or so) of coax from the injector box to the Kiwi as many turns as possible around a similar ferrite ring. I think I got about 5 or six turns on, the BNC plug limited this. Now THAT made a big difference!

I am pretty pleased to have persevered and enormously grateful to those who stuck with me.

Downside is MF / LF amateur digital performance has markedly deteriorated. Is it the smaller circumference of the new loop? The 30 to 35 or so degrees rotation of the loop form its orientation looking down from the sky (plan view)? Originally the loop in plan view ran almost east to west, it's now skewed about 35 degrees or so anti clockwise and a bit lower overall....


Testing has been made a bit problematic as my TS-580S which has had a hard, no, very hard life, has started to lose sensitivity and sometimes goes totally dead on receive. It seems heat related, but it's years old and had one incident where I managed to shove a kilowatt of LF 137 kHz up the receive antenna port.

Needless to say it didn't like it and I amazed and astounded myself by managing to repair it with my scope and a sig gen. More good luck, strong coffee and a good light source, plus a huge taped together print out of the schematic.

I think I might treat myself to a newer (if still secondhand) rig soon. As an aside what modern transceivers hear well at LF and MF and will TX a milliwatt or so on LF and MF to act as an exciter, anyone here any experience of anything suitable or should I just get a newer TS-590?

Critical comments welcome:



Thanks again everyone.

Best regards,
Chris mailto:chris@...


A> Martin

A> As Andrew said shorting the input is not a good idea and will not do
A> what you think it will. Leaving the terminals open will but you need to
A> disconnect both terminals. The amplifier is a Zwischenbasis type, as
A> you have plotted in the past the input reacts to the signal source
A> impedance. This form of noiseless feedback is the complement to the
A> Norton Amplifier where the output impedance is a transformed version of
A> the input impedance, here the output impedance hardly matters but you
A> get to optimise the matching to the source over a much wider range than
A> a conventional "dumb" input , it is NOT a virtual earth amplifier in
A> the normal sense ( which also goes nuts with a shorted input !) but a
A> much cleverer configuration due to Cantz from 1953.

A> However before disconnecting the loop I would remove the power to the
A> injector then disconnect the coax to the injector. That would show what
A> is leaking into to the coax and then what remains after the coax is
A> removed. It seems futile to disconnect the loop when you can just power
A> it down.

A> I used a naked ALA100LN until recently, it works very well from LF to HF
A> and beyond. The IMD performance is outstanding six miles from Brookman's
A> Park. I now use a new arrangement that drops BP signals an additional
A> 30dB. I spot to PSK reporter from a tiny urban back garden, Don't do too
A> bad for an antenna 3m high surrounded by switchers although BT has
A> blocked 30m very effectively.

A> 73, Alan G8LCO.





A>

A transformer with a 5:6 turn ratio would convert 50 ohms to 72 ohms, so a 50:72 could be used at one end of the coax and a 72:50 at the other. Selecting a suitable ferrite core and winding technique is left to the student :)

However the losses in this approach might be higher than the slight loss caused by the mismatch of using the 75 ohm cable alone.

John KK6IL

Thermal cycling is not mentioned on the wikipedia site but I thought that
thermal cycling may have been the reason that Belleville washers were used on the link hardware of aircraft Nickel Cadmium batteries.

To clarify, Belleville washers are spring washers, much better than split ring if your intent is to provide a spring pressure that allows some movement and change in length. Much stiffer than a spring and less likely to bounce and break contact than a battery spring.

I think the guidelines for Belleville washers may include that they should not be torqued down flat. I do know even the Wikipedia page specifically says they are NOT a locking mechanism.

The Wikipedia page Ron links to makes a fascinating read.

In any case, for antenna mounting we need hardware that can sit up there for years in the sun, wind, snow, rain, etc. without requiring constant inspection and tightening.

--
Steve Greenfield AE7HD

Thanks to all for the excellent information.
I'm going to give Ian's solution a try. The youloop looks easy to build. I've got the parts already. I also have an LNA that I can put at the feedpoint and power with the Bias from the Miniwhip. As you say I might need to adjust the power.
I assume that a round toroid can be used in lieu of the binocular core. 5 turns on one side, 5 turns on the other. Keep 'em separated.

I have a magnetic loop for transmitting which works quite well. For example, I made an FT8 contact with Japan from Toronto today on 30m. Not the best antenna in the world but probably the best thing for a small balcony, three floors below the roof.
I'm looking for a solution that fills in the coverage gaps (0 to 7mhz, 7.5 to 10 mhz) and is more broadbanded. The range is about 30 khz which means constantly tuning the capacitor.

Thanks again to all. I'll be sure to report back.

Since you aren't going to use a high end receiver, and you aren't wanting longwave reception I would recommend the inexpensive MLA-30 loop. Sure, in a super quiet location with an excellent receiver, there would be better options than the MLA-30. However in your case the MLA-30 could have a few advantages. It has a gain pot that can be adjusted up or down to help keep your rtl-sdr v3 from overloading, its fairly invisible to keep nosey neighbors and landlords from asking questions, it can be rotated to help null out some of the noise, and its dirt cheap. It will definitely pick up tons of shortwave and broadcast stations.
Tom

Hi Paul

Other thing to mention is..if you have caught the swl “ bug” then maybe invest in a better sdr as well. Not that expensive ?100 or so gets you an ok one.certainly better than an rtl dongle by far.

Can you get to the roof?? As that WOULD help with antennas!! ( you say on 10th floor)

Simon

开云体育

The Mini-Whip antennas do not function very well indoors and probably not very well on a balcony. If you're into a bit of home construction, a YouLoop or Moebius antenna is definitely worth a try and is very cheap to build yourself as it is basically two short lengths of coax cable and a small 1:1 transformer on a binocular ferrite core. I have two home-made ones used indoors and I use a BN73-202 core with 5 turns of 30 AWG wire-wrap wire for each winding of the transformer. Although better results are obtained with the Airspy HF+ or Discovery, it does give reasonable results with the RTL-SDR v3 and Spyverter. I have used a HiLego LNA from e-bay to improve results, but careful adjustment of its gain by varying the supply voltage was necessary. Fortunately I don't have any strong transmitters near me which might cause many spurious signals. As this LNA needs a supply of around 6 to 12 volts, depending on required gain, the dongle's bias-tee cannot be used. I use up to 8 rechargeable AA batteries. The e-bay UK link is as follows:

Ian Brooks, Verwood, UK.

Why would anyone use locking compounds on plastic?

Or.. a 1m loop with suitable preamp..

Ie ccw, Lz1aq, wellbrock etc.

Advantage of loop is you can null out a local noise source..disadvantage is bigger than e probe. Both need 12v dc supply.

I would start with a ccw ( cross country wireless) as good and cheaper than the rest.
No point in spending $$$$ for a try out antenna .( incase you dont get on with,) Please avoid the mla30.

Simon

Good fit-for-purpose cautionary advice here Alan....

Leigh
VK5LT

I would NEVER USE LOCKING COMPOUND ON PLASTICS. Many locking compounds can destroy plastic parts over time, they are formulated for locking metal part not plastics.? Same goes for some greases. One former employee used locking compound on plastic nuts, cost ?35,000 to replace the parts.

One Italian manufacturer used a grease to ease driving screws into plastic pillars. After a year the pillars disintegrated and cost the manufacturer a lot of money.

73, Alan G8LCO.

--

The website says:
Use of EZNEC Pro/4 and EZNEC Pro/4+ require a license from Lawrence Livermore National Laboratory (LLNL) because of their incorporation of NEC-4.2 code for which LLNL retains the rights.

It also says:

--
Steve Greenfield AE7HD

I have a 10th floor balcony and would like a no tune solution for an rtl-sdr v3 with an upconverter.

I've tried a miniwhip from aliexpress. It was pretty deaf.

The youloop looks interesting but I think it needs a more sensitive SDR and using an LNA with the rtl-sdr v3 only elevates the noise from what I understand.

I have a homebrew magnetic loop for transmitting between 17m and 40m but tuning is cumbersome and I would like to receive below 7Mhz.

So what would you install to get a decent signal from 0.5 to 30Mhz? Some sort of passive loop?

Thanks.



.

On Sun, Jan 2, 2022 at 07:47 AM, Steven Greenfield AE7HD wrote:

Absent any other method to lock the parts in place, split-ring lockwashers can actually hasten loosening under vibration and temperature changes. See the graph on the last page in the PDF I linked to below.

Let's see if I can link to the PDF:
http://hillcountryengineering.com/wp-content/uploads/2011/10/Split-Lockwashers-Separating-Myth-from-Truth.pdf

Sadly, there are a lot, a LOT of websites, mechanics, and even mechanical engineers giving out bad advice about split-ring lockwashers.

Steve - Thanks for the link to the article.? I learned something from your comments and that article.

Roger