EMRFD Message Archive 14915

Message Date From Subject
14915 2018-07-17 18:52:25 ka7exm Happy Summertime EMRFD

Just a test message from a very curious moderator.  I hope everyone is having a great summer.

14916 2018-07-17 18:55:55 Bill Carver Re: Happy Summertime EMRFD
Doin' great Roger, hope same for you and Wes.

14917 2018-07-17 20:08:50 Phil Sittner Re: Happy Summertime EMRFD

We're all having a great summer thanks to the efforts of guys like you. Have a great summer.

Phil, KD6RM

14918 2018-07-18 14:45:50 kerrypwr Re: Happy Summertime EMRFD
I'm not having a great summer; I'm having a great Australian winter.

Here on the east coast, in latitude about 33S, it's cold (around 5C) overnight and around 16-20C during the day.

It's also fearfully dry; the RH was below 30% during the daytime yesterday and was 22% at one point.

Much of Australia is in severe drought; scientists think that it's one of the worst-ever.

My regards to all our members.

Kerry VK2TIL.

14919 2018-07-18 19:30:58 Jim Strohm Re: Happy Summertime EMRFD
Doing great!

Today, one of my co-workers  asked me about something OT for work -- we work for a company that makes phone systems -- and it's a little OT here too, but he asked me about:

An ultrasonic pest repellent device, up-sized to the level of weaponability against large dogs.  He has a cute little pocket-sized device for a driver, but needs enough ampage to turn away a large dog.

Obviously OT for here.

I have an interest in this kind of device, because I used to have a next-door pit bull that would hop the fence and desecrate everything in my yard.  I had designed a suitable ultrasonic device, but the neighbors got rid of the dog before somebody else killed it.  And then we got a bunch of bunnies, so I can't use such a device now.

I advised my colleague to get a rather large amp from ebay and to remove the input/output roll-off circuitry, but he's not as electronically savvy as I am, so there may be some educational sessions involved in this.

My up-side?  For my annual Helloween display in the front yard, I plan an infrasonic radiator device, and I face the same tasks of disabling the input and output roll-off circuits on a subwoofer amp rated in the hundreds of watts.

I'd love to hear any experience stories about doing this.  Obviously it's not too hard to pick a signal off an ebay amp PCB, but my colleague and I would prefer an elegant and sophisticated approach.

Plus, it's good to share theory about what roll-off filters look like in the audio realm.

Thanks in advance, and 73

14920 2018-07-18 20:18:20 Bill Carver Re: Happy Summertime EMRFD
I got rid of mice with a pair of  electostatic tweeters operated at about 20 watts of ultrasonic bursts.

Hmmm. I have a neighbor who sold his house, said his wife was going nuts trying to sleep at night with barking neighbor dog. I'm not sure I believe that 100%, but it could well be a factor.  He has a tractor and has borrowed  backhoe and done all kinds of nice things for me.....and I have another project. They haven't closed escow, and I heard a rumor the buyer was getting cold feet. Maybe I should suggest to him I can build something that might suppress the barking.

Bill - W7AAZ

14921 2018-07-18 22:55:11 Dana Myers Re: Happy Summertime EMRFD
14922 2018-07-19 09:11:27 Mike Nothdurft Re: Happy Summertime EMRFD

Very good summer.  Just got my uBitx gong on FT8 after some trials and tribulations with the computer interface and started working HF for the first time in over 55 years.  Seems you can really work the world with 8 watts and a piece of wire in the attic.  Worked VK7 and ZL1 on 20 meter FT8.  See my antenna on my QRZ page.  Just received my new Siglent  Sva1015X.  Now I can really so some filter work ;-)




14923 2018-07-19 10:18:34 Ashhar Farhan Re: Happy Summertime EMRFD
On my bench is a uhf fm receiver. We tend to imagine fm receivers as an infra dig. Well, this is, then, a case of reverse snobbery..
I have used two saw filters between a BGA416 LNA, an ADE1 mixer followed by another BGA416 LNA as post mix for an If of 45 Mhz. On the other side of the 45 MHz filter, I use an SA612 to down convert to 455 khz. A ceramic filter and a 2N3904.amp feed to an MC3357. No, I am not happy with the MC3357. 
The magic part is called TH72011 from Melexis. An 8 pin part directly multiplies a fundamental 12 mhz crystal 32 time to provide uhf LO. It takes just 5 ma current. 
All in all a very satisfying summer project. A lot of learning. Here is a great tip : next time you start a design, spend time on mouser.com.
- f

14924 2018-07-19 16:32:51 glenn Re: Happy Summertime EMRFD

There was a dog repellant article published in our local Electronics magazine a few years back.   Used several tweeters and a high powered amp tailored to suit the frequencies used..


www.altronics.com.au used to or may still have, a kit for it.  You can order copies of the articles from the link above though.

(I have no connection to these companies)


--  vk3pe

Virus-free. www.avast.com
14925 2018-07-19 17:12:57 arfghans Re: Happy Summertime EMRFD
I built a bark-off system that was acoustically triggered. Directional mic with a bandpass filter and threshold detector. The oscillator was a pair of 555s, one to FM modulate the other with a triangle wave, like a police siren, and another to gate it. Set the pitch just below 20 kHz and verified that the particular dog could hear it. Used a 50 W power amp driven right at the edge of clipping into an array of piezo tweeters mounted at the fenceline. It measured about 140 dB (unweighted) at 1 m. This system was completely effective and I’ll never forget the dog’s reaction the first few times it triggered. I took it down after a couple weeks and the chronic barking never recurred. Missi
14926 2018-07-19 21:41:02 Gary Sutcliffe Re: Happy Summertime EMRFD
Years ago I made something similar with a pair of 555’s. One modulated
another running at an ultrasonic frequency. It drove a small speaker.

I was working for a small company owned by husband/wife engineers. They
had large dogs they would bring in the office. The dogs smelled and
drooled on stuff. Sometimes they chewed up things and it would be our
fault. One liked to sleep on the floor in front of my desk.

I hid it in my in-basket and turned it on whenever the dog came by. She
would go someplace else.

There is no question I would have been fired if the owners discovered
it. :-)

Gary, W9XT

14927 2018-07-20 08:58:19 peter_dl8ov Re: Happy Summertime EMRFD
Either a) we've been watching the football, b) been enjoying the sunshine, c) constructing or d) operating.

If nothing else it's good weather for antenna work and my stealth long wire now has a new coat of sky blue. gray and white paint.

Peter DL8OV
14928 2018-07-20 10:31:07 Mark Schoonover Re: Happy Summertime EMRFD
Search for "Steve Gibson portable dog killer". Note, it really doesn't kill dogs!