Archive for September, 2009

Matching the 6V6 link to a low pass filter

September 30, 2009

Continuing our discussion: “How do we get a low pass filter in the circuit between a link coil output (balanced) and a low impedance low pass filter (unbalanced)?” . The simplest way we found is to use a variable capacitor between – in series with – one leg of the link.  In our 6V6 transmitter design on 80 meters we have found the value needed is less than 250 pf.  The spacing between plates must be adequate to handle the power level. In our case,  running about 3 1/2 watts output using the Pastime Projects power supply spacing can be minimum.  We will be more detailed in the next email newsletter.  Using a watt meter and dummy load, we clearly see a peak in power when the match to the 50 ohm dummy load is best. And of course, the reflected power is minimum. There we are!  A low impedance output.  This is the way the vacuum tube mobile transmitters of yesteryear were tuned. The impedance of a mobile antenna is very low.  BCNU! Glenn NN8G

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Propagation and Postings Sep 25 2009

September 25, 2009

We have just published the Pastime Projects e-mail newsletter.  If you are not receiving these 3 or 4 page emails, please let me know through pastimeprojects@yahoo.com. We will add you to the list. If you have received these in the past, and are not receiving them now, please let us know! there are a few bad addresses in our system and we need to correct them.  The best news is HF propagation. This Old Man is predicting the  new eleven year cycle has really begun!  Ready your radio and antenna for a great adventure. Remember to be professional and courteous as the band become busier.  We are all in this together! 

The newsletter also talks about filters for transmitters. It is getting too wordy to be reproduced here. Please follow us in the newsletter.  Glenn NN8G  pastimeprojects@yahoo.com  9.25.09

Matching 50 ohm antenna to 6V6 transmitter

September 21, 2009

The Pastime Projects 6V6 transmitter kit is based on a design that was first published around 1948.  Our kit followed the design shown in several ARRL publications, including the 1948 handbook . A reproduction of that article is included in each kit, with ARRL full written permission.

For many years I took a couple reproductions of this transmitter to Ohio and Indiana ham-fests. Many hams who were licences as novices in the 1950 and 1960 years, came up to my display and said “I remember when I was starting out I built one of those transmitters”.  Later, when Pastime Projects introduced the kit for sale,  we called it the “Remember When” transmitter kit.

One common thread among the hams who built this kit was a problem with second harmonic interference – as often reported back to the unlucky ham by the F.C.C. !  To prevent similar problems with our current kit, we researched and built harmonic filters which we sell. These are the latest and greatest design. Read more about them on our web site.  They do require point to point wiring on a perfboard.  And, you wind the toroid coils.  But not bad for the price.

The problem is you need a low impedance match from the transmitter to the coaxial coil to conveniently match the low pass and/or second harmonic filters.  We will discuss the methods of matching the 6V6 output link to a 50 or 75 ohm load.  If your antenna is a balanced line,  we will cover that conversion  from 50 ohms to 200 ohms a little later.

We are writing this up in our monthly e-mail newsletter. If you want a copy email us at pastimeprojects@yahoo.com.  Meanwhile watch here as we discuss the ongoing experiments we are conducting right now.  We are having good results with matching the link to a 50 ohm dummy load with little if any  reflected power….. in other words, low SWR. Stay tuned! 

73 Glenn NN8G 

Matching 50 ohm antenna to the 6V6 Xmtr

September 8, 2009
Pastime Projects 6V6 Transmitter Kit, Power Supply, and Key

Pastime Projects 6V6 Transmitter Kit, Power Supply, and Key

SEPTEMBER 7, 2009    A recent builder of our 6V6 transmitter reports the kit “works great” but is concerned about 2nd harmonics and attaching low pass filters. You see, he is using an inverted L fed with ladder line. While this a great match to his link coil on the 6V6 transmitter, this design is much like the original 1940 and 1950 configuration.  It caused 2nd harmonic interference back then, and still can. He wants to know how to best get some low pass filtering into the system. We will look at this ASAP and make some suggestions. These will  be published in a special edition e-newletter. If room, it will be republished here.  Whatever we say can be copied at your convenience. It is for public  information. Just understand I write from and to hams from a practical background. I am not a professional registered electronic engineer and my advice is worth every cent I will charge – absolutely free!  If you do run copies of my writings, would you please credit us and our company? (The manuals in our kits is an exception – they represent a lot of work, and we ask you to  buy the manuals from us rather than run copies)
If you want the copy of the article on matching antennas, just email me at pastimeprojects@yahoo.com and we will add  you to the list.  
 
Very Best Regards  Glenn Brown NN8G

September 4 update

September 5, 2009

We have replaced the photo on the ‘cover page’ of the web site – the one to the left of the receiver – with a short video of the receiver picking up CHU – Canada  – just below the 80 meter amateur band. Tonight’s signal has a little fade on it. Be sure to turn up the audio on your computer to hear the station.  Our antenna this evening was our 80/40 trap dipole fed with  75 ohm coaxial cable. However, we chose to use it as a straight wire. This required disconnecting the ground side of the cable with the clip provided and resetting the remaining clip on the link for best signal.  Sounds complicated, but it just takes a few minutes to learn. After all, you are always listening for the loudest and best signal.  Other activities here at Pastime Projects continues… More later… Enjoy this weather the days are getting shorter!  73 es bcnu!

Glenn NN8G