6647	2011-09-12 19:51:24	Jim Miller	Lambda diode and Transmitting Loop antennas
Message	Date	From	Subject
Just finished browsing the Sept/Oct 2011 QEX and the article on lambda diodes. One interesting issue of transmitting loop antennas is tuning them particularly when they are high Q. It occurred to me that temporarily switching a lambda diode onto a loop antenna feed might yield an oscillator that could be sensed to know its resonant frequency and observe it while tuning. The two terminal nature of the lambda diode might facilitate this. Of course it would be best if the oscillator formed was as low as possible in power. In practice you'd create the oscillator, observe via freq counter the resonant frequency while adjusting the capacitor, then remove the lambda diode/freq counter to return it to operational status. With no need for a tap it might be possible to do this at the transceiver end of a feedline. Feels like a breadboard coming. Jim ab3cv [Non-text portions of this message have been removed]
6648	2011-09-13 01:07:31	cbayona	Re: Lambda diode and Transmitting Loop antennas
At 09:51 PM 9/12/2011, you wrote: >Just finished browsing the Sept/Oct 2011 QEX and the article on lambda >diodes. > >One interesting issue of transmitting loop antennas is tuning them >particularly when they are high Q. It occurred to me that temporarily >switching a lambda diode onto a loop antenna feed might yield an oscillator >that could be sensed to know its resonant frequency and observe it while >tuning. The two terminal nature of the lambda diode might facilitate this. >Of course it would be best if the oscillator formed was as low as possible >in power. > >In practice you'd create the oscillator, observe via freq counter the >resonant frequency while adjusting the capacitor, then remove the lambda >diode/freq counter to return it to operational status. With no need for a >tap it might be possible to do this at the transceiver end of a feedline. >Feels like a breadboard coming. > > >Jim ab3cv Lambda diodes have been used to make a grid dip meter, I used one to make a regenerative AM radio a couple of years ago,very simple circuit. < http://users.tpg.com.au/users/ldbutler/NegResDipMeter.htm > I'm not so sure you can hook up the circuit at the end of the cable, the propagation delay would affect the resonant frequency of the oscillator. Cecil k5nwa < <http://www.softrockradio.org/>http://www.softrockradio.org/ > < http://thepartsplace.k5nwa.com/ > < http://parts.softrockradio.org/ > Never take life seriously. Nobody gets out alive anyway. [Non-text portions of this message have been removed]
6657	2011-09-14 06:42:25	Jim Miller	Re: Lambda diode and Transmitting Loop antennas
Cecil You're right of course. Thanks for reminding me about the phase delay. I think it wouldn't be hard to implement at the loop itself as an alternative. Just need a relay to add/remove it from the circuit. Control wires are needed anyway to service the tuning capacitor. Post your regen if you wouldn't mind. Thanks for the link. 73 Jim Lambda diodes have been used to make a grid dip meter, I used one to make a regenerative AM radio a couple of years ago,very simple circuit. < http://users.tpg.com.au/users/ldbutler/NegResDipMeter.htm > I'm not so sure you can hook up the circuit at the end of the cable, the propagation delay would affect the resonant frequency of the oscillator. Cecil k5nwa [Non-text portions of this message have been removed]
6658	2011-09-14 07:08:43	victor	Re: Lambda diode and Transmitting Loop antennas
Remember that such an oscillator will transmit its power (~10dBm - 10mW) on the air at the antenna resonant frequency. You might also suffer from injecti
6659	2011-09-14 07:30:41	Jim Miller	Re: Lambda diode and Transmitting Loop antennas
anything used to probe antenna resonant freq will transmit, including antenna analyzers. it can't be avoided. moderation always required. good point on the injection locking. Jim
6660	2011-09-14 12:02:31	cbayona	Re: Lambda diode and Transmitting Loop antennas
Nothing fancy, it was based on this article, see figure 8; < http://www.zen22142.zen.co.uk/Theory/neg_resistance/negres.htm > I used a 400uH Ferrite rod and a 270pF variable cap because that is what I had in stock. I tried a whole bunch of FETs that I had mostly in a dual FET configuration but the FET/Transistor combo worked well specially with a 2N5486 FET. As you can see from my old store page I bought a lot of FET devices and their complementary versions, I also tried a few other FETs that are not listed; < http://www.dspradio.org/catalog/28 > At 08:42 AM 9/14/2011, you wrote: >Cecil > >You're right of course. Thanks for reminding me about the phase delay. > >I think it wouldn't be hard to implement at the loop itself as an >alternative. Just need a relay to add/remove it from the circuit. Control >wires are needed anyway to service the tuning capacitor. > >Post your regen if you wouldn't mind. Thanks for the link. > >73 > >Jim > > > Lambda diodes have been used to make a grid dip meter, I used one to >make a regenerative AM radio a couple of years ago,very simple circuit. >< http://users.tpg.com.au/users/ldbutler/NegResDipMeter.htm > > >I'm not so sure you can hook up the circuit at the end of the cable, >the propagation delay would affect the resonant frequency of the oscillator. > >Cecil >k5nwa > > >[Non-text portions of this message have been removed] > > > >------------------------------------ > >Yahoo! Groups Links > > > Cecil k5nwa < www.softrockradio.org/ > < http://thepartsplace.k5nwa.com/ > < http://parts.softrockradio.org/ > Never take life seriously. Nobody gets out alive anyway. [Non-text portions of this message have been removed]
6661	2011-09-14 12:02:49	cbayona	Re: Lambda diode and Transmitting Loop antennas
If built properly the unit will have very low power in the low mW or even uW range so it would be less obtrusive than most other methods. At 09:30 AM 9/14/2011, you wrote: >anything used to probe antenna resonant freq will transmit, including >antenna analyzers. it can't be avoided. moderation always required. good >point on the injection locking. > >Jim > >
6687	2011-09-19 14:41:41	Kerry	Re: Lambda diode and Transmitting Loop antennas
VK6APH described a negative-resistance GDO some years ago; I can't find the article on the net so I have put it here; http://imageshack.us/photo/my-images/849/page1ui.jpg/ http://imageshack.us/photo/my-images/198/page2xi.jpg/ http://imageshack.us/photo/my-images/402/page3re.jpg/ http://imageshack.us/photo/my-images/707/page4sa.jpg/ This is my build of it; http://imageshack.us/photo/my-images/13/photozh.jpg/ http://imageshack.us/photo/my-images/585/photo1yn.jpg/ I found it difficult to use; it was very much influenced by things other than the antenna it was measuring and it was easily "pulled". This may be a problem in the proposed use but Jim's idea is certainly an ingenious one. Kerry VK2TIL.
6689	2011-09-19 17:48:19	Kerry	Re: Lambda diode and Transmitting Loop antennas
My mate Roderick VK3YC has pointed-out that VK6APH's GDO article is available on the N2PK VNA site; http://groups.yahoo.com/group/N2PK-VNA/files/VK6APH/ I had forgotten that I was even part of the discussion at the time :) ; http://groups.yahoo.com/group/N2PK-VNA/message/5207 Kerry VK2TIL.