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Author Topic: Designing & Building a High-Peformance Subminiature-Tube Regenerative Receiver  (Read 177115 times)
KB1WSY
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Posts: 1309




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« Reply #255 on: April 15, 2016, 02:50:28 PM »

...use a much larger loopstick antenna.

Makes sense. If this is an absolute constraint ... then the "shirt-pocket" format only works in areas with very strong AM stations. This radio works great here in Boston, and it worked well in Manhattan when I was there a few weeks ago. ("1010 WINS-News, The News Never Stops" and about a half dozen other stations.)

Your basic problem is finite gain and an antenna that's very very small for that wavelength.  For example for 1mhz that's 300M band and for 162khz its about 1850M.  So electrically that antenna went from minute to microscopic.

I may muck around a bit more with the ferrite antenna: winding my own Litz coil instead of using the commercial component I have been using. Perhaps trying to squeeze a larger-diameter ferrite rod into the case. But you are right, this is probably just tilting at windmills. The upside is that my tiny two-tube radio actually works in Boston and New York!

The next step is to learn how to use PCB-layout software (probably Eagle) and build a "production" version of this radio, rather than the crude perfboard prototype I have now. I don't really care about its very low sensitivity, I'm just excited that I was able to build a 2-tube radio that actually works and fits into such a small format.

From there, to building a shirt-pocket 40-meter CW receiver, will be easy -- although in that case I will be assuming usage of an external antenna such as a straightforward dipole.

Allison: great to hear from you. One of these days I will actually get on the air. Meanwhile I'm having fun with these rather limited experiments.

73 de Martin, KB1WSY
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KB1GMX
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« Reply #256 on: April 16, 2016, 05:14:46 PM »

one of the things that can hurt regen gain is LC ratio.  When you went to VLF you upped the C
and didn't increase the L.  Hence my earlier comment you need a bigger loop.  More turns
alone may help, but more ferrite and a higher mu ferrite could both help.  Your test signals
can be NDB (non directional beacons) still in operation in the region and generally low power
and in the 200-400khz range.

Allison
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KB1WSY
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Posts: 1309




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« Reply #257 on: April 17, 2016, 09:57:41 AM »

one of the things that can hurt regen gain is LC ratio.  When you went to VLF you upped the C and didn't increase the L.  Hence my earlier comment you need a bigger loop.  More turns alone may help, but more ferrite and a higher mu ferrite could both help.

Good point. Even on Medium Wave (530KHz-1710KHz) I had lowered the L somewhat because the small variable capacitor didn't have a low enough minimum C to bring in the top of the band (and in fact it still tops out at around 1400KHz). Another noticeable factor is that the set seems to be much more sensitive at the top end of the band than at the bottom; at least that is how it appears when tested with my signal generator, and from the fact that the bottom of the band is "dead" even though I know there are stations there.

Today I researched the stations that come in strongly on this radio, from my location in Chestnut Hill, MA. The strongest is WXKS (Bloomberg radio, 1200KHz) which broadcasts at the legal limit of 50KW and turns out to be only a few miles from my home. The second-strongest is WRCA (1330KHz) which is also very close to my QTH and pumps out 25KW. When I was in New York City earlier this month, I got very good reception of "1010 WINS, the newswatch never stops" which transmits from near the Meadowlands at 50KW.

(For VLF) ...Your test signals can be NDB (non directional beacons) still in operation in the region and generally low power and in the 200-400khz range.
Allison

Good idea. For Long-Wave (153–279KHz) I should probably switch in an extra winding on the ferrite. I also need to figure out some tricks to get higher L on the ferrite. The store-bought Litz coil on my existing ferrite uses a trick that seems to double the L for a given coil length, apparently by using a twisted pair. But I have read that it is not a good idea to use a multilayer coil on a ferrite antenna. Anyway I will experiment both with the size of the ferrite and the quality/mu of the ferrite. The length is already maxed out; I might be able to squeeze in a larger diameter but only by shrinking the component space, which would require a carefully designed new PCB.

As I said, there is a sharp dropoff in sensitivity even at the bottom end of the MW/AM band, so it's not surprising that LW reception was dead in Europe.

Edited to add: if anything, this experience has encouraged me to try building a small superhet, although getting it into the same "cigarette packet" form factor with subminiature tubes is going to be tough -- it will probably requie using up some of the battery compartment (there is a small amount of free space above the batteries, so I could raise them onto a shelf and put components underneath).

OTOH, I am not sure that a superhet would have greater sensitivity....

73 de Martin, KB1WSY
« Last Edit: April 17, 2016, 10:02:32 AM by KB1WSY » Logged
KB1GMX
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« Reply #258 on: April 17, 2016, 10:50:21 AM »

Do a hybrid.  Down converter to a regen IF at ~300-400khz using one tube
maybe two for gain.  The big issue is still antenna.  A longer case can allow a
longer loop and better capture.

The problem with multilayer coils is self resonance.  If it falls net the desire
range its a Q killer and leads to reduced performance.  A longer coil with
taps would be better but only to a point (self resonance again).

Allison
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KB1WSY
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Posts: 1309




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« Reply #259 on: April 17, 2016, 11:53:26 AM »

Do a hybrid.  Down converter to a regen IF at ~300-400khz using one tube
maybe two for gain.  The big issue is still antenna.  A longer case can allow a
longer loop and better capture.

That sounds worth a try. Another possibility is this 3-tube reflex superhet (which admittedly uses a semiconductor diode as the detector). A Japanese gentleman posted his circuit on the internet and said it could be "used freely" so I am posting it here:



This design uses relatively high-power (and relatively high B+) levels for a subminiature tube because he used 5678 tubes, apparently because that's what he had on hand. It should work with lower-power/lower-voltage tubes also, I assume.

He has several other designs for tiny radios using subminiature tubes (click on the English-language links for more details):

http://www.hi-ho.ne.jp/ux-45/index.htm

73 de Martin, KB1WSY
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WA2ISE
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« Reply #260 on: April 24, 2016, 03:53:50 PM »

I did a superhet AM radio using sub mini tubes

Details at my page http://pw2.netcom.com/~wa2ise/radios/AA5submini.html
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KB1WSY
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Posts: 1309




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« Reply #261 on: April 26, 2016, 03:23:54 PM »

I did a superhet AM radio using sub mini tubes

Thanks! That is cool ... I am going to be experimenting with various options.

Space is a major issue. The "shirt-pocket" Hammond box I am using makes it hard to use more than 2 tubes and (probably more importantly) greatly limits the size of the ferrite antenna. I have purchased some somewhat larger Hammond boxes (still in the "shirt-pocket" category but larger) which will allow more tubes and a larger antenna.

73 de Martin, KB1WSY
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KB1WSY
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Posts: 1309




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« Reply #262 on: April 26, 2016, 03:46:21 PM »

Yet another topic to add to this thread. Those among you who have visited broadcast AM recently may have found that it is a bit of a desert island, in terms of what is nowadays called "content." So within my household, I have rigged up a 60-year-old Eico 315 RF signal generator and modulated it, on the AM/MW radio band, with signals from Internet radio stations. This enables me to listen, on AM/MW radio, to any station that streams on the Internet -- by rigging the audio output of a PC to the Eico signal generator. My current favorite is London-based "Classic FM" (classical music) but my musical tastes are eclectic!

The downside is that the Eico 315's output is very low. To get "reception" on my shirt-pocket radio, I have to run a wire from the 315 to an inductive link on the shirt-pocket radio (a few coils of wire around the shirt-pocket radio).

So I would like to build a hollow-state "FCC Part 15" radio transmitter (https://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf). These are very-low-power, un-licensed, transmitters for very local use. Seems pretty straightforward to me. It just needs to be a bit higher powered than my Eico signal generator, and have the best possible audio quality in its AM modulator. I think this would make it possible to listen to any of these "streamed" stations anywhere in the house, using my hollow-state shirt-pocket radio.

Eons ago there was the Knighkit modulator but I want to do better: the best possible audio quality in an FCC Part 15 AM/BC transmitter (but hollow-state). Does not have to be with subminiature tubes!

Suggestions?

73 de Martin, KB1WSY
« Last Edit: April 26, 2016, 03:53:38 PM by KB1WSY » Logged
WA2ISE
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« Reply #263 on: April 27, 2016, 11:06:50 AM »

For micro-AM-transmitting, I've built small transmitters to provide listenable material for my AM radios.  http://www.wa2ise.com/radios/amxmit.html


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KB1WSY
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Posts: 1309




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« Reply #264 on: May 03, 2016, 11:51:23 AM »

For micro-AM-transmitting, I've built small transmitters to provide listenable material for my AM radios. 

Thanks Robert, that's useful. Lots of fun stuff on your website....

73 de Martin, KB1WSY
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THOMASHA
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« Reply #265 on: April 22, 2017, 03:39:37 AM »

Hi,
nice thread, I'm a little late here, but I built some amplifiers with subminiature tubes too, but always used bulkier transformers for the OT.

May I ask where did you found that tiny one? And is it around 20k? 

I'm trying to build a portable radio using some russian subminiatures and a 5672 tube but can't find a small OT for it.

There is some material in a japanese site, where they adapt a sansui 50k audio transformer, but I think that this kind of transformer is only available in japan, since I couldn't find an equivalent. Please correct me if I'm wrong.

as for the radio I'm building, I'm starting from this design from a German website>


Thank you!

Thomas


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KB1GMX
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« Reply #266 on: April 22, 2017, 12:02:49 PM »

There are some great ideas there....

My favorite is the Mountaineer a tube battery transceiver but the receiver alone could be easily done.

See QST September 1950 page 17.
I have a electronic copy but see ARRL website if you are member and look it up.

The basic radio was 1R5 convert from 80m to about 500khz, 1T4 regen detector, 1T4 audio.
The if was tuneable and the converter was crystal controlled in the article.  I made the
converter tunable and the If fixed and it was equally good and the regen was easily
set an forget for most of the battery life.

You can substitute 1AD5 for the 1t4 easily.  you might do a self oscillating converter
with 1AD4 as well.  With three of those the heater current at 1.5V is about 300ma
for three 1ad4s compared to 150ma at 1.5V for 1r5/1t4/1t4 mix.  The difference is size.

The Gachapon design a few postings back can have a regen IF as detector and be even
more selective though for AM BC high selectivity is not needed. The Same japnese
fellow did several others worth looking at too.

The wa2ISE pages are good fun too and have some neat ideas that worked well
when I tried them on a oddball am chassis.


Allison
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KB1WSY
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Posts: 1309




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« Reply #267 on: April 22, 2017, 05:08:44 PM »

May I ask where did you found that tiny one? And is it around 20k?

I believe it was a Hammond 144S. Yes, it is a 20K primary (there is also a 10K model, the 144Q). Power rating 50mW. About $20 from Mouser. The relatively high price is probably because these are aimed mainly at audiophiles. There is a data sheet here: http://www.mouser.com/ds/2/177/5c0045-46-77704.pdf.

73 de Martin, KB1WSY
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THOMASHA
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« Reply #268 on: April 23, 2017, 01:48:01 AM »

Thanks!

never saw these small hammond transformers, I was looking at the TM42 and TL42 series all the time.
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