Hello,

I thought that I've seen this in print many times, but I cannot re-locate it!

Can someone please tell me what documents that I will need to present
to the VE's when taking the Extra exam?

I hope to take the exam tomorrow am :-)

73

--KC9KEP

Re: my earlier post “Help understanding single-signal reception via i.f. regeneration, please ..”, I believe that I have the circuit functioning now!

As per the 1941 ARRL handbook instructions, I aligned the i.f. strip by removing the antenna-tank and local oscillator plug-in coils.  Then, I insured that the BFO was OFF and applied a 455 kH (1-kHz AM modulated) test signal across the input tank capacitor.  Using a scope and monitoring the audio output from the (second) detector, it was a simple task to align the i.f. coils.  It required a few iterations to get them to fully peak.

Then I turned on the BFO.  I wanted the BFO to zero-beat with the applied 455 kHz in order to center the front panel BFO control at 12:00.  In this manner, I could rotate the BFO cw or ccw for a higher/lower BFO pitch than the i.f.  I could "see" the zero-beat on the scope with BFO turned "on" and the applied 455 kHz unmodulated.

Then, I put my antenna tank and local oscillator plug-in coils back into the set and connected the antenna.

I immediately noticed that the CW signal was much stronger on one side of zero-beat than the other.  As a matter of fact, the CW pitch became even louder as I tuned towards the zero-beat and located a sweet-spot where the CW/BFO tone seemed to resonate dramatically.

But, SSB signals had a problem:  The SSB signals were loudest on the “wrong-side-of-zero-beat” so I couldn’t “decode” them.

I don’t know what shifted, but I discovered that my BFO was no longer centered in its range with respect to the i.f.

An adjustment (by ear) of the BFO coil brought the front panel BFO control back to where I wanted it, no BFO beat at 12:00 and +/- pitch when turning the BFO control CW and CCW.

I could not actually measure the BFO frequency because any probe that I brought near the BFO output would pull the oscillator and detune it :-(

At any rate, this is pretty cool!  I’ve never operated or experienced such a set, so I was not certain what I was looking for ..  But, the Single-Signal effect does work quite well if one has the patience to dial it in carefully.

Copious thanks to all the help!

73

--KC9KEP

OK gentlemen,

Thank you for your expedient and thorough responses!

I did peak the i.f. transformers for 455 kHz.  Now, I'll take some measurements
to see where I've got the BFO set.  I had simply adjusted the BFO "by-ear" to
achive a "pleasing" CW tone, but I do not know exactly where it is.

(I am using the i.f. transformers (Millen 64456 64454) as sepcified by the Handbook.)

I'll see if I can locate the 1948 ARRL handbook to review their i.f. information too.

73!

--KC9KEP

Hello all,

I have added an "optional" i.f. regeneration component (C15) to my 1941 Single-Signal receiver.

http://www.bignick.net/images/RadioPix/7_tube/schematic_7_tube.jpg
http://www.bignick.net/Morgan_Radio/Radio_6.htm

It provides a degree of regeneration in the i.f. stage, sharpening response.

The handbook tells me to re-align the i.f. stage after the installation of the feedback capacitor (C15), which I did.  The i.f. peaking adjustment was much more touchy than it had been when aligning the i.f. without the feedback component.

Now, when I advance the r.f. gain, the audio will squeal if adjusted too high, which is expected because the i.f. stage breaks into oscillation.  The optimum r.f. gain setting is just prior to the i.f. stage breaking into oscillation according to the handbook.

The receiver sounds differently than it did without the feedback component, as expected.  The sharper i.f. has a narrower band pass and hence less background noise.

The whole idea of adding the i.f. regeneration is to allow the operator to be able to tune to a CW signal on just one side of zero-beat instead of on both sides, as is the common case.

The problem is that I still cannot seem to achieve the single-signal reception that the sharper i.f. tuning is supposed to provide.
For that matter, I cannot locate any theory of circuit operation that explains why this sharpened regenerative response will create single-signal reception.

Does anyone have experience with this circuit/methodology or could point me to a reference?
The ARRL handbook talks about phasing of crystal filters in the i.f. which makes sense, but I do not see why a sharp regenerative i.f. peak could provide single-signal reception?

Thanks!
KC9KEP

Thank you all for your replies!

Yes, to reiterate:

1.)  I am using a 3-prong AC line cord, the safety ground lead is connected to the chassis
2.)  I have added an AC line fuse
3.)  I have added a Triad N51-X isolation transformer
4.)  I have moved the DC blocking capacitor to a location prior to the output PI filter

The AC line still gets routed to the 117L7's filament, however, the chassis ground
connection and the plate of the rectifier are both sourced from the secondary of the
isolation transformer.

I made a successful QSO with this transmitter this past weekend on 7049 KHz. 
It was during the afternoon and "only" 104 miles away.
But I'm completely blown away!  Only 2 watts (less than a nightlight) and 104 miles!
(I was using an end-fed wire antenna, home brew antenna tuner and home brew tube receiver.)

Thank again guys,

-- KC9KEP

Hello all,

I'm building a simple one-tube (circa 1941) QRP rig.

(I've added an isolation xformer, fuse, & 3-wire AC line cord for safety.)

A link of the schematic is here:

http://www.bignick.net/temp/1941_QRP_rig.bmp

My question is about the PI filter in the output section.

For some reason, they have placed the DC blocking capacitor AFTER the PI filter.
This means that both tuning capacitors and the tapped inductor are all at the B+ voltage.
In most schematics that I've seen, the blocking capacitor is wired BEFORE the PI network,
(and an RF choke is usually wired from the output of the PI filter to ground.)

Can I move the DC blocking capacitor to a location BEFORE the PI filter without
affecting performance?

It would seem to me that the RF would pass thru the 0.001 uF DC blocking capacitor
an on to the filter, but I'm not sure.

For that matter, if I'd like to do some circuit analysis of the PI filter, what input
output impedances would I use for calculations?  I would assume that input impedance
would be the plate impedance of the tube, and the output impedance ideally 50 Ohms?

Thanks!

73

--KC9KEP

Hello,

The vacuum tube transmitter construction projects featured in the early ARRL handbooks frequently utilized a large primary/secondary coil type arrangement to couple the transmitter output to the antenna.

Then, somewhere in the late 50’s, the popular scheme seemed to change to the more “modern” PI filter for the output section, featuring a plate and load capacitor and a single coil.

I would guess that the PI filter may “tune” sharper and do a better job of filtering out any harmonics?  Also, the PI filter may provide better provisions for load matching?   And, the coil taps can be switched/shorted to accomodate different bands.  But, these are just guesses.

Does anyone know why the one scheme was dropped in favor of the other?

73!
--KC9KEP

Hello all,

I was putting together a presentation for the local Amateur Radio Club about homebrewing.
This clip is part of the presentation.

I hope it entertains!

Here it is:

http://www.youtube.com/watch?v=cfxrM74Tk4M

73!

--KC9KEP

Thank gentlemen .. very inneresting 

Hello all,

I bought a "new" (well, new to me) car recently.  (I think it's a 2006).

The FM radio displays short text messages indicating the call letters
of the station that your tuned to, such as WKLH.

It also displays the title and artist of the song currently being played.

It's not subscription or satellite radio (at least, I'm not subscribed to
any such thing :-)

Does anyone know how this is being done?  Sub-sonic carrier?
Parallel digital transmission?  Invisible carrier pigeons? :-)

Thanks!

--Tom Nickel  KC9KEP

Hello all,

Recently, I took a week of vacation time, naively thinking that building some
new shelving storage space would enable me to organize my lifetime's collection of parts
and books. 

Ha!  (or "HI HI" in ham lingo!)  What a total joke!  I think I may need professional
help, but that would likely translate into me buying more eBay/Amazon books about
how not to buy more books!

I actually have saved 1/2 Watt resistors that I had scavenged from old TV sets ..
when I was in the first grade!  (That was a long time ago!)

I guess that one of my biggest fears is to start home brewing a nifty rig just to find
out that I am missing the one essential ingredients that I grudgingly, just threw out
last week.  (Horrors!)

Maybe this eHam forum can offer advice about one hording arena; Databooks.

I have many books about 8-bit processors & programming .. I HAVE to save those!
(I loved the Z80 and Intel 8051!)

But, do you suppose that all the National, Burr-Brown, Analog Devices, Motorola TTL databooks
can all be found on line now?  Is there any point in keeping these?  (I've got boxes of 'em!)

I do see that people sell these on eBay.

Now I'm glad that I kept my Heathkit and Newark catalogs from way back :-)

Rambling ends here .. thanks all!

--Tom Nickel AKA KC9KEP

Thank you for your replies, gentlemen :-)

It all makes sense.  I can see what I'd be up against.

That's one of the reasons I love homebrewing .. One learns stuff!

73

--Tom Nickel AKA KC9KEP

Hello all,

A ways back, I built an ARRL "Three-Band One-Tube Novice Transmitter" (Dec 1957 QST)

A link to my project is here: http://www.bignick.net/Morgan_Radio/Radio_11.htm

I'd like to operate this unit on 20 meters.

The transmitter is specified to operate on 80, 40 and 15 meters.

Why do you suppose the author skipped past 20m and included frequencies above and below 20m?

Could I get a 40m crystal to resonate at 20m?  Would I need an additional tap to the PI network
in order to achive this resonance?

Thank you!

--KC9KEP AKA Tom Nickel

Hello all,

I finally got around to documenting this project that I had built
a ways back.

I hope this video link works.

http://www.youtube.com/watch?v=F_0DDkXPd60

The source is the Lindsay Radio Experimenter Volume 5.

I thought that someone may find it entertaining :-)

Thanks,

--Tom Nickel AKA Big Nick AKA KC9KEP

Karl,

I think you've received some good suggestions.

I've built this radio myself 

http://www.bignick.net/Morgan_Radio/Radio_4.htm

If you need to compare notes, let me know.

--Tom Nickel  KC9KEP