KC9KEP's Superhet Receiver with HOMEBREW 455 kc IF Transformers

No store-bought 455 kc IF cans for Big Nick!  FB OM.  Great stuff.

We have featured Big Nick's beautiful work twice before:

http://soldersmoke.blogspot.com/search?q=kc9kep

More of his videos here:

https://www.youtube.com/user/KC9KEP/videos

Be sure to check out his coil winder.

Reduction Redux: Searching for Some Smooth Spin

OK, here is yet another picture of my Mighty Midget's Mate receiver, this time with yet another main tuning dial. I gave up on the large reduction drive on the right -- it worked fine but was very stiff.  I cracked open a smaller version of this very common Japanese-made reduction drive, but in this smaller one I was kind of surprised to find  a Jackson Brothers drive in there.   I now had three of these beauties available -- all of them worked fine but with considerable difference in ease of turning.  I picked the one that was easiest to turn.  

I had to cut the main shaft of the beautiful Hammarlund 35 pf variable cap that I am using. This was dangerous, because of the risk of messing up the delicate bearings.   I stayed out of trouble by putting the tip of the shaft in a vise and then cutting the shaft with a small coping saw.  This prevented any force from being transferred to the bearings.  It worked. 

I was careful to try to line up the shaft and the reduction drive as closely as I could. 

I needed something to serve as the tuning indicator.  I used one of those small CDs that often carry the drivers for cheap electronic devices.  It fit nicely.  A standard sized CD was too big. 

The final element was the knob itself.  I had an old Drake 2-B knob in my junk box (who sent me that?).  It was perfect and added a nice touch of soul to this old-new machine.

I built this receiver in 1998 and when I finished it I thought it was pretty good.  But it is much better now.  It has a nice 455 kc Toyo Crystal-Mechanical filter.  The tuning ranges on 40 and 75 now line up perfectly with the phone bands.  It now has a fuse in the power supply. And the tuning is now SMOOTH.

   

Always Listen to Pete! Second Thoughts on the S38-E

After working a bit on the Hallicrafters S38-E receiver, I am forced to admit that Pete was probably right about this receiver when he warned me that I'd be putting lipstick on a pig.  For those of you who have a sentimental attachment to this receiver, please don't take offense -- I understand.  But while I had one of these as a kid, I never really BONDED with it. That Drake 2B was stiff competition for my radio affection. So I can be more objective about this thing.  And I now think Pete was right. 

Problems: 

-- It is mechanically rickety.  It jiggles around mechanically and, as a result, electrically.

-- The front end is no match for Northern Virginia RFI.  All it has between the antenna and the converter tube is one puny LC circuit.  Not enough.

-- The LO mixer and the LO are stuffed into one 12BE6 tube.  The IF amp and the BFO cohabitate in another tube. In each case there  just seems to be too much going on between one plate and one cathode. 

-- The whole AC/DC transformer-less thing is kind of nuts. You have to get used to TWO ground symbols on the schematic: one symbolizes B- (and is not attached to the chassis).  The other is to chassis ground.  Turns out that my E model is not really a "widow maker" -- they have a 470K resistor and a cap between B- and chassis ground, so the damage you could do to yourself was quite limited.  Still, it is all kind of goofy.  I have an isolation transformer on the chassis, ready to move this receiver into the 1960s if the spirit ever moves me.  KB2WIG commented:  "At closing time, I don't care if the S38 has lipstick."  

As I worked on this thing, I began to realize that the little homebrew 6U8 receiver I have next to it on the bench is a much better receiver.  So I began to lose enthusiasm for putting lipstick on the S38-E.  At least for the moment.  I do like the cool 1950s place names on the S38-E's front panel:

Java
USSR
Vatican
Singapore
Edmonton (!)
Congo
Milan
Iceland
Angola
And of course, the CD (Civil Defense) frequencies. (For when you wanted to do some shortwave listening while ducking and covering. )

But for  now, me and the S38 are on a break. 

A Reduction Drive for the Mighty Midget's Mate Receiver

This morning I put a reduction drive onto the main tuning cap of my 6U8 Mate for the Mighty Midget receiver.  Before I had been directly turning the 35 pf variable cap.   The tuning rate was a bit too high for easy tuning of SSB stations.  This drive went in nicely and it does reduce the tuning rate considerably, but it feels a bit tight.   Is there anyway to loosen up one of these drives?

Meeting up with ARRL CEO Tom Gallagher, NY2RF

On April 12, Tom Gallagher NY2RF was in DC and was kind enough to make some time in his schedule for us to get together and talk about radio.  As we mentioned on a recent podcast, Tom, who has recently taken over as Chief Executive Officer of the American Radio Relay League, is a true FB ham.  He has a restored Drake station that he keeps on the air, and was recently talking up the Michigan Mighty Mite during his interview with Eric 4Z1UG in the "QSO Today" podcast.  And he is a SolderSmoke listener.  It was great to finally meet Tom.  We are all lucky to have him at the ARRL.

Pigs, Lipstick, and my old Hallicrafters S38 "Widow Maker"

I blame Grayson for this.  After getting my old 6U8 superhet running nicely on 80 and 40, my attention turned to an old Hallicrafters S38-E that had been relegated to the car port (Armand saw it out there, looking abandoned.)  I didn't like it because of its "transformer-less" "widow-maker" power supply. I was afraid to even GIVE it away for fear that someone would electrocute themselves.  But Antique Electronics Supply had an isolation transformer, so the order went in.

I have to rewind or replace one of the primaries on the input antenna coil.  This was a victim of the original cheapo power supply.  Apparently the antenna terminal got grounded when the chassis was "hot."  POOF -- smoke was released.    

The bands do seem to sound better through thermatrons... And there is an undeniable 3-D aspect to working on these old rigs.

So yes, in a certain sense  REAL RADIOS GLOW IN THE DARK.

.............

Bill, I think that as long as you don't work on it in the car port in your bare feet you'll be fine!  Good luck with it and don't blame Grayson too much.  I think it was destined to come back in the house eventually.  The radio gods have been whispering in your ear!
 Ciao! & 73, Armand

............

Bill:

I’ll take the blame, no problem!

S38 is nice to work on, plenty of room, no magnifying glass required.  But I have to admit I am not a big fan of working on low cost AC line powered “raft-anchors” (too little for a boat).  Definitely give it a isolation xformer and replace the filter cap(s).  If it doesn’t weight 50+lbs, a bit lightweight for me.

If you need a good thermatron homebrew project (and who doesn’t really), I’ll send you plans for a nice 4-thermatron (including compactron) AM/CW 20/40M 5 watt transmitter I am finishing up (90% of the work is “finishing up”).   Designed from scratch.  Actually works.  Uses a new construction technique I’ve been working on. 

Grayson

..........

Hi Bill,

As I read about your next project – kept thinking –you can put lipstick on a pig BUT it is still a pig. I had one and put an isolation transformer on the front end –but found I was showing signs of carpal tunnel syndrome on my left hand as I kept retuning the radio because it drifted so much. Have fun.

Pete

Pete:

I don't know.  Simplicity is a virtue, and this thing is pretty simple: RF amp, mixer, LC oscillator, detector, audio amps.  Broad as a barn door with just two 455 kc IF transformers for the filter. Lots of room on the chassis. 

As for drift, my little 6u8 RX with LC oscillators in both LO and BFO settles down very nicely. 

Bill

...............

Hi Bill,

 I surely didn’t mean to denigrate your next homebrew project and perhaps it was that the one I had was a  dud in the lot.

 But I then moved up to the SX-99 and was in tall clover. Besides today we have some things we can do to enable “tamer” oscillators. So why not? You need to team that up with the M^3 and make some contacts.

 Pete

.............

Pete: I KNEW  you would try to get a synthesizer of some sort inside the S38-E.  But I say NO!  I had a lot of fun getting the LC oscillators in my 6U8 rig to tune exactly where I wanted them to tune.  You know, play around with the cap in series with the main tuning cap to change the tuning rate (better than removing plates -- they are hard to put back on!).  Then changing the values of the L and C elements to get the thing to oscillate in the desired range.  Then wrap it all up with some Dymo tape on the 1/2 CD "tuning dial."   Sure, I know, that would have been a few keystrokes on the Arduino, but somehow this old way puts you closer to the physics, closer to the electrons. Take a look at the e-mail about Wooden Boats, VFOs and PTOs on yesterday's SS blog. 

The "widow maker" potential of the S38-E was apparently on the minds of the guys who designed the cabinet. The whole box and the front panel are all very carefully insulated from the chassis.  Plastic nuts!

Nice looking pig, by the way.  She may appear on the blog soon. 

73  Bill

Wooden Boats, VFOs and PTOs -- Recovering Lost Arts

Photo from radiomuseum,org

I couldn't resist posting another great message from Rick Campbell, KK7B.  This one was sent by Rick to the r2pro mailing list.  Rick mentions the Collins Permeability Tuned Oscillator.  More info on this magnificent bit of old tech can be found here:

http://www.radiomuseum.org/forum/design_excellence_the_collins_pto.html

Rick writes:

Great stuff here on different approaches to designing-building-experimenting with stable VFOs. Some of it is a mature art, and some really is a lost art--but that's good.  There's nothing quite so gratifying as recovering a lost art while taking advantage of modern tools and techniques, and perhaps exchanging ideas on some new-fangled communications medium.

If you ever want to see folks having a blast recovering a lost art, head to a wooden boat festival and watch the kids learning from old codgers who can do magic with a little bit of centuries old technology.  Just don't mistake it for reenactment--some of the new boats these kids are designing, rowing and sailing may include some venerable tools and techniques and give an aesthetic nod to classics, but they are lighter, easier on the environment, easier to transport, and much much faster than historic craft.

We can do the same with our radios.  Spend as much time designing and building your VFO as I spent designing the small sailing rig for my little boat--or convert an old Collins PTO to solid state.  For highest performance use a mix of old and new--I use hand stitched 1968 sails from the Schatteaur Loft in Seattle on my bigger old boat.  Old radios are a treasure trove of parts and technology, and since 1959 well-designed HF gear has been stable enough for SSB.

I measured one of my converted old Collins 2.5 to 3.5 MHz PTOs at 18 Hz per hour drift.  It was originally built in the mid 1950s.  Some problems were solved long ago, and the techniques and solutions hold up well over time.

As with the kids studying old wooden boat techniques and then taking their new creations out on the Salish sea, it is well worth our time and effort to spend some time studying how our forbears constructed a good VFO a half century ago.  It's not just the schematic: the construction, materials, temperature coefficients...all are important, and the quickest way to come up to speed is to study old stuff that works well.

Good stuff, and have fun with the experiments.

Best Regards,

Rick

K.P.S. Kang's Pixer Superhet

K.P.S. Kang (VU2KR and VU2OWF) has been contributing ideas and circuits for many years from his QTH in Punjab India.  He is the source of what became known as the VU Transmitter circuit:
http://www.zerobeat.net/g3ycc/week1.htm

Today I spotted a recent blog post by OM K.P.S. on a simple superhet receiver he is working on.  He has a knack for describing the design considerations (needed gain, IF selection, etc.)
Check it out:

http://smallwonderqrp.blogspot.com/2016/04/pixer-empirical-hf-superhet-receiver-i.html

and

https://plus.google.com/111066147552844651495/posts

WSPR Party Balloons Make it Across the Pond

		Hans Summers April 15 at 11:25am
VE3KCL/QRP Labs S-9 balloon finally reached Europe! What a crazy way to cross the Atlantic. Crossed Portugal, now into Spain. France is next! 16mW 30m WSPR signal was reported in ZL and VK (19,000km DX). Who says you need 5W on HF WSPR? 73 Hans G0UPL http://qrp-labs.com

My Kind of Math! The Wooden Fourier Transform Machine

fourier analiser from Gymnasiumnovum on Vimeo.

Mixer math with plywood and gears.

http://www.instructables.com/id/Plywood-Math-Machine/

http://hackaday.com/2016/04/11/fourier-machine-mimics-michelson-original-in-plywood/#more-199177

http://hackaday.com/2014/11/18/harmonic-analyzer-mechanical-fourier-computer/

VE3KCL Balloon makes "several loops around Greenland"

Oh, I really want to do this.  We had a bunch of balloons for my daughter's birthday and I found myself trying to guestimate how much they could lift.  There is a balloon store that sells the metalized party balloons used here.  They have a helium tank.   I hate to be a party pooper (!) but wouldn't the antenna represent a bit of a hazard?  If it came down in power lines, that wouldn't be good right?
In any case, three cheers for Dave VE3KCL and for Hans, G0UPL, the wizard who makes the QRSS/WSPR transmitter that is currently flying over Iceland.  

Hi all

Some of you must have seen this already - but the rest of you may find it interesting. Dave VE3KCL launched his S-9 balloon 4 days ago (2 standard party-balloons, hydrogen-filled) with modified QRP Labs Ultimate3S QRSS/WSPR transmitter onboard.

We are using WSPR messages for tracking - one normal WSPR message and one with a special data protocol to provide altitude, speed, Maidenhead 5/6th characters, battery voltage, temperature and GPS/satellite status. The transmitter has about 16mW power output, on 30m band. It is sending CW and JT9 as well. Altitude is a little over 10,000m. So far it has traveled in several loops around Greenland and the North Atlantic. Currently it is near the Faroe islands. See live tracking at QRP Labs website http://qrp-labs.com/ultimate3/ve3kcl-balloons/ve3kcl-s9.html

G-landers, don't get too excited that it appears to be heading your way - the wind prediction shows it likely to head back West almost as far as Newfoundland, before turning back East towards Spain!

73 Hans G0UPL

http://qrp-labs.com

http://hanssummers.com

Some Thoughts on Noise and Receiver RF amplifiers from Scotland (and listening to sun noise on 2 meters!)

Bill,

Just listened to the latest SolderSmoke podcast where you asked why is it that an RF amplifier may be required on the higher bands but not on 40m and 80m for example.

At high frequencies the atmospheric and ionospheric noise levels are lower, so if noise figure of the receiver is reduced it will improve the signal to noise ratio you get from the receiver.  Adding gain -after- the mixer will not improve the noise figure of the receiver as it will be limited by the noise figure of the mixer. You need an RF amplifier which will itself have a lower noise figure than a mixer (certainly a passive mixer), to lower the total noise figure of the receiver to take advantage of the lower effective antenna noise temperature at higher frequencies.

This becomes very important at VHF and above, where antenna noise levels are much lower than at HF.

So, it isn't so much the overall gain of the receiver that is important with weak signal work, but the overall receiver noise figure which is determined to the largest degree by the first stage of the receiver.

There are spreadsheets available that will easily calculate the noise figure of cascaded receiver stages knowing the individual stage gains and noise figures.

One also has to be careful with the gain distribution throughout a receiver, if you have too much gain early on in an effort to improve the noise figure overall, you may overload the subsequent stages producing IMD with multiple strong signals. So there is a compromise to be met between noise figure and strong signal performance.

Going back to VHF and above if you have an antenna fed by coax with some appreciable loss then improving the receiver RF stage noise figure is not the best way to go because you are amplifying the signal after the loss the of the coax. What you need to do in those circumstances is to use a low noise masthead RF preamplifier which will give you gain and establish the noise figure of the receiver before the loss of the coax. Again there are spreadsheets to help with these calculations.

At VHF where an antenna is pointed at the horizon, the antenna sees the noise from the ground on the noise from the sky. As we elevate an antenna for EME or satellite working, then the effect of the ground noise should reduce (there will always be some due to side lobes) and then the receiver can benefit from even lower noise figure as the effective antenna noise temperature is now mostly determined by sky noise which at UHF is much lower than ground noise.

These last two days I have been able to see and hear the sun noise on my 2m receiver as the sun  set on my single 10 element yagi pointed at the horizon. Using WSJT's noise level scale I could see it  measure 12dB noise level and then once the sun set it dropped back to about 3dB noise indicated, most of that being local QRN from an antenna  sidelobe from my neighbour's house and his electronic devices which put out quite a bit of wideband noise on the band. (about 8dB above the lowest background level  I can normally detect).

To summarise, at LF where noise is high you don't gain anything by having a low noise figure receiver, and you actually lose out if you have too much gain early on as it will degrade strong signal handling.

At HF as manmade, atmospheric and galactic noise levels are lower, you can benefit from lower receiver noise figure and the way to lower your noise figure is to use lower noise amplifiers in the early stages of the receiver. Adding gain in later stages does not reduce the noise figure overall as the noise figure is largely determined by the first stage or stages.

At VHF using even lower noise figure devices in the RF stage will improve signal to noise.

Here is a practical test you can carry out. Switch between a dummy load and your antenna. If the background noise level increases when you switch to the antenna, then your receiver is sensitive enough, lower noise figure in the receiver isn't going to help.  If it doesn't increase then you have scope for improving the sensitivity of the receiver by reducing the noise figure of the receiver as you are no longer limited by antenna noise. 

Incidentally it is good to have a preamplifier that can be switched in an out of circuit so that you can reduce the noise figure when conditions allow ( low noise atmospheric noise levels for example), but switch it out if noise levels are high and signals are strong so that receiver overload and IMD don't occur. You can do something similar with an input attenuator to reduce strong signals where necessary.

I don't have a link here to the graph of manmade, atmospheric and cosmic noise levels versus frequency, but once you see one it becomes obvious why low noise figure receivers are not required at LF and MF generally.

73 from David GM4JJJ

Bill,

I found the article with graph of noise v frequency at last, in Ham Radio Magazine 1975!

A good read and as valid today as then.

http://www.r-390a.net/Receiver-Specifications-Explaned.pdf

I don't have a link here to the graph of manmade, atmospheric and cosmic noise levels versus frequency, but once you see one it becomes obvious why low noise figure receivers are not required at LF and MF generally.

73 from David GM4JJJ