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Thursday, December 8, 2016

WW2 Paraset Spy Radio... Part 2

Construction of the radio has begun.  The front panel- made from a layer of .040" PCB material sandwiched with a layer of .040 aluminum- left over from the small camping trailer I built.  These materials were chosen because they were on hand... as well as- I didn't think the trailer aluminium was thick enough to be sturdy enough by itself- and the copper PCB allows for dead-bug and/or Manhattan component installation.  Holes were drilled per one of the many scale drawings found on the web. 

Sandwich of PCB, Aluminum sheeting and drilling guide.  The front panel is cut to be 1/4" wider on each side to provide a lip for the chassis to fit in its wooden box.
Aluminum front with many components installed.  [The annotation is 'photo-shopped'- not actually stenciled on the panel.  Note error:  RX Band switch should read 'TX' Band switch. ] 

Some components shown from the back.  

All holes drilled with .013" drill bit for #4 screws.  Holes for capacitors and other devices with a shaft were enlarged with a step bit.  The tube socket holes were drilled with a 1-1/8" hole saw.  

The two major challenges for me to create the Paraset replica like I have in mind are: 

1. The National model 10009 Tuning Dial with 'pinch wheel' gear reduction tuning for the receiver.  Some builders don't bother with the pinch wheel mechanism- instead they install a small variable tuning capacitor in place of the pinch wheel shaft.  The large tuning knob is course tuning; the small knob provides vernier tuning.  This method is a good disguise and probably functions quite well.  

2. The built in Telegraph Key.  

A very nice replica shows the tuning dial I desire to have on my set.  Underneath of the large tuning knob is a brass wheel almost the same size as the knob skirt.  The small tuning knobs pinch wheel mates with the large wheel which creates an approx 3.33 to 1 ratio.

1. No pinch wheel dials were found scouring the web and radio club builders didn't have exactly what I was hoping for.  I found that some builders had built their own dials.  So I set out to do same- with some help.   .026" brass sheet (for hobby use) was obtained from Amazon.  pQRPer- PJ N7PXY generously offered to fabricate the brass wheels for the tuning dial in his metal working shop.

Here we are in PJs shop.  The brass disk was cut using a 3" hole saw.  The mandrel in the chuck is a 1/4" bolt.  The disk was cut down to 2.5" to fit behind the 2.75" tuning knob skirt.  

The drawing called for .75" wheels with .15" center hole.  The small wheels were cut using a smaller hole saw and sanded smooth.  The end result size was .79".  Close enough.

Back in my workshop... the large brass wheel was drilled to attach to the large tuning knob skirt- using the same screws that hold it to the bakelite knob.  The small pinch wheels were assembled to their shaft and inserted into its bushing through the chassis.  

Curses!! It did not work. Somehow the bushing or capacitor hole is in the wrong place by 1/8".  The pinch wheels were just touching the large wheel- but not over lapping it.  Recovery was accomplished by making new pinch wheels using the next larger hole saw size.  It's a good thing that the pinch wheels do not need to be precisely round- as there's no metal lathe here.

The larger sized pinch wheels [ .97" dia and no spacer between them] hug the larger brass wheel with about 1/16 inch of meshing surface.   The pinch wheel shaft is 1/4" diameter aluminium stand-off material with 6-32 threads.  The shaft bushing is from an old junk box bakelite bodied 5 watt potentiometer that was easy to harvest with a few hammer blows.     

 2.  The Telegraph Key- As a CW straight key user... I am hoping for a key with a firm feel- not flimsy that feels like it is about to fall apart or a key that goes click-clack when the knob is pushed down.  It's noted that some builders have adapted industrial electrical switches and others used PCB material to create their key.   

On line info reveals that there were two styles of keys used in the original sets-

Paxolin version key was included in the wooden box radio sets- which were built first.  The metal "Cash Box" sets had the plastic body key.  

The plastic key was attempted- but using hard maple in lieu of lexan or plexiglass.  But the key body parts couldn't be cut precisely enough without putting my fingers in danger.  A cutting jig assembly needs to be built.  The Paxolin version was attempted. [Paxolin is an electrical insulating material with sandwiches of plastic and paper molded into sheets- sorta like PCB but no copper face].  Since the diagram came with a scale in MM- the drawing was imported into a CAD app, enlarged to scale, and printed to be a cutting guide.  The keys parts were cut from PCB material with a diamond wheel in a Dremmel tool.  

Ver 1 prototype of Paxolin design PCB key.  The spring/lever is .040" thick and .5" wide.   It feels sorta flimsey.  I am toying around with using a metal lever- but harvested from what?  Hacksaw blade with brass screw contacts? 

Whilst looking for a toggle switch... This switch was discovered.  Perhaps the lever with contacts can be harvested and melded into the PCB Paxolin key.

Some useful Paraset links that are inspiring to me:

End of Part 2.  Thanks for reading this far.  For Blog entry Part 3- I hope to have either the RX or TX working.  QHH es 73 DE KR7W CL

Sunday, November 27, 2016

November QRP-Tech Challenge Build - WW2 Paraset Spy Radio - Part 1

This nice Paraset replica built by Dan W7OIL.  Check out Dan's Website here:

Chuck K7QO, the spark plug of the QRP-Tech Yahoo Group challenged the members to build some kind of QRP project during the month of November.  This challenge became the stimulation to get my Paraset build started.  My goal is to have my Paraset working and presentable for the Radio Club of Tacoma's Straight Key Night Celebration (Dec 31, 2016) and hopefully make  QSOs with it.  

To build and operate a Paraset has been on/in my bucket list for about 5 years now.  At the 2015 pQRP's Salmoncon... member Steve WG0AT brought his Paraset that he was gifted from Paul W0RW.  Looking and touching Steve's little radio motivated me to start collecting parts for my someday build.  

A BOLO to fellow Radio Club of Tacoma members who are home builder hams (one who has previously built his own Paraset)... was initiated to obtain the parts I was missing.  Hat tips to Jack's Corner Parts Store and Bob's Surplus... Still missing is the National 10009 friction drive receiver tuning dial mechanism...  Construction has begun anyway.  

The first order of business is to build the AC Mains Power Supply.  Years ago I obtained from the "Free Table" at the radio club- a defunct CB power supply which is about the same size as the original Paraset AC Mains supply. This power supply was loosely engineered and built to fit inside of this metal box.

Reading the blogs of other Paraset builders reveals that their PS HV (also called HT in old documents) output ranged from 300 to 370 DC volts.  Found in my box of 'heavy iron' was a suitable (to the voltage requirement and to the enclosure) HV power transformer.  No volts will be wasted using a vacuum tube rectifier and there will be way less heat inside of the PS enclosure with a full wave solid state rectifier using 1N4007 diodes.   

The next PS puzzler was HV filtration.  Choke Input?  Capacitor Input?  Minimum HV voltage swing in the XMT mode when the key is up vs key down is the goal.  Too big of swing creates a a poor sounding chirpy note from the Paraset's 6V6 transmitter. [note 1:  some distinguishing chirp is OK in my book.  Note 2:   4 to 5 watts output is expected; bordering on the upper edge of QRP].

Ha!  What a mess.  Prototyping the HV PS.  I did shock myself by picking up a charged up Electrolytic cap by the leads.  

Goldilocks and 3 Bears method of PS testing:  Using Capacitor Input HV filtering resulted in too high output voltage (over 420V).  Choke input lowered the voltage down to 330V.  Both methods resulted in a 80 to 95 output volts swing from Key Up DC load of 15mA  vs  Key Down load of 60mA.

Many Pre WW2 entertainment radios that I've restored placed the power supply filter choke (the speaker magnet field coil) in series with the transformers secondary (HV) center tap winding.  This method is rarely mentioned in old ARRL or Jones radio handbooks and provided no techy pros or cons for doing this.   Experimenting proved this method to be best for key up vs key down voltage regulation.  Now KU vs KD swing is around 20 volts but the output voltage is 300 V instead of the 350 V originally hoped for.  Now XMTR output watts will be more QRP.  Baby Bear again wins.  

Cocktail Napkin Final PS Design

The RCVR in the Paraset is a "2 Tube Blooper" regenerative receiver.  (more on this down in a future blog entry).   To prevent 'tunable hum' in the Regen receiver- the filaments are powered by DC volts.  The 5 V and 6 V filament transformer windings are connected in series to a bridge rectifier then fed to a switching buck-boost Voltage Regulator module:   Measured VR watts IN vs watts OUT reveals 80% efficiency using a 5.6 ohm resistor = 1 amp load to emulate the Parset's 3 tubes.  Also no noticeable heat present.  5 of these VRs came from Amazon for $9.  See spec:  The VR module cleaned up the output voltage measurable AC ripple voltage to 2 mV.

For the more Geeky:  Inside of PS... Copper clad Printed Ckt Board is used as a ground plane substrate.  There's some Manhattan and Dead Bug this build.
Upper L white gizmo is a 6V incandescent light to indicate the DC filament voltage is available.  Round blue gizmos are SAFETY CAPS from AC line to GND.  [I recently learned that these are useful to bypass RFI to GND that might be generated within the PS circuitry.  Also to bypass unwanted interference the AC power cord might be receiving plugged into house wiring.]

Upper R KOOLOHM device is the HV Bleeder Resistor- which consumes 11mA @ 300 VDC to somewhat stabilize key up vs key down voltage swing.

 Front panel view:

The NE-2 bulb indicates High Volts above 80V or so.  

Thanks for reading this far.  

End of Part 1 of Paraset Spy Radio Build.  73 DE KR7W CL

I began prototyping the Paraset two tube Blooper Regen Receiver per the schematics found on line... and it didn't work very well- which has been my experience with other vacuum tube regens I have attempted to build.  I consulted with the ham club member who has built many regen receivers and I walked away thinking that I do not know what to look for to know if the RCVR is working or not.  Further investigating was needed.

Googling took me to an in depth article about the Design of Regen Receivers from Nov/Dec 1998 QEX magazine by Charles Kitchin N1TEV.   Since the Paraset uses the same tuning caps and coils as the receivers showcased in Mr Kitchin's article and I had the solid state parts on hand... I'm in progress to build a receiver that I could be more successful getting to work.  When I am satisfied that 'I get it'... then I'll substitute the 6SK7 vac tubes + 300 VDC for  6 volt 2N2222s and J310 FETs.  

Rich KR7W

Saturday, January 16, 2016

2 Meter ARDF Attenuator Project- project build notes

Prologue:  When I was a 12 YO kid, just getting into ham radio- the old guy hams who smoked cigars would take me along in their sedans to turn the broom handle with the loop antenna on it- outside the window.  The loop antenna was connected to a Heath Twoer- 2 meter AM transmitter/receiver. How they could determine which direction to go from there is still a mystery.

The Hidden transmitter- another Twoer or 2M Gonset Gooney Bird was located in another sedan parked in an alley or someone's driveway.  The Hider, Fox, or Bunny would transmit for a while to taunt the hunters to find him- then the hunters would rotate their broomstick loops to determine a direction to drive towards. I have fond memories of tagging along with the old guys to find the elusive Bunny in the '49 Chevy in the alley behind the Jones' house.  Now I am that old ham- but no cigars.  

Heathkit Twoer- AKA "Benton Harbor Lunchbox" 2M AM Transmitter-Receiver.  Circa 1960.  

Now-a-days, it's 2 Meter FM Hidden transmitter hunting, AKA Hidden T Hunting or Fox Hunting or Bunny Hunting.  For effective hunting- an  attenuator is needed between the Directional Antenna and the Hunters receiver.  Beginners as well as thrifty advanced hunters use a Tape Measure Yagi Antenna, an attenuator of some kind that is connected to a good Handy Talkie.  

Simplified schematic of ARDF Attenuator.
Factoid:  S meters on most HTs  operate at full scale while receiving a pretty low level, like -100 dBM.  With some exception, when looking for 2M hidden transmitters- the hunter's radio can not discern any difference in receive signal level when the hunter rotates their Yagi- unless the transmitter is really far away.  The exception is that sometimes direction can be discerned by listening to the receive audio.  The direction of the most clear/noise free audio just might be the direction to head.  Note:  It is important for me to say that Baeofeng HTs are not suitable for hidden T hunting using an Offset Attenuator.  Use a better quality HT with a selective front end in the receiver.

S-meter bar graph shows full scale at -101 DBm- a very low level.
Two popular ARDF attenuators are Resistive with switches to switch in various levels of loss and the Active Attenuator which contains electronics.  This blog addresses the  Active Offset Attenuator.

Example of Resistive Step Attenuator.  Switch in dB increments of loss between the antenna and receiver.

 ARDF Offset Attenuator 

The OA  reduces the received level of the hidden transmitters signal so the S-Meter on the hunter's HT will show a High as well as a Low reading when rotating the Yagi.  It does this (see schematic below) by controlling the amount of level that passes from the ANT to the RECVR via the diode mixer by varying the level of the MPF102 XTAL Oscillator signal into the mixer via the 1K pot.    

A huge benefit of the OA is that the hunter can quickly and easily reduce the signal level that the hunters HT is receiving with a simple level control- sort of like a volume control- before the transmitter times out and goes quite for its programmed interval.  Of course, there's trade offs.  One is that the OA offsets the receive frequency by plus or minus the Local Oscillator frequency.  The OAs that I build use a 4.0 MHz LO which sometimes can be a problem if the hunter does not remember to 'do the math' and offset their HTs input frequency + or - 4 MHz of the hidden Ts output frequency. [Example:  If the hunter is receiving 147.570- then the HT must be set at 143.570 or 151.570] The second  trade off is that the OA unit does not have Zero loss when set to minimum attenuation.  It will always have an inherent or minimum loss of approx 30 dB.  Normally the added loss is not a problem, unless the hunted transmitters signal level is quite low.

OA schematic
The OA I build comes from this website:

After trial and error experiments with OAs that use 4 MHz oscillator triangle/square wave output modules in a can- I've determined the OA with the crystal controlled oscillator- with sine wave output to the single diode mixer works the best.  Harmonics in triangle waves?  Dunno, but the XTAL OSC version's attenuation is more smooth and easy to control.

Inside of the 4 MHz XTAL OSC OA.  Enclosure fabricated from 3/32" Copper Clad PCB Material cut with diamond blade in Dremmel tool and soldered together.  This view shows the OA upside down.  The cover- to the left- is the units bottom.   The interior depth dimension is 3/4" which makes the finished product 1" thick.  
I will not go into much detail of how I DIY'd this OA- but I do use dead-bug blob solder electronic construction.  I   started out by measuring and cutting out the printed circuit material enclosure to fit a double AAA cell battery holder.  It turns out that the JFET oscillator circuit wouldn't oscillate using 3 VDC as Vcc.  4.5VDC, Yes.  3.0VDC, No.  A 9V battery fits well in the battery chamber- so now Vcc=9V.  The current draw is 1.6 mA, or .015 watts.  The 1K ohm Local Oscillator level control is equipped with an ON/OFF switch to turn the Vcc on/off. 

Note that the Mixer has its own shielded compartment.  Past experimenting revealed with no shielding- the JFET oscillator running full blast would bleed into the diode mixer area and wipe out the OSC Level Controls sensitivity- especially with the control set to provide close to maximum attenuation- when the hunter is very close to the transmitter. 

Finished product.  The sorta un-square enclosure corners are rounded over with sand paper to remove sharp areas.  The antique instrument 'big knob' gives a little bling to an otherwise boring electronics device.  Stick on Velcro is applied to the bottom of the OA- so it will adhere to the  pad on my TM Yagi (blue plastic w/ black strips).  Sorry- No DNAC controls this time.  

I certainly hope that 2 Meter Hidden Transmitter hunts will become popular again in Tacoma, WA.  If so... I will post more DIY ARDF info in this ham radio blog.  I am open to questions regarding this project.  72 Rich KR7W

Monday, March 10, 2014

QRP Fun... Heathkit HW7 - Chapter 2 - RIT and CW Offset

Prologue:  Today is 3/10/2014.  I added this mod back in Dec 2013.  I am looking at my work to come up with a description of what I've done... and I am having a hard time remembering what some of my initial thinking was.  With that said, I will attempt to be clear to describe what I've done.

As mentioned in Chapter 1, Googling found me an article for RIT.  The article was sritten by John Grebenkemper, WA6BVA, and appeared in the July 1975 QST, simply titled RIT for the HW-7.

Here's how I think RIT is created in John's HW7:  The battery supply feeding the VFO is stabilized using a Zener diode to bias a NPN switching transistor to be a voltage regulator.  Now that the VFOs FET is stable then the FETs Biasing can be altered to predictably change the frequency.  Resistors in series with the cold side of RFC-1 (Q2 Source to GND) alter the bias to change the frequency.  On 40 meters additional biasing is needed so an extra resistor is added between the Drain and cold side of RFC-1 (via extra contacts in the 40M bandswitch)...Please read the article for more in depth info and to check my accuracy.

I did the mod as John's QST article prescribed.  It worked very well... but I didn't like the fact that the range of the RIT adj pot increased as the frequency increased.  Example: On 40M a 1.4 KHz shift occurs, On 20M there's a 2.4 KHz shift, and 15M results in a 3.4 KHz shift.  It works and the VFO is amazingly almost drift free...but there's too much RIT range for my liking.  Using the RIT Pot for fine tuning was not all that fine especially on 20M and 15M. Tic marks on the front panel for each band are needed.

Here's how I think RIT is created in kr7w's HW7:  Since transistors Q103 and Q102 switch in/out the RIT adj pot while on receive... and on 40 meters a spare set of contacts from the band switch are used to add the additional 3.9K biasing resistor... I axed myself, "Can I use additional contacts in the 20 and 15M bandswitch to operate transistors to add the appropriate resistance for preset RIT of 700 Hz for CW offset as well as a RIT adj pot?"  After some pondering... that's what I ended up doing.  

But first, do this for me:  If you are interested in modifying your HW7 like I did or want to use the concept for another project... then please read John's QST article and get a more techy description of what he did.

Comments below refer to this schematic from the QST Article.  

VFO Voltage Reguator:  The Q104 voltage regulator BJT takes the place of the original R23- 100 ohm resistor.  Using the holes in the PCB from R23 and a couple of additional drilled holes- I added Q104,the 11V Zener diode, and 4.7K.  I didn't have the exact Zener, so I soldered two 5 volt Zeners in series.  [Sidenote:  according to my super Geeky engineer ham radio friend, Bob... this type of voltage regulation is far superior to Linear regulators and/or Zener diodes by themselves].  The regulator output is the Zener value minus .7 volts from the voltage drop across the transistor, BTW.

I added transistor Q101 and R101 next to original RF Choke RFC1.  I drilled holes in the PCB... but the VFO tuning capacitor must be removed to do this. (I will have, "If I was to do this differently- this is how I'd do it" thoughts at the end of this blog entry).  A wire was run to the  12V Key Line (+12 volts applied when key is down) and to the RIT pot.  C101 bypass cap was installed under the PCB in the area of RFC1. 

The QST article shows a 3.9K ohm resistor-R104 being switched in when on 40M only.  For an unknown reason to me now, I soldered this resistor in permanently.  All 700 Hz offset resistor values were determined with the R104 in the circuit on each band.

This is my rendition (first hand drawn then annotated with Photoshop) of the RIT modification to my HW7.  Circuit description follows...  Note:  Just like there are no A, B, or C ionospheric propogation layers... there is no Q102A- there used to be... but it was removed to lessen the complexity.

Example of Operation:  40M RCV- When RIT pot is set in the center (~50 ohms) the bandswitch applies +12V (thru 10K) to the B of Q102B.  This transistor conducts and GND appears on the Collector.  This completes the path of 220 ohms in series with the RIT Pot which causes the VFO to shift its frequency ~700 Hz from the Transmit Frequency.  Note:  The 220 ohms was determined by trial and error using my Icom transceiver with my Fluke VOM.  The procedure is described below.   

40M XMiT:  When the Key is down, Q103 conducts and grounds out the Vcc on the Collector.  This causes Q102B to not conduct which opens up the RIT 100 ohm pot path.  Also, with Key Down... Q101 conducts and GNDS its Collector which places the 120 Ohm resistor in place of the RIT pot resistance path which determines the XMIT frequency.

This is the circuit board I fabricated to contain Qs102B-D and Q103.  Construction is in the Manhattan and dead bug style.  A hand held Dremmel tool with a conical shaped dentists grinding stone was used to route out some islands for wires and BJTs to be blobbed soldered to. Looks messy- but it works.  Wires to/from the board route along the vertical sides of the chassis.  No X-country wires.  All transistors are BJT MPS2N2222 acting as switches.

Regarding the RIT pot I installed... I lucked out and found an old junked out Cushman CE-3 service monitor at my radio club.  I harvested a very nice 100 ohm pot with a long enough shaft to fit through of the two front panels of the HW7.  

Here's a foto of the location of my RIT pot.  Also seen is the bandswitch where I picked up spare contacts for the RIT/offset circuitry.

Here's a foto of my HW7s inner front panel.  Hole 1, 2, and the RIT pot hole were already drilled in the inner panel (but not the front panel) before I rescued this radio.  The once pristine green front panel has been defaced with holes for the RIT control... and most recently holes 1 and 2 have been drilled in the front panel for push-button switches for the upcoming Freq-Mite and PK-4 Keyer controls. 

If I were to do this again:  
>Even though Q101s functional position is where I put it- next to RFC1, under the VFO tuning capacitor... I would put it on the homebrew PCB.  My reasoning is that since all wires are DC control (no RF signals) then having Q101 on the PCB would ease in trouble shooting and would lessen a couple of wires running along the chassis walls.  

>I will order some small 500 ohm Ten Turn pots to adjust the offset resistor value for each band. The pots should be easy enough to solder to the PCB with the transistors.  

700 Hz Offset test procedure:
Note:  When the HW7 is transmitting the RIT Pot has no affect on the output frequency.  

Pick a band and transmit a carrier with the HW7 into a dummy load.  Tune in the HW7 with a good HFT (HF transceiver).  Zero beat the HW7s signal in the HFT or make sure it is tuned in properly for a 700 Hz offset.  Do not touch the HW7s VFO dial from this point on.

Connect the HFT to a dummy load and transmit a CW carrier on the exact same frequency that the HW7 was received.  On the HW7, make sure the RIT Pot is in the middle of its range.  
Do not touch the HW7s VFO dial to tune in the HFTs signal. 

Measure the beat tone from the HW7s Audio out with an audio frequency meter- Fluke VOM or equivilent device.  This is the HW7s offset frequency.  It should be 700 Hz or the frequency you like to listen to CW with.  Adjust the resistor value in series with the RIT pot for the band you are operating on... until 700 Hz is obtained.  

End of procedure.

I was working on adding the Freq-Mite and PK-4 keyer to the HW7... and in the process of not treating sensitive semiconductors properly... I somehow blew out the PIC chip in my PK-4 keyer.  I ordered two new chips plus a complete unit with circuit board to install in my HW8 someday.

Still to come:

> Progress on the 'new ears-best it can be SA602A Mixer direct conversion receiver.
> PK-4 Keyer for paddles + SK + sidetone.
> Freq-Mite frequency Morse Code output frequency counter + its sidetone.

Sidetone is a big deal to me.  I do not like to listen to my Morse sending via square wave audio tones, like the HW7, RockMite, PFR-3, NE555 Astable oscillator and PIC based audio generators.  I've been experimenting on how to filter out the squares in square waves for more pleasant CW listening. 

End of this Blogger Entry.  Please email me for info or if you have some ideas to share regarding this project.  71r5, Rich KR7W... -30-

Sunday, March 9, 2014

QRP Fun... Heathkit HW7 - Chapter 1 - New Ears

Prologue:  I have a complete Heathkit HW9 Station- the transceiver, antenna tuner, SWR meter, and the matching rare speaker.  My HW9 is a Work In Progress and am currently performing mods on the transmitter to make it more stable

For a long time I've wanted to add a HW8 QRP transceiver to my collection of unique radios that I take off the shelf, operate from the shack table, or set up on a picnic table in the park, or out back packing to make some QRP Morse QSOs. Hamfest and Ebay HW8 prices were way too high for my liking.  One day I was surfing Ebay and found the HW8's older brother- an orphaned HW7.  The seller advertised as "Guaranteed Not To Work (instead of UNTESTED)  Buy it Now!
".  The 'not to work' grabbed my attention- just like the street person with the sign that says, "I need money for beer".

Here's someone else's HW7, circa 1972-75, that is better looking than mine.  After reading about the disappointing receiver performance and lack of 700 Hz offset and RIT, this has got to be the second worse Amateur Radio product that Heathkit produced- Note: this is my humble opinion.  


Sure enough, the HW7 did not work.  Armed with the schematic, VOM, and O'scope I found two burnt traces on the PCB and the RF Choke in the output PA burned out. I thought that maybe lightning was the cause- but no solid state devices were damaged. 
 I soldered jumper wires around the burnt traces and rewound the RF Choke.  This brought the radio back from the dead- Abracadabra!

I had great fun troubleshooting the radio and making some QSOs on 20 and 40 meters.  The stations I had QSOs with were hard to copy because they were 'Zero Beat' in the receiver.  If I adjusted the VFO to copy better then my XMIT frequency changed and the far end Op couldn't copy me some times.

Other issues I encountered:
>I was being QRMed by couple of nearby 50KW AM BC and strong SW stations like Radio Habana and WWV- received along with CW signals. 

>AC hum in the audio (when on AC supply).
>Selectivity seems about 2 KHz wide.

>Microphonics in the audio.

!! But not is all is crappy- the 2.5 watt transmitter part of the radio seemed to work pretty well.  I became determined to improve the HW7s receiver. 

While having those QSOs... I discovered that the HW7 has no means to offset the transmit vs receive frequencies.

I could live with the BC + SW QRM but not the lack of 700 Hz CW offset, wide bandwidth, nor the microphonics.  I didn't find a lot of published modifications for this radio on the web or in my HW8 Handbook- which covers mods for the HW7, HW8, and HW9.  Then it dawned on me- maybe there just wasn't enough time for geeky hams to come up with a lot of mods- as Heathkit came out the HW8, only four years later in 1976.

Googling deeper, I found a mod from a 1975 QST that added a RIT pot for the user to offset the receive frequency separate from the transmit frequency but it did not produce a predictable 700 Hz offset like the RockMite, HW9, or modern transceivers.  

Producing a 700 Hz offset on each band seemed difficult due to the design of the VFO.  The 40M VFO operates on 3.5 MHz and is doubled.  On 20M, the VFO also operates on 7 Mhz and is doubled.  15M is 3 x 7 Mhz. RIT on 15M is 4X as effective as on 40M.  Using the principle of the original RIT mod, I came up with a more elaborate method of obtaining a 700 Hz offset for each band and a plus/minus 100 Hz RIT pot for fine tuning.  This mod will be described in a future blog entry.

Regarding the AM+SW QRM in the detector... I read that balanced and doubly balanced Mixers are the solution to eliminating unwanted QRM. I found two more promising modifications.  One used a CA3028A balanced mixer IC (remember when ICs were round?) and a mod that added a SBL-1 passive mixer chip.  I harvested both mixers from junk found at my radio club.  I wasn't able to get the SBL-1 to work for me. Then it dawned on me... the popular RockMite and other simple QRP radios have a Direct Conversion receiver like the HW7.  I had two RockMites and made lots of QSOs... and the receivers worked pretty well aside from the BCI (broadcast interference).  

I began to pursue a receiver design that uses a SA602A Gilbert Cell mixer IC that includes an on board RF input amplifier. I've noticed that the Elecraft KX1 and K1 radios also use the SA602A mixer IC (these radios are not Direct Conversion- they have an IF).  Now I have the wheel without reinventing it very much.

On the left is the 700 Hz offset / RIT control circuitry.   I added a pot on the front panel for + / - RIT- which works quite well as a Fine Tuning control.  The lightened area on the right side of the PCB is where approx 70 components were removed from the receiver and audio circuitry.  On the right rear panel is the HI-Per-Mite 50 dB gain audio amp / 700 Hz audio filter.  I purchased this kit from the Four State QRP club.  It works exceptionally well, BTW.

Before I began the SA602A receiver prototype... I removed all of the receiver components from the HW7s PCB to see how much real estate I have to work with.  My goal is to build the new Direct Conversion receiver on a piece of PCB using Manhattan and/or Dead Bug style construction and mount it on top of the HW7s PCB. 

Here's RCVR Prototype # 1.  A PC Board like this will fit in the open space where the receiver components used to reside. The Pre-selector tuning cap will still reside on the front panel.  

I've plagiarized a composite receiver design from web sources that use a pre-selector parallel tuned circuit (much like the original HW7 receiver) that doubles as a Z matching transformer  to provide balanced input to the SA602A at approx  3K ohm Z.   T50-6 toroids  and the toroid app were used to calculate the # of turns and tuning capacitor size for 7-21 Mhz.  

I'm not sure that the Z match between the Preselector and the SA602A mixer is the best it can be.  Further experimentation is needed.

This sketch shows the mixer output and the Hy Per Mite Audio Filter/Amp.  Pin 6 is the external signal input from the HW7s VFO.   

I wanted good audio filtering at ~700 Hz.  So, I've added a 4 States QRp Club's Hi-Per-Mite active audio filter with 50 dB audio amplifier was obtained and installed.

Side note:  Working along side Geeks in my professional life.. I've noticed that they have a tendency to "Gold Plate" a project.  Something tells me that I will be going down that path here.

At this point in my experimentation- these issues do not make my HW7 not ready for prime time:
>RF Pre-selector not sensitive enough of 40 and 15 M vs 20M.
>Lack of audio gain.
>Loud BC and SW stations still being detected when propagation is good.

Future blog 'Chapter #' entries planned:
>Techy info on the 700 Hz offset and RIT.
>Addition of PK-4 Keyer for Iambic + Straight Key + side tone.
>Addition of Freq-Mite frequency meter.
>Making the 'best it can be' Direct Conversion Receiver' for this rig... or knowing when to stop.

End of this Blogger entry.  Please email me for info or if you have ideas for my project.  71r5, Rich KR7W...  -30-


Thursday, March 6, 2014

The Lectrokit Spider Page...

Dah dit dit dit dah... Looky Here!  It's the Lectrokit Spider QRP Rig.

Info:  The content in this blog entry was originally authored on Sept 8, 2012 and posted on the old ham radio hobby website.  Slowly I am transferring old web pages into blogger entries.  Please read on...

I've had my Lectro-Kit Spider SP-1 for about 10 years.  Someone from my radio club gave it to me cuz I am one of those 'QRP Hams'.   I couldn't figure out what make and model it was so I've never tried to get it on the air.  Recently I stumbled across a photo of it on the world wide web... which led me to the newly archived 73 Magazines on the web where I found the SP-1 lurking in the January 1993 issue.

The SP-1s came in three flavors:  80, 40, and 20 Meters.  I can tell from the number of turns on toroids that my unit is a 40 meter model.  The 73 article says it outputs 1 watt.  There's a RIT control that changes the voltage on a varactor diode to pull the crystal oscillators output frequency in the receive mode.  The receiver appears to be a direct conversion design.  It is sort of like a RockMite without a controller IC chip.  The complete kit back in 1993 cost $39 postpaid.

I spent some time with my SP-1 and know that it does not work... and I bet it never worked.  A lot kits that are given to me by radio club members have been built incorrectly and it seems like the builder didn't delve into resolving the problems.  In this kit...  At first glance... it looks to me like the crystal oscillator has the wrong  transistor installed.  I am sure that I can find a 2N2222 around here someplace.

So for now- back to the shelf it goes... as I am currently frying up other fish from the Retirement Things to Do List.  I hope to get back to the SP-1 after the cold rainy season begins here in the Pacific Northwest.

 I am especially fond of the 'Built In Hand Key' (a piece of brass strip with a rubber foot as the key knob) on the SP-1.  But if you don't like the feel of the built in key... you can plug your own key into the 1/8" aux. key  jack.  Also there's an earphone jack for receive audio from the LM386 IC audio amp (like Rockmite, Heathkit HW-9, KX-1, and others).  It's too bad that this SP-1 has been hacked with the addition of the RCA jacks (Antenna and +12 V) just below the brown bakelite terminal strip.

This little XTAL Controlled QRP radio reminds me of the WW2 resistance fighter  Paraset Spy Radios equipped with One Tube 6V6 XTAL controlled XMTR and one tube Regen detector with a one tube audio amplifier.  Here is One Ham's Paraset Page      Use Google for others.

One day you will hear me calling CQ SOTA from a 6,000+ ft peak in my SOTA neighborhood with the SP-1.   

Thanks for reading this far.  71's, Rich KR7W