Areas of Interest

Monday, March 14, 2016

My Former Heathkit HW-9 w/ WARC Station

SOLD to a nice gentleman in MN.

Prologue: Time has flown... About 12 Years ago I acquired a used HW-9 (w/ WARC).  Over the years- all of the components needed to make up the complete station were collected.  Many of the recommended modifications were made to the little radio.  A couple of times- the mods killed it dead.  But recovering from the errors and making it work again provided joy as well a learning experience.   All mods made a noticeable difference- some made a huge difference in performance.

I have always been fond of the Brown Heathkit line of amateur products.  I had big visions of having a complete Brown high power station with a HW-5400, SB-1000 linear amp and a SA-2060A tuner...  but a lot of other things came along that were just as interesting to do.  As of late- I am reducing  items in my ham radio collections (or is a hoard?).  Since I haven't used this HW-9 in about 4 years- It's now for sale... and I am hoping that whoever buys it will use it and enjoy it as much as I once did.

Visible Mods to the rear:  RCA Key Jack is changed to 1/4" Mono [the old RCA Jack is included in a "parts package"].  The Headphone jack is now Stereo for now-a-days headphones.  A mono plug will also work.

Included is a spare Power Cable with Anderson Power Poles.

This PSA-9 has been modified per Gary Surrency's popular article.  The voltage regulator was changed to a LM317 for superior regulation.  

The SP-99 was originally built for the HW-99 (non QRP transceiver) which had a couple of watts of audio output.  The HW-9's audio output was meant to drive headphones.  A LM380 Audio Amp (for normal loudness) and a AA battery tray (for picnic table ops) are added to this SP-99.  The original speaker was replaced with a commercial radio service NEC communications speaker.  There's a Red LED to remind the operator that the power is ON.   All additions and modifications did not alter the originality of the speaker. Mods are easily reversible and all parts are provided to restore to original.  

Amplifier and batteries mount on plywood base which is attached to the SP-99 with industrial Velcro which as easily removable.  Wall-wart power supply  plugs into the coaxial jack- which disconnects the batteries.

In this dropbox folder are more photos of this HW-9 w/ WARC station- as well as a couple of movies of On The Air action.

Best regards,  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

Wednesday, January 29, 2014

W7EAT Winter Bunny Hunt... Nov 19, 2011

I let the original website and domain name expire because I didn't want to keep funding it.  Recently one of the occasional 3 viewers of the original asked me if I would re-post the photos from the ARDF Hidden Transmitter Bunny hunt that was held near Eatonville, WA on Nov 19, 2011.  

Here are the same photos as before.  The names have not been changed to protect the innocent.
Al, N7OMS on the hunt.
After the monthly W7EAT South Pierce County Club meeting breakfast gathering in Downtown Eatonville, we headed out to the hills above Alder Lake.  We were greeted with almost three ft of snow to find the 4 and sometimes 5 transmitters that "Huntmaster Bob" had hidden before the pasture area became a winter wonderland. [Note:  the 'sometimes 5th' transmitter was the one that didn't transmit on a regular basis.  Cold temp?  Low battery?  Dunno].

Huntmaster, Bob K7MXE

Rich KR7W (on the right) observes Chuck AC7QN trying to figure out what Huntmaster Bob has planted for us to find.

At this point... is when I figured out that the rules of the hunt had changed again.
"Wait a minute, that's not what you said before", I quip.

Back at the Tailgates to socialize with participants came out to cheer us hunters on.  Lorraine K7LJN, Stan K7DKK, Rich KR7W (back to camera again), Alan N7OMS.  1/2 of Huntmaster Bob K7MXE is seen on the right.
After a break... the hunt continued on.  Huntmaster Bob included a bit of 'trickery' in this outing.  He hid a dummy antenna close enough to the radiating antenna to fool some of the hunters.  This resulted in a conflict where two hunters were disqualified.  

Ousted from the game for breaking some rule that hadn't existed until the last minute.  Just like working for a large corporation that practices TEGWAR... aka The Exciting Game Without Any Rules.  Corporate America in the snowy bucolic hills above Alder Lake.  Who wudda thought?
A late comer to the party, Casey WW7CH (left) chats with Chuck AC7QN in the Tailgate area.  Hot coffee was a welcoming break.
It turns out that somehow Casey WW7CH was the grand prize winner of this hunt.  The mystery still lingers of how he found all of the transmitters in such a short time.

Oh well,  no hard feelings as it was all in good fun.  This Hidden T - Bunny hunt was the most fun of all the hunts I've participated in.  I think it was the nice people and unique hunting environment made it a great outing for me.  So Bob, when the heck is the next W7EAT Winter Bunny hunt?

He is still snickering about this hunt...

Also, it was nice for me to dig out these photos and re-post them for all to see.  Old folks love to reminisce, don't we?  

It really was a pristine winter wonderland.
End of this blog entry.  Best Regards,
Rich kr7w

Tuesday, January 28, 2014

Collins R-388 Receiver Explorations

I like to restore old radios.  So far of the 100 or so radios I've restored only a couple of those have been communications receivers.  Enter the Collins R-388.

A couple of months ago, the W7OS Museum at the Radio Club of Tacoma (which I am involved with) received as a donation an old R-388, circa 1950. 

At first glance the radio seemed to play well but had 60 Hz hum in the audio.  It was easy to replace the power supply filter capacitors which did not help.  Listening closer I noticed that when there was no signal being received then there was no hum.  This 60 Hz hum was riding on the B+ rail and measured at 1.0 VAC RMS.  In addition to the hum- the S-Meter did not work very well- no matter what receive level was received- the meter never rose more than 20 percent of its travel.  Investigation revealed a possible AGC (Automatic Gain Control) issue.  More on that issue later.

History Lesson:  In 1949 Collins began building the 51J which was intended for military or commercial users who required a drift free and very stable receiver with extremely accurate frequency readout.  The 51J was to be used for RTTY reception but could also provide good AM listening.  The cost of this receiver was $900.  The military bought the 51J and improved 51J-2 which evolved into the R-388.  This receiver has a 500 KCs IF output jack that provided a signal for additional equipment for decoding RTTY.

The World Wide Web has a couple of good R-388 sites with enough valuable information to get me started on the Museum receivers repair.  Note that this is a work in process… with progress being made.  The websites will be listed below.  I joined a Yahoo Group for Collins 51J, R-388, and R390 receiver aficionados to gather more information.   I think it is interesting that the rules of the Yahoo group state that a new member must post an introduction of them self and the (implied) purpose of joining.

I posted my introduction to the Yahoo group.  Some helpful members provided information on the most popular components to replace that might fix the Museums receiver.  C204 and C136 were the culprits.

  Geek talk follows:  C204 provides a signal from the last IF amplifier to the AGC detector and AGC amplifier which manages the gain of three IF amplifiers and the front end RF amplifier.  If C204 is open then no signal would be detected and the receiver would be at full gain.  C136 was reputed to become leaky and apply plate voltage from the Crystal Calibrator Oscillator tube to one of the input grids of the first mixer.  That would make a mess of the mixers amplification which would severely distort the received signal.  It was hard to find C136 as well as replace it… but perseverance prevailed.  Note to self:  Get some longer needle nose pliers.  After the cap swap-outs, the receiver was connected to an antenna and viola!  No more 60 Hz modulated audio.  High power AM broadcast stations sounded much better than before- much more intelligible audio.  But something was still wrong.

C136 and C204 are in there somewhere.  New terminal strip in lower left is the AGC mod mentioned later in this blog entry.  The cylendrical gizmo in the top-center is the PTO, which Collins is famous for.  The PTO is part of the VFO that provides a super linear and accurate tuning dial.

The receiver sounded weak, with more noise than signal.  The AGC was working but not on CW and SSB with the RF Gain turned all the way up.  On AM, the AGC worked pretty well but the audio sounded better with the RF gain turned down a bit.   The S-Meter still did not indicate a high reading on loud signals- like the 50KW AM station 6 miles away.

The Army TM854-25 instruction manual is a very good document that explains in detail the operation of each of the radios stages.  There's even a section on how to destroy the radio so it will not fall into the hands of the enemy.  But some internet enthusiasts have posted that "The manual has errors.  Trust the schematic inside the radios cover”, they say.  I did find an error, BTW.

  The TM has a section on the S-Meter that reveals the higher the amplification of the IF stages then the higher the meter reading- which means that the S-Meter works with the AGC OFF if the RF Gain is all the way up.  Also, low IF amplification could be caused by defective AGC circuitry.  Armed with the Tech Manuals tube voltage chart, simplified schematics, and my Fluke VOM… I set out to measure the front end RF amplifier and the three IF amplifiers (all gain controlled by the AGC) tube voltages looking for discrepancies. 

Tubes V101, V107, V108, and V107 pins measured pretty close to the chart, EXCEPT pin 6 of V107, which is the screen grid of the first IF Amplifier.  I measured +3 V instead of the required +47 V. 

Remembering my Dark Ages vacuum tube electronics training… I knew that the tube will not conduct (and therefore not amplify) without a large value positive voltage present on the SG.  It turned out that R126, a 27K ohm resistor, in between the B+ and the SG, had changed value to many meg-ohms.  I calculated the voltage drop across this resistor to determine the wattage needed I substituted 3 various values in parallel to come up with 27K at .7 watt.  Knowing Ohms Law has benefits, me thinks.  I'm excited... let’s take it for a drive.

The R388 now connected to an antenna works hundreds of times better.  Stations were loud, proud, and the noise was lower.  And the S-meter worked as it should.  With the RF Gain all the way up still caused SSB and CW signals to distort.  It seemed like the AGC wasn’t fast enough to deal with the quickly changing signal level of these modes.  Whilst listening to AM Broadcast… the receiver sounded pretty good and the S-Meter tracked the more solid signal pretty well.   Again, R388 aficionado’s websites mention that the R388 AGC is lacking.  The search is on for AGC Mods.

I knew a small bit about AGC from restoring many 30s, 40s, and 50s entertainment radios… but after reading the 388s Tech Manual I was a bit puzzled over attack and decay times and how it happened. I found a nicely written article by the modern day Flex Radio folks that was enlightening.  Also, the website reveals there are four different AGC mods to consider. 

The AGC Modification I settled on was written by Dallas Lankford in an obscure publication called HSN (Hollow State News) Summer 1990 edition.   My friend Google found HSN #26 which contains info on the R388s Band 1 sensitivity, the PTO, and the AGC Mod.  Mr Lankford’s modification is dependent on the AGC no signal voltage being -1.60 to -1.80 volts.  The Army Tech Manual says this voltage should be -1.40 volts.  Other AGC articles want the voltage to be 1.40.  Mr Lankford’s article reasonably states that if the AGC voltage is too positive then the dynamic range of the receiver will suffer.   The R388’s AGC voltage is derived from R149, R148 Pot, R147, and R146.  I replaced R147 because its value had changed 40 percent.  This resulted in idle AGC voltage of 1.7 volts. 

Photo shows the terminal strip I added to add the AGC mod components to the AGC amp circuitry.  With this set up I can easily reverse the modification.  More info in the Dropbox folder listed below.

I performed the Lankford AGC mod with low expectations and was greatly surprised with the results.  Now the R388 copies CW and SSB quite well with the RF Gain all the way up.  AM Broadcast works quite well also.  Of course with a really loud CW or SSB signal it is prudent to turn the RF Gain down for more comfy listening.  The AGC attack time is quite rapid and decay is slow in comparison.  I suspect that this AGC would not work well for QSK CW when listening to my own transmit signal in the receiver as it would take a while for the amplification to ramp back up in order to quickly hear the far station.  I have been using the R388 with my circa 1950s Globe Chief transmitter with manual T-R Dow Key type non-QSK operation.  Slow decay AGC is not a problem with my station. 

AGC Movie:

The next step is to figure out if I want to do the product detector mod.  The suggested mod on the neidlinger website seems pretty easy, but it involves removing the front panel.  On this radio I’d have to swap the AGC SPSP switch with the Noise Limiter DPDT switch to make the product detector work.  Before I do this I will be seeking opinions and personal testimonies.

This dropbox link is to a folder that contains the documentation that I acquired during this receiver repair.  I found most all of it on the web... so it's not new news.  But it is all in one place.  

What's in the folder...
+ Photos of my attempt of the AGC mod
+ A movie of the AGC in action
+ The Army Technical Manual (two parts)
+ Annotated schematic
+ PDF files that contain the content of the web pages I found useful.
+ An article on AGC that I found useful
+ The Hollow State News collections in PDF (the entire set of HSNs are worth reading if you are a boat anchor kind of hobbiest)

+  Something I am forgetting to mention

But wait, there's more... in another blog entry.
That's all for now.  Regards,  KR7W