September 4, 2012

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Analyze This!  ... PFR-3, a 3-Band Portable Field Radio  

The PFR-3, the KD1JV-designed QRP CW transceiver from Hendricks Kits
 ... what it is, how it works, best features, technical breakdown & analysis.

Overview

There's been so much positive feedback on our  Analyze This!  theme that we decided to expand it a bit by tackling a popular commercially-available radio, tool or accessory each month.  In this regular slot we'll try to be the "independent observers" and comment on the features, build-ability, performance and other factors that we all might find of interest when considering purchase of the product.  Because of time limits for the CWTD show, as well as other good analyses usually being available online from reviewers, we'll just skim the surface and discuss the main points ... but that free-form discussion is often what is fun to listen to and participate in!  Plus, you might learn a little about the technology incorporated into the products we analyze!

Okay, this week we are taking on the very cool 3-band CW transceiver coming from the NH-based KD1JV Design labs.  It is kitted and sold by Hendricks Kits, and is a pleasure to use.  We are told by some experts that this transceiver fits a specific niche just right ... let's see how it does that!

73, George N2APB  & Joe N2CX

Audio Recording ... (Listen to the MP3 podcast)

Discussion Notes:

<20:19:27> "Paul - wa0rse": I do have a comment on the PRF-3 design -- the switches! Are these slide switches robust in the field?
<20:20:48> "Paul - wa0rse": I do -- Partially built!
<20:21:15> "Dale - WC7S in Wy": I have one
<20:21:31> "Dale - WC7S in Wy": I've built a couple doz
<20:24:28> "Rick K3IND": how wide is the preselector?
<20:24:43> "Dale - WC7S in Wy": It is handy to detune if being confronted with strong unwanted signals too
<20:26:34> "Paul - wa0rse": @Dale: Is failure of slide switches an issue? '
<20:27:24> "Paul - wa0rse": I'm concerned about grit and dirt in the field causing some intermittent operation...
<20:29:02> "Dale - WC7S in Wy": If dirt is a problem, Paul, then felt can used on top of the switchs and under the top case to control the influx of dirt... sealing the red works well
<20:29:14> "Dale - WC7S in Wy": I'll go check my mike
<20:36:31> "Paul - wa0rse": Those LED's work great when it's dark out -- the only time when a backpacker operates!
<20:37:22> "Rick K3IND": compare with nuepsk display
<20:37:39> "Ray K2ULR": Same idea in the KX1.
<20:38:25> "Dale - WC7S in Wy": I think I am back..... cw is easier
<20:39:26> "Joe N2CX": Ray, yes the KX-1 display ahs the same basic design and the bright snlight visibility issues.
<20:40:38> "Lee KM4YY": Dale. I can see your typing just fine.
<20:41:31> "Dale - WC7S in Wy": Hi Lee, not sure about this mic... thing... cw is so much easier...
<20:41:45> "Paul - wa0rse": Sid turn off your VOX!
<20:42:00> "Paul - wa0rse": Or use headphones on your computer....
<20:42:22> "George - N2APB": SID, IF YOU CAN SEE THIS ... YOU MUST MUST MUST DISABLE YOUR VOX. YOU ARE TRANSMITTING WHEN YOU SHOULD NOT BE.
<20:42:34> "Dale - WC7S in Wy": someone once said...I have a face for radio.. and a voice for cw... that fits me too.
<20:42:49> "George - N2APB": Ha!
<20:43:09> "Dale - WC7S in Wy": The finals in the PFR are less sensitive to swr issues because the tuner has a load in it..
<20:43:31> "Dale - WC7S in Wy": Yes.. no one can tell but the finals are happy
<20:43:58> "Dale - WC7S in Wy": but the PFR can feed a cw decoder
<20:44:39> "Dale - WC7S in Wy": use the switch on the back panel.. the toggle...
<20:52:00> "Dale - WC7S in Wy": IF you put the memory in... then you can access them with a paddle.. but there isn't any selection for a straight key to choose which memory
<20:52:33> "Joe N2CX": ATMEGA48
<20:52:44> "Dale - WC7S in Wy": there are two memories... but with a straight key you can only access one memory
<20:52:54> "Dale - WC7S in Wy": and that is very messy
<20:53:07> "Al K8AXW": TY Dale
<20:53:19> "Dale - WC7S in Wy": Hi Al
<20:53:56> "Lee KM4YY": Al is a a buddy of mine here in wv
<20:57:32> "Lee KM4YY": Joe - What IC number are you talking about now?
<20:57:48> "Paul - wa0rse": bubble 3
<20:58:01> "Lee KM4YY": TKS
<20:59:19> "Dale - WC7S in Wy": microphones are fussy.. keys aren't
<20:59:30> "Dale - WC7S in Wy": the bandpass filters keep the rx sens
<20:59:34> "Dale - WC7S in Wy": yep
<20:59:45> "Dale - WC7S in Wy": the bandpass of the IF filter... not audio on board
<21:11:50> "Dale - WC7S in Wy": yes bright in daylight
<21:12:57> "Alan W2AEW": I use the Emtech ZM-1 Z-match tuner, which also includes this same SWR indicator
<21:13:34> "Pete - WB2QLL": polyethylene
<21:14:17> "Pete - WB2QLL": transistor radio caps
<21:14:44> "Alan W2AEW": oh, that's probably what I have too
<21:15:22> "Joe N2CX": Indeed the ZM-1 does work and has a wider match range though it is twice the size f the BLT
<21:16:32> "Alan W2AEW": yeah - mine is the ZM-2 also.
<21:19:24> "Todd K7TFC": I've read lots of buzz over the last year complaining that the LM386 is noisy and that there are better choices. Comment?
<21:20:04> "Paul - wa0rse": gotta run, guys.
<21:20:06> "Paul - wa0rse": 73
<21:20:07> "Dale - WC7S in Wy": If you swamp the if filters in an attempt to widen the rx for audio that drops the rx sens a lot
<21:25:25> "Todd K7TFC": Doesn't the 602 have better specs?
<21:25:29> "Al K8AXW": Lee, you might want to make a copy of the Whiteboard with each "bubble" circuit description in case you have to get into your PRF-3 at a later date
<21:25:38> "Dale - WC7S in Wy": The replacement cost is less than some others and this one isn't likely to go outta source
<21:26:25> "Lee KM4YY": Al - I save all the podcasts and white boards.
<21:27:28> "Dale - WC7S in Wy": The Scout
<21:27:33> "Dale - WC7S in Wy": Regen Scout
<21:27:54> "Lee KM4YY": NorEaster?
<21:28:16> "Todd K7TFC": Diz is the one who claims the 602AN is superior to the 612AN
<21:28:43> "Todd K7TFC": In fact he won't sell the 612
<21:29:04> "Joe N2CX": For ham use there is very little difference between the two chps.
<21:31:51> "Todd K7TFC": It usually works to just Google the part number.
<21:31:55> "Joe N2CX": www.digikey.com  no - in between
<21:35:38> "Alan W2AEW": in google - if you type "filetype:pdf" then the IC's part number. you'll often get a datasheet on the first few links
<21:36:29> "Alan W2AEW": Here's a datasheet for the SA612A: http://www.nxp.com/documents/data_sheet/SA612A.pdf
<21:36:43> "Todd K7TFC": Another winner, George and Joe! Many thanks!!!
<21:37:06> "Lee KM4YY": What topic next week??
<21:37:07> "Al K8AXW": TY Alan
<21:37:44> "Ray K2ULR": :)
<21:37:54> "Dale - WC7S in Wy": Thanks George and Joe! Great Job. Have a Tri-Bander?
<21:38:23> "Terry WB4JFI": I hope a Cube will be there!
<21:38:36> "Al K8AXW": Excellent Podcast!! Also thanks George for the detailed information on locating the Whiteboard. This week it fell right into place!!
<21:38:51> "Ray K2ULR": George promises to bring a Cube. :)
<21:38:58> "Dale - WC7S in Wy": You're certainly welcome any time
<21:39:40> "Dale - WC7S in Wy": Happy to help!
<21:41:15> "Bryan AA3WM": Thanks everyone!
<21:42:04> "Todd K7TFC": How about an episode on something SSB? 20 Meters?
<21:44:08> "Terry WB4JFI": Sounds like a line level driving a mic input Sid
<21:44:20> "Ray K2ULR": Too much gain in the first stage.
<21:45:53> "Todd K7TFC": 73 CL
<21:46:08> "Terry WB4JFI": Yeah Sid!!! It's good to hear your voice on here!
<21:48:32> "Joe N2CX": 73!
<21:58:06> "George - N2APB": Thanks again Dale!
<21:58:23> "Dale - WC7S in Wy": You're very welcome
 


SESSION NOTES .... The PFR-3 "Portable Friendly Radio" from KD1JV Designs and Hendricks Kits

 

The PFR-3 is a marriage of KD1JV ATX-series of portable QRP transceivers with BLT Zmatch tuner and AA battery pack ... all in one unified package!

 

 

Intended usage:  Simple all-in-one CW transceiver for casual operation in the field.

 

Pros:

 

-         all-in-one self-contained QRP CW transceiver

-         no plug-in band modules

-         DDS synthesizer for good stability

-         simple uncomplicated operation

-         Iambic A/B keyer with memories

-         Numeric function/frequency display

-         RIT and Direct Frequency Entry functions

-         Tuner handles balanced and unbalanced feedlines plus single wire and ground

-         Internal battery pack or external DC power jack

-         Operates from 9 to 12V DC

-         Covers popular portable 20/30/40 meter bands

-         proven KD1JV design based on ATS-X series rigs

-         low cost (<$250)

-         Yellow case color hard to lose in the wild

 

 

Cons:

-         Larger size than some other portable rigs

-         Cannot be expanded to other bands

-         Bandswitch by multiple slide switches

-         Manual receiver preselector tuning

-         Tuning is only by up/down pushbutton switches

-         No XIT

-         LED display can “wash out” in bright sunlight

-         Receiver has narrow passband for CW – not usable to receive voice or digital modes

-         Cannot receive outside ham bands

-         DC power above 12.5V can damage final amplifier

-         No automatic tuner

-         Cannot be connected to or operated by external computer

-         Yellow case color is garish

-         Paddle accessory no longer in production

 

 

Technical Discussion

 

 

 

Schematic Discussion

 

 

Bubble #1:  Microcontroller & Display

         ATMEL ATMEGA48 microcontroller

      Controls operation of xcvr

      Iambic keyer function and message memory

      DDS frequency control from up/down switches

      RIT

      T/R switching, sidetone and mute

      Frequency/control display

      low supply current

      low RF noise

 

Bubble #2:  User Interface Controls

         Keyer functions

         Up/down and Tune buttons

         Bandswitch sensing via voltage divider

 

Bubble #3:  DDS as the LO

         Direct frequency synthesizer

      Fast frequency change and T/R offset

      Xtal stability and accuracy (50 MHz reference)

      Low  supply current

         Low noise and spurious outputs

 

Bubble #4:  LPF for the DDS

         5-pole design to minimize harmonic and “birdies”

         built-in 2nd harmonic traps

         Toroidal coils and NP0 capacitors for low loss

 

Bubble #5:  Tx Finals

         Solid square wave drive by digital IC

         Robust low cost MOSFET devices with low on-resistance gives good efficiency

      Inexpensive and easy to replace from operator error

         3 in parallel for low loss at 5 watt output

         Parallel Zener diode helps withstand high SWR

 

Bubble #6:  Band-Selectable Low Pass Filters

         5-pole filter for each band gives good harmonic rejection

         Manually switched by in/out side switches

         Toroidal coils and NP0 capacitors for low loss

         second harmonic trap built in

 

Bubble #7:  SWR Bridge

         Tayloe SWR bridge

         S8 operate/tune switch

         Resistive bridge gives high SWR protection while tuning

         D4 variable intensity LED indicator

 

Bubble #8:  Antenna Tuning Unit (BLT)

         BLT Z-match tuner

         S1 for balanced/unbalanced operation

      Sharp tuning means high Q and low loss

         S10 for high or low Z

         S9 for BLT or bypass

 

 

 

Bubble #9:  RF Front End & 1st Mixer

         2N7000 MOSFET switches to antenna through transmitter output

         Manually adjusted dual-tuned circuit for Rx preselection

         Familiar SA612 (nee NE602) mixer

         Local oscillator provided by DDS with IF offset

         Output at 4.95152 MHz IF

 

Bubble #10:  IF Crystal Filter

         4-pole crystal ladder filter for good shape factor

         Uses computer clock crystals

         600 Hz bandwidth

 

Bubble #11:  2nd Mixer

         Another SA612 mixer balanced mixer provides audio from IF

         Crystal oscillator at correct audio offset

         Balanced audio output for most gain with minimum components

 

 Bubble #12:  Audio Processing

         High gain op-amp boosts audio and filters out high frequency noise

         Simple active filter peaks audio at CW note

         Audio level detected to provide AGC to MOSFET at Rx input

         MOSFET switch mutes audio during Tx ... no clicks!

 

Bubble #13:  Audio Amplifier

         Old faithful LM386 boosts level to drive low-Z headphones

         Manual audio gain control

         Tx sidetone injected from microcontroller

         Added components to prevent oscillation and keep RF out for clean audio

 

DC Power Internal or External

         Manual switch to select internal or external power

         Reverse protection diode

         8-AA cell holder

      12V with alkaline or Lithium cells

      9.6V with NiMH cells

         2.5x5.5 mm coaxial power jack for external 9 to 12V power

      Use external series diodes for 13.8V

         Multiple voltage regulators

      Stabilize operating voltages over wide supply voltage range

      Also provide power supply isolation between sections

 

 

    Photos by Larry L2LJ   ... See his great website at http://www.w2lj.qrpradio.com/index%20page%202.html

 

 


 

 


REFERENCES

1.     Hendricks QRPkits: http://www.qrpkits.com/pfr3.html

2.     W4DU review: http://www.qrpkits.com/files/QQ0708_46-47.pdf

 

 


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