Monday, January 10, 2011

Building a PFR-3A - First Impressions

Building a PFR-3A is not difficult, in fact it is quite easy, although the kit takes a lot of patience.
The first bit of patience I needed for the period between ordering and actually receiving the kit. I ordered November 10th, the shipping documents show that the kit was taken to the post-office December 21st.
I ordered paddles to go with the transceiver, however, there were none in the box, which dropped in January 7th. Although Doug refunded immediately, I would have appreciated some communication in an earlier stage.

The build manual reads that "some of the yellow, monolithic caps may be supplied with the leads being formed for 0.2" lead spacing, while the holes on the PCB are designed for 0.1" lead spacing...". WELL, this is where I needed a lot of patience. The manual should better read that most of the capacitors, be it monolithic or disk type capacitors, are supplied with a 0.2" lead spacing... and the builder therefore should be prepared to bending many many leads to fit the 0.1" spacing used on the PCB.
Ceramic disk capacitors with "narrowed" lead spacing will stick out somewhat higher above the PCB.

Speaking of the manual, there are some errata available on Doug's web-page. However, care must be taken if those are still valid.
Some supplied components may have values other than mentioned in the manual. My kit came with "green capacitors" having a 22nF capacitance, contrary to the listed 10nF. The receiver however, and this is where those capacitors are in, is working excellently.
The manual is short, which I like, but in places it is maybe a little too short. With reference to the schematics, everything can be figured out however.

Another thing that I felt was unnecessary, some of the vias were too narrow, namely the ones of the volume pot and the phones and key connectors. I solved the problem by reducing the width of individual leads.
All of that mechanical work is not difficult, however, it is also not something you would expect building an electronics kit.

The PFR3 employs a DDS. Such systems require calibration. In the PFR3 this is provided by zero-beating vs WWV. Neat, when being able to receive WWV. It would have been nice if one could set a frequency to zero beat against, e.g. RWM, which is much more accessible to Europe.

There is another calibration step, specifically calibrating the BFO. This is done in an ingenious way! Works pretty well.

One thing was striking my eye whilst building the transmitter: L7, which feeds the final, is made from 8 turns #28 magnet wire on a FT37-43 core. To my understanding, in a switch mode PA, ohmic losses should be kept minimal. Consequently, I wound the inductor from 1mm diameter magnet wire (corresponding to #18 AWG).

Enough words, here's some imagery:
some ceramic disk capacitors are bent down to fit the space available

note, the two wires from under the fat red toroid are "binding post wires"

Some additional remark to a comment I found on the internet. I do like the bright yellow color. It makes the transceiver visible, just as intended by Doug.

In an interview on youtube, Doug states, the display was chosen to be LED, rather than LCD, for better visibility in bright sunlight. This only can be a misunderstanding. Clearly LCD would perform superior to LED in bright sunlight. However, I do prefer LED over LCD. In particular red LED is perfect during night-time. Reason: rods do not see red! Therefore, night-vision, which is performed by the rods in our retina, will not be affected by red light, cf. scotopic vision and rhodopsin.

The kit contained magnet wire of several colors, nice touch, I did not need those, since no complicated multi-wire transformers are part of the design. Further I had some electronics elements left overs, namely, 1 transistor, 13 capacitors and 4 resistors, even though the PCB is fully populated. I am not sure what this means, at least I was not missing any parts ;-)

As seen from the photographs, I was ignoring the hook up wire provided in the kit and replaced it by heavier gauge speaker wire.
I also intend to act against the teachings of the build manual by using actual coax cable (RG58 or RG174) to connect the BNC connector to the PCB.

Prospect: This radio will serve me in three functions: it will be a grabber-receiver, it will accompany me on trips and travels and it will be a companion on board of my boat.
And... if time allows (I kinda doubt that), I may write my own firmware for the rig, allowing to receive maritime TTY.

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