Difference between revisions of "ΜBITX"

Latest revision as of 22:15, 14 September 2023

Notes on µBITX assembly and use.

Assembly

Parts that took some time to decide on approach to:

Case: used a cookie tin from Goodwill for $3 as a case.
Mic assembly: TODO

Antenna setup

20m dipole

Inverted V dipole made with Amateur Radio Supplies 20m dipole antenna wire (two 18' strands, trimmed, wrapped around insulators, strung up in attic) and 450Ω window line.

Originally was sent two 16ft strands, which is really too short. Customer service was great and sent me the 18ft strands and a prepaid return envelope for the 16ft strands.

QRPGuys Multi Z Tuner

See my notes on assembly for the Multi Z Tuner

QRPGuys 12W dummy load

Still no luck getting power measurements working.
dummy load works when diode is removed (??)

Items from QRPGuys took about 2 weeks from date of order to arrive.

7-band OCF dipole

Ordered 7-band OCF dipole from gniklat1 on eBay.

Mods perfomed

Fuse before diode

Applied this fix during initial assembly.

The diagram there appears to be labelled incorrectly, though.

Have blown the fuse ~~twice (first time forget, second time transmitting on 40m with untuned antenna)~~ quite a few times, so it seems to work.

Mitigating heat on LM7805

I started by adding a small 5V switching power supply before LM7805. This created a ton of noise on RX, so I took it out.

Instead, I relocated LM7805 to case (up against case and screwed to it). The first time I got the leads switched, though, and smoked the nano, so had to replace that.

This arrangement seems to dissipate heat nicely.

I also have a heatsink in some old electronics that I've been meaning to try out too.

Dim the LCD

As documented here. At first it had no effect, but then found I hadn't cut the trace between the two leads first, which I did 2018-09-06.

CEC firmware

After getting some extra nanos, I flashed one with CEC firmware. Works great!

TX LED

Soldered up red LED per BITX20 message 46853 on 2018-09-06. Works great!

Leveling out power

Replaced some of the transistors (etc.) per this solution:

Replace the 2N3904 transistors in driver stages (Q911, Q912, Q92, Q93, Q96, Q97) with 2n2222 transistors (in TO18 metal can),
Parallel up R941, R911, R96, and R942 to get 11 ohms each by placing a 22 ohm resistor across each existing resistor (stacked 1206),
Replace Q90 with a BFR106 transistor,
Increase R81 to 2.7K,
Change C81 to 470 pF.

Reducing spurs

Replaced L5 and L7

Reducing harmonics

Replaced relays with Axicom D2n 12v relays (model V23105-A5403-A201)

Power measurements

Before and after the 3 mods above (levelling out power, reducing spurs, reducing harmonics)

Mods planned

SWR meter (rx)
Red-on-black or amber-on-black display (for night-time operation)
- And/or a 6-8 digit LED display
More buttons - I like PH2LB's approach (part 2)!
- band up, band down, left/right digit selection for tuning, ...?
Foot-pedal controlled TX
- Have obtained an old (working) foot pedal switch for this purpose (edit: now have two somehow?)
Some sort of audio pre-processing?
Fix filters??
line out
- Again, PH2LB's approach is great.

Other things on wish list

~~external SWR + power meter~~
- YL got me a DAIWA CN-501H for my birthday, 2021-03
Antenna analyser / antuino

@@ Line 4: / Line 4: @@
 Parts that took some time to decide on approach to:
-* Case: used a cookie tin as a case.
+* Case: used a cookie tin from Goodwill for $3 as a case.
 * Mic assembly: TODO
 == Antenna setup ==
+=== 20m dipole ===
 Inverted V dipole made with Amateur Radio Supplies [https://www.amateurradiosupplies.com/product-p/20405.htm 20m dipole antenna wire] (two 18' strands, trimmed, wrapped around insulators, strung up in attic) and 450Ω window line.
@@ Line 16: / Line 18: @@
 QRPGuys [https://qrpguys.com/12w-dummy-load-power-meter 12W dummy load]
-* Items from QRPGuys took about 2 weeks from date of order to arrive.
+* Still no luck getting power measurements working.
+* dummy load works when diode is removed (??)
+Items from QRPGuys took about 2 weeks from date of order to arrive.
+=== 7-band OCF dipole ===
+Ordered [[7-band OCF dipole]] from gniklat1 on eBay.
+== Mods perfomed ==
+=== Fuse before diode ===
+Applied [http://ubitx.net/ubitx-fix-reverse-polarity-protection/ this fix] during initial assembly.
+The diagram there appears to be [https://groups.io/g/BITX20/message/56007 labelled incorrectly], though.
+Have blown the fuse <s>twice (first time forget, second time transmitting on 40m with untuned antenna)</s> quite a few times, so it seems to work.
+=== Mitigating heat on LM7805 ===
+I started by adding a small 5V switching power supply before LM7805.  This created a ton of noise on RX, so I took it out.
+Instead, I relocated LM7805 to case (up against case and screwed to it).  The first time I got the leads switched, though, and smoked the nano, so had to replace that.
-== Mods ==
+This arrangement seems to dissipate heat nicely.
-Applied during assembly:
+I also have a heatsink in some old electronics that I've been meaning to try out too.
-* Added a fuse before diode (succeeded, afaict)
-Attempted after tested working:
+=== Dim the LCD ===
-* Mitigating heat on LM7805:
+[https://ubitx.net/2018/02/10/reducing-display-brightness/ As documented here].
-** Added a small 5V switching power supply before LM7805 (failed; created too much noise)
+At first it had no effect, but then found I hadn't cut the trace between the two leads first, which I did 2018-09-06.
-** Relocation of LM7805 to case (succeeded, but got leads switched the first time and smoked the nano)
-* Dim LCD (failed—no effect; succeeded 2018-09-06—hadnt't cut line first time)
-Also working:
+=== CEC firmware ===
-* Using CEC firmware
+After getting some extra nanos, I flashed one with CEC firmware.  Works great!
-Plan to attempt at some point:
+=== TX LED ===
-* TX LED (2018-09-06)
+Soldered up red LED per [https://groups.io/g/BITX20/message/46853 BITX20 message 46853] on 2018-09-06.  Works great!
-* SWR meter
-* Red-on-black display (for night-time operation)
+=== Leveling out power ===
+Replaced some of the transistors (etc.) per [http://ubitx.net/fix-fix-uneven-tx-output-across-bands/ this solution]:
+*    Replace the 2N3904 transistors in driver stages (Q911, Q912, Q92, Q93, Q96, Q97) with 2n2222 transistors (in TO18 metal can),
+*    Parallel up R941, R911, R96, and R942 to get 11 ohms each by placing a 22 ohm resistor across each existing resistor (stacked 1206),
+*    Replace Q90 with a BFR106 transistor,
+*    Increase R81 to 2.7K,
+*    Change C81 to 470 pF.
+=== Reducing spurs ===
+* [http://ubitx.net/2018/10/10/rajs-second-spurs-mod-simpler-again/ Replaced L5 and L7]
+=== Reducing harmonics ===
+* [http://ubitx.net/spectral-purity/ Replaced relays with Axicom D2n 12v relays (model V23105-A5403-A201)]
+=== Power measurements ===
+* Before and after the 3 mods above (levelling out power, reducing spurs, reducing harmonics)
+[[Image:µBitX mods power readings 2021-07.png]]
+== Mods planned ==
+* SWR meter (rx)
+* Red-on-black or amber-on-black display (for night-time operation)
+** And/or a 6-8 digit LED display
+* More buttons - I like [https://www.bolkesteijn.nl/blog/index.php?page=ubitx-mods#ubitx-mod5 PH2LB's approach] ([https://www.bolkesteijn.nl/blog/index.php?page=ubitx-mods3#ubitx-mod16 part 2])!
+** band up, band down, left/right digit selection for tuning, ...?
 * Foot-pedal controlled TX
+** Have obtained an old (working) foot pedal switch for this purpose (edit: now have two somehow?)
 * Some sort of audio pre-processing?
-* Leveling out power?
 * Fix filters??
+* line out
+** Again, [https://www.bolkesteijn.nl/blog/index.php?page=ubitx-mods3#ubitx-mod13 PH2LB's approach is great].
+=== Other things on wish list ===
+* <s>external SWR + power meter</s>
+** YL got me a DAIWA CN-501H for my birthday, 2021-03
+* Antenna analyser / antuino
-[[Category:Amateur Radio]]
+[[Category:Amateur radio]]