Re: SB II build project


ajparent1/kb1gmx
 

John,

Looking forward to getting mine.  My 20M SB-I gets a lot of use.
I like that there is a simple agc, makes tuning around the band less painful.

I  run the SB 1 on 3S1P (2800mah) or 3S2P (5000mah) pack of Lipo 18650s
as that hits the working range and easily nets 7-8W at 20M.   Teh SB-I was
designed very much similar to SBII for 14V max.  I also considered more
voltage but for most usage the advantage is near negligible and not worth
the stress and weight.

Note the assumption is LiPO at 4.2V full charge and 3.7V nominal at discharge.
The extra voltage is a stress factor.   The A123 and LiFePo types that is more
like 3.75 and 3.2V and not a concern.

So changing a few caps will not only be needed it may require a dropping resistor
for U1 so it does not overheat.  Its also rated to a max input of 18V so you pushing
close to the design limit.  So pushing the voltage 2.8V (at full charge) over max is 
not a good thing for a lot of the circuitry exposed to unregulated voltage.

I've used the SSM2167 and if  the levels are right and the compression reasonable
it works well without undue distortion.  I found the radio was plenty effective without it.
I left it out as then it was just one more piece that needed power.  I may include it in
a Mic and set it to the same levels are a standard electret mic would put out.

The use of Pmos diode will buy milliwatts maybe and will not buy operating time over
the schottky diode.  This is not the FT817 as it doesn't suck down 400mA on RX. 
The 40-50ma RX makes 10 AA 2200mah NiMh practical.   Running 3S LiPo you
will get 50-60% of the battery before you get under 11V and for 4S LiPo you will
run the battery to cutoff (very bad thing to do) before the radio quits.  That would
also be the same case for 4S A123 or LifePo.  The power consumption for this will
be unlike the  FT817 if that is why your doing this.

Package I've used is a wood (copper foil lined), craft box with decent latches and hinges 
large enough that the radio is half the box and everything (Mic, antenna (EFHW 20M), 
battery, small Key) fits with space to spare.   Packaging it that way and shoulder strap 
its grab and go portable and complete.  Its not the smallest possible case but convenient
and cheap and durable.

For SWR indication I went with the KITSANDPARTS.com SWR detector and a real
100uA (tiny) edgewise panel meter.  SWR is just for a check and also monitoring
power. No tuner as the antenna is tuned already.  If needed a Zmatch or my T1
does the trick.  All that in its own pouch for use with any radio I have.

I have a larger assortament of QRP radios including FT817, SB-I, KNQ7A,
Tentec 505 (QRP 5W), and 5 others SSB of my design for HF.  

Allison

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