Audio filters... first keep the RF out.? opamps are the ultimate solution as?
they can be applied to higher order filters with excellent performance.
But when I go that far I like to add an audio notch filter as well.

?Look at survivor-75, its also old school but works and the?TX line up I've
used many times (shamelessly borrowed) and it performs well across HF.?
If you want to see what Steve (kD1JV) did later using SMT you need to
look at his Slopbucket I and II.? ?SSB/CW radios for 20 and 40M.? The
lineup used is SMT JFET, SMT 2n3904 as buffer, then a 2n3904 leaded
part, 2n2222A (plastic) and then IRF510.? With a good filter at 20M
(less than 2db IL) after the SA602 and 13.6V the output seen is about
10-11W (peak).? ?The output of the SA602 is more like?.1mW (-10db) is
the mixer drive is correct.? Hint he 602 max voltage is 9V and running
it at 5V cripples it some as it does perform better at 6.8 to 8V.??

You mentioned the KNQ7A,? I have one for 40m (VXO version) and?
its a good radio.? ?With only three devices for the RF output chain its
good for 8W at 13.8V.? I copied it for 20M and got the same result
there too.? Its only one device 2sc3357 that is smt, the driver is a flat pack
bolted to the chassis (heat sinking)? and final is IRF530 aslo using chassis
for cooling.? ?Very minimalist, but good layout and parts it performs well.
Its fun? to use the KNQ7A on 40m and?never had issues with RX overload
(lots of very strong signals here).

Single ended mixers are ok but I find balanced mixers advantageous for
eliminating products.? Often that is not a sacrifice but a improvement.

SMT parts are good and offers lots of useful? parts. I will not even touch availability
of SMT VS leaded, industry went that way and so the supplies are SMT.? However
power is not their forte.? The finals dump a lot of heat, the drivers before that can,
and the prediver may be SMT.? generally that's not where SMT excels.? I like SMT,
early adopter and many decades of industry experience.? At VHF and up SMT is by
far the way to go until you want power and then the breakpoint is around 3-10W? for
non-linear modes.? Linear modes due to standing currents make removing heat a
major issue.?

Yes parts and design have advanced since I started in the late 60s. I was cutting edge
then.? For HF analog the biggest advantage of SMT is machine placement and smaller
board size.??

As to relays I'd rather use diodes or CMOS analog switches. 74hc4053 comes to mind
and it makes a very good balanced switching mixer however it has no gain but lower
loss than diodes.

Things to consider..? DC switching without hearing? transient pops and sans relays.
AGC even a low gain RX while it may not overload the users ears can.

Allison
------------------
Please use the forum, offline and private will go to bit bucket.

And suddenly the tx audio is back.. very strange. Codec in funky state? weird.. anyway, not popping the hood yet.. :-)

Hi All, was doing some initial testing with ssb today. I made a contact at 15w and the signal was good but the audio was not stellar.. so this morning I was doing some tests at lower power and suddenly there was no tx power at all. cw still works fine, but can't seem to recover the ssb audio by rebooting. any ideas?? Do I need to start over from the initial image?
Antenna was? a resonant 80 meter dipole with little swr at the freq.?

73 Brad N8YG

The "S" version is for the configuration with an extra nano that monitors, swr, s-meter, and decodes cw.? If you dont have that configuration, then you want the one without the "S".

73
Mark
AJ6CU

Quick and dirty solution. Easy access to underside of pcb for removing burned fets and solder the new set. And best of all only 8 screws needs to be removed.
de oz9ny, niels

Jim, diversing,? can you say what the difference is in Ians firmware with the v1.200 hex files..? There are 2 of interest, but don't know which to
use? first one is uBITX_CEC_V1.200_nx.hex? ?and the second one is? uBITX_CEC_V1.200_NX_S.hex.. Am loading via Xloader..thanks

Art

Thank you Allison for clear explanetions.
Of course I compare Fahran's design with lot of similar on the web, and on similar TX boards usually they have 2 transistor and an IRF .
2 TX transistors are tuned-tuned, or tuned-large band or both large band.
About audio low-pass filter you say:
The Rs and Cs are going to be there if opamps are used for filters. might make a small difference?
and most modern opamps are low power.
A low pass Sallen-key single operational requires only 2 resistors and 2 capacitors, plus 2 resistor if we need gain., if you? look at
pic of my PCB you see 25% of it is populated by transistor low pass filter, inexpensive but really big. Final result is due to filter,
dimension and quality of loudspeaker, dimension of box, personal preferencies of listener, etc. Lot of other shematics only use
a simple resistor+capacitor? as LPF. Is daylight so noisy to require all that big low-pass?
Relais: somewhere I have some screened professional single commutation relays I will use.
Auto-oscillations: a well designed PCB is the way to avoid them, as every modern transistor works perfectly on VHF too.
SMD is the way for very short connections, big GND, etc.Very common to have auto-oscillation on audio amplifiers too, not only on RF,
on poor designed circuit and PCBs.
You also say:
None of them are good for .5W dissipation.? I'd consider not going SMT there.
Lot of common components can be used "the SMD way", but now we have also lot of very powerfull SMD components: why not use them?
WHen I started with electronics in 1966, everyone said: do not use transistors, they will never be successfull! Then : please do not use ICs, ,
this fashion will not last long, then: what do you want to do with such stupid digital? And then : I still have a good typewriter,why do I need a PC?
And finally: the old high school examiner? in 1974 told me: you are talking about science-fiction when you talk about computers, you are really a stupid ! :-)))
It's always interesting to see how other designers solved the very same problems :right now I'm looking at KN-Q7 schematic?
( I have a file with lot of similar schematics) for RX-TX VCC commutation and I'm interested on 3 transistor RF board too.
Thank you !
Paolo

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Yes, I opened the top and ensured the boards were mated well.

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Hi Glenn;

Is it time to ask for a refund?? I was really excited to play with this radio.? It's so annoying to instead be sitting here with a boat anchor.

The trap is a must or a hi-pass at the input if you use the 5mhz IF filter.
ITs a USA thing as 2.5/5/10//15 and 20mhz are WWV.

When i started that was an Oh, no I'm not going down that path again.? I've had
troubles with 10mhz (previous bitx) and I knew 5mhz would be pain so I
rounded up a bunch of 4.9152 rocks and built a filter around that.? It was a toss
up as I also have a large supply of 4.456mhz and 5.0688 crystals which would
have also worked. The 5.0688 is very common so easily sourced cheap.


Allison
--------------

One thing those 3x5 cards go into the engineering notebook. and any other
handy scrap I've written on.? ?I've been doing that?since I was a kid.? Back
then it was told to me if you do not document it, it never happened and
cannot be reproduced.? ?I have a shelf of notebooks very handy.


Allison
--------------

Never had a noise issue but if there was the easy fix would be a long?
low tension expansion pring indie the tube to keep a metallic contact
and also keeping the screw under some tension.

Keep in mind the screw is inside the tube making contact as well as
the pin to assure it turns.

Allison
--------------

Barry,

Ask and ye shall receive.? Spent a whole career asking and answering.


Allison
--------------

Jack,

I put in 50 years before retiring, occasionally it looks like majik to me.
That and I can fix farm equipment.? ;)


Allison
--------------

For some, fixing farm equipment is magic.

Bruce W. ~KV4OE~

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