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Author Topic: Need Advice On Multiband Rig  (Read 1897 times)

Posts: 203

« on: May 17, 2008, 02:12:54 PM »

Hello to all:
I need some advice for a rig I am building out of some
Small Wonder Labs (and other companies) kit boards.
It will be a 4 band 35 watt PSK-32 transceiver with
built in computer interface and an auto matic antenna tuner. The transceiver boards will be SWL PSK-10,
PSK-20, PSK-40, and a Warbler, all completed and
working FB. The PSK baords already have their computer interfaces built into them, either by Serial Cable
for the older boards (PSK20 & 40) or by VOX on the Audio In from the computer (PSK10 & Warbler)
The PA section is an 35 watt HF Packer
Amp by K5 OOR, already assembled and working FB.
The auto tuner is one of the early LDG QRP tuners when they were still offered as kits, Z-11 I beleive. Rated at 60 watts, 30 continuous.

My dificulty is figuring out how to switch all the audio, RF, DC lines into and out of the different PSK boards. Of course there are multi pole, multi throw switches, but can I use audio, DC and RF in the same one, I think not. Each PSK board requires a switch for DC In. The Audio into the PSK boards from the computer
I can parrallel in and just tie into the input of each board with no problem. NOT SO with the AUDIO OUT, because it will go back into the other boards. And I want two Audio Outs from each PSK board, one for the computer, one for the headphones/speaker. I already decided I can run the serial port connections from the cable to all of boards that need them in parallel. I dont think that this will cause any harm.

 THEN I have to figure
out a way to get the (only 2-3 watts) RF out of the powered up PSK board into the amplifier. I really don't want 5 rotary switches, one for each job. I though maybe I could put the RF from the 4 boards into an open parallel circuit of relay contacts, and when i applied DC to that relay, the contacts would close the rf from that board will go into the amp. Yes, I already know I can't get around a band switch for the HF Packer Amp.

Even if I DID find a high quality 5 throw,multiple pole switch at a decent price,I don't think there would be any isolation between the RF from the PSK boards and the audio in the audio in and out lines, not to mention the DC to that particular board.

I was thinking that maybe a 5 pole switch could be used
to kick in banks of cheap open paralel contact relays.
So say if I turned the rotary switch to the "20m" position, relays would kick in that would close the circuit to divert audio out, DC in, RF out in isolation
from the rest of the other boards.  Or is this WAY too complicated than it needs to be? I want the front of the rig to have two bandswitches, one for the psk boards, and one for the amplifer section. Of course
there will be some controls from the auto tuner but those will just be paralled switches from the auto tuner board, which I plan to isolate by dividing the enclosure horizontally in two, with the PSK boards on 'top' section and the amp and tuner on the 'bottom'
section with the divider double sided copper clad.

I MAY throw in an Elecraft W1 computing SWR/Power meter if I get the other problems solved but that is way, way down the on the list.

I have been thinking about this rig for a long time and it is one of my homebrew, or "Kit Brew" dreams.
All of those boards operate so well and I have had many, many QSO's all over the world with them. I just HATE having to disconnect one and hooking it up to the amp, then the tuner, etc, etc. Would be nice just to have a box
with everything, then all I would need would be my laptop, a 12v battery, and an antenna.

Thanks, any thoughts by all you guys who design your own rigs from scratch will be appreciated by this OM here who is only trying to throw some kits together in one enclosure.

You can also e-mail me at:
73, Ken  5R8GQ/AD6KA

Posts: 17481

« Reply #1 on: May 19, 2008, 11:02:44 AM »

The old-fashioned rotary switches with multiple contact
wafers on a single shaft often are used for DC, audio,
RF, etc. at the same time.  If you need additional shielding
you can disassemble the switch and insert a layer of
circuit board between sections.

Another approach is to use some of the electronic switch
ICs for low level signals.  Things like the CD4066 or
CD4051/4052/4053 would allow a single pole switch on the
panel to control multiple signals throughout the rig.
You can then use relays for the RF signals if you aren't
using a multiple-pole switch.

Actually most modern rigs make extensive use of diode
switching in the low-level signal paths:  multiple diodes
are connected to the common terminal and reversed biased
when not selected.  One of them receives a voltage from the
band switch to establish forward conduction and pass the
signal.  Relatively cheap and easy to do.

Posts: 203

« Reply #2 on: May 19, 2008, 06:11:27 PM »

Thanks for the helpful advice!
73, Ken  5R8GQ/AD6KA
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