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SAFE Ark Two Newsletter
August 11th, 2013
Radio on the Rampage
Once again the subject of the newsletter is the radio. It has been the
subject of my daily concern here now for years. I started this project
in February of 2011 which is over two years ago. I am going to once
again write a bit about the history so that you understand where we are
at.
The History
In the fall of 2010 I got my advanced Ham License and started looking
for the best solution for a SAFE Ham Net. For our members it needed to
be:
a. Simple
b. Reliable
c. Cheap
We did really consider EVERYTHING. There were very strong advocates for
anything you can imagine. Modified Citizen Band, RTT (Radio Teletype),
CW (Continuous Wave) Morse Code. I could list thirty others. Most people
who suggest that we do something different have not really studied the
problem.
We thought we had found a remarkable solution. The designer of the
system, Skip Teller, had a truly genius idea. A simple little radio
built around a NTSC color crystal. This is what was used to provide the
color bar on old TVs. The crystal was dirt cheap and readily available. A
number of people used his circuit or modifications thereof.
The first such radio was called the Warbler and there were raves about
it. I tried to get the kit manufacturer to provide us his boards but he
refused and suspended production. We hired an engineer to build our own
board based on the circuit but got ripped off and he provided us
absolutely nothing.
We quickly went through three more engineers. They all had problems but
with the fifth engineer we finally got a bench prototype working and
built a prototype board. This latter (the present one) we could never
get to work satisfactorily. It turns out that the crystal system had a
stability problem. This is why the Warbler was discontinued. We thought
it was just an amateur user assembly problem and that we get around it
by controlled manufacture - but it turned out to be more serious than
that. Fatal.
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Our Engineer felt that other manufacturers such as Softrock would have
the same difficulty when we tried to use their designs to drive an
amplifier. There was nothing to do but start over. Once again we
reviewed everything that was out there and what had happened in the
interim. SDR (Software Defined Radio) had always been a dream and we
thought we had found a lead in that direction but it turned out that it
was going to be way to expensive.
Suddenly, in this seemingly hopeless situation, Carlton found a
completely new and different solution. Actually, a very old solution.
Since Skip's solution of the inexpensive NTSC crystal wasn't going to
work - someone else had decided to go back to 30 year old technology and
had designed what they called The Survivor Radio. It supposedly became
available in February of this year but we probably won't be able to get
our hands on a kit until around October. The distributer is undergoing
remodeling and their answering machine says that I can't even talk to
them for another week and it will take that long before we could get
delivery.
The New Survivor Solution
a. It is not simple
it is a kit that you have to build.
b. It is not reliable
(it is rated at 10w) and we feel that we need 20w.
c. It is cheap.
Our New Solution
a. Simple
we would have the units factory built
b. Reliable
We would modify the design as discussed below
c. Cheap.
Under $200 as was our original goal.
Details about the Survivor
Until I can reach the company I have no idea how we might cooperate with them. However, here are the details:
The Survivor is based upon the Epiphyte, a ssb transceiver designed by
the now deceased Derry Spittle, VE7QK. Some modifications have been made
to that circuit by Steve at http://kd1jv.qrpradio.com/
I have talked with Steve and we are free to do our own redesign of the
circuit. You can look at the Survivor as it now stands at http://www.qrpkits.com/survivor.html
On the latter link you want to go about half way down the page and look at "The Background of the Survivor".
To really understand about it download the .pdf for the Survivor Assembly Manual
Details about the Modifications we would like to make
One engineer in our group has suggested:
1. that we might more fully utilize the Power MOSFETS and that the one they used COULD net 60 watts out.
2. that twenty five components of the 2N3904 "Gain Blocks" could be
replaced with one op amp chip if done in a modern way, and would work
better than a bunch of NPN discretes and support components.
3. that there may not be much receiver sensitivity since the antenna drives a mixer chip.
4. that it would be better to replace the VFO tuning that is being done with a zener diode, with a variactor.
5. that regarding the IF filter string... a pair of narrow 10.7 crystal
filters and a 10.7 carrier oscillator for a good voice-grade bandpass
would provide a full waterfall in our application but I am wondering if
it may not be that our waterfall is software restricted rather than
hardware restricted.
6. that the "SA612A" data sheet needs to be checked to see if these are deployed properly.
7. that the Q4 & Q8 stages and support components can be replaced by
1/4 of a modern Quad op amp. As shown, it is right out of the early
1960's.
Q4, a soft transistor is driving an untuned T2 for a mere voltage step
up for the gate of Q16. These MOSFET's gates are essentially a big
capacitor. A torroid is NOT the best way to present a signal to them.
And, the gate will pierce [damage] and at surprisingly low voltages.
Driving the gate directly with a modern hard op amp is the preferred
method. (Another section of the quad) This way, the Vcc rail will not be
exceeded and the gate not killed.
8. that Thermal tracking for the Class B operation (an unpreferred
method for MOSFETS but can work, is more simply facilitated at the input
of the driving op-amp. Presenting a one-fifth-ohm load for the MOSFET
in order to get 60 watts out will need a far different output network.
If one were going to change all of that, then change all of that to a
Class D PWM output which these days is an easy task with modern design.
9. that the need for a heatsink would likely vanish, then.
Not all our people agree with all these points. Another engineer says:
I'm not sure I agree with some of the fundamentals -- like driving a
power mosfet with an op-amp? That seems like one of the worst ideas I've
seen. Mosfet gates have a lot of capacitance and also a lot of "charge"
related to the gate-drain junction, and most op-amps (not all) are very
unhappy driving capacitive loads. I've not analyzed the circuit but the
2n3904 is a pretty versatile part... And besides, you want a linear
amplifier here, so the FET is biased partially on so that it is
operating in a linear fashion (meaning that you don't want to be
switching it hard, you want to be driving it "soft"). If it were a CW
transmitter you could slam everything on/off hard and simplify the
design, but SSB/PSK/AM/ETC you really want something resembling linear
operation.
Some of my own comments:
While 60w would be splendid - our original target was 20w - but I agree a bit more would be even better.
I think that since the Survivor uses the PTT on the microphone that we
would also need to add a PTT switch - or at least put one in the
microphone line coming from the computer.
I am wondering if antenna tuning and RF isolation might not still be
concerns. The latter might still be helped by doing a two board design.
Most everyone other than Adam agrees about this - but Adam prefers a
single board design.
The current Survivor design will fit into our shipping can - although we might need to look for a couple of lower profile knobs.
The current Survivor cabinet is only half the height of our proposed
cabinet - so our proposed cabinet would accommodate two boards - and
provide the additional room for the increased MOSFET Power and increased
RF with a separate amplifier board - and provide better grounding on
that board.
So there - you have all the current thinking. I will try to answer any questions you may have.
The Current Strategy
I have been energetically trying to find an engineer who can execute
these design changes. The reason that I am putting all these details
into the newsletter is that I hope you will share them with any
engineers that you know and help me in my search.
Today alone, I have gone through the qualifications of over 400 EE RF
engineers and have sent invitations to 17. I have gotten back 7 replies
but none of them turned out to be qualified.
Current Situation at Ark Two
We are definitely getting older and needing help. Two nights ago had to
go to emerg for the first time in a year. Wouldn't have gone but was
deteriorating and concerned if I got worse I knew that Jean couldn't
take me and we would have to call an ambulance.
When I got there alone it turned out unknown to me that my blood
pressure was 157 and I was running a fever. They got it back down to 127
(I don't generally have high blood pressure) and stopped the fever
before they sent me home with a bag full of medicine for the next day.
The good news is that they did a CAT scan and I don't have a kidney
stone - which is what they suspected. Just an infection and I am on an
antibiotic for the next two weeks.
The weird thing is that I can't lie down. No pain sitting up. So I sleep in my chair. But only naps - so I am getting lots done.
Peace and love,
Bruce
DawnSayer@webpal.org
US National
Coordinator's Corner
Christopher Verreos
coordinatorsafeusa@gmail.com
Christopher Verreos and his wife Regina
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Greetings SAFE Team!
There's a lot going on, but first, we need to keep the recent flood
victims and others who are in need in our prayers!
Can you imagine dealing with your home being washed away - really! OK,
now imagine that happening in the pitch black of night! Throw in the
separation of family members and you start to see what I'm talking
about. Play it SAFE!
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Now that member lists are being distributed by our Database Mgr.
Jonathan Lucas and his Assistant Nick Soriano,
SAFE is entering a new phase. SAFE members in each state will quickly be
able to network in a whole new way!
Each STL is being asked to develop a Yahoo User Group or equivalent to
facilitate things.
Each STL has been asked to appoint at least two Assistants, and identify
any HAM radio operators in their state, and report that to their
Database Mgr.
Several STLs have already gotten their User Groups rolling, and I have
to say - YOU ALL ROCK!
One suggestion came in from Matt in Kansas: Have STLs invite each other
to their respective User Group/Bulletin Boards. It's optional but has
potential for much good. Please consider it.
As you know, SAFE doesn't sell anything, nor do we want your money. We
also DON'T want burnout! Please know that the coming developments should
not require much time/effort. The emphasis was and still is on
creating/developing our networks/Triads. STLs: 1) please find members
who are eager to assist and plug them into your network, 2) please feel
free to contact your RTLs. If that fails, contact me, and I'll do my
very best to help. Thanks to you all, we're making good progress. Stay
SAFE!
Peace & Action,
Christopher Verreos
National Coordinator, SAFE USA
coordinatorsafeusa@gmail.com
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Bruce Beach
161 Main St.
Horning's Mills
Melancthon
Ontario L9V 1X7
Canada
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