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Re: MicroWave: 1296 Transverter design advice



> Date:          Sat, 27 Feb 1999 17:49:58 +0000
> To:            davemetz@muscanet.com
> From:          Steve Harrison <ko0u@os.com>
> Subject:       Re: MicroWave: 1296 Transverter design advice
> Cc:            microwave@wa1mba.org
> Reply-to:      Steve Harrison <ko0u@os.com>

> At 09:22 AM 2/27/99 -0600, Dave Metz wrote:
> >[snip]
> >
> >A big help in the transverter quest would be a cost effective wide band
> >amp to go from the 10 - 50 mW level to the 1 watt level.  From there a 
> >hybrid amp can take us to 15-18 watts.
> 
> You're looking for around 20 dB gain; no sooner sought than found!
> Consider, for example, using a MAV-11 followed by a HELA-10. Unfortunately,
> the HELA-10 cost is rather high at $19.95 plus another few bucks for balun
> input-output transformers (which you can easily wind yourself, however).
> And the HELA-10 is a fairly-inefficient power-sucker, too, requiring about
> +12V at around 300 mils for only a watt output power. Worse yet, it
> dissipates all that extra power through a solderable "slug" on its "belly",
> which must be sweat-soldered to a PC board ground plane with some surface
> area. I've use it and although it performs nicely in terms of distortion,
> man, did it get HOT!

I just read about the HELA-10 on Mini-Circuits web page.  A very interesting
device!  I wondered about the heatsinking too.  Devices that run hot bother
me.   You never know how long they are going to last.....  I like well shielded
circuits that run cool.   On the hand, at $25 with the baluns, a HELA-10 is 
a lot cheaper then a 10mW to 1W hybrid.   BTW, I've used the MAV-11 for
years, a great device!  The new ERA-5 is also very nice.  I've run them at
100mW out with no problems.
> 
> There are several other devices that used to be available, initially made
> by Avantek and then second-sourced by the SGS Thomson plant (which bought
> and resurrected the old Microwave Semiconductor Corp., MSC, plant in
> Pennsylvania about 1987 or 88). 
> 
> >From the 10-milliwatt-drive level, you might use a small pad to drive a
> MAV-11 or Avantek (now known as Avantek-HP) MSA1120, around 11 dB gain
> through 1 GHz and about +17 dBm power compression (50 milliwatts).
> 
> You can follow that with a Avantek MSA0520, which is sort of like the
> HELA-10 in that it has no heatsinking flange and must be solidly pressed
> against the PC board ground plane for heatsinking. This device only has
> about 8 dB gain in practical circuits and mine have compressed at just
> under 250 milliwatts (but is speced only to +23 dBm).
> 
> Or, you can use a MSA1023, also good for around 8 dB gain in circuits, but
> compression at around half a watt (+27 dBm). Best yet, the 1023 is in a
> small flange package for good heatsinking. 
> 
> Then in my 1296 XVTR for over a watt output, I used the Motorola
> MRA1000-3L, a 3-watt class A transistor which can be matched for good
> broadband performance from below 50 MHz to over 1 GHz at gains to 9 dB.
> 
> The fly in the ointments is that all of these devices have price tags in
> two digits.
> 
> The MAV-11 and HELA-10 both exhibit around 11 dB gain. The HELA-10 is
> actually speced for only 50 to 1 GHz, but with a handwound balun
> transformer using a Fairrite 2873002702 core, the 1-dB lower point drops to
> around 10 MHz. The MAV-11 will operate from DC to over 1 GHz.
> 
> Always subtract from 1/2 to 1 full dB from the specified gain figures if
> you are not going to use a high-quality choke to feed Vcc to these
> broadband devices. For the lower-power types, I try to set the amplifier's
> source Vcc high enough that the current-limiting resistance is at least 100
> ohms and preferably higher. For resistors, metal-film have proven best but
> sometimes, I've used carbon composition. I don't like to use the carbon
> comps because when they get hot, they change value and don't return to the
> original value.
> 
> Then I use a single small ferrite bead over the resistor lead connected to
> the broadband amp which helps a little more to isolate the resistor from
> the device's output and reduces gain drop due to the device's output load
> being both the desired termination impedance and the current-limiting
> resistor. I rarely use a molded choke because I've found that even if I
> order the same part number, manufacturing tolerances and changes in
> construction procedures sometimes cause a choke that did not originally
> have any undesired resonances below 1 GHz to now have something down there.
> And also, chokes using ferrite forms often will compress under high power
> which results in excessive distortion products (i.e., harmonics and IMD in
> the case of multiple-tone input signals).

I've even see ferrite saturation cause problems in broadcast audio equipment!
I would never place a ferrite bead on any lead that carried audio.  I've had
ferrite core RF chokes do strange things to.
> 
> If you don't keep the leads short on the resistor where it connects to the
> amplifier, the lead will radiate and can cause feedback to the front-end
> devices, resulting in oscillation.
> 
> In my former life in Virginia, I also used some wideband power FETs from
> PolyFETs. These were really neat devices because being FETs, the design of
> wideband input matching circuits was very easy to perform and build. Being
> FETs, gain figures were higher than comparable bipolars. And the devices
> were designed to operate into the GHz range. The major fly in the ointment
> with these was that having, as usual, double-digit price tags, a ham can't
> afford to blow too many before he's up a crick without a paddle. And I blew
> more than my fair share before I finally learned how NOT to blow them...
> 
> PolyFETs had a very nice and large application circuits handbook for all of
> their devices, the ones of which I tried working just as claimed (something
> kinda unusual for most RF FETs from other vendors, I've found).
> 
> >> Another consideration for the amateur is the fact that the lead spacing of
> >> these surface-mount devices dictates that interconnecting PC traces be much
> >> narrower...
> >[snip]
> >
> >Another desire of mine and perhaps not a practical one is to keep the
> >requirements for the PC board within the ability of the average homebrewer
> >to reproduce.  This is why I have stayed away from the "no tune" designs,
> >I'm not sure I could reproduce them.
> 
> I cut out PTFE-glass boards using an ordinary Exacto knife for these
> 50-mil-lead-spacing ICs all the time; it's not real difficult to do but
> requires more time and pretty good eyes (mine are going more each year). I
> feel the real key is to use a stainless rule to draw the circuit on the
> board and by which to cut the traces; simply trying to do the cutting,
> particularly of straight traces, by freehand, rarely comes out very neatly
> and leads to uneven trace widths which causes impedance bumps. The second
> most important aspect is to maintain a solid back-side ground plane and to
> use copper tape soldered to the edges of both top and bottom. When doing
> hand-cut boards of this type, it's often not easy or practical to bore
> one's own through-holes. So I try to lay out circuits that require
> excellent grounding close to the board edge where the edge-wrapping will be
> of greater value. Even so, one often will find that because the top and
> bottom ground planes have no via holes, they may be at slightly different
> RF potentials across the board. You may notice performance changes, for
> example, if you mount such a board right on a solid metal chassis; and so
> you may need to mount the board OFF of the chassis by a small amount. Of
> course, better yet is to mount the board inside its own shielded box.

Have you tried the Techniks, Inc PNP Blue laser printer transfer method of
PC manufacture?  It works amazingly well.  This is not to be confused with the
common waxed mylar laser printer transfer junk.  The Blue film really does work.
I've made 10mil traces with it all the time.  You can read about the process on the
SEITS website  http://www.seits.org or at the Techniks web page at
http://www.techniks.com  You try this method one time and you will toss your
exacto knife away!

> 
> Several years ago, I asked Rogers for a price quote on Duroid 5880
> (standard PTFE-glass board). They talked me into trying their new 2003
> board material, saying that the PTFE stuff was on its way out because of
> the difficulty in both edge plating and plating through-holes.
> (Subsequently, I discovered that this was true; of a half dozen PC board
> etchers in New England, I could find only ONE that would do via-hole
> plating on PTFE board anymore!!). This 2003 board was both cheaper and
> easier to plate the edges and via holes. BUT... it turned out to be almost
> totally useless, compared to 5880, for breadboard construction because it's
> much, much harder, which makes it really tough to cut traces evenly using
> an Exacto knife. I kept slipping and crossing "wanted" traces, for example,
> since the knife blade was no longer digging into the soft PTFE substrate
> material, which gives one some control over the knife's tip. Out of
> consideration for my finger tips (which I haven't sliced off yet), I quit
> trying to do hand-cut prototypes with the 2003 stuff.
> 
> Worse, this new 2003 stuff HAS to be cut with a saw; an Exacto knife will
> hardly make a scratch in the dang stuff (normally, I cut out PTFE boards
> using the Exacto knife which allows me to cut the board's dimensions to,
> usually, within 0.03"). Saw-cutting leaves as much dust residue as glass
> board (although without the glass dust flying around to make you itch all
> over for the rest of the day!). Rogers has several varieties of this 200x
> material with different dielectric constants for different applications.
> But ALL of the series is a very hard substrate that is murder on the knife
> blades! They had no comment when I objected how difficult it was to
> hand-cut prototype boards from it.
> 
> >Have you published anything on these designs.  The size alone is 
> >impressive!  Your transverter is smaller then one of the helical resonators
> >in my 220 rig!
> 
> No, for several reasons: most of the solid-state devices that I used were
> obtained as "scrap" from the salt mine from prototypes and breadboards, and
> are not anywhere close to what hams would consider "inexpensive" since
> their prices were in the lower two-digit range. But also, my transverters
> are essentially copies of lots of things pulled together from all the
> literature. And I doubt that pictures of the things would come out looking
> like anything other than some kind of Rube Goldberg apartment complex for
> rats! Anybody remember Bill Hoisington, K1CLL, and Frank Jones, W6AJZ, and
> all the neat V/UHF converters and QRP transmitters they published in 73
> magazine back in the mid- and late 1960's? My construction techniques are
> somewhat similar to theirs except that being the ham-fisted kludge that I
> am, my stuff never comes close to matching the appearance of those old
> masters (even if it eventually does work) :o(

I'm planning to buy a digital camera.  As soon as I do I'll publish photos of
my transverters.  I spend a lot of time on cosmetics.  For some reason I've
never been able to haywire anything.  Everytime I do, all the smoke gets out
of the parts :-)
>  
> But that's no excuse, I know: I like to read of some other guy's hand-built
> radio just to get ideas, not to simply copy his whole radio; so I suppose
> there could be as much interest in something I built that works, too. Maybe
> I'll try writing something up. The 220 XVTR might be of some special
> interest if only because the IF is 144 MHz instead of the traditional 28
> MHz; yet, the filtering is more than sufficient to keep spurs better than
> -80 dBc, including the 3rd harmonic of the LO at 232 MHz. But 220 MHz is
> just DC to this Microwave reflector, so I won't elaborate on that here any
> further.

Not really, I hope you do not mind if I  crosspost your excellent 
comments to the AMSAT reflector.  You made some most valuable points 
that others are interested in.  I would strongly encourage you to publish
some of your designs.  If no where else do it on a web page.  See the 
before SEITS webpage for some of my efforts, mostly two meter FM
speaking of "almost DC" :-)!  
> 
> 73, Steve Ko0U/1
> 
>--73-- David WA0AUQ 

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