Running a Tube-Type Radio on "Car Batteries" - PART 1-

This was starting to get a bit looong, so I'm splitting it into two parts... 

I also made a few changes so "Part 2" shows up after "Part 1".

I was having a discussion with Harry over on his blog on the subject of shortwave listening, types of receivers, and other things.

I made my standard "If you're worried about EMP, take your little solid-state (transistorized, but more likely uProcessor controlled DSP radio these days) radio with the batteries out (because if you don't, you will forget they're in there, they will leak, and likely ruin the radio. Trust me, it WILL happen!), and seal it up in a steel ammo can, using adhesive-backed aluminum tape on all the seams. NOT aluminum colored duct tape, but real metal aluminum tape. You can get it at big box home improvement stores. This gives you a homemade Faraday Cage, and should protect the radio".

Have I tried this?

No, mostly due to the lack of a suitable EMP generator, but I consider it sound advice, knowing what I do about EMP.

I'd tell you more about why I know this stuff, but uh...well...you how that goes...

Yes, you could make a special box from "Mu Metal", but Mu metal is expensive, hard to work with, and generally difficult to buy in small quantities.

Then we started talking about types of receivers, and the subject turned to tube-type radios.

Tubes are inherently "hardened" to EMP because of their construction. They have large metal elements, separated by substantial spacing (compared to solid-state devices), and all the metal elements are encased in a vacuum envelope. Granted, the vacuum isn't "perfect", but the breakdown voltage (aka "Dielectric Strength") between two metal elements in a vacuum is is substantially higher than the breakdown voltage in air.

Wikipedia lists the breakdown voltage for air as 3e6 (3,000,000 Volts) per meter of spacing, and vacuum as 10e12 Volts per meter.

That's TEN TERRA Volts per meter, a staggering amount of voltage!

That's a thousand billion Volts.....

Speaking in term of "Volts/mil" (voltage per .001"), air breaks down and conducts at around 800 Volts per .001" of spacing (I always remember "1000Volts/mil") and breakdown in a vacuum is something like a MILLION times higher.

ANYWAY......before I ramble too far off the original topic, tubes should survive an EMP (especially if powered off), while conventional "wisdom" claims solid-state devices will be destroyed.

SO......In all of our favorite TEOTWAWKI/TSHTF novels, there always seems to be some "Old Guy" who just happens to be a Ham operator, always "lives on a hill top", has "big antennas", and he just happens to have some old tube-type radios laying around. Of course, they get pressed in to service powered up by "car batteries" scavenged from all the abandoned/broken/non-functional cars which just happen to be strewn around everywhere.

It makes for a great read, and shows how ingenuity can overcome adversity, but would it work?

Well, that's what I'll try and analyze here (whew! finally got back on topic), and give some recommendations for trying to do this.

The closest radio manual I had at hand is for my Heathkit SB-310, so that's what I'll go with. This radio is not "100% Hollow State", as it has three rectifier diodes in the power supply (B+ and bias rectifiers), two "small signal" diodes for the Automatic Noise Limiter ("ANL"), and two more small-signal diodes in the Automatic Gain Control ("AGC") circuits. Since this is an AC to DC conversion, the rectifier diodes will be bypassed, and you can use the receiver with the ANL and AGC diodes clipped out of their circuits if they get blown from an EMP-type event. It wouldn't be as "pleasant" to listen to with those two circuits disabled, but it will work just fine without them.

The principles involved with doing this to most any tube-type receiver would be the same, but some of the voltages will probably be different.

YMMV, don't try this at home, don't blame me if you get zapped or blow up your receiver, and yes, I am a professional at this stuff!

First, let's look at how the receiver is powered during "normal" operation.

Tube-type receivers use a power supply (transformer, rectifiers, filter capacitors, dropping resistors, and possibly a filter choke) to produce the required voltages from the 120 VAC power line.

There are (usually) three voltages required to make the receiver operate:

1. An "A" voltage, which is the filament voltage, either 6 Volts or 12 Volts. Some receivers may have a mix of both 6 and 12 Volt filament tubes in them. The filaments "don't  know/don't care" if they're being fed AC or DC. Some people claim that running the filaments from DC will give a "quieter" receiver, while others claim that running them from DC will shorten the filament life due to metal transfer off the filament to the other tube elements, similar to what happens during electroplating.
Way back when I was repairing/modifying electronic stuff for all my musician friends, I did a full make-over on a buddy's Fender Twin Reverb amp. I went completely gonzo on it, beefing up the power supply, regulating all the voltages, converting the filaments to a regulated DC supply, redoing all the grounds inside, and shielding the daylights out of it. *I* couldn't tell much difference, but *he* could, and I wound up doing a half-dozen or so for other people. AFAIK, there was NO difference in tube life.

2. A "B" voltage, commonly called "B+", which is the plate/Anode supply voltage, and generally the highest voltage in the radio. Sometimes there are multiple B+ voltages used at different points in the circuit, and these are generally derived from the highest voltage using dropping resistors. This voltage is always well filtered DC, and in some cases is regulated over a narrow range. This voltage is positive with respect to ground.

3. A "C" voltage, which is the bias voltage applied to the tube grids, and used to set the "operating point" of the tube. This voltage is negative with respect to ground.

In "Ye Dayes Of Olde", long before residential homes were wired for that new-fangled "AC" stuff, these voltages were all supplied by batteries, so running tube radios on batteries is nothing new.

An "A" battery powered the filaments, a "B" battery powered the plates, and a "C" battery provided the bias.

First, we have to deal with how to get the voltages we need from "car batteries", and discuss some things about "car batteries" that need discussing. Then we'll move on to modifying the wiring in the radio to use our new external voltage sources.

At this point some of you are probably scratching your head and wondering why all this talk about using ONLY "car batteries" to power the radio, and you'd be correct. The simplest thing to do is get a 12 Volt DC to 120 Volt AC inverter, and just run the radio that way. Most receivers don't draw a whole lot of power, so you don't need a big inverter. The SB-310, for example, only draws 50 Watts AC power, less than 1 Amp, so even a small El Cheep-O inverter like this $20 one from Harbor Freight would work. My Drake R-4B, a superb ham band only receiver, draws 60 Watts, still well under 1 amp of AC line current.

BUT, as all the stories go, we're stuck using "car batteries", so that's why I'm writing this (very long...) post.

You'll notice I keep putting "car batteries" in quotes. There's a reason for that.

"Car Batteries" fall into a couple of broad classifications. First, and most common, are what's called "SLI" rated batteries, for "Starting, Lighting, and Ignition" batteries. This type is designed to put out a huge blast of current (several hundred amps) for a short time to get the vehicle started, and then to be recharged by the alternator immediately. They do NOT like to have a constant, low drain applied to them, like the drain that a radio would cause. If used in this service, they will not produce their rated "Amp Hour" capacity, will go "dead" quickly, and will get to the point that they will no longer hold a charge, or even accept a charge. I've personally ruined several SLI batteries by using them as a back-up power source for my "12 Volt" Ham radios. Even though I kept them charged with a properly deigned "battery tender", and watched them carefully, they never lasted more than 12 months.

Expensive lesson, but well-learned.

The next common type is the "Deep Cycle" type. These batteries are designed uses that require a lower current draw for extended periods. Sometimes they're called "motive" batteries, and are used for wheel chairs, golf carts, trolling motors, and solar power storage. Every time I've replaced my car battery I've always replaced it with a deep cycle battery, as there's times I'll run my radio for extended periods without running the engine, and I want to make sure I have enough power left to start the car.

And within the battery types are some sub-classifications depending on the type of construction used.

"Flooded" types have the liquid electrolyte (aka Battery Acid) and removable caps to check the levels. Most of us grew up with this type, and are somewhat familiar with it. I always used distilled water to top off the level, although many sources say that any potable water is OK. Personally, with the cost of distilled water being so low, I could never see using tap water, especially in areas with hard water.

"Valve Regulated Lead Acid" (VRLA) batteries were first seen in the late 1960's, and were marketed as "Maintenance Free" batteries. They used a slightly different chemistry and construction/

"AGM" or Absorbed Glass Mat batteries are newer still, and have a different construction that keeps all the electrolyte in a fiberglass mesh.

And as of 2016 some cars are using Nickle Metal Hydride and Lithium Ion batteries for their power source.

So, with that said, be aware that using old fashioned, flooded construction SLI batteries would work, but the batteries probably won't last as long as you'd like.

Now as to "How Many Batteries Will We Need", we need to look at voltages, and we'll use my trusty SB-310 as our example.

The SB-310 "requires" 185 Volts for the B+, -85 Volts for the Bias, and 6 Volts for the filaments.

Nominal, fully charged voltage for a "12 Volt" automotive battery varies some with the type. We'll go with the current VRLA batteries as they're most common in newer cars.

Fully Charged = 12.66 Volts

50% Charged = 12.10 Volts

25% Charged = 11.95 Volts

  0% Charged = 11.70 Volts

We'll pick 12.5 Volts just to make the math a bit easier.

185 Volts/12.5volts-per-battery= 14.8 batteries.

Kinda of hard to have 8/10ths of a battery, so we'll say 15 batteries.

Fully charged, 15 batteries gives 189.9 Volts, a few volts higher than the nominal 185 Volts for the B+, but nothing to worry about. These radios were designed with 10% tolerance resistors, and most of the capacitors (except in critical tuned circuits) were about as "loose", and the AC line voltage was never exactly "117VAC", so plus or minus a few Volts on the B+ isn't going to matter.

Fully discharged, we'd have 175.5 Volts, enough to keep the receiver running, but pretty hard on the batteries.

For the -85 Volt Bias Supply, we have it easier. Since the Bias Supply is feeding the grids of the tubes (a very high impedance), the resulting current draw is extremely low, on the order of microamps. Rather than lugging another 7 car batteries to make the bias supply, it's much easier to use ten 9 Volt "Transistor Radio" batteries, or any other combination of standard dry cells that gives about 90 Volts.
Then we'd make a simple resistive voltage divider, and adjust the voltage for the 85 Volts (or other required voltage) we need. The bias voltage is a little more critical than the B+ voltage, because if the tubes aren't biased close to where they should be, the radio won't operate properly.

This radio has  6 Volt filament tubes exclusively, with a total draw of 3.3 Amps.

While there are ways to drill and tap into a 12 Volt battery at the 3rd cell and get 6 Volts from it, I've never done it, and only seen pictures of it. I'm going to assume that whoever is attempting to do this (the old "Ham on the Hill"!) has a pretty extensive "Junque Box", and would just make up a 2:1 resistive voltage divider, and use a single 12 Volt battery for the filaments.

So that gets us our required operating voltages. 15 car batteries in series for the B+, one more for the filaments, and a bunch of dry cells for the bias voltage.


In "Part 2" I'll get into modifying an actual radio

Running a Tube-Type Radio on "Car Batteries" - PART 2 -

OK....on to the radio....finally!

There's nothing magic or wizardly going on here. The circuitry doesn't care if the voltages come from AC, DC, Solar, Nuclear, coal, or filtered unicorn farts. If you supply the radio with the correct voltages, it will operate.

In order to take an AC powered radio and run it from batteries, we'll need to make some changes to the wiring. Specifically, we'll need to connect the correct voltages to the correct circuit points for both the B+ and Bias supplies. To do that we'll add some wires to those points and bring them out of the radio for the external power to be applied, along with a ground connection to a new plug.

And we'll need to separate the filament wiring from the secondary of the power transformer, and bring those two (or three, in the case of a radio having both 6V and 12V filaments) leads out, too.

So, we'd need to use a 6-conductor plug and socket, rated to withstand, say 300 Volts.

But in a real SHTF/TEOTWAWKI situation, we'd probably just run wires out of any convenient opening in the radio case.

Here's the schematic for the power supply section of an SB-310 General Coverage receiver:

Just about smack dab in the middle, you'll see two symbols that look like right-pointing arrows, labeled "D6" and "D7". The right side of this symbol, the direction the arrow is pointing, are the positive (Cathode) ends of the rectifiers. Solder a red wire to this point, and bring it out for later connection. The wire has to be rated for at least 300 Volts to be safe, but wouldn't have to be much more than 20 gauge as the current draw is pretty low. Since we'll be feeding in a positive voltage, and that voltage will be blocked by D6 and D7, no other surgery is required. *IF* D6 and D7 are shorted (blown by that commie EMP blast!), just clip them out of the circuit.

A little below that point, you'll find D8, which is the rectifier for the bias supply. This time you'll want to solder an orange wire to the junction of D8, the capacitor C233, and the resistor R211. This will be where we apply the -85 Volt bias supply. If D8 is shorted, just clip it out like you did to the rectifiers.

Damn commies.....

Underneath the chassis should be numerous terminal strips. Look for one with a "foot" that's grounded, and solder a black wire to it.

On the terminal strip pictured below, the "#2" position is the "foot" I was talking about, which bolts it to the chassis, and provides a ground point.

That takes care of the "high" voltages. Just make sure the red, yellow, and black wires you added are long enough to come out of the radio a foot or two, so you'll have some length to work with when you connect your battery bank.

For the filaments, we'll have to be a bit more careful. Since we'll be using DC to power them, we must disconnect the secondary winding of the transformer or otherwise it will short out the new DC supply to the filaments.

Look back at the schematic for "T1", which is the power transformer. You'll notice (sorry, but I'm assuming you can "read" a schematic...) that leads "1" and "3" are the yellow filament power leads. One side is grounded, which means it's common to the B+ and Bias supplies. Pick the yellow lead that's NOT grounded, and cut it loose from the terminal strip. Add a new yellow wire to this point, and bring it out like you did the others.

That should complete the modifications to the radio. Simple, and pretty easy to reverse if the AC power ever comes back!

The battery connections will simply be 15 car batteries connected in series, with the positive lead going to the red lead coming from the radio, and the negative lead going to the black lead coming from the radio, and that takes care of the B+ supply.

For the bias supply, you'll have ten 9 Volt transistor radio batteries in series, with the NEGATIVE side of your battery stack going to the orange wire coming from the radio, and the POSITIVE side of the battery stack going to the black lead coming from the radio.

For the filament supply, you'll have a single battery in series with a 2 Ohm, 25 Watt resistor (drops the 12 Volts down to 6) on the positive side connected to the yellow lead coming from the radio, and the negative side of the battery going to the black wire from the radio.

Will this work, and power the radio as if it were plugged in?

I have no doubt it will. As I said at the beginning, the radio doesn't know/doesn't care where its power comes from. Apply the correct voltages to the correct points in the circuit, and it will function, assuming it was an operating radio to begin with.

If anybody wants to loan me 16 car batteries, I'd be willing to modify the receiver just to prove this will work!

Personally, I'd rather just buy a few inverters and some extra ammo cans to keep them in. Saves a lot of work lugging batteries up the hill the old Ham lives on.......

Now....a few words of caution here.....

CAUTION! 

You've just built a 185 Volt DC power supply capable of SEVERAL HUNDRED Amps output.

This is a LETHAL voltage source! You will NOT get a second chance if you accidentally contact the positive lead while grounded.

Use EXTREME care when operating this power supply!

You have been warned!

It would definitely be a good idea to fuse the positive lead of the battery string, and properly insulate ALL exposed metal connections, but make sure you use a fuse rated for 250 VDC, and with a very high "interrupting rating" so that the fuse doesn't turn into a bomb. Fuses for this service usually are packed with sand, and use a ceramic body instead of glass, so that when the fuse link inside opens, the grains of sand fall into the gap, and quench the arc. Otherwise, with a supply this "stiff", there will be enough energy available to keep the arc "lit" when the fuse link opens, and a plain glass body fuse will violently disintegrate, possibly causing somebody to get hurt.

And a 1 or 2 Ohm, high wattage current limiting resistor in series with the positive lead wouldn't hurt anything, either.

Thoughts on Iowa

No, not my beloved BB-61, but last night's goings on.

I'm no political analyst, and I sure don't play one on TV, but a few things immediately struck me.

1. Hillary is in deep doo-doo. If Bernie Sanders can wind up in a dead-heat TIE with her, I think she's doomed. I wonder what's going to happen next week in New Hampshire....

2. Cruz is much stronger than I expected, and I think that's a Good Thing. I thought the final numbers for Ted and The Donald would be flipped around. And Rubio's results surprised me, too. I figured he'd get about half what he did. Carly and Dr. Carson did poorly, and I wonder how much longer they'll slug it out. I think Dr. Carson is a fine man, a wonderful surgeon, and a great example for young people of ANY race to emulate, but I'm not sure he's got the stones to be President.

3. O'Malley and Huckabee are doing the right thing. I'm sure we'll hear more from them.

4, The people of Iowa were sure full of surprises, weren't they?

Voting, and other distractions.....

Found cartoon over at, and shamelessly borrowed from, Rev, Paul's place.

I haven't decided yet who I'm 100% behind, but it sure aint The Hildebeast.

Some people say we're too far gone to "vote ourselves out of this mess", and that ANY candidate is merely a puppet for one of the New World Order groups.

I don't think we're quite past Claire Wolfe's "Awkward Stage", but we're pretty damn close.....

If you or I tried some of the stuff The Hildebeast has done, we'd be locked up in a "Federal Pound-Me-In-The-Ass Prison", probably for 25-to-life.







And yet The Hildebeast continues to walk free, and is even running for President.

I wonder who I ticked off, to be consigned to live in such "interesting" times......

Friday Already?

Still waiting for the "4-pin" cable from the Maestro RR people so I can finish installing the new Kenwood radio into my Jeep. They're in Canada, so it might be here today, but I'm betting it won't be here until next week.

And the two switches on the steering wheel that control the radio channel selection (left switch) and the volume (right) switch haven't shown up yet, either.

The USPS "tracking number" claims they were delivered last Saturday, but my buddy where my mail drop is hasn't seen them.

I dropped the vendor a note, and he sent another set out on Wednesday, so they also might be here today since he's in AZ.

And of course, it's supposed to rain some this weekend, starting on Saturday night. *IF* the parts get here today I should be able to swap out the radios tomorrow before it starts raining.

And on the Iowa, we were (FINALLY!) able to get audio routed from one of the "Red Phones", through the "Coke Machine", and the transmitter audio switchboard, down to transmitter #3, and were able to get 500 Watts output from the transmitter into the dummy load. We then noticed that the Power Output knob was backed off a bit, and once we ran that up to max, we were getting 1000 Watts out.

The Power Output control knob is VERY nonlinear in it's action, and turning it down just a few degrees drops the power from 1000 Watts to 400~500 Watts. We don't really need full power out of the transmitter, and considering the two antennas we'll be using, we don't WANT 1000 Watts, as the tour route gets to within 5 or 10 feet of the antennas, and we have to limit the RF exposure to our guests.

On The Workbench This Week

Only this time it's not something being repaired, but something being assembled.

A few months after I bought my Jeep in the fall of 2006, I decided I wanted a navigation unit for it. I'd just helped my son install a Pioneer AVIC nav radio in his Xterra, so I started looking into an aftermarket unit, as the Jeep came with a pretty generic AM/FM/Sirius radio with a single-disc CD player, and I wanted something more integrated to the vehicle so I wouldn't have to reach over and grab my hand-held GPS when I wanted to see where I was.

WELL......at that time, in order to keep my steering wheel controls, I would have had to add several aftermarket modules, and cut into the wiring harness in several places, and it still wasn't guaranteed that everything would work.

SO....I opted for an OEM navigation unit from an eBay seller who came highly recommended on several Jeep forums.

I bought the radio at a great price, and then got the replacement plastic bezel for it, and installed it in less than 45 minutes!

The first thing I was unhappy with was that it did NOT have a touch screen, and I had to enter the street name and number one.....character.....at.....a.....time.....using the scroll knob.

What a huge PITA!

You simply didn't have enough time at a red light to do anything, and as soon as your speed went over 5~7MPH, it would lock out the front controls, so your passenger couldn't even use it!

Yeah, I understand the safety aspect, but if the car's  computer is smart enough to trip the seat belt warning chime when my dog is riding with me, why couldn't it be "smart" enough to sense a passenger is there, and unlock the controls so the passenger could make adjustments?

Damn lawyers.....

ANYWAY...fast forward 10 years to the present. The joystick/scroll knob used to input data or move the on-screen navigation cursor has been getting intermittent, and the 6-disc CD changer has gotten to where it maybe will/maybe won't play a disc, depending on ambient temperature, the day of the week, and possibly the phase of the Moon. It might be fixable, but I 'd really like a touch screen, and the Sirius/XM tuner has started getting funky, too, dropping signals and suffering "digital breakup" more and more often.

Things have progressed to the point that I was able to get a single box adapter that splices in between the OEM plugs in the car, and the wiring harness for the new radio, and retain full functionality of my steering wheel controls.

This little gem is called a "Maestro RR", made by Automotive Data Solutions, based in Montreal, Canada.


Just a little black box that captures and manipulates the data from the steering wheel controls, and turns it into something the radio can understand.

So, being somewhat of a Kenwood aficionado,  I ordered a DNX771HD from Cructchfield, a Maestro "Rr" interface unit, and all the other wiring harness adapters.

After going through some of the spotty documentation, I finally figured it all out and sat down and soldered the two wiring harnesses together.



Here it is, with the Kenwood on the left, the Maestro RR module in the middle, and the gray plugs on the right  which connect to the existing Jeep OEM wiring harness:

The Maestro RR module also has connections to the OBD II port, allowing various engine parameters to be measured, and displayed:

And it all plugs into the Kenwood radio using the Kenwood OEM connectors:

I used my typical "Good Amateur Practice" from the ARRL Handbook, and soldered the connections together, and covered them with heat shrinkable tubing:

And then we hit some snags.

The M5 screws provided with the Kenwood were too short to go through the thick plastic brackets in the dashboard adapter, so I had to hit the hardware store for some longer ones:

And, of course, some washers to spread the clamping force on the plastic, so it won't crack, which I've had happen before:

Since installing an aftermarket head unit loses control of the OEM Sirius/XM radio, a new receiver module is needed, seen here with the mating plug to the new head unit:

The new receiver has a $70 up-front cost, but when I call to cancel the service on the existing one, and activate this new one, I'll supposedly get a $70 gift card, making the receiver essentially "free". I'm also told that any remaining time on my existing contract will be added to the new contract for this new receiver.

And finally, the last remaining snag that stopped me from having this installed this weekend.....

This radio is an "iDatalink Compatible" model, which means that it's designed with the Maestro module in mind. Besides all the small plugs on the Maestro adapter harness and the OEM harness, which allows the Maestro to tap into the CAN bus of the vehicle, there's two addition connectors on the radio that go to the Maestro module.

WELL.....guess what? One of the cable assemblies that transfers data between the radio and Maestro module was missing from the new, sealed box the Maestro was in!

I went to "the12Volt.com" forum, where the Maestro technical reps hang out, and after a few days, I have a replacement cable on the way. Hopefully it went out Monday afternoon and I'll have it by Friday, but with the weather problems on the East coast, who knows when it will show up.

I'll do another post detailing the actual installation into my Jeep Grand Cherokee and a mini-review of the whole shebang once I get the missing cable.

Background Checks?

Found this over at Miss Lisa's blog.

It's funny, true, and very sad, all at the same time....

Any Huey Pilots Out There?

I've flown in the Bell civilian version of the twin-engine "Huey" (a Bell 212, IIRC) numerous times, but never in a real UH-1.

My question is based on what you see in the movies, where the pilot jumps in, starts flipping switches, and gets airborne really quick,

BUT, since we all know Hollyweird tends to take great liberties with real-world things, I know it's probably not anywhere near realistic.

So, assuming your bird is sitting there in good flying weather, full of fuel and fluids, and is 100% preflight checked, and tagged as  "good to go" by a Crew Chief you really trust, and you have clearance for immediate take-off, just how fast could you get airborne?

This is a real, "somebody's life depends on it" scenario, where you roar up to your bird in a Jeep, jump in the bird, and start flipping switches even as you're buckling up and getting your helmet on.

When I was flying with the contractor pilots at Sea Launch, it was all extremely scripted and scheduled. They stroll out to the bird, climb in, buckle up, put their helmets on and plug-in, and run through their preflight checklist, and then start waking up the bird. They always had enough time that they'd sit on the pad, engines idling, and rotors turning, until they received clearance, and then they'd power up and lift off.

It probably took about 30 minutes from when they got in until they lifted off. Safety was tantamount with everything these guys did, and they were very good pilots, well experienced with off-shore operations, and landing on a moving, pitching, rolling platform.

So, assuming things are damn near perfect before you launch, how fast can you get airborne?

RIP Glen Frey

What a bummer.....

The Eagles have always been one of my favorite bands, and now they've lost one of their founders.

Truly a sad day for music....

One for Miss Lisa and Wirecutter

Enjoy!

Antenna Work, Part II

OK, so I dropped the antenna down today, and swapped out my homebrew PVC adapter for the OEM metal version.

I took a bunch of pictures....BUT.....I had my camera set wrong, and the pix came out so overexposed that I couldn't even save them with GIMP.

So, all I have to show are some before and after plots, and those didn't covert very well, either.

Here's the 2 Meter VSWR graph with the plastic mounting:

And here it is with the OEM metal mounting:

Here's the 70cm plot wth plastic:

And here's the plot with the OEM metal mount:

Sorry for the terrible size disparity with the plots. I had to "print to file" on the Windoze machine, then convert them to png's on the Linux machine, and the "print to file" utility that creates the pdf dows whacky stuff.

I have the Linux version of the capture/display software for my AA-520 analyzer, and I think it's high time I install it, and learn to use it!

ANYWAY......the plastic vs metal plots don't look much different, so I'm not expecting much difference in performance. I called "CQ" on our "club-comm" frequency of 145.510, but couldn't raise anybody on either radio, so I assume they're all busy tonight.

Now one thing kind of jumps out at me, and that's how FLAT the VSWR curve is on 2 Meters. That kind of "flatness" over a wider bandwidth than the antenna is rated for can be indicative of an excessively lossy feedline.

I'm going to run some plots on the little GP-1 antenna, and see if it looks more like the published curves. I physically inspected the feedline on the GP-3 today, and there's no external evidence of damage to it, the PL-259's are properly soldered and the one at the antenna was still nice and shiny and clean after I took the tape off of it.

Yeah, I know, I should have made some loss measurements, but I got clobbered with some Honey Dews right in the middle of this today.

It's an easy 10-minute job to lower the antenna and disconnect the coax, so if the plots on the GP-1 look like the ones Comet publishes, I have a feeling I'll be dropping the GP-3 down again on Monday......