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SpitFire AM Transmitter

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WOES was a High school

WOES was a High school station running 100 Watts I think it was 91.5 Mhz.  It broadcasted around 1979-1985 or so and my friend Dean played some great Album Rock.  The format was Adult contemporary during school hours till 3pM and Rock till 5 PM Mon-Thurs and Friday Rock after 3pM-9pM.  They too had listeners.

 

 

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

More Power for Hobby Broadcasters

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Back On Topic

Anyone wish to comment on the SpitFire AM Transmitter?

:-)

Doug

ATU

Dugger,

I am curious about the ATU section of the Spitfire.

What do the instructions say about it's operation?
How does it work? Is it hand tune from a pot in the transmitter or automatic?

Barry

 Barry of Blue Bucket Radio 1620 AM  - http://bluebucketradio.com - WQYY 664

The Internal ATU

There is a 4-DIP Switch ATU and a trimmer cap, Barry. I had no luck with it at 1530. I switched the ATU to the OFF position and changed to 1500 and BOOM! A 10 foot wire! All over the place! Two houses on either side of me, one in the back and several across the street and in the cul-de-sac. 

I have the antenna taped to a six foot piece of wooden trim, and that is mounted on my camera tripod. I'm on the 2nd floor corner, so I put the antenna in the corner. Pre and post sunrise, it's terrible, but once the sun comes up, she beams!

There is mention of using loaded coils with the wire antenna. 300-400 uH is recommended. Never done that. Wound a coil, that is. My neighbors seem happy with it. Just can't do a damn thing at night, That's why I bought a Part 15 FM Transmitter. Not sure how that's gonna work out. It was a very good deal.

But the SpitFire has potential to be a little blowtorch! Very much like the SSTRAN AMT-3000. I need to play with the ATU some more. I'm just afraid to wreck the coverage I have now, if I change something.

Doug

Spitting Fire

"Pre and post sunrise, it's terrible, but once the sun comes up, she beams!"

Night time is a good time to tinker with the tuning when your coverage is limited to a smaller area. I do my best work at night despite getting older and my body craving sleep.

I am curious now, if it's doing that well now on just the wire antenna what would it do on a coil loaded vertical with ground elements.

Barry

 Barry of Blue Bucket Radio 1620 AM  - http://bluebucketradio.com - WQYY 664

Do you have a Smartphone?  If

Do you have a Smartphone?  If so I suggest taking pictures of how it is set now.  Then you can always go back to where it was.  I know a hair turn of a variable cap can make a huge difference.

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

http://thelegacy.shorturl.com

More Power for Hobby Broadcasters

http://the-initiative.boards.net/

I've seen a picture of the

I've seen a picture of the Spitfire's board on an auction, and it looks like the tuning is similar to the older AMT unitswith molded inductors selected to be in or out of the circuit by 4 dip switches.

That means you can set the switches to use combinations of inductors in series that get the system close to being resonant with the antenna connected, and then using the tuning capacitor for final tweaking for a maximum power output peak.

The capacitor should be across the junction of the last output inductor and the antenna, and ground, and should be a low loss dialectric cap.

I've noticed that most of the Part 15 transmitters on the market have similar output circuits. The components may be different, but the circuit is similar, probably because it's a tuner that really works, and it's simple enough.

It's pretty much a straight 'L' network, transforming low into high impedance for the short antenna.

The older AMT 3K uses the set of moulded inductors, the newer 5K replaces the inductors with what looks to be a powdered iron toroid, something like a T-200-2, that would have better efficiency on the broadcast band than than the small inductor set.

Instead of switches, it uses jumpers, but really, it's doing the same thing, selecting sections of the coil in and out of the circuit, and again, the output variable capacitor peaks up the circuit for highest output.

The Rangemaster looks like it's based on the same idea, while the Chez Procaster is the only common commercial transmitter I know of using an air core inductor, no core. That could help by being lower loss, no ferrite or iron magnetics to cause losses, but the Chez's coil also isn't adjustable, meaning you're likely going to end up using more capacitance than if you could select coil taps.

You want the most inductance, least capacitance for the highest efficiency, and the more inductance you can use, the less capacitance you'd need to get to the peak output.

A little capacitance across the output at the antenna is good so the tuning is more broadband, but too much will kill the efficiency of the circuit.

I don't know who first pioneered that style of tuner for P15, the large inductor, small cap L network, but everyone seems to use it now, and it was probably one of the larger breakthroughs that made the commercial part-15 transmitter possible.

Older circuits always seemed to use a parallel resonant circuit, a coil and capacitor output tank, with the antenna wire attached to the top of the coil, the high impedance end, especially with tubes. Transistor circuits carried that on for a while.

Wow! Nate, you are BRILLIANT!

This is valuable info. Coils, capacitance and inductance...OH MY! Outside my expertise. I am just amazed at the sound of this little box! Cyndi Lauper is singing "All Through The Night" right now. Yeah, it's the Orban, I know. That DOES make a difference. Incredible. And the neighbors love it! Wait'll they hear the FM! LOL!

Doug

I'm always reading and

I'm always reading and learning plus experimenting and trying to think up something new, all this RF has fried my brain maybe!

I'm glad you like the Spitfire, it has to be one of the best deals in a transmitter out there, built or not, it seems like a good basic circuit that's engineered well, since you report good sound.

I don't think that some other transmitters are that well engineered, like the Talking House and the Ramsey PLL, AM-25 I think. Those have good points, but shortcomings where it hurts, the sound quality.

SpitFire AM Transmitter

i'm thinking of getting one after i seen what you said about it cool thanks

i was wondering if this

i was wondering if this transmitter was good  i mite try to get one

Mite?

You mean, "Might"? Yeah. Good little unit. On on eBay right now...$90+

Doug

Just Playing Devil's Advocate

This Spitfire transmitter you speak of.  From the UK.  Non FCC certified. It's illegal for them to sell them here without certification. Of course it's legal to operate one as long as you are meeting the Part 15 AM rules.  But it is not legal for them to sell one here without certification. 

Which also means that should the FCC visit you you will need to be prepared to show that you're meeting the rules and you have no certification to back you up.

Just pointing out a technicality. Not necessarily one that would get anyone in trouble here, as long as you're operating legal. 

TIB

A Bigger Issue

From Reply 74, above:  ... Just pointing out a technicality. Not necessarily one that would get anyone in trouble here, as long as you're operating legal.

__________

Just wondering ...

How could anyone reasonably expect to prove that the radiation from their unlicensed AM/FM broadcast band transmit system is legal under Part 15, if/when an FCC field inspection shows otherwise?

Even transmitters with traceable FCC certification as being compliant with Part 15 rules when measured in a test lab environment can be installed and adjusted by the final buyer/operator of same so as NOT to be compliant with Part 15.

And likely moreso for such hardware never having been officially certified as compliant with FCC Part 15 -- as shown by the measurements of same reported here by TIB.

In the case of AM

In the case of AM transmitters someone who knows how to operate a multi-meter and knows Ohm's Law should be easily able to determine compliance.

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

... and a tape measure.

... and a tape measure.

That's funny. :-)

That's funny. :-)

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

? ? ?

RE:  Clips Just Above --  Ohm's Law, multimeters and tape measures existed long before §15.219 was added to FCC Part 15, and before the FCC ever issued NOUOs for non-compliance with §15.219 (including those reporting long ground leads).    So apparently those resources were/are not always used by those setting up and operating such unlicensed systems.   The FCC certainly knew that a ground conductor added to the radiation of a ~ 3-meter whip attached to a transmitter operating in the AM broadcast band.   This is the reason why the length of the ground conductor was included in the overall antenna length permitted by §15.219(b) in the first place.

The Spitfire...Illegal?

This Spitfire transmitter you speak of.  From the UK.  Non FCC certified. It's illegal for them to sell them here without certification.

Ha ha! I know! Tell that to eBay! Or 6v6! Get 'em while ya can!

Doug

The Spitfire has been for

The Spitfire has been for sale for over 10 years and before that was the Metzo SSTran clone. The Spitfire replaced the Metzo. Obviously eBay doesn't care in the slightest.

Rich correctly stated: "RE: 

Rich correctly stated: "RE:  Clips Just Above --  Ohm's Law, multimeters and tape measures existed long before §15.219 was added to FCC Part 15, and before the FCC ever issued NOUOs for non-compliance with §15.219 (including those reporting long ground leads).    So apparently those resources were/are not always used by those setting up and operating such unlicensed systems."

Snob DHR commented: "Then those operators should not be operating radio transmitters when these measurements can easily be made."

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Not sure what the point of

Not sure what the point of your post is, Rich.

We are all aware that you cannot measure compliance of a Part 15.239, or a Part15.209 transmitter without measuring field strength.  And that different environments can cause these transmitters to produce wildly varying field strengths.

But it is also true that with a simple multimeter (and a tape measure), you CAN measure compliance of a Part15.219 transmitter.

I would add that the FCC has an expectation of the field strength of a compliant Part15.219 transmitter - they measure field strength only at first and if a transmitter is obviously above this limit, then they would inspect.  I seem to recall a discussion here a few years ago about what that field strength was, but I can't recall if any conclusions were arrived at.

I also don't know what any of this has to do with the Spitfire transmitter.

Reply to #81

Ebay is like Amazon, they aren't the sellers so the question is are they partly liable for allowing these to be sold by companies through them?

 

Mark

Thanks for Asking

(Response to Reply 83 Above)

Not sure what the point of your post is, Rich. ...  with a simple multimeter (and a tape measure), you CAN measure compliance of a Part15.219 transmitter.

The point of my post was (is) that meeting, and proving compliance with FCC §15.219 depends upon more than the possession and use of a multimeter and a tape measure.

It also depends on the ethics, knowledge, experience, and website guidance/documentation to such operators available over the years provided by transmitter manufacturers, and others.

Review the case of KENC.

O - M - G...

I really don't think the operator will need to prove compliance one way or the other.  The FCC will TELL the operator how they're doing.  

Especially as Rich pointed out, it doesn't matter if the unit is certified, there are too many variables which could render the unit out of compliance such as whether you have metal piercings or metal cleats on your boots, time of day, time of year, weather conditions, where your vehicle is parked...  

Well the list just goes on and on and on...

by MRAM 1500 

Charter Member - Association of Low Power Broadcasters

Chairman - ALPB

Spitfire

Question for those of you that physically have a Spitfire...

I see in the specs that the audio frequency response goes to "10K / 25K"

Is the difference accomplished via some sort of switch?  If so, how is the audio between the two?  Is the 10K steep enough to replicate an NRSC filter?  And I'd assume the 25K audio sounds nice and full on a wideband receiver.

Just wondering what your experiences have been with the audio quality of the Spitfire unit.  My goal is not to get range, but to get good, solid, full AM audio from my studio to the transmitter, and then to stream that "AM sound" back over my internet station.

 

 

Reply to #81

Ebay is not the seller, they just provde the medium for sellers and buyers to connect.

I can't use the Spitfire here in Canada at all...meeting the rules or not as ISED(formerly Industry Canada) says any transmitter has to be certified and that is the most important thing they look for. Not approved in their data base, $3000 to get the approval or can't use.

The certification fee is the same for a company and since it comes ready built it could be certified by the manufacturer for legal use in Canada and the USA.

 

Mark

My Experience With The Audio Quality

Hi ASchuelke! 

The SpitFire puts out very good audio. As good as AM gets. What makes mine sound full and punchy is my Orban Comp/Limiter. A 422a is perfect! This one:

My Mackie mixer (1402) has EQ on each channel and I boost the low and high ends a bit. With a GE Super Radio set on "wideband", it sounds like FM...it's all in the receiver after that.

The audio is rolled off at 10K. You cannot get 20-20k frequency response out of AM. Impossible. 

Doug

Why the sudden interest in Spitfire?

Not "legal" for sale in the United States. You have 2 models of Sstran out there. No comparison in quality. And nothing is "Impossible."

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Legal?

"Not "legal" for sale in the United States."

Tell that to eBay:

http://www.ebay.com/itm/Spitfire-AM-Medium-Wave-Top-Band-Transmitter-/17...

C'mon! Not legal! That's a joke. Of course it's legal, or you wouldn't be able to buy one. Nobody cares about those stupid "laws" that are not enforced nor even acknowleged.

"You have 2 models of Sstran out there. No comparison in quality."

That may be true. I have not compared them. Seeing Phil B is being so slow in delivering his product, I can't see why not buy the SpitFire. It's plug and play.

"And nothing is 'Impossible.'"

I like your thinking there..

Doug

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