SSTran & 102" Whip How Much Range Should I get

[DJboutit3]

I think about setting up a part 15 am station if were to get a SSTran & 102" whip how much range should I expect to get? With this setup could I get 4 miles & could I link 4 or 6 of them together.

 

[RadioMan203]

You would be hard pressed to get 4 miles of range with most any legal Part 15 setup with the rare exception of one I heard of that was located within short distance of a lake.

If Part 15 transmitters regularly got this sort of range there would be little reason to have such features like multiple transmitter synchronization.

The SSTRan is a great unit for the budget-conscience would-be Part 15 broadcast enthusiast. You would have to spend many times more to obtain a higher performance unit such as the Rangemaster. Of course, you would be able to purchase a few SSTrans for the cost of a Rangemaster and that may help you get your signal around, but you would need a method of distributing your program audio feed.

 

[rfry]

I think about setting up a part 15 am station if were to get a SSTran & 102" whip how much range should I expect to get? With this setup could I get 4 miles & could I link 4 or 6 of them together.

The green trace in the link below shows about the best range that can be expected for a fully compliant Part 15 AM setup, and two others that are functionally non-compliant.

(edit) it takes about 0.150 mV/m for a ~tolerable amount of noise heard on a good, indoor AM receiver using an internal antenna -- even in a low noise area, with no interference.

http://i62.photobucket.com/albums/h85/rfry-100/Part15AMSystemComparison.gif

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[audioguy]

I agree with the findings of R. Fry with one exception. It should be possible to achieve better than 30% efficiency with modern RF design techiques. This is rather low, even for a traditional Class C output stage. However, it is probably representative of the performance of units such as the SSTRAN. Using a Class E output stage should enable the power to be increased to the neighborhood 0f 80-90 mW applied to the antenna system. This would improve the performance of a compliant ground mounted Part 15 system considerably.

Even so, a range of much more than 1/2 mile in a typical urban area is unlikely to be achieved in practice except under unusual circumstances, due to the high noise and interference level on the AM band.

 

[rfry]

It should be possible to achieve better than 30% efficiency with modern RF design techiques. This is rather low, even for a traditional Class C output stage. However, it is probably representative of the performance of units such as the SSTRAN. Using a Class E output stage should enable the power to be increased to the neighborhood 0f 80-90 mW applied to the antenna system. This would improve the performance of a compliant ground mounted Part 15 system considerably.

A well-designed and traditional Class C r-f output stage including its load matching network has ~ 70% DC-RF efficiency into a matched load Z , or maybe a bit more. That applies to the unmodulated carrier, only. Whether or not there is sufficient audio power in the design of a particular transmitter to fully amplitude-modulate that Class C output stage is another matter (regardless of the DC-RF efficiency of that output stage).

There are digitally-modulated designs with a final stage DC input to RF output efficiency of better than 90%, but they are patented, and the costs to implement them probably are beyond what Part 15 OEMs and their customers could support.

AFAIK, none of the commercially-available kit or assembled/FCC-certified "Part 15 AM" transmitter OEMs has specified the fully-modulated r-f output power that can be achieved by their transmitter into an optimum r-f load. For that matter, none of them has ever specified what constitutes an optimum r-f load for their transmitter.

The output power values for some of the most popular "Part 15 AM" transmitters reported on line by degreed individuals using good test equipment and methodology was about 30 milliwatts, which is the reason I used that value in my calculations.

RF http://rfry.org

 

[audioguy]

Agreed that the efficiency of most commercial and kit-built Part 15 AM transmitters is dismal, and probably not much better than 30%. Rangemaster may be an exception; I have no way to determine the output of mine since it does not match to 50 ohms.

However, it is certainly possible to build a much more efficient output stage if one is knowledgeable in the art. Nathan Sokal (Design Automation) published an article on Class E RF amplifiers in RF Design magazine many years ago. Hams have built RF amplifiers based on his design. As far as I know there is no restriction on building one for personal hobby-type use. There are several web sites dedicated to Class E-- just do a search.

It takes no more audio power to fully modulate a 90% efficient output stage than a 10% efficient one. Sure, you can build a fancy digital modulator like one of the Harris designs, but you can also just use plain old high level modulation. It's not that hard to come up with 100 mW of audio power; a lot of power op amps will provide more than that. If people are interested to experiment... I did, and it does work! I designed mine to match into 50 ohms so I could measure the power accurately, and then I built an efficient matching network to match the 3M radiator.

 

[rfry]

Using a Class E output stage should enable the power to be increased to the neighborhood 0f 80-90 mW applied to the antenna system. This would improve the performance of a compliant ground mounted Part 15 system considerably.

If the r-f output power was 90 milliwatts instead of the 30 milliwatts I used in my chart, then all the field intensities shown in it would increase by SQRT(3), which is about 73%.
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[carlvenorden]

The sstran doesn't accept a 102" CB antenna.

 

[radioman148]

The sstran doesn't accept a 102" CB antenna.

What is the best kind of antenna I can use since I don't have room for the ground mounted radial?
There must be something that will work better then the wire.

 

[RadioMan203]

The sstran doesn't accept a 102" CB antenna.

Carl, can you clarify this for me? Does it not accept the 102' whip due to simply not having the appropriate connector on it, something regarding the output tuning network or another reason?

 

[radioman148]

The sstran doesn't accept a 102" CB antenna.

Carl, can you clarify this for me? Does it not accept the 102' whip due to simply not having the appropriate connector on it, something regarding the output tuning network or another reason?

That's the same question I was going to ask. Can't you hook up a proper connector for a 102 inch whip?

 

[carlvenorden]

I'll answer a couple of the questions that were raised in this thread.
The SSTRAN delivers 100% of it's power to the antenna. Some power is lost in it's travel thru the lengthy wire of the coil.

The SSTRAN does not have an internal coil per se: it does have switches to help tune the supplied 102" wire antenna. The SSTRAN needs to be modified in order to accept the external antenna.

The ground system I build acts as both a counterpoise and a lightning arrestor. At minimum it is 10 feet long by radial, 20 feet across completely. If not using this, then the tx should be grounded via a lightning rod or two.

The SSTRAN will not work with a CB whip, nor does it require coax. The external antenna requires a loading coil to properly tune the antenna to resonance.

If you need information on the antenna/coil/ground system I build, email me with the word "antenna" in the subject line. I will send you my SSTRAN information sheet.

[email protected]
Thanks,
Carl

 

[carlvenorden]

CORRECTION;
My email address is [email protected], not as stated in my previous post.
Sorry for the typo.
Carl

 

[trojanrabbit]

The SSTRAN is shipped with (and the PCB is designed for) an RCA connector for the antenna. However, the manual states that Part 15 does not allow for an antenna connector and for a compliant installation the antenna needs to be soldered to the PCB.

 

[radioman148]

The SSTRAN is shipped with (and the PCB is designed for) an RCA connector for the antenna. However, the manual states that Part 15 does not allow for an antenna connector and for a compliant installation the antenna needs to be soldered to the PCB.

Can you solder a 102 inch whip & if installed at a height of say 35ft, how much coverage can one expect?

 

[rfry]

The sstran doesn't accept a 102" CB antenna.

Carl, if the SSTRAN can drive a ~3 meter conductor using one of your loading coils, then no doubt it could also drive a 102" whip through a suitable coil, couldn't it?

The most important thing for optimum performance with short monopole antenna systems is that they present a very low reactance (hopefully zero ohms) to the transmitter.

That should be just as possible with a properly resonated 102" whip as with any other linear conductor used with the proper loading coil.

Hopefully PhilB will add his comments to this.

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[radioman148]

I don't have room for Carl's ground antenna with radials. There must be someone out there who can report on rooftop or any other antennas that they've been able to use with SStran successfully.

Thanks

 

[rfry]

I don't have room for Carl's ground antenna with radials. There must be someone out there who can report on rooftop or any other antennas that they've been able to use with SStran successfully.

For the same frequency and applied power to the antenna system, an SSTRAN mounted on a rooftop and driving a 102" whip through the proper loading coil will produce about the same radius to a given field strength as any other transmitter at that location using the same, properly loaded whip and r-f ground configuration.

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[audioguy]

Of course you can use the SSTRAN with a 102" CB antenna. How well it will work will depend on a number of factors.

First, the kit ships with no antenna connector because the FCC does not allow it. However, you as the kit builder may install any kind of connector you want. As long as your operation complies with Part 15 regulations, it does not matter.

If you directly connect the 102" CB antenna to the output of the SSTRAN, it will work exactly the same as a wire of the same length. With a typical setup inside your house, it will cover the house and out into the surrounding yard but not much more. That is because the matching network inside the transmitter, although it can tune over a wide range, is not very efficient. And also because the transmitter will not have an efficient ground system to work against.

If you follow the procedure in the kit manual and short out the internal inductors and use an external loading coil of the kind Carl sells, it will work much better. This is mainly due to the fact that the external coil is much more efficient. But it is also due to the fact that the coil will be tuning with the antenna capacitance only, and you will not use any auxiliary loading capacitance as you would if you used the internal matching network. The auxiliary capacitance in the internal network makes it easy to tune the transmitter, but you are shunting signal to ground that could otherwise contribute to useful range.

If you want to obtain the best range, you need to mount the transmitter outdoors over an effective ground system. In most cases, that means installing radial wires on the surface of the ground. Elevated mounting is not recommended unless you have a large metal surface that you can ground to, such as a metal roof. Beware of using a long ground wire; your system would likely be out of compliance with Part 15 rules in that case.

 

[radioman148]

Thanks audioguy.