Is it possible to marry a SSTran transmitter to a Talking House ATU?

[Deano]

Since the week of Christmas last year I have been running a Talking House 4.6 transmitter with their external ATU. The struggle from day 1 has been poor range (even with a solid 8 on the signal meter of the ATU), tinny fidelity, low modulation and major hum issues inside the house. I also have an assembled SSTran transmitter that also suffers major hum issues when the supplied wire antenna is used. What I was wondering is if I found the right adaptor to go from RG-6 to RCA at Radio Shack, would it work to marry the SSTran to the Talking House ATU? The superior modulation ability of the SSTran just might be the ticket to help me cover up the hum issues in the house, and if I can achieve the same signal strength on the meter of the Talking House ATU then I should still achieve the level of coverage to which I have become accustomed with the TH 4.6...1/8 mile clearly, close to 1/4 mile usable on a car radio.

Is there anything I should be aware of before trying this? I don't want to burn up the SSTran or ATU while conducting this experiment.

Deano

 

[audioguy]

I don't think this will work very well unless you are willing to make major modifications to the ATU. It contains a PA stage, and I don't think you will find it easy to drive it with the SSTRAN unless you know what you're doing.

Your hum problems are probably due to two things: improper setup of some of the jumpers in the SSTRAN and an appliance that is plugged into the wall in your home that is rectifying the AM signal and adding hum to it. This is very common. If you do a search over on the other board where you also posted your question, you'll find a number of helpful posts that will explain this phenomenon. I posted quite a few of them myself. About the internal jumpers; most of them should be shorted-- you don't want any impedance in the ground side of your audio input or your power ground.

If you install the SSTRAN outdoors with a loading coil similar to the one made by "antenna guy" you should get results that are quite similar to the TH with the ATU. Keep in mind that range is determined by quite a number of factors, including co-channel and adjacent channel interference, ground conductivity, receiver sensitivity, and electrical noise to name just a few. Most range claims that you will read about are overstated. If you get good quality of 1/2 mile to 1 mile in a city, you are doing well.

 

[Tom Wells]

Is the hum the same on battery and AC operated radios? How about 300 feet from the house on a battery radio?
AC operated radios SHOULD have both sides of the line bypassed to the DC common point of the radio, but many don't
and hum will result. Another issue could be the lack of metal conduit over the AC wiring, which would greatly increase
RF pickup and re-radiation with hum. If this is the case, you'll need to get the antenna more electrically uncoupled from
the AC lines by greater distance, or add RF filtering to the AC lines, connecting the "ground" of the filter to the RF common point of the transmitter ground. This will collect "wasted" RF in the same way radials do, and add to the overall efficiency.

 

[Deano]

To one degree or another, the hum is on every radio in the house. Battery or AC powered. In the car or outside and away from the house the signal is crystal clear. I know the hum isn't a transmitter/antenna issue, it has got to be a house wiring issue that I have spent many a weekend trying to resolve with not improvement. My biggest problem with the Talking House is that you can't modulate it very much without distortion. For it to be clean playing music, the modulation can only be a whisper. I can modulate the SStran much louder and still be distortion-free. Better modulation helps overcome the hum issue. It just has horrible reach using the wire antenna that came with the kit. I was hoping that the TH ATU might remedy the coverage issue a bit.

 

[audioguy]

Again, if you search over on the other board you will find a lot of useful information about how to track down the hum problem.

A few quick suggestions: Try turning off breakers and see if you can isolate it to one area of your home. Try unplugging appliances, especially those that use "wall-wart" power supplies, as well as "instant on" appliances like TV sets. Somewhere you'll find the main contributor(s).

 

[Deano]

I had great success today running the SSTran into the Talking House ATU. The hum is gone. The audio is loud, clean and hum-free. I am not getting near the signal strength reading on the ATU signal meter as I do when feeding it with the TH 4.6 (down from a '8' to a '3'). But the signal is still strong enough throughout the house to deliver full quieting with a thunderstorm close enough for me to hear the thunder.

Today's outcome begs the question, is the reduced RF field (as depicted on the ATU signal strength meter) the reason for the hum disappearing? It would seem that during today's experiment that I dropped the RF field reaching the house wiring and the result was the hum on 1630 (my transmitter frequency) is gone. Hum is still present on several frequencies of stations with towers/arrays within 10-15 miles but no longer on 1630. BTW audioguy, when I first got the Talking House transmitter I tried the "breaker box" experiment. With no breaker energized except the one powering the outlet that the transmitter PS was plugged into, I had the hum issue on a battery powered radio.

So here is the history leading up to today. SSTran using supplied wire antenna in the house = hum. Talking House 4.6 using supplied wire antenna in the house = hum. Talking House 4.6 using Talking House ATU ('8' signal strength) in yard = hum. SSTran using Talking House ATU ('3' signal strength) in yard = crystal clear, hum-free audio.

 

[Tom Wells]

Glad to hear things are getting better, and it's hard to say if reduced signal would mean less hum, but would certainly
mean less radiation into the AC wiring. Do you know if your AC runs in conduit, and have you checked to see if your wiring is correct? I found a number of outlets in my house where AC hot and neutral were reversed. If the transmitters have non-polarized plugs, try 'em both ways. And what is your (RF) grounding in the above cases? The more, the better.

 

[Deano]

It's a home from the late 70s. It is conduit out of the breaker box into the ceiling, but I truly don't know from there. I have walked around the house with one of those cheap plug-in outlet circuit testers and didn't find anything that didn't get me three green lights. My RF ground consists of two 8' copper coated grounding rods of the Lowes/Home Depot variety. One is driven into the ground next to the post to which the Talking House ATU is mounted. The other is about 15 feet away and connected by one of the ground radial wires. There is a total of 16 ground radials ranging in length from 10 to 50 feet. The mistake I think I made was running them with insulated wire. I am in the process of fixing that with a bare copper radial ground system I am ordering from Carl Van Orden this weekend.

With today's developments I am full steam ahead with trying to maximize things. It is so wonderful to sit in my comfy chair tonight and listen to a loud, clean hum-free AM signal.

 

[PhilB]

With today's developments I am full steam ahead with trying to maximize things. It is so wonderful to sit in my comfy chair tonight and listen to a loud, clean hum-free AM signal.

In the time-honored spirit of experimentation, I am happy to provide the following information.

The Talking House remote ATU circuit diagram is shown as Figure 7 in the US patent #6973294 (Google the patent number). It consists of an RF transformer feeding two switch-selectable adjustable tuning coils and a circuit to sample the RF antenna voltage to drive the meter. The two tuning coils are provided to cover the broadcast band in two ranges, high and low frequencies.

The electrical principle of this tuning configuration is identical to the AMT3000 tuning configuration for the external base-loaded antenna: the tuning coil resonates in series with the capacitance of the antenna at the operating frequency. Physically, the difference is the TH ATU is adjusted by continuous movement of a ferrite core while keeping the antenna length constant while the base-loaded coil antenna is tuned by selecting coil taps and adjusting the antenna length. So, the ATU will work with the AMT3000 as long as the transmitter setup is done as it would be for the base-loaded antenna.

The AMT3000 must be get slightly modified per the instructions at http://www.sstran.com/pages/sstran_amt3000mods.html The modifications are minor, but without the modifications, performance with the ATU or the base-loaded antenna will not be good.

Minimization of the coax length is important for both the Talking House and the AMT3000-Talking House ATU configuration because the coax adds loss to transmitters that already suffer from FCC power restrictions.

The AMT3000 base-loaded antenna has been optimized for efficiency. This includes the low-loss 3.5” coil and direct-connect to the transmitter via a short wire (no coax). The TH ATU configuration will suffer from the losses incurred by the small ferrite core tuning inductors, and the coax interconnect.

I understand, and encourage experimentation and I realize the base-loaded antenna is in a completely different arena when considering bulk, fabrication complexity and tuning complexity. I would encourage experimentation with the Talking House ATU. The results should be compared between the two alternatives. I expect experimenters will find the base-loaded antenna to be superior to the TH ATU.

 

[druidhillsradio]

It appears the the ATU likes to see something in the 50 - 75 ohm range. The modified SSTRAN likes to see 800 ohms. My guess is that this will not work.

 

[stormy01]

It appears that the ATU likes to see something in the 50 - 75 ohm range. The modified SSTRAN likes to see 800 ohms. My guess is that this will not work.

"Matching Transformer" comes to mind, would that be a possibility? (I have no idea how to design one... Sorry, I don't have that kind of
expertise, perhaps check the ARRL handbook for ideas or ask in the r-i Engineering forum, since Engineers may or may not think of looking in this Community Radio forum)

I expect experimenters will find the base-loaded antenna to be superior to the TH ATU.

I can understand getting a lower power output to be radiated "in the clear" (outside and above obstructions like buildings and trees), and keeping the transmitter indoors, but it does not seem to make sense to send an already low powered signal through up to 100 feet of coaxial cable. But it must work, right? (since the manufacturer can't seem to keep these ATU's in stock on the shelves for $295.00 each, LOL... The manufacturer would be getting returns if the ATU's really did not help extend the range of the TH transmitter)

 

[druidhillsradio]

I think by the time you get the match transformed you will have more loss than if you married it the the base loaded antenna.

 

[Ermi Roos]

A poster on another website claims that it is not legal to use a Talking House ATU with any transmitter other than a Talking House. His reasoning is as follows:

The Talking House with the ATU should never have been certified because the long coaxial cable that is used does not comply with the 3 meter limit of Section 15.219(b). Nevertheless, the TH transmitter with the ATU is certified anyway; and so the user of the TH transmitter with the ATU is protected from being charged with a violation because of the FCC certification. Howevever, if the ATU is used with another transmitter, the certification is not applicable, and the user is in violation, because the ATU does not comply with 15.219. In that case, the very low field strength limit of Section 15.209 would be applicable.

I note that Talking Sign once marketed an external antenna with a long coaxial cable, but the FCC has stopped Talking Sign from selling theirs. So, the FCC has been inconsistent when dealing with external antennas connected to the transmitter with a long transmission line.

 

[Deano]

There seems to be some confusion as to FCC Type Certified equipment and how it relates to Part 15.219. You can be fully compliant with 15.219, for example, if a SSTRAN transmitter (not FCC Type Certified) were to be installed in a weatherproof box and mounted just under the Talking House ATU (not FCC Type Certified for use with the SSTRAN) using 1-foot of coax to connect the two and a 8-inch ground lead to connect the ATU to a earth ground. In that example you are using a transmitter designed to produce a maximum final input power of 100 mW and an antenna, transmission line and ground lead (if used) of 3 meters or less. That meets both the letter and spirit of 15.219. I don't believe the FCC is in the business of telling you what brand of transmitter or antenna you use. What they care about is that your set up complies with 15.219 (if that is the section you are attempting to operate under).

It is worth noting that as it relates to the end user, 15.219 makes no reference what-so-ever to needing or requiring FCC Type Certified equipment. Certification is a requirement placed on the manufacturer or seller by the FCC so that they may legally market and sell a fully-assembled Part 15 transmitter in the United States. Its value, benefit or protection afforded to the end user is unclear in light of the recent NOUOs given to Part 15 radio stations who were using FCC Type Certified equipment.

 

[rfry]

You can be fully compliant with 15.219, for example, if a SSTRAN transmitter (not FCC Type Certified) were to be installed in a weatherproof box and mounted just under the Talking House ATU (not FCC Type Certified for use with the SSTRAN) using 1-foot of coax to connect the two and a 8-inch ground lead to connect the ATU to a earth ground.

Functional compliance with Part 15.219 depends in large part on what is considered by some to be an r-f ground, versus what really constitutes an r-f ground.

For example, an r-f ground cannot and does not exist at the top of a long, vertical "massive ground wire,' or metal flagpole, tower, billboard or building frame -- as a matter of physics. Attaching a short conductor from the transmitter chassis to the top of such objects does not connect it to an r-f, or "earth" ground.

If a transmitter ground terminal connects to the top of any of those conductors (whether or not those conductors connect to a ground rod or water pipe at their lower end), then the entire length of those conductors becomes a radiating part of the antenna system, which conductors easily can produce more radiation from the Part 15 AM system than the 3-meter whip considered to be "the antenna."

RF

 

[Ermi Roos]

I agree that the Talking House ATU with only one foot of coax can comply with Section 15.219(b) because the total length of the antenna, transmission line, and ground lead can be less than 3 meters. It is when a long length of coax is used that the ATU is not compliant.

 

[rfry]

If you install the SSTRAN outdoors with a loading coil similar to the one made by "antenna guy" you should get results that are quite similar to the TH with the ATU.

That should be true if both the SSTRAN coil-loaded, 3-m whip and the TH remote ATU and whip are installed with their base within several inches of the earth (and other things equal).

But if the remote ATU and whip are installed on an elevated mount, then there can be more radiation from unfilter/unchoked r-f current flowing on the outer surface of the shield of the coax cable feedline attached to the ATU than from the 3-m whip considered to be "the antenna" -- which functional configuration is not covered by 15.219(b).

RF

 

[druidhillsradio]

I know we are talking about the TH ATU and the SStran. But what I found interesting is that the certification of the Chez Radio Part 15 transmitter, was accomplished with the slightly less than 3 meter antenna AND a 30 inch ground lead attached to the ground plane below the table. Do a search and see the photos. So the combined length of the antenna and ground lead exceeded the 3 meter limit. This may be where the conversation about FCC inspectors allowing a 3 foot ground lead for Part 15 transmitters started.