Talking House Mods

How about 100% modulation? lol Very nice work.

Very nice work and thanks for sharing. Regarding further improvements, the modulation percentage may need improvement. You might check this if you can with a scope.

Here's a link to some very nice software based audio test meters and generators:

http://www.darkwood.demon.co.uk/PC/meter.html

I use the "Audio Test Generator" available in the linked page for a test tone generator. This allows setting and observing the modulation envelope with a scope. You might find that undistorted modulation is only present below about 70% or so and this could be another area which you could work on for improvement. In my Ramsey AM25 unit I found the undistorted modulation percentage could be improved by adjusting the bias to the RF final amplifier.

Regarding the RF waveform not being a sine wave, I have noted this on the transmitters I have when not connected to a tuned antenna system. The antenna loading coil suppresses the harmonics when properly tuned to the point where distortion is not observable on the scope. If you connect the scope to the RF output this can detune the circuit and produce a non sine waveform. Try coupling to the RF by placing the probe near the antenna but not connected to it.

Fine work with the mods,care to pass along more detail so others can try them out? I find the frequency pulls or "FM's" when modulating fully,any mod for that? I thought about adding a stout electrolytic to the Vcc rail near the PLL and/or modulator circuits. I also notice the frequency will change just by the proximity of my finger anywhere near it,maybe a better shield?

Thanks for the response!

* The audio software is great to play with, thanks for the weblink!

About the harmonics:
You're totally right and I know what you mean, I think the bandwidth of your antenna is very narrow so the harmonics will not be transmitted in air.
The situation here is different; I live in Europe and LPAM transmitting is NOT allowed, so we have to be very carefull while experimenting with those little transmitters!
But, we can connect every antenna to the Talking House we want to 😉 even a fullsize dipole....
In that case it's better to be a little bit carefull when putting a signal with a lot of harmonics in the air.

So, here is some additional information about the mods in the Talking House:
Some pictures and the printlayout for the 5kHz audio filter
http://www.speedyshare.com/files/23764831/Talking_House.rar

The maximum modulation of my TH is now about 85%
I will try to make it better but I think it won't be easy....

@ WilcomLabs:
About the FM by maximum modulation:
Maybe there is a little problem with the supply voltage of the PLL.
When the TH is modulated maximum, the RF amp is using maximum current.
It's possible that the power supply voltage of the oscillator and the PLL is fluctuating and then you'll get FM....
Or is the supply voltage free of RF signals (rimple)? Maybe some extra decoupling!

And finally here is the RF lowpass filter coil data:
(See attachment for diagram and filter plot)

4,73uH: D=19mm, l=8mm, 15wdg, 0,5mm wire, no space between windings!
9,09uH: D=19mm, l=12mm, 23wdg, 0,5mm wire, no space between windings!

Cool mods, worthy of note.

The TH on my boat does quite well with upstream effects in Nicecast .... which seems to have access to many appropriate AU's ... which are the same ones also available to Garageband and Logic .. multiband compression, declipper/limiters, etc.

I could use a little more modulation, but I'm happy with the overall on-air sound, considering it gets pulled from the internet. Took months of tweaking with upstream effects that are a compromise for the internet, because that's where the audio for the TH tx comes from.

One thing I noticed was noise generated by a DVD player about 4 ft. from the TX. I found it by using a cheap RatShack transistor radio in the cabin. I expected distortion from being so close (right under the antenna/ATU system), but not the noise. I started by unplugging power strips not used directly by the TX, but on the same circuit. Then I plugged it back in and went through the cords one at a time. When I unplugged the DVD player, it went quiet. So now, I only plug it in at night when I'm just running NOAA weather which has poor reception here, but gets cleaned up with effects, mostly BIAS SoundSoap.

However, the older TH I have sounds terrible. It has a single (monoi) RCA audio input jack.

What I suspect is that TH transmitters, models not withstanding, are not all the same. Judging by the various comments on these things, I think they basically stick in parts with values within a range that will work. IOW, like many imported electronic units, the parts buyers are always looking for the best deals. I.e., if they find a million resistors of values that are marginally within operational range, they buy them and the batch of units assembled with them won't perform as well as a batch with the correct design values. But at least they won't catch fire, so they go ahead and ship them out.

Kind of like the Klingon programming guide ... Klingon applications don't get 'released', they escape, leaving a trail of battered IT professionals in their wake. 😉

Havent had time to dig into my TH5 yet,wonder if the schematic is available anywhere? I may try to split the power supply between the pll and the modulator/output sections. The pll isnt that clean to begin with. A schematic would help a lot with making mods...

Well I can get the audio sounding pretty choice but it still has a buzz sound that seems to ride on the audio. I tested without any audio,it sounds like the sawtooth wave in the pll is not filtered very well,it doesnt produce a clean carrier. Another appeal for any schematics for the TH,anyone???

I'm sure I don't have anything like 100% modulation, but the sound is not bad. The playlists come from iTunes on an Intel iMac. plus live vocals, cell phone connection, etc. fed to a Presonus FireStudio from a Tascam M-320 analog board, using Nicecast to send it to the Internet. That is cranked up pretty high with multiband EQ compression plus a declipper (like a brick wall limiter). The signal could be better I suppose, but it's doing quite well in town.

No noticeable distortion from the pickup computer or on-air, but it was getting a hum. At first it turned out to be the power supply, which I switched out with a big chunky HP printer PS ... no more buzz at the time.

Later, it got a hum back in the signal, so I checked it out with a small cheap portable radio around the TH tx. After testing around power strips etc. I determined it was coming from a cheapo DVD player, even when it was "off". Unplugging it from the power strip made the hum go away.

The lesson I learned was that noise is not always the fault of active, gear connected to the transmitter. In this case it was radiating from a nearby source, probably getting into it from the ground.

Once in awhile I play a DVD on that player late night. If I forget to unplug it, the hum in the signal heard on my car radio the next day lets me know .... and I have to run back down to the boat and unplug it.

Ken,

Your comment above regarding hum hits home here. I just installed a new device here in the cave where my computer and part 15 transmitters are housed. To date, the AM and FM have been hum free but as soon as I plugged in the wall wart for this device the AM signal is flooded with hum. Unplug it and the hum goes away.

This is a tiny 12 VDC 1 Amp supply so it is a switcher.

Interestingly, this wall wart has the FCC compliance label which states it is "tested to comply with FCC standards for home or office use". It is rather surprising that it is causing trouble since FCC home standards are fairly strict. On the other hand, the "tested" comment makes me wonder if it was tested and failed. They don't claim compliance or that it passed.

Neil