Talking House AM xmtrs

[af6im]

Got one of these used, dirt cheap, employed by real estate agents to broadcast house details to drive by customers. Synthesized AM broadcast band xmtr, with digital voice recorder performing an endless loop tape function. Synth won't go higher than 1700 KHz in stock configuration. The amazing thing is that the set has a servo tuned antenna coupler with has a motor driving a slug in and out of a loading coil. Who will be the first to make a 160 meter QRP AM xmtr out of one of these?

[Opcom]

Where did you find that gem? Maybe like other things, there is a wire or diode to cut to enable tuning out of band? Or maybe changing the crystal of the PLL?

[af6im]

lots of em on ebay... Search talking house

[k4kyv]

But do they come with space-shuttle audio?  I picked up a Radio Shack 10m AM/FM/slopbucket 10m transceiver on clearance sale just as the last cycle was headed into its decline.  The audio on the the thing is horrendous.  I thought about modifying it, but upon looking at the schematic and examining the circuit board, I decided it wouldn't be worth the trouble I would have to go through.

[John K5PRO]

One step up is a carrier-current broadcast transmitter. LPB made hundreds of them, for college campuses. Many universities have gotten out of that mode, keeping their FMs on the air and focusing on that territory. The contact person would be the engineer of the FM station, if they shared studios. The CC transmitters were often left in closets, steam tunnels, elevator rooms, abandoned.

I made a reasonable monetary donation to my favorite college station and picked up a LPB 50 watt, that uses two 6550s for audio and two more for RF, plate modulated. 6550s are not super for higher freq as the plate comes out in the socket, not on a cap on top. The other one from same station was a LPB 25W, that used a Compactron for RF and pair 6CA7/EL34s for modulator. Its in very sad shape since the fan quit and it baked. Both are XTAL controlled, and have real 600 ohm balanced input transformers and metering.

[W3RSW]

The experimental BC'ers seem to think for almost the same money that the SStran is better.

http://part15.us/node/692
and
http://www.sstran.com/

Looks like it could be converted to 160 using the freq. calculator, but I haven't researched too closely yet. OTH, 1700khz might be relatively BC free in a lot of the country so why convert to 160 (unless you want to amplify, of course.)

[af6im]

1990s technology, digital voice recorder. The motorized automatic antenna coupler is pretty cool, two coils with racked ferrite slugs driven by a cheap but effective geared DC (non stepper) motor. I used a sensitive field strength meter and you can watch it peak as the coupler finds the sweet spot. Seems to be able to match just about any antenna you can connect to it.

They are on eBay a lot, prices are as high as $100 and as low as $20 on occasion. OK audio, not hi fi but not horrible. Seems to be some minor coupling btwn the synth and modulator or PA, tiny bit of FM on voice peaks. Might be a power supply issue. Will see if I can diagnose it.

Harmonic suppression is surprisingly good.

Wish it could tune down into the lowfer band. Would make a great beacon. Synth only works btwn about 500 and 1700 KHz.

[flintstone mop]

The name of the company slips my mind(as usual) that produced a very nice sounding SSB exciter using phase modulation and it used the 6550's for RF. This arrangement would call for a linear and enjoy the 6550's, but beware of their shortcommings noted in another thread about them and the 6L6/5881.

And Don I ran across the same barrier on my Shadio Rack 10M rig. I wouldn't want to get into that electronic mess either. But I guess for 10M into a linear it's going to be ok.We get into the old problem when 10M awakens, that when there's multiple hops and DX the hi-fi audio has to be narrowed down a bit. The overbass sounds don't cut it over a long distance path.

Fred

[af6im]

New DX report, heard my talking house AM xmtr at 3.4 miles from a hilltop. Not bad for 100 mw. Weak but very readable.

[Bacon, WA3WDR]

Some friends who have a self-defense and personal training center got one, and they made some funny ads.

There was hum from a poorly located input filter capacitor, so I added a few wires to make some ground cross-connections on the bottom of the board.  There's a 4.7K resistor in series with the audio in the unit that I saw; a 0.1uF cap across that resistor brightened the audio quite a bit.  But the unit would overmodulate then, so I added an audio compressor.  It was about 33ppm high in frequency, so I added a 25pF trimmer cap across the reference oscillator and set it, and it has been dead on ever since.

Some car radios with PLL AM detectors still lose lock on the signal when it modulates heavily.  That still happens even though I added a negative peak clipper to prevent carrier cutoff, so I think I need to improve the power grounding to the 5V regulator and the PLL.

Its auto-tuner is cool.  You hook a ten foot wire to a post on the back, and it moves a ferrite slug around in a litz-wire coil when you turn it on.   If it can't tune to its satisfaction, it gives a failure indication and shuts off.  It also has a direct output on an F connector; there is a switch to select either that, or the auto-tuner output.  I measured just under 100 mW carrier output.

[af6im]

Thanks for all the VERY helpful tech info. I get a little FM on voice peaks. I have reduced but not eliminated the problem by improving PS regulation. The supply output now looks flat and clean on my scope even during modulation peaks, but I still get a tiny amt of FM. Any ideas?

My talking house synth is spot on, no xtal padder needed. I know just what you mean about the newer car radios being unable to receive off freq signals. That makes the cheap free running oscillator part 15 xmtrs just about useless for getting a message to car radios.

I just love that little motorized automatic antenna tuner. Seems like a lot of extra cost, probably some ham designer who had no finance guy overseeing him. I bet it would have been an OK (but not optimal) product without the autotuner. Mine seems to be able to tune a huge variety of antennas without giving up and indicating failure on the LED readout.

Wish this could operate in the LOWFER bands without huge mods. Would make a great LF beacon xmtr.

[KM1H]

That old SSB TX was the Central Electronics 100V and 200V. The two 6550's easily made a clean 100W out even on 10M. The 100V had a DSB with carrier mode and it sounded very nice on AM as expected for a phasing rig. I used to drive a NCL-2000 to around 350W with an excellent monitor display. This was 1964-87 that I had the 100V, still have the amp.

Carl
KM1H