i am trying to get that carrier current working. i am anal retentive when it comes to oem parts and i am trying to locate that ceramic biasing trim pot that is on the tr20 phase2 amp board.
i am trying to get that carrier current working. i am anal retentive when it comes to oem parts and i am trying to locate that ceramic biasing trim pot that is on the tr20 phase2 amp board.
it's 10k single turn ceramic and been told it handles less than 1v at about 80ma although i do not want to i am starting to dig through my stuff and find a large 10k pot of the traditional type to put in place of the missing trimmer.
i was going to attempt neutral loaded i have a nems clark FIM and a tenna SA along with a whole suite of various RF and modulation test gear at my disposal.
only thing is in discussing with radio engineers here 1670 which is out of range of the FIM is where i need to be.
so i will have to old school it with a sangean portable all band receiver. i will just have to be overly cautious and maybe have the signal die into the grass at half of the legal f/s so i am sure to be in compliance.
the 15.219 is the other issue. i am 12ft from dirt ground in an apartment. i can run w/o ground since it would be on porch or i can lay out symmetrical ground plane and plop tx in middle of porch only connecting power and audio leads.
Robert, I understand what you mean about keeping equipment in a "pristine" state as I also like to keep things as original as possible. If you can find a suitable, but not original, replacement for the pot then tell yourself that this is temporary pending finding the exact part. This way you can get the transmitter running and move forward and if, in the future, you find the original part then you can install it.
We, as a group, apparently haven't solved the problem of an "apartment" antenna which would comply with 15.219 regarding grounding. Using a water pipe or electrical neutral/ground works but these methods of grounding may be disallowed by an inspector.
There has been some posting previously about using a center fed dipole but I don't know if anyone has tried it. It would be a matter of constructing an antenna with a total length of 3 meters with the transmitter located in the center and a loading coil in each of the dipole elements. A variant would be one with a single loading coil in the center which is link coupled to the transmitter but there could be problems with Z matching and maintaining a high Q with this arrangement. I admit that I haven't thought this through carefully but this might be a nice winter project for you or me to tackle.
Neil
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In my slow-going Indoor Antenna blog I did report on the use of a baseboard dipole wire, center tapped by transmitter ground, with a vertical reaching the ceiling, which is often about 9-feet.
Using a loading coil only on the vertical, I am able to reach the type of resonance needed per the antenna instructions for the AMT3000 at sstran.com, which cannot be done indoors without the baseboard dipole.
Good news is that the indoor signal (AM) is ultra solid everywhere in the building. Bad news is that outdoor reception is sketchy and mostly close to the building.
I had a self-imagined formula for deciding the length of the baseboard wires, which is explained on that thread.