Maybe your Talking House is just bad. I at one point owned 3; 2 worked fine, but one was DOA from the get go. It transmitted, but very weakly.
Your test radios are not run of the mill portables, and you also state that you have tested with a car radio and got similar range. So it's likely not the radios at fault.
I just wonder; when you're not transmitting, do you hear anything on your frequency with those test radios? I once chose a frequency that had nothing on it at first, but when I actually installed my transmitter at the studio site, a station could be heard. My range (FM) was probably 100 meters or so; when I switched the frequency to an empty one, it increased almost 10 fold. You don't need stations bleeding into your signal to cause interference; that interference might already be on your frequency.
I am beginning to think the TH unit might be problematic. Impossible to tell without real meters and gear I do not have.
Realizing my environment is a very bad one for radio transmission. Urban concrete, asphalt, high power lines in all directions, big brick buildings of ours, low ground conductivity, etc.
My radios do well, better than what I've owned in the past. Can't say either truly impresses me, but both have good reception and sensitivity in my experience. Often impressed what they pull out of the air 🙂
I selected the frequencies based on radio-locator.com and signals in area. Then from those reduced empties on the high end of the AM band, I went outside with radio and tuned in listening and walking about looking for interference.
Started out down near 1600 and found signals from Toronto coming in strongly on a few frequencies. Skipped one other due to NOAA weather on a another. Ended up at the top testing, 1700.
It appears to be clear/clean station frequency. Will retest over next few days just to be sure (as weather changes in a big way).
Setting aside the possibility of a problem with your TH unit, any Part 15 AM station, in any setup situation, will find that the upper frequencies from 1400 to 1700 are the best, with the X band 1620-1700 being the absolute best since the wavelength is much smaller than those below 1400, thus the 3 meter radiator will be at it's most efficient equaling greater range. Keep that in mind while conducting your experiments.
RFB
Well, I managed to get an improvised mount up for the whip today.
Took a mount intended to put a CB antenna on a truck mirror (tractor trailer) and unscrewed the back plate intended to sandwich mirror steel bar.
That left me with an L bracket with the screw in portion for the whip up top and cable underneath. Took (4) framing screws and screwed that bracket into the front corner outside of the greenhouse. That gives me a few more feet from the massive brick wall. Screwed the whip up on top and threw my coax on a F to PL-259 adapter from Radioshack, Catalog #: 278-258.
From there, my < 2 foot section of RG59A/U used before to direct wire the antenna got screwed into the new terminal on the L bracket mount.
Then I took the cable up under the eaves and into the greenhouse. The eaves are actually wide open as the fabric roofing hasn't been tacked up and under permanently.
Inside I screwed an old wood plant shelf up to the greenhouse. The shelf sits a few inches above the eaves opening where the cable routes in. A terminal screw down of to the ATU built in port and we were done.
Probably took me two hours all told. Lots of planning before doing.
By then it was dark, so no testing today.
I did a quick walk around informal signal check today with the Eton FR250 in hand.
Back at the greenhouse, I balanced the Talking House up in the corner of the greenhouse temporarily and draped the default wire antenna out through the eaves and did a slope antenna run to a sunflower plant carcass from last summer wrapped up in vines.
Went for a walk up my front street (heading north) which has some big trees along the way. The street is probably 15-18 feet wide I'd estimate. Street is fairly level in that direction.
as able to hear my TH broadcasting at around 2600-2900 feet before it went away midway across a viaduct (bridge). I stopped there and turned back. Possible the signal might have reappeared on the other side, but that's a test for another day.
Tried walking a parallel street one block up and got nothing like that range there. Range seemed way less on street parallel. Looking at environment, it makes sense as to get signal that direction means overcoming the bricks.
So notes from this are:
1. The TH unit seems to function properly, at least with the wire antenna.
2. 2000 ft range seems doable and listenable outdoors.
3. Brick buildings seem to crush AM signals or at least cause deflection or other unwanted redirection.
4. The whip antenna hack connected to the internal ATU might not actually be as efficient (have to get the wire antenna vertically mounted on a piece of wood or in a piece of PVC to do a real comparison)