Thanks, I needed that.
So, the combination of a monopole and loading coil will always have a feedpoint impedance equal to the radiation resistance of the monopole plus any other copper losses. This is because after the loading coil offsets the capacitive reactance of the monopole the only thing left is the resistance of the network.
So it would seem the ATU input transformer actually must transform the coax impedance to a lower value assuming the reactive components are cancelled out and assuming no ground loss.
"Thanks, I needed that."
Good to see that we can keep our discussions on a ~professional level.
I added something to my Post 60 that may get missed, so I'll repeat it below.
Note that losses in the matching network and r-f ground system will raise the value of the real (non-j) term of these input impedances for both of these radiators. The biggest difference in percentage will be for the 3-m monopole, for which the real term might rise to 50 ohms or more -- but still much less than the real term of the full-sized 1/2-wave monopole with those losses included.
I'm glad we were able to continue this discussion 'till my light bulb came on.
I'm also glad that Robert shared with us his real world measurements of the TH/ATU combination.
Robert,
I ran some quick calculations and my results are orders of magnitude different than you measurements. I wonder if we can explore this a little deeper.
The bottoms of the primary and secondary of both transformers, one in TX and one in ATU, are both connected to the coax shield. In the TX, the coax shield is connected to ground which is also connected to the AC plug ground. I assumed a sort of worst case ground path resistance to earth at the ATU of 100 ohms. I also added 15 ohms for coil resistance for a total of 115 ohms. I assumed a ballpark power to the coax of 95 mW.
The signal strength at 30 m for the 1 meter high antenna was 4,739 uv/m at 30m, and 12,845 uV/m at 30m for the 6m high antenna. That's a difference of +8,106 uV/m at the higher elevation.
Did you record the FS measurement at both elevations in addition to the 20 uV/m difference? It would be beneficial to resolve this major discrepancy. I'm thinking that possibly you had the scale factor switch set wrong on the meter. It's something to check.
Also, did you peak the tuning at both elevations. Tuning at 1m and 6m are close, but different enough to make a major change in the FS measurement if you didn't re-tune.
Also, it seems that if the absolute readings were in the 4,739 uv/m to 12,845 uV/m ballpark, resolving a 20 uv/m difference on the analog meter would be nearly impossible.
Accidental double post. See next message.
why Radio Systems Global just won't release all the data they have on the transmitter remains a mystery. why rangemaster wont release theirs as well is a mystery.
Because they don't have to.
might not have retuned the antenna when putting it up high and the setup on the FIM is a little complicated and i had just received it not long before this experiment so it is conceivable i botched something on the FIM setup as well. was long time ago i did this test and didn't make any notes was just a curiosity experiment.relative wise your AMT5k beat out the AM1k and THII/ATU with more f/s than either. i used the FIM to tune amt5k for peak f/s then set for 100mW input. i would like to build a large air wound coil similar to the manteca magnum to test out on the amt5k and see what kind of difference that makes in terms of f/s.
Well after reading all of this I have to say I have a smile on my mug 🙂
Robert C thanks for the numbers and the test .. I am now going to build a 100 foot tower and put the ATU on it with no ground 🙂 Ok maybe not , but heck it sure would be intresting to see what kind of signal distance we would get with that.
Ever hear the story about the researcher who trained frogs to jump on command? He would then cut off their legs and when they no longer jumped upon his command he concluded that frogs without legs are deaf!
The idea of elevating an AM broadcast antenna for better performance falls into this category in that the elevated antenna produces more range but not for the reason which is commonly assumed. The elevated antenna gives more range because the ground conductor radiates and not because the BCB AM signal radiates better from a high antenna.
Consider that (and why) AM BCB station antennas are almost always placed at ground level and only rarely on the roof of a building. (I am aware of one that used to be atop the Hotel Alms in Cincinnati and that was a dipole... see 
. The station used to identify with the phrase "...with towers high atop the Hotel Alms". It was WKRC)
Neil
In the 60s I went across the Mississippi River just on the other side of where the future St. Louis Gateway Arch would be built, and visited the Broadview Hotel in East St. Louis, Illinois, with studios and tower for WTMV, 1490kHz, 1kW.
The hotel wasn't all that high, maybe 5-stories. The tower was up top, but didn't look very tall, maybe 75 to 100-feet.
Are things different today? Don't know. Haven't been over there for more than 40-years.
Living now about 10-miles from the station, the daytime signal is good, but at night they tend to be sort of in and out of competing skywaves, renamed to WQQX.
Neil one of the reasons I like the ATU on the roof , is that it gets the ATU above the trees and bushes and houses in the area . would it being at the ground level with proper grounds and such be better for TX Distance ? I am asking this in a very serious manner as I want to be a leagal as I can and also get the TX distance that I can.
Lefty,
The TH transmitter and ATU were certified to operate together and presumably it would be legal to elevate the ATU using the transmission line but it gets a bit fuzzy since certification allows the manufacturer to sell the equipment but it doesn't grant the user any special exemptions for use. If it is legal with the ATU on the ground using the transmission line then elevating the ATU should be essentially the same thing.
Most likely driving the ATU with another transmitter and a transmission line may not be so under 15.219.
Any antenna, ground, and transmission line configuration is legal under 15.209 which has field strength limits. It is generally accepted that an optimized system under 15.219 will provide greater range than one under 15.209 but, as you reported, decent range can be had under 15.209.
From my experience trees and bushes near a ground mounted vertical will affect (reduce) the radiated signal as observed by a monitoring antenna nearby however the effect is small and no reduction in usable range resulted with my station.
Buildings and obstacles which are small with respect to wavelength do not block the signal so the typical residence or small business buildings are not a significant factor. The signals may be attenuated inside the structures but externally they diffract around the structures.
Neil
