- July 25, 2007 at 9:52 pm #6972am1670acrParticipant
Total posts : 15
Section 15.219 specifies operation in the band 510 – 1705 kHz. Besides the electrical length of even a 1/4 wave antenna at 520KHz being 450 feet long, is anyone currently running a station at these lower frequencies. According to Radio-Locator, no one is using 510 or 520 in the US. I ran through the binary equivalent of the dip switch setting on the SStran and it seems to cover almost DC to 3 MHz. Perhaps a larger diameter of PVC tubing would be necessary for a loading coil. What has been done at this end of the band so far??? Besides beacon stations between 500 – 510, is anyone else using these frequencies?July 25, 2007 at 10:50 pm #15841RichGuest
Total posts : 45366
Other things equal, the radiation efficiency of 3-m, ground-mounted Part 15 AM antenna systems at 1620 kHz and above can be about ten times greater than at 540 kHz.
This is related to the radiation resistance of the 3-m antenna vs the typical resistive losses in the loading coil and r-f ground on those frequencies.
Groundwave propagation losses are less for lower frequencies in the AM broadcast band than for higher frequencies. Even so — the physics of Part 15 AM as concerns field strength and r-f bandwidth at the receiving antenna favors the higher MW broadcast frequencies.
//July 26, 2007 at 5:44 am #15843PhilBGuest
Total posts : 45366
From what I see, all common AM BC receivers tune to 530 kHz minimum.
The AMT3000 frequency divider range is 20 kHz to 2560 kHz. The PLL will not lock above about 2100 kHz due to optimization for stability at lower frequencies. I can send a pdf showing the switch settings for all these frequencies. If you want it, send an email request to: firstname.lastname@example.org.
Rich is correct about the 3M antenna radiation resistance being about 10x lower at the low end of the band vs. the high end.
At the low end I suggest using the base loaded antenna, but you will need to replace the coil with one that resonates with the antenna capacitance (about 28 pf) at the low end freq. A large diameter coil will have a very high Q (high efficiency) that will help to offset the lower antenna radiation resistance. I’m talking about a diameter of 12” or more and a low AWG # wire.
The HAMCALC package of radio software (available free on the web) has a nifty Coil Q Calculator program that shows the relation of coil diameter to coil Q.
L = 3220 uH (resonates with 28pf at 530kHz)
AWG = 12
Coil Diameter = 12 in.
Number of Turns = 171
Length of Coil = 27.697 in.
Approximate True Q = 1383
Some other diameters:
Diameter = 18”, Q = 1667
Diameter = 24”, Q = 1754
The length of the coil winding decreases with increasing coil diameter.
Have fun experimenting!
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