NJDTechnologies

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OFF AIR - but back tonight after dark for more CW

Another very average Summer night in North America; Quiet geomagnetic conditions but plenty of noise; Very consistent openings between KH6 and VK; W5EST presents ”Part 2: 630m Capacitively Segmented TX Loop Reduces HV RF”

– Posted in: 630 Meter Daily Reports, 630 Meters

The details for June 28, 2016 can be viewed here.

IMPORTANT REMINDER: Neither 630-meters nor 2200-meters are open to amateurs in the US yet.  Please continue to be patient and let the FCC finish their processes.  Click here to view the proposed “considerate operators” frequency usage guide for 630-meters under Part-97 rules that was developed with the input of active band users.

Evening noise conditions included wide-spaced lightning crashes that were quite intense locally due to a number of small but very active storms in North and East Texas.  By morning real-time lightning data suggested that strikes were not so wide-spaced so I imagine that it was a very noisy morning, particularly in the central US.  The Caribbean and Gulf of Mexico was also very active in addition to pockets of storms  across Canada, parts of the Northwest and New England.

11-hour North American lightning summary

 

Geomagnetic conditions were quiet.  The Bz is pointing to the North and solar wind velocities are averaging near 440 km/s.  DST values were more consistent than previous sessions and continue to ride the centerline.  Values were generally positive.

 

 

 

Roger, VE7VV, submitted this short NASA video on the coming solar minimum.  There are interesting comments on long-lived coronal holes and elevated galactic cosmic rays which have recently been theorized to increase D-layer absorption during the deepest minima.

Ken, K5DNL / WG2XXM, reported that he decoded four WSPR stations and he was decoded by 23 unique stations including WH2XCR and three Canadian stations.

John, WA3ETD / WG2XKA, reported that he decoded seven WSPR stations and he was decoded by eleven unique stations.  John indicates that his noise level was “very high” due to storms to his East and West.

Neil, W0YSE/7 / WG2XSV, reported that “Prop and/or activity was down this session from Vancouver WA. Normal noise I guess for this time of year. Heard 3 and heard by 7. Merv/XCR was my DX. All others were western states and provinces.

WG2XSV
Hearing: WG2XXM, WH2XGP, WH2XXP
Heard by: N6RY, N6SKM, VE6JY, VE6XH, W7IUV, WH2XCR, WH2XGP

Many thanks to these consistent participants. Without them we would have no idea how far we are reaching.”

Mike, WA3TTS, reported “8 stations decoded overnight on 630m on my NW EWE antenna . By 0230~0300 there was a high QRN level–more or less constant S8, which was still present in the 0630 time frame.  I did manage 2 XGP decodes in the mid -20s for best DX closer to SR….

Other stations decoded were WG2XXM (75 spots best -6 @ 0206), WG2XKA (36 spots best -4@ 0146), WH2XZO (51 spots best -15 @ 0856), WI2XUF (7 spots best -22 @ 0904), VE3CIQ (41 spots best -14 @ 0146),  WH2XNG (3 spots, best -6 @ 0130).  Also 11 spots overnight for WH2XND on 2200m with similar high QRN with split IF output to second receiver. Best decode -26 @ 0936.”

Trans-Pacific report details, excluding KL7 and KL6, can be viewed here.

Roger, VK4YB, reported “Low QRN continues but storms are forecast over next two days. WH2XXP provided a few spots at his sunrise. JA path was not there tonight. Signals may have been just below.  I was VK6YA in Geraldton many moons ago. I am gathering new info on my antennas’ performance on a new bearing. Thanks Edgar.”

Ward, K7PO / WH2XXP, received reports from 25 unique stations including VK4YB and ZL2BCG.

I was QRV only briefly during the even, shutting down relatively quickly due to changing weather conditions here in North Texas.

Regional and continental WSPR breakdowns follow:

North American 24-hour WSPR activity

 

European 24-hour WSPR activity

 

Japanese 24-hour WSPR activity

 

Oceania 24-hour WSPR activity

 

Eden, ZF1EJ, reported that he was off air due to thunderstorms in his area.

Laurence, KL7L / WE2XPQ, provided reports for two WSPR stations and he received reports from WH2XCR (two-way reports).

WE2XPQ 24-hour WSPR activity

 

Merv, K9FD/KH6 / WH2XCR, had a good night, providing reports for VK5FQ and sharing two-way reports with VK3HP, VK4YB, ZL2BCG, and WE2XPQ.  He received reports from VK2XGJ.  Merv’s DX report details can be viewed here.

WH2XCR 24-hour WSPR activity

 

Jim, W5EST, presents, “PART 2: 630M CAPACITIVELY SEGMENTED TX LOOP REDUCES HV RF”:

Monday’s blog asked what kind of designs for a 630m antenna could reduce kilovolts of HV RF typical of top hatted verticals. http://njdtechnologies.net/062617/  What kind of designs might avoid high resonating reactances that bring in HV RF as their side effect?
Safety conscious operation of 630m antennas can, of course, employ HV RF resonated TX antennas such as conventional 630m verticals by stations licensed and permitted to operate 630m in their countries. (Such as Part 5 in USA, but not yet for hams in USA.)  Here, I use the question of HV RF reduction primarily as a design fulcrum to leverage insights about alternative 630m TX antenna systems.
Suppose for 630m a big single-turn loop of heavy gauge wire or tubing goes through an RF power toroid capable of handling the power and having a multi-turn primary coil rather like Fig. 27 of an example HF web site:  https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm (scroll 1/3).  Readers can specify the mix and size of the toroid.  Readers will also recognize the practicalities to securely support this antenna in position. 
Today’s illustration models a 40’x40’ loop of #10 copper wire elevated 10 feet above the ground.  RF current of 10A courses through this loop. The loop inductive reactance is about 250 ohms. Without more, the peak RF voltage would be 10A x 250Ω /0.707 = 3540 volts peak.
Instead of inserting a single resonating capacitor at top middle of the loop, as one would likely do at HF, the technique here inserts four resonating capacitors at the four corners of this MF TX loop.  Thanks to the capacitors, the RF voltage varies among remarkably low levels along the length of the loop. The RF voltage may peak at potential differences here and there between one-eighth and one-quarter of the 3540 volts calculated above.  Instead of HV RF voltage accumulating meter by meter all the way around the loop, each capacitive reactance subtracts from the RF voltage stepwise at the four corners of the antenna.
In today’s first illustration, lower left, you see the applied RF voltage is only 22V rms at 10A. TX power output TPO is 136.2 watts, and -17.58 dBi leads to 2.38 watts EIRP.  I modeled the lossless counterpart of this antenna, which led to an estimated 0.63% efficiency.  Most of the losses arise in the #10 copper wire and not in the ground conductivity.   
Is the result a high performance antenna?  That depends on your point of view. Being a vertical loop, there’s no zenith null and the low angle pattern is quite attenuated broadside to the loop. However, the 2nd illustration shows an acceptably low elevation pattern in the plane of the loop for 630m work.  (See elevation patterns in lower center of each illustration). 
I think the idea of any 630m antenna model yielding 2w EIRP  with at most only a few hundred RF volts across any two points is what’s interesting.   Some 630m stations may also want to radiate power toward the zenith for NVIS work and for high angle sky wave propagation experiments, or may want to constrain radiated power broadside to the antenna too.
The structure forms a 630m capacitively segmented TX loop that reduces HV RF. The bottom center of the loop antenna is grounded to provide an earth ground voltage reference. Chances of flashover to nearby tree branches presumably is reduced.  With lower RF voltage, RF safety is easier to manage.  Less displacement current is likely to “leak” away from the antenna via its stray capacitances because RF voltages are much less. 
The 10A RF antenna current calls for 4700 pF capacitors built for HV RF duty: Compare  http://www.mouser.com/catalog/supplier/library/pdf/VishaySinglelayerCerCaps.pdf  The RF current from the #10 wire must properly conduct into each capacitor.  Use insulating rain shields to prevent dirt, fog and rain from shorting around the capacitors.  I’ve not determined the cost and weight of such capacitors which of course matter to the affordability and physical support requirements.
The closed loop with its capacitors will offer some residual reactance even with the four capacitors in place.  The 630m segmented loop’s residual reactance will be multiplied by a factor– the square of the turns ratio of the RF transformer. That’s as seen across the multi-turn primary coil wound on the toroid. For example, when the capacitor values make the capacitive reactance a little larger than what cancels the loop’s inductive reactance, the residual reactance is net-capacitive. The net capacitive reactance will be multiplied along with the loop’s ohmic dissipative resistance and its desirable radiation resistance into higher values at the multiturn primary coil on the toroid. In the process, the primary current will be less according to the turns ratio itself, and the primary voltage will be higher according to the turns ratio too.   
The coax run from the shack is electrically quite short at most 630m ham/experimenter stations, amounting to a tiny fraction of the 630m wavelength.  So, the purpose of this loop antenna’s toroidal RF transformer is not really to match the coax characteristic impedance to the antenna. If the coax current isn’t so much as to lead to excessive coax losses, then what’s mainly important is for the overall matching system to match transmitter TX output to the antenna, and I take 50 ohms as TX output impedance.
The model predicts 1.351 – j0.2257 ohms (illustrations at upper left). To match 50 ohms, use a 6:1 or 12:2 turns ratio in this RF power toroid example.  36:1 impedance ratio (6×6) then leads to 48.64 – j 8.13 ohms impedance. In practice, the reactive part of the impedance will be known only after the actual antenna is constructed, so probably 50 uH of loading coil should be provided even though very little of it would be needed to deliver 2-3 uH and cancel the 8.13 ohms of capacitive reactance in the illustration. 
Calculated coax current would be 10A/(6:1) = 1.67A.  Coax voltage would be 132 v rms or 187 v peak—much like RF voltages found for work in the HF ham bands.  
A horizontal loop could have an omni pattern with a zenith null, but its horizontal polarization would likely suffer ground cancellation, so it’s not considered here.
Do you have ideas for a high performing 630m antenna of alternative design offering low RF voltages below, say, 1 KV?  Or, can your experience provide us commentary on this or some other type of 630m antenna for this blog?  We appreciate your contributions!

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Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!