NJDTechnologies

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Current Operating Frequency and Mode

OFF AIR; QRT Thursday night but back Friday morning by 1100z

Spike to storm levels did not appreciably impact session, at least at lower latitudes

– Posted in: 630 Meter Daily Reports, 630 Meters

Last night was a good example of a session opening late.  A pre-sunset flash to storm levels near 0z allowed solar wind (above 500 km/s) to complicate the geomagnetic field but at lower mid-latitudes the band seemed to clear and almost perform as if it were enhanced through the session after 0200z.  Perhaps the “bump” provided the energy to allow relatively efficient propagation.

planetary-k-index 050316

 

Kyoto DST 050316

 

Australia 050316

 

This was not the case at higher mid-latitudes, as reported by Neil, W0YSE/7 / WG2XSV:

WG2XSV 050316a

 

WG2XSV 050316b

 

So performance last night really depended on where you were located and as we have seen before, active geomagnetic conditions favor better band conditions further away from the auroral ovals.  I think we are getting to the point in this season where you cast your net and see what you can pull into the boat.  Winter is over and consistency is likely gone until the Fall.  The good news is that there are lot of surprises to be found for active stations as we progress to summer conditions.

Phil, VE3CIQ, also noted a slow start and noisy conditions but was rewarded with WH2XGP this morning.  Phil provided these comments:

VE3CIQ 050316

 

VE3CIQ map 050316

VE3CIQ session WSPR activity

 

Regional and continental WSPR breakdowns follow:

NA 050316

North American 24-hour WSPR activity

 

EU 050316

European 24-hour WSPR activity

 

JA 050316

Japanese 24-hour WSPR activity

 

VK 050316

Australian 24-hour WSPR activity

 

There were no trans-Atlantic or trans-African WSPR reports during this session.

Eden, ZF1EJ, continues to report my station as storms pound the southeastern US:

ZF1EJ 050316

ZF1EJ 24-hour WSPR activity

 

Laurence, KL7L / WE2XPQ, operated in receive-only mode during this session and provided reception reports for WH2XGP and WH2XCR, both of which were lucky enough to make it through the ionic fog.

WE2XPQ 050316

WE2XPQ 24-hour WSPR activity

 

WH2XCr WE2XPQ 050316

WH2XCR, as reported by WE2XPQ

 

Merv, K9FD/KH6 / WH2XCR, has been hearing well, reporting my signal even at unsettled and storm levels.  He also continues to share two-way reports with VK4YB, even seeing another peak on the approach to sunrise.  John, VK2XGJ, reports a quieter night in eastern Australia and also provided a report for Merv.

WH2XCR 050316

WH2XCR 24-hour WSPR activity

 

WH2XCr VK2XGJ 050316

WH2XCR, as reported by VK2XGJ

 

VK4YB WH2XCR 050316

VK4YB, as reported by WH2XCR

 

WH2XCR VK4YB 050316

WH2XCR, as reported by VK4YB

 

Today Jim, W5EST, discusses “ESTIMATING TPO USING MODELING dBi FOR GIVEN EIRP”:

“The April 27 blog discussed modeling of an antenna over EZ-NEC Demo’s “real ground” while omitting explicit ground system resistances that you might otherwise put into loads or L-networks. By omitting, you can get total radiated power TRP(dBw) from a desired EIRP level such as 7dBw. To get TRP from the EIRP, subtract the antenna gain dBi vs isotropic value EZ-NEC Demo displays with the antenna elevation pattern.

Some FAQs take the topic further.

Q1: How can you figure the transmitter power output TPO from the modeling results when all antenna and ground resistances are effectively in series?

A1TRP = Irms2 Rradiation.  In simpler models all the antenna and ground resistances in the antenna system are effectively in series.  So add them all up and call their total “R”:

TPO =  TRP x R / Rradiation.

To get TPO with series resistances, just multiply the TRP times the sum of all the resistances in the system divided by the radiation resistance.

Q2: Can you calculate TPO the same way if you specify an estimated ground resistance allocable to hat and a separate ground resistance allocable to vertical?

A2: You can enter separate ground resistance values into an EZ-NEC Demo L-network at the base and into an RLC load in the top hat.  Remarkably, we saw in the April 28 blog that ground resistance under an extended top hat doesn’t just add arithmetically to ground resistance near the vertical.  These combine in a more complicated way because of the multiple paths the displacement current traverses at various places in the system.

Fortunately, you can execute a model on EZ-NEC Demo by entering your estimated allocable ground resistances separately there. From them, let the software calculate the weirdly-combined antenna impedance seen by a specified Source connected directly to the base of the antenna.  (The vertical wire number for the antenna is specified in EZ-NEC button “Wires” section.)   Do this calculation before you subsequently specify ATU inductance(s) and capacitance(s) in L-networks.

TPO =  TRP x R / Rradiation.

TPO = {10^ [(7dBwEIRP –dBiRealGnd,Rgnd=0)/10]} x R / Rradiation.

The “R” is found in the resistance part of the combined impedance R+jX that shows in the “SWR” display window.  It signifies overall system resistance now seen by the Source instead.

Q3: Isn’t there some easier way?  And, what if the SWR isn’t 1:1 because you match the TX in the shack to some resistive impedance like 75Ω from the ATU instead of 50Ω from it—how do you estimate TPO then?

A3:  Run EZ-NEC with allocable vertical and hat ground resistances entered from your estimates. Click SWR, and then FFPlot. The FFPlot elevation pattern windows reports dBi including both antenna gain minus ground loss. Get TPO in dBw and convert to watts using FFPlot window dBi as follows:

TPO = 10^[(EIRP(dBw) –dBiRealGnd,Rgnd=YourEstimates)/10] watts.

You get the same TPO estimate regardless of which method A2 or A3 you use.  This one doesn’t require you to know anything but the dBi the FFPlot window reports for your specified model.  Use it, it’s simpler!  No separate calculation of radiation resistance is needed to estimate TPO. The appended TABLE illustrates an example how it works either way you do the calculation.

Q4: How can you figure the RF current at the antenna base from the modeling results such as dBi with ground system resistance? 

A4: From answer A3, get TPO.

IBase(rms) =sqrt(TPO/ R).

The combined system resistance R is displayed in the R+jX values in the SWR window of EZ-NEC Demo.  IBase(rms) here gives the ATU output rms current amperes to the antenna base.  If you want the ATU input current required to get that EIRP, then for a lossless ATU:

IATUinput(rms) =sqrt(TPO/ 50Ω).

(For a discussion of lossy ATUs, see this blog March 2931.)

REMARKS ON DOUBLE-LOADING OF 630M ANTENNA “F”

It turned out the double-inductance loaded 630m antenna “F” described yesterday improves the radiation resistance but not the antenna efficiency.  Increased loading inductances are disproportionately increasing the ground current and increasingly coupling some of the transmit power into ground loss beneath the arrow end of the top hat. Murphy’s Law prevents the greatly improved radiation resistance of loaded antenna “F” from benefitting you!  Nevertheless, the main conclusions blogged yesterday (May 2) remain.

If various real structures like HF tower and home AC ground wiring cage could destroy the 630m antenna performance, you can design around them and move the displacement current where you want it. You do this by inductively loading antenna “F” even if you can’t outperform the model results of an unloaded antenna “F” that assumed no interfering structures.  Moreover, you can null out the usual kilovolts on the antenna base at ground level.

TABLE: MODELING TPO FOR DOUBLE-LOADED ARROW-HAT 50’ ANTENNA “F”

Loads (uH)   RANT  Gain (dBi)/TPO  Effic.   TPO     Rradiation   dBi (Rgnd = 0,0)

2×400        76.7Ω   -13.91/123.3w    1.72% 123.7w   1.32Ω    +3.72

2×300        54.4Ω   -13.26/106.2w    2.03% 106.8w   1.11Ω    +3.64

2×200        43.9Ω   -12.95/ 98.9w     2.23%   98.8w   0.98Ω    +3.57

2x   0         35.3Ω   -12.89/ 97.5w     2.30%   98.0w   0.81Ω    +3.47

*NOTE: TPO is RF forward power minus the reflected power from the ATU input.  If your SWR departs from 1.0 : 1, then the transmitter RF output power will need to be more than the TPO just calculated.  EZNEC demo gives you reflection loss report in the “SWR” display window as if you feed a non-50Ω antenna with a 50Ω transmitter. Adjust the TPO estimate higher by that reflection loss if you drive an imperfectly matched antenna with a 50Ω transmitter.  Better yet, match the non-50Ω antenna perfectly by using a TX autotuner or a shack tuner.  Then for TPO calculations you can ignore the reflection loss in the SWR display window.”

 

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