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When it comes to discussion of 630m, the topic of antennas seems to top the list. One of the easiest ways to enjoy what 630m has to offer is to try and utilize a low band antenna that may already be in place. An 'inverted-L' for 80 or 160 can be readily bottom-loaded and with a few radials, can provide a good starting point ... but with a little additional work, its efficiency can be easily improved by expanding the top horizontal (top hat) section.

Jim, W5EST, has posted an interesting description of the pros and cons of the 'top hat' in a recent KB5NJD daily 630m report. Those thinking about getting on the band or those considering ways of improving their present antenna might find the information helpful.

Top Hat Advantages:

Higher EIRP comes from a more nearly uniform current distribution all the way up a TX vertical. https://en.wikipedia.org/wiki/T-antenna . But remember that adding top hat doesn’t help you if your license is subject to a legal limit EIRP that’s reached by your station already.

A vertical without a top hat has no current at its tip, meaning the upper part of a hatless vertical is inefficiently used.  Average RF current for a hatless short vertical is only half what an RF ammeter shows at the antenna base.  Top hat lets a shorter vertical antenna yield same total radiated power TRP by increasing its degree-amperes, as discussed March 31, this blog.

2 amperes of 630m RF base current in a 10° tall hatless short vertical can give 10 degree-amps (2 x ½ x 10°) and yield 15 degree-amps with an ample top hat.  A top hat can increase average RF current by about a quarter to half, which could as much as double the TRP.

Top hat increases antenna system capacitance. You get more flexible QSY by decreasing the system Q.  SWR increases rapidly as your frequency departs from antenna system resonance, see graph Feb. 10, this blog. With lower system Q the SWR doesn’t increase so rapidly. Then you can QSY temporarily a little way without retuning or by just retuning a little in the shack instead of outdoors at the ATU.

Decreased Q somewhat lowers antenna voltage KV from antenna base to top hat. On 630m Q = (2π 475)L/R by definition and Vantenna = 1.4 Q  P / I  <  Vbreakdown.  See Jan. 16, this blog.

Top hat wires can be symmetrically or asymmetrically positioned to give approximately similar capacitance whichever way.   I’ve not modeled the effect of a top hat on the azimuth and elevation antenna patterns of an electrically short vertical.  I don’t think the effect is very significant. But if you know a link or some better information about this, let us know.

If your radials have extended way beyond the extent of a small top hat high above, then providing longer top hat conductors above the radials can more efficiently utilize the radials.   If the radials mostly go in one or two directions, then for highest antenna system capacitance the hat wires should extend in those directions to couple best with the radials.  Your experience may suggest this last is not too important, especially if you have a perimeter conductor and/or several ground rods and your soil has favorable conductance.

Another top hat advantage is that top hat conductors are compatible with structural support and stabilization for the very top of an MF/LF vertical antenna.  You get added degree-amperes–and steadying at the top to boot.

If the top hat slants upward, its system capacitance contribution is somewhat decreased compared to a top hat of same length horizontally, but the vertical slant contributes radiated power. Depending on the arrangement of antenna and trees on some properties, using a shorter vertical with an upwardly slanting asymmetrical top hat may make the antenna system both easier to guy and less obvious to neighbors.

Putting in a top hat or improving a top hat increases the degree-amperes of a short vertical mainly by distributing the same RF amperes more uniformly.  Adding more radials and longer radials decreases the antenna system resistance and increases the degree-amperes of a short vertical mainly by increasing the RF amperes of antenna current itself.

Top Hat Disadvantages:

A top hat obviously requires outdoor work to construct or revise it.  You may be able to simply increase your transmitter power TPO more conveniently than to do the outdoor work.

A top hat needs to extend more or less horizontally from the top of the vertical, although the angle is not too critical within +/-45°.  Distant supports for the top hat at that top level may be unavailable or expensive and inconvenient to provide. If the top hat were attached to the vertical below the top of the vertical, the otherwise radiation-beneficial top segment of the vertical becomes mostly unused.

If the top hat slants quite steeply downward, its effect on system capacitance may be a wash– more capacitance by closer approach to the ground and less capacitance because same length top hat conductor extends less outward over the ground below. That defeats a reason for putting up a top hat in the first place.

Moreover, if the top hat slants steeply downward, then vertically downward RF current in the top hat cancels part of the radiation from the vertical antenna and at least partially defeats the improvement in vertical antenna current uniformity that the top hat is intended to confer.

A long top hat may not fit on the available real estate.  Even if it fits, it may add to visibility as far as difficult neighbors are concerned.

Adding a top hat means you need to retune the ATU after the addition. But so does improving the radials or just about anything else you do.

Top hat conductors add more weight on a vertical than lighter-weight guying does.  The weight of the top hat likely adds to the support demanded of the antenna base.  If you put downward-slanting top hat conductors under tension at their far ends to keep them from drooping in the middle, then a lot of that tension will be imposed on the vertical too.   That can produce a buckling force on the vertical which may call for additional guying halfway up the vertical.

Top hat conductors convey a declining but substantial RF current along their length.  That involves I2R losses in the skin effect resistance of the top hat conductors. However, if your earth resistance is high or your radial/grounding system is not very elaborate, some loss in the top hat probably does not decrease the RF amperes of antenna base current very much at a given TPO compared to the improvement in radiation TRP that the top hat gives you.

If skin effect resistance losses in the top hat are significant compared other losses in the system, reducing top hat losses generally means more conductors or heavier conductors in the top hat.  That translates to more weight for the whole system to support.

A top hat translates KV of antenna top voltage to its ends. If the top hat extends all the way to leaf cover of trees or shrubs, unexpected sparks might jump to them in quiet weather, or in windy weather, or sometime when such trees or shrubs grow nearer to the top hat end(s).

Generally top hat advantages outweigh their disadvantages so long as you plan intelligently. Please tell us your experiences with top hat advantages and disadvantages!”

A G3XDV LF top hat

Jim often adds an interesting op-ed piece to the KB5NJD daily report and sifting back through the past few weeks will provide some great 630m 'food for thought' bed time reading!
Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

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Richard Carpenter, AA4OO, is a regular contributor to AmateurRadio.com and writes from North Carolina, USA. Contact him at [email protected].

Here is this week’s space weather and geophysical report, issued 2016 Apr 04 0340 UTC.

Highlights of Solar and Geomagnetic Activity 28 March – 03 April 2016

Solar activity was at low levels on 28 March due to an isolated C2 flare from Region 2524 (N15, L=277, class/area Eho/340 on 19 March) at 0228 UTC. The rest of the period was dominated by very low levels as Region 2526 (S05, L=178, class/area, Cso/200 on 29 Mar) was the only spot group on the disk until the emergence of new flux on 03 April. No Earth-directed coronal mass ejections were observed during the period.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was at normal to moderate levels throughout the period.

Geomagnetic field activity ranged from quiet to major storm levels (G2-Moderate) during the period. From 28-31 March, solar wind parameters indicated the influence of a positive polarity coronal hole high speed stream (CH HSS). Solar wind speeds increased from near 450 km/s at the beginning of the period to around 590 km/s by early on 30 March before declining to a low around 330 km/s by 02 April. Total field slowly declined from 8 nT early in the period to 3 nT by 01 April. The geomagnetic field responded with quiet to active levels on 28 and 30 March with quiet to unsettled levels on 29 and 31 March. Quiet conditions were observed on 01 April through midday on 02 April. At approximately 02/1344 UTC, a solar sector boundary crossing occurred into a negative (towards) sector followed by an increase in total field to a maximum of 18 nT at 02/1406 UTC while Bz reached a maximum negative deflection of -14 nT at 02/1522 UTC. Solar wind speed increased to near 540 km/s around 02/2131 UTC indicating the arrival of a co-rotating interaction region followed by another CH HSS. The geomagnetic field responded with unsettled to major storm levels (G2-Moderate) during the second half of 02 April. By 03 April, solar wind speed was in decline to around 400 km/s while total field measurements were near 6 nT. Quiet to active levels were observed on 03 April.

Forecast of Solar and Geomagnetic Activity 04 April – 30 April 2016

Solar activity is expected to be at very low to low levels for the forecast period.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at normal to moderate levels with high levels on 04, 06-10, 14-18, and 26-29 April in response to recurrent CH HSS activity.

Geomagnetic field activity is expected to be at unsettled to active levels from 05-08, 11-15, 24-27, and 30 April with (G1) minor storm levels likely on 13-14 and 30 April and (G2) moderate storm levels likely on 12 April due to recurrent CH HSS activity.

Don’t forget to visit our live space weather and radio propagation web site, at: http://SunSpotWatch.com/

Live Aurora mapping is at http://aurora.sunspotwatch.com/

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Today's Sun courtesy: http://sdo.gsfc.nasa.gov/

With the sun remaining reasonably quiet over the past several days, a sudden spike in the geomagnetic field on Saturday afternoon saw a number of trans-Pacific spots showing up on 630m WSPR mode.

courtesy: http://wdc.kugi.kyoto-u.ac.jp/

In the predawn hours of Sunday morning, my own system decoded the VK3ELV WSPR beacon, located in south east Australia, 12,992 km from here. From an e-mail exchange, it seems that VK3ELV is using a 'drifting' IC706M2G on 10Mhz with a VK3XDK Transverter into an old HF AMP (2x 2SC2290) modified for 630m. This is running about 130-140 watts output. The antenna is an inverted L about 30 metres high and 1/4 wave long.

courtesy: https://www.google.ca/maps

VK3ELV 630m

Further to my south, the WG2XGP WSPR beacon run by Larry, W7IUV in central Washington, was reported down under by two different VK's on Sunday morning as well ... VK4YB and VK2DDI, both some distance from VK3ELV.

courtesy: https://www.google.ca/maps

It's interesting to note the time difference for these receptions, with Larry's reception being several hours earlier than my own (1304Z), close to my sunrise. As well, the 'spotlight' effect of propagation over such a vast distance is somewhat intriguing. I would have thought that if I should see any VK's on 630m, it would be the closer ones and not the further one, yet it was just the opposite.

Although VK3ELV's signal was right at the edge of WSPR decoding levels (-29db), it would only take a few more db to allow a two-way JT9 digital mode QSO to take place ... maybe something that will be possible in the coming years of solar minimum and much better LF/MF propagation. To be readable on CW would need an equivalent true power output increase of at least 16 times, requiring VK3ELV to run around 2,000 watts output!

Over the years I have seen ZL6QH a number of times on 2200m (QRSS CW mode) but this is my first reception of VK and, hopefully, not my last.

To keep up to date with overnight activities on 630m, visit the excellent site of KB5NJD. John posts a detailed daily summary of events. In addition, you will find some excellent resources to help you get involved in this part of the spectrum ... and remember, you don't need a big backyard or a big antenna to have fun on 630m.
Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

A detailed look at Icom’s Innovative IC-7300 Transceiver. Complete review of most features and operation plus your questions answered. Recorded live at AmateurLogic Studios March 17th, 2016.

YouTube

George Thomas, W5JDX, is co-host of AmateurLogic.TV, an original amateur radio video program hosted by George Thomas (W5JDX), Tommy Martin (N5ZNO), Peter Berrett (VK3PB), and Emile Diodene (KE5QKR). Contact him at [email protected].

April has arrived with not showers but a snow storm! We have had snow falling and accumulating all day today and it's forecast to snow most of the evening. To me it seems a good time as ever to think about my summer portable operations. A few weeks ago both Julie and I purchased new bikes and these bikes are amazing compared to our old ones. My plan this summer is to utilize my new bike for portable ham radio outings. My first step is to check out some areas in the neighbourhood were I can have my first few radio outings. I was looking for locations that would allow me to concentrate on my portable setup and workout the operational glitches. Each day I go out for a 40 min walk in and around the Lake we live on. These last few days while walking I was paying attention to spots that would be possible portable radio op spots. My criteria was close to home just in case something is forgotten, an easy ride to get there and sites that are easy radio setup and operation. This would allow me to work out the radio "stuff". Here are 3 locations I have scouted out so far......
This spot being right on the lake during a very warm day will have a nice cool breeze. Also if the sky is threatening rain I would have shelter to continue my operations.










This location is nice as it has a large bench to setup on but the weather will have to co-operate as it's out in the open.










Once summer arrives the trees at this spot will provide some nice shade plus it's a nice view to boot.
Mike Weir, VE9KK, is a regular contributor to AmateurRadio.com and writes from New Brunswick, Canada. Contact him at [email protected].

In this episode, Martin M1MRB / W9ICQ is joined by Leslie Butterfield G0CIB, Edmund Spicer M0MNG and Matthew Nassau M0NJX to discuss the latest Amateur / Ham Radio news. Colin M6BOY rounds up the news in brief, and this episodes feature is  - Renovation Projects

• Hams Pass 100 Years
• UK Government to Sell 750 MHz Spectrum
• Ham Radio Antenna Dispute in Canterbury
• UC Berkeley Elmers Hundreds of Hams
• SBE Urges FCC to Improve MW Noise Environment
• UK Host for YOTA 2017
• 17 June 2016 - QRP Day
• Special Amateur Radio QSL - OE16M

Colin Butler, M6BOY, is the host of the ICQ Podcast, a weekly radio show about Amateur Radio. Contact him at [email protected].