Monday, 26 September 2016

The Amazing BOG

courtesy: http://www.wd0m.com/antennas1.html

A recent inquiry about 'BOG' antennas on the topband reflector reminded me of my own experiences with this simple yet very effective antenna. A 'BOG' or 'Beverage On Ground' seems to come in many varieties and is usually, out of necessity, shorter than a 'real' beverage.

In many instances, BOGs are as simple as running a wire out on the ground as long and as straight as practical. Not always, but usually, the BOG is fed by a small homemade balun to isolate and match the impedance to a 50 ohm feedline. Most real Beverages are terminated at the far end with a resistor to ground, while for BOG builders, some use it and some don't.

My own experience with a BOG, or as close as I could come to one, was an extension of my 160m half-sloper. The topband half-sloper was quite normal, being about 132' long and fed at the top of its supporting metal tower with 50 ohm coax ... the hot-side of the coax going to the wire and the shield going to the metal tower.

One afternoon I wondered how the antenna would work lower in frequency, in the NDB band below the broadcast band, if I were to extend the sloping 132' element further. I added another length of wire to the lower end and proceeded to run the wire along the ground on the bankside above the beach. I was able to run out another 500' approximately, in a straight line to the east, before running out of beach. I left the far end unterminated and waited for darkness to to have a listen.

The first thing I noticed when tuning the NDB band was how quiet it sounded. There seemed to be almost no noise, man-made or nature-made. Disconnecting the antenna showed a small drop in what little noise there was, indicating that sensitivity levels were still being determined by skynoise ... a good thing.

What amazed me however, was that signals just popped-up everywhere and although not as strong as on my normal NDB antenna (a loop at the time), they were much better copy since there was virtually no noise. The BOG produced a significant improvement in my SNR on all signals. It had been several months since I had logged any new beacons on the NDB band but over the next three weeks I was able to put 65 new catches in the log ... all previously unheard!  Switching between the loop and the BOG almost always produced no copy at all on the new signals, compared to an easily copied one on the BOG.

My experience was very similar to that shown in these videos by VO1HP ... with solid signals well out of the low noise background and no sign of atmospheric noise to mask them.


It is clearly evident that the BOG delivers a much better SNR than the comparison loop and is the reason so many topbanders use a separate antenna for receiving. The next video compares the BOG with a 160m 'Inverted-L', a very popular antenna on topband.


BOGs need not be really long and good results can be had with just 200' of wire. Many BOG users employ a simple preamp to boost the low level of signal but often the switchable 'preamp' built into a receiver or transceiver will be enough to overcome the low gain of shorter wires.

I've often thought that if I had a lot of acreage, the ideal receiving system for MF and LF work would be a centrally located radio shack with long Beverage wires fed-out in various directions ... like the spokes of a wheel. Having the ability to directionally switch antennas would produce 'beam-like' capabilities on LF.

There is a ton of web information available on the BOG and the Beverage should you want to give this simple antenna a try and have a narrow strip of space where one might be laid out without causing a problem.

A very comprehensive source of BOG and Beverage information can be found on WØBTU's Beverage Receiving Antennas page here. 

A nice compilation of Beverage / BOG exchanges from the Topband Reflector may be found on N1EU's Beverage Antenna Tips page here.
 
In addition, N1EU has a useful page of discussion about transformers used in these antennas.

PA5MW offers a colorful description of his own BOG experience here.

Bruce, K1FZ has a nice BOG 'hint's' page here and also passed this advise to the original BOG inquiry:

A BOG can do a good job unterminated. If too long they self terminate. Depends upon the soil as to length.

The biggest mistake is making the BOG antenna too long. Try not to go
over 200 feet for 160 meters. Longer will work in some locations
soil like desert, sand, other non/ partial conducting types.

Its been a few years since my last experience with a BOG but I may run one out again for the DX season, now that most of my neighbours have left the island for the winter.

Tuesday, 20 September 2016

Hunting For NDBs In CLE211

'OO'- - 391 kHz Oshawa, ON




This coming weekend will see another CLE challenge, this time in the 15 kHz slice from 385.0 - 399.9 kHz.





A 'CLE' is a 'Co-ordinated Listening Event', as NDB DXers around the world focus their listening time on one small slice of the NDB spectrum.

A nice challenge in this one is to hear the Oshawa, Ontario NDB, 'OO' on 391 kHz. This one runs at just 7 1/2 watts output and gets out amazingly well having been logged here last year. It has even been heard in Europe!

From CLE organizer Brian Keyte, G3SIA, comes the usual 'heads-up':

Hi all,

Our 211th Listening Event is only a few days away.
The Northern Hemisphere summertime storms have subsided, the equinox
will have passed when the CLE starts and we can all hope for some good
reception conditions.
Whether you are a keen propagation watcher or just a take-what-comes
listener (like me), please join in.

Days: Friday 23 September - Monday 26 September
Times: Start and end at midday LOCAL TIME
Range: 385.0 - 399.9 kHz

Please log all the NDBs you can identify that are listed in the range
(it includes 385 kHz but not 400 kHz) plus any UNIDs that you find there.
We last used this frequency range for CLE194 in May 2014.

Please send your CLE log to the List in a plain text email if possible
(not in an attachment) with 'CLE211' at the start of its title.
Show on each log line:

# The date (e.g. 2016-09-24, etc., or just 24) and UTC.
(the date changes at 00:00 UTC)
# kHz (the nominal published frequency, if known)
# The Call Ident.

Show those main items FIRST - other optional details such as Location
and Distance go LATER in the same line.

As always, tell us your own location and brief details of the equipment
that you were using during the weekend.

Good listening - enjoy the CLE
----------------------------------------------------------
From: Brian Keyte G3SIA ndbcle'at'gmail.com
Location: Surrey, SE England (CLE co-ordinator)
----------------------------------------------------------

(If you wish you could use any one remote receiver for your loggings,
stating the location and owner - with their permission if required.
A remote listener may NOT also use another receiver, local or remote,
to make further loggings for the same CLE).
  
73 

Brian


These listening events serve several purposes. They:
  • determine, worldwide, which beacons are actually in service and on-the-air so the online database can be kept up-to-date
  • determine, worldwide, which beacons are out-of-service or have gone silent since the last CLE covering this range
  • will indicate the state of propagation conditions at the various participant locations
  • will give you an indication of how well your LF/MF receiving system is working
  • give participants a fun yet challenging activity to keep their listening skills honed

Final details can be found at the NDB List website, and worldwide results, for every participant, will be posted there a few days after the event. If you are a member of the ndblist Group, results will also be e-mailed and posted there.

The very active Yahoo ndblist Group is a great place to learn more about the 'Art of NDB DXing' or to meet other listeners in your region. There is a lot of good information available there and new members are always very welcome. As well, you can follow the results of other CLE participants from night to night as propagation is always an active topic of discussion.

If you are contemplating getting started on 630m, listening for NDBs  is an excellent way to test out your receive capabilities as there are several NDBs located near this part of the spectrum.

You need not be an ndblist member to participate in the CLEs and all reports, no matter how small, are of much value to the organizers. 'First-time' logs are always VERY welcome!

Reports may be sent to the ndblist or e-mailed to either myself or CLE co-ordinator, Brian Keyte (G3SIA), whose address appears above.

Please ... give the CLE a try ... then let us know what NDB's can be heard from your location! Your report can then be added to the worldwide database to help keep it up-to-date.

Good hunting!

Friday, 16 September 2016

First VK-VE 630m Contact!

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


Shortly before sunrise yesterday morning, VK4YB (Roger) and I were able to work each other on 630m ... 475.300 kHz to be exact!








This is the first-ever QSO between North America and Australia on the relatively new 630m MF band. As well, at 11,802km, it presently represents the furthest two-way contact on this band, worldwide ... but I don't expect this record will last very long once the U.S. gets the band as I believe Roger's fine station is very capable of reaching much further afield.

Our contact on JT9, the WSPR QSO mode, was made at 1319Z, about 30 minutes before my local sunrise with the sky surprisingly bright. Blog readers will know that Roger and I have been carefully watching the pre-dawn Trans-Pacific propagation path for the last week. I have been checking-in with him via the ON4KST LF/MF chat page every morning at around 0345 local time at which point a decision is made ... "get out of bed and head for the shack" or "go back to sleep". Each morning's (or in Roger's case, each evening's) propagation quality is assigned a code number by Roger, based upon what he has been hearing during the early evening hours ... a '6' or below is 'sleep-time', a '7' is a 'you decide' while an '8' or above is 'get your butt moving'.

Yesterday, Roger issued a 'code 7' but as I joked with him later, I think he tricked me as it seemed more like a '6.5' from this end! Trans-Pacific conditions were very good about 500 miles to my south but seemed to drop-off quickly much further to the north. I also need to get over a significant obstruction immediately to the SW of me and in line with Roger. That's me directly at the base of the hill on the right while the remaining peaks are on nearby Saltspring Island and then Vancouver Island before reaching the open Pacific.

courtesy: http://www.heywhatsthat.com/profiler.html

I believe this requires some enhancement of high-angle arrival (and departure) which often occurs around dawn due to a short period of ionospheric 'tilting'. This is often noted by topband operators near their local sunrise, who regularly observe stronger signals on low (cloud-warming) dipoles than they do on their normal large (low-angle) verticals or beverage antennas.

We enjoyed significantly stronger conditions a week ago, but unlike Thursday when I could run at full 5W EIRP, I was only able to generate a little less than 1W EIRP at the time. So far, this week, conditions have been improving steadily each day, from a 'code 3' to a 'code 7'. Hopefully they will continue to improve and we can do it all over again sometime soon.

With my new antenna / transverter / amplifier relay control box working nicely, it seems that Roger and I can now fully take advantage of TP propagation from 'mediocre' to 'excellent' but we have yet to see just how good it can get.

Roger's signal is at +1100Hz
As noted on the screen grabs, both of us were operating near the limits of JT9 detection and we have both seen each other's signal several db stronger on previous mornings. For a two-way CW QSO to take place (a possible new goal), we will need to see an improvement of at least 10db ... probably something that the propagation gods will eventually deliver. Hopefully we will be ready for that should it materialize, providing I can continue to crawl out of bed in the ever-lengthening fall darkness.

It is hoped that our contact will inspire new interest among amateurs worldwide and particularly in North America. If you are planning a station, it seems that the main mode of two-way communications will be CW or JT9 ... a simple transverter would allow both modes as well as the use of the WSPR beacon mode. More information may be found here as well as in earlier 630m blogs.

See also: http://www.arrl.org/news/a-record-breaker-on-630-meters

Thursday, 15 September 2016

Transverter-Amp-Antenna Relay Control Box


As mentioned in my last blog, using a transverter to drive a separate amplifier requires some method of switching system in order to automatically handle the antenna, transverter and amplifier input / output ports. To run a relay switching system in the WSPR or JT-9 modes requires that the switching be controlled by the transceiver's PTT line which in turn is controlled by the WSPR software. Using VOX keying is out of the question as it causes the relays to be 'hot-switched' and with higher power will eventually lead to their demise.

For many years I managed PTT line control via my laptop's comm port but these are now things of the past, requiring switching to be done via the USB port. There are many commercial products available that will do this nicely as well as handle the audio feed from radio to computer and vice-versa, but I found that my homebrew version worked just fine. Making it work via the USB port however required a serial-to-usb converter. This was described here, in an earlier blog and for the few dollars invested has proven to be a very reliable interface.

The schematic of the switching control unit is shown below. It uses two inexpensive OMRON G2RL-1-E DC12 relays purchased from Digikey. Although not coaxial, the $3.09 (U.S.) relay will easily handle a kilowatt as decribed by W6PQL. These relays have large contacts, rated at 16A. I added a few extra components that absorb any relay switching transients as well as remove any RF on the control lines.

Relay Control Unit

Keying Line Damper: courtesy: KK5DR
The relays are shown in the 'receive' (none keyed) mode. In this position, the antenna is routed directly into the transverter's output connector. In 'transmit' mode, the transceiver's PTT line is grounded, switching the relays. The antenna moves over to the amplifier's output and the transverter's output gets connected to the amplifier's input.

I must say a few words about Digikey's service. I really am amazed at what a superb job they do in supplying hobbyists with small orders. So many companies nowadays cannot be bothered with such things or demand a large minimum order for the privilege of handling your purchase! From what I can tell, Digikey bends over backwards to help out the little guy, with no minimums as well as dirt-cheap, fast shipping. Living in Canada, I'm used to U.S. dealers making me jump hoops to place an order, only to find out that the cost of shipping is often prohibitively high or they ship only via UPS which I will not accept.

I placed a small two-page order with Digikey via their excellent web site on a Tuesday afternoon. On Friday morning, there was a knock at my door at 0800 hours ... it was a courier service delivering my parts! To put this in context, I live on a small island in the middle of Georgia Strait, accessible only by air or by ferry. To me this service is incredible and the cost of postage was only $6.00 (U.S.). I really have no idea how they do this but they obviously have put into operation a very efficient system ... hats off to them and their skilled management that has figured this all out. A few years ago I sent in orders to both Digikey and to Mouser, each within an hour of each other. Like my recent order, the Digikey parts arrived in just a few days while the Mouser parts took over three weeks ... perhaps things have changed since then but this is the reason I use and recommend Digikey whenever I can.

Once I had the needed parts, I quickly built a PCB for the switcher and put it together in a day so that I might begin 630m skeds with VK4YB as soon as possible.


If you would like a full-size layout suitable for the iron-on toner PCB construction method, I'll be happy to send you one via email.





The first test run with VK4YB at 0300 local time proved problematic. When I fired up at full ERP, I immediately saw some output instability on the scopematch screen. Before I could shutdown however, I had blown a FET in the amplifier, shutting me down and sending me back to bed to worry about the situation.

Having had time to think about the problem made me suspect something in the new relay changeover unit since that was the only new variable in the system. I suspected that perhaps the relays were not fully seated before being hit with full RF output and the possible hot-switching had caused enough short-lived SWR to take out the very reactance-sensitive FET final. In many years of operation with the amplifier, this was the first blown FET I have had. When I built it, I made sure that the FETS would be easily accessible (see below) should such an occasion arise ... unlike my initial transmitter, where replacing a FET was a nightmare.



Fortunately, when FETs go south on a push-pull amplifier, only one FET will blow ... whichever one was conducting at the time, thus preserving the remaining FET. I flipped a coin and unsoldered the source lead of the left hand FET and measured it. Sure enough it had a drain-to-source short. My day was off to a better start. Once replaced, I set out to determine what had caused it to blow in the middle of the night.

Since I didn't want to blow another FET, I could only 'key-up' in very short bursts and see if the instability was still present. I put the amplifier on a dummy load and everything seemed normal but when put onto the antenna, it reappeared. Suspecting an arc in the loading coil, I checked it carefully. I indeed did find a charred blackened section near the top high-voltage end of the coil but that could have been a short-lived event from the past as I'm sure small crawly things often meet their demise between the windings without causing any problems other than a quick puff of smoke or a short-lived arc to the PVC coil form.

After cleaning the coil and removing any carbon paths as well as giving it a few coats of varnish, I was hopeful that the problem would be gone ... but no, the scopematch indicated it was still misbehaving. As well, I could hear a weak but audible high-pitched oscillation coming from somewhere in the amplifier's circuitry. I suspected that it came from one of the output transformers but with the fan noise it was impossible to accurately locate the source of the rogue 'squeal' when briefly keying-up.

Fast forward several hours of pulling out what was left of my hair and I was no further ahead. The amp continued to work fine at high power, via the new relay system, into my dummy load but into the perfectly matched antenna, the problem remained. It was at this point that I decided to look at the input signal from the doubler, a nice squarewave at 950kHz for the amp's divide-by-two input chip. The scope instantly indicated a dual squarewave with more than one frequency present!

Recently built W1VD 'Frequency Doubler'
I control the input to the doubler by setting the transverter's output to 1W but at 0300 that morning had set it to 1/2 watt, noting that the amplifier seemed to be happy at that level. I then increased the drive from 1/2 watt to 1 watt while watching the 950kHz signal and immediately saw it morph into a wonderfully clean squarewave once again! Sure enough, the amplifier returned to complete stability into the antenna.

It looked like the doubler was not getting enough 475kHz input to actually double properly and its output was a mixture of 950 and (mostly) 475kHz. The amp's divide-by-two input would then try and turn this into a mixture of 475 and (mostly) 237 kHz which the highly-tuned antenna system would balk at, producing the unwanted FET-killing reactance. Being passive and none-reactive, the dummy load was quite happy to take the signal all day long if I let it.

With the mystery solved, full ERP beaconing and scheduling with VK4YB has begun once again, but the TransPacific path has been stingy for the past few mornings ... hopefully this will change now that I'm ready again, barring any further complications.

Monday, 12 September 2016

630m Early Morning Skeds



This past week I was eventually able to mate my W1VD frequency doubler with my 630m FET amplifier and run some higher powered tests on 630m WSPR and JT9 modes.


Up until this time, I have been limited to about 1/2 W EIRP but using the amplifier allows me to get to the 5W EIRP limit. I have been using the VK4YB transverter's 475kHz reduced output of 1W and driving the doubler previously built as part of a transverter project. The doubler produces a nice 950kHz squarewave to drive my amplifier's divide-by-two flip-flop input circuit which in turn produces the dual antiphase outputs needed to drive the push-pull switching FETs in the final amplifier. Being a linear transverter, when used alone at 70W, it will run any mode that the IC756 ProIII will produce such as SSB, WSPR etc, but my switching FET amplifier is class-D, non-linear, which limits it to non-linear modes such as CW, WSPR and JT-9, the most popular modes on 630m.

A few days ago, VK4YB and I ran our first 630m sked on JT9 as conditions looked favorable. Unfortunately, this was before I had my transverter / antenna switching system completed so I was limited to the barefoot transverter at ~ 1/2W EIRP. Using a transverter to drive an external amplifier means the antenna must be switched between the amplifier output and the transverter input in addition to switching the transverter's output between the antenna and the amplifiers input. I'll post details of my switching system, and inexpensive but power-capable relays, in an upcoming blog as there are probably many 630m operators planning on doing something similar.

Thanks to Roger's huge antenna, his 90W signal was making it through well enough on this end but he was not able to decode anything from me.



1109 -26 0.3 1098 @ VE7SL VK4YB QG62
1111 -28 0.3 1098 @ VE7SL VK4YB QG62
1147 -24 0.1 1100 @ VE7SL VK4YB QG62
1149 -27 0.1 1100 @ VE7SL VK4YB QG62
1153 -27 0.1 1100 @ VE7SL VK4YB QG62
1159 -26 0.1 1100 @ VE7SL VK4YB QG62
1209 -26 0.0 1100 @ VE7SL VK4YB QG62
1225 -25 0.1 1100 @ VE7SL VK4YB QG62
1227 -26 -0.0 1100 @ VE7SL VK4YB QG62
1229 -24 0.1 1100 @ VE7SL VK4YB QG62
1239 -23 0.1 1100 @ VE7SL VK4YB QG62
1247 -26 0.0 1100 @ VE7SL VK4YB QG62
1249 -26 0.1 1100 @ VE7SL VK4YB QG62
1253 -23 0.1 1100 @ VE7SL VK4YB QG62
1255 -28 0.1 1100 @ VE7SL VK4YB QG62
1257 -26 0.1 1100 @ VE7SL VK4YB QG62
1303 -27 0.2 1100 @ VE7SL VK4YB QG62
1305 -23 -0.1 1100 @ VE7SL VK4YB QG62
1307 -25 -0.1 1100 @ VE7SL VK4YB QG62
1309 -23 -0.1 1100 @ VE7SL VK4YB QG62
1313 -25 0.0 1100 @ VE7SL VK4YB QG62
1319 -27 0.0 1100 @ VE7SL VK4YB QG62
1323 -22 0.1 1100 @ VE7SL VK4YB QG62
1325 -25 -0.1 1100 @ VE7SL VK4YB QG62
1327 -24 0.0 1100 @ VE7SL VK4YB QG62
1329 -25 0.0 1100 @ VE7SL VK4YB QG62

My location on the 'wrong' side of Mayne Island requires me to fire directly into a very nearby 600' hilltop, directly in Roger's path.

I'm at the base of the hill on the far right.
The large mountains are on Vancouver Island and then open Pacfic.
Later WSPR beaconing, using the new doubler and full power, tends to indicate that a two-way digital QSO should be possible with good conditions. Roger is now able to hear my signal at levels good enough for the JT-9 WSPR QSO mode.











 VE7SL  0.475633  -25    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475633  -26    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475632  -23    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475632  -26    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475632  -30    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475634  -28    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475634  -30    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475634  -30    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475633  -28    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475633  -29    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475633  -27    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475632  -28    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475630  -28    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475629  -29    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475629  -31    CN88iu  5  VK4YB  QG62ku  11820  
 VE7SL  0.475629  -30    CN88iu  5  VK4YB  QG62ku  11820  

With the antenna / transverter / amplifier switching unit complete, Roger and I will continue to watch band conditions favorable to the Trans-Pacific path and hopefully exchange signals sometime this fall before the path disappears until next spring. For Roger, near Brisbane, the path peaks for him in the late evening while for me, it means crawling out of bed at 0330 local time to check the prop, hoping to find good signals from down under ... working VK on 630m would be well worth losing a few hours of nightly sleep!