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ZS1ZC South Africa flag South Africa

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Licensed since 1982. Major interest is in HF. Rigs are Kenwood TS-830S,  Drake TR7 and TR-4CYaesu FT-101ZD and FT-101E, 1kW NEC linear (2x3-500Z tubes), antennas are horizontal phased array for 40m, homebrew "Silver Spider" Spiderbeam for 10-20m. Beam is at 15m height. VHF/UHF is FT-897D with interleaved 2m/70cm yagis.


See here for photos of antenna, rotator and tower.

QSL Info: Via Buro, QRZ.COM, LOTW preferred.


Electronic engineer by training, telecoms programme manager by experience.

You can contact me at zs1zc.za@gmail.com


The Antenna

March 2011: The ZS1ZC Silver Spider is up! This a variant on the original Spiderbeam design. The original design is a ten-element wirebeam (three each on 20m and 15m, and four on 10m) set on a horizontal cross of fibreglass tubing. There are no wavetraps and each interleaved yagi has its elements optimally spaced. The only design compromise is that the elements are bent in the middle to fit on the corner-to-corner axis, but the effect on directivity is low - the Spiderbeam performs as well as or better than any three-element tribander. It's light and easy to put together. What makes Spiderbeam unique is that they're happy to have you build your own without getting the parts from them. They will even provide you with the free construction guide here. You can get the manuals for construction of the Silver Spider here and here.

So what makes the Silver Spider unique? You'll notice that Spiderbeam use fibreglass spreaders in a symmetrical cross formation, lashed together, to provide tie-points for the various wire elements. When I investigated fibreglass suppliers in Cape Town their tubes were either too expensive or the wrong size. So I made two observations:

1. The booms of most symmetrical antennas like yagis are invariably metal, and the parasitic elements are often mounted directly on them. How can this be? It's because the centre points of the parasitic elements are at low impedance, and therefore a direct connection between them has no effect on performance. So the front-to-back spreader could be replaced by a similar sized (and cheaper!) aluminium tube.

2. The 20m driven element is almost as long as the left-to-right spreader. This means that the 20m DE could be replaced by an aluminium tube like the boom. I ran simulations on 4NEC2 and found that using a 30mm tube required a slightly shorter element, but the solution worked. In other words, the end of the 20m DE would serve the same purpose as the end of the spreaders for holding the shorter, higher-frequency wire elements in place.

How did it perform? Well, a simulation of the original "classic" Spiderbeam (dimensions based on their literature) and the Silver Spider (so-called because the "spreaders" are now metal) shows that the radiation patterns are very similar, but the 20m performance of the Silver Spider shows improved front-to-back ratio (not by much in practice). The situation is reversed on other bands, yet the gain remains within a dB or so of the original. I designed and built it for 20m, 15m and 10m, but in principle it can be extended to cover the intervening WARC bands too. I've found this antenna to be very effective in actual use, providing significant gain over my inverted vee as expected. It also seems to have quite deep front-to-side nulls which is nice.

The important thing is that aside from the main bracket, construction is performed exactly as Spiderbeam specify in terms of the main structure - only the relative lengths and positions of the wire elements change. You will of course require a bracket that insulates the 20m driven element from the boom like a regular beam antenna.


July 2015: Completed a restring of the entire Silver Spider, this time with speargun line instead of fishing braid for the guys and stainless steel cable for the wire elements. I rewound the balun with RG-58 instead of the thin coax I'd used before just to ensure that there'll be no problems with our newly increased power levels. It works a treat once again.

December 2015: 40m is sorted! After trying an inverted V and a delta loop and finding the background noise was too great, I spent a few days building a 2-element phased array (picture above). I built a phasing unit for the shack to switch directions. There were a few compromises, the distance between my tower and the edge of my property is just a little short, so I had to use little droopy pig-tails at the end of each element, as well as generally sloping the array. It's arranged North-South so unfortunately doesn't handle the greyline too well, but it does differentiate beautifully between East and West. I can get up to 20dB front-to-back depending on the conditions. In one case I was switching between QSO's ocurring in Japan and South America by flicking the phasing switch. I drew inspiration from Charles, K5UA, who wrote this design up a few years ago at http://www.k5ua.com/main.htm. If it's built as a rotatable array I'm sure it'll be a great performer.

May 2017: Brought the Silver Spider down for a service and added a driven element and reflector for 17m. Once it was up, SWR was around 2:1 - good enough for me, and not bad enough to go through adjusting it all again. At least now I can get active on 17m, which seems like a really interesting band.


The Real Deal

April 2012: Now we're cookin' - the new addition to the shack is an FT-101ZD MkII. I'm the third owner. What a beauty! She shrieks like a banshee with the full 140W on 20m and 100W on 10m - nothing wrong with those finals. Having been an 897D man for the past four years, this is quite an experience. Way back in '82 when I got my licence, I had a TS120S which is also a knobs-and-dials rig. Compared to the menus and buttons of the 897D the 101ZD is like coming home again. It has subtleties like being able to tune through the 100Hz step continuously (analogue VFO), rather than the discrete steps of the 897D. The channel width control is right there on the panel, not buried away in the menus. Same with RF power, mic gain etc. The warm-up frequency drift, lack of electronic keyer, absent digital interface and no communications receiver are small sacrifices - besides, I have those on another shelf.


I had more unsolicited "great-audio" reports in the first weekend than I have in four years on the 897D. I use a Dominion DS-V10 dynamic microphone from Equation Audio - these were new guys on the block that produced a very robust mic with built-in pop suppression; the supercardioid pattern has really good off-axis supression which ensures that you don't modulate your audio with noise from your equipment (e.g. fans). This mic retailed for around $180 in the US, making it a very good alternative to microphones like the Heil range. There are many options in this price bracket.

Also, the receiver just seems to come alive compared to the DSP-based younger brother. I've always believed that if you can hear band noise your receiver is sensitive enough - I can do that with both these rigs, but the 101ZD just seems to provide a more signal-filled band. I can only assume that if the 897's noise figure is decent, the 101ZD's is simply better. Receive audio is excellent too. Still have to use it in crowded bands, but if there's any problem with intermod I'll consider putting in a Mini-Circuits double balanced mixer to help things along.

Tuning the finals for each band is easy, and you get the feeling with tube rigs that you really are tweaking the insides - wideband transistor transceivers don't have that. Even after thirty years, the tuning dial feels like it's suspended in oil it's so smooth and light. And then there's the smell. Nothing has the scent of a tube transceiver when she's hot! When I was a kid, a local ham had Heathkits wall-to-wall and the smell of warming glass, bakelite and dust is unmistakable.

I've read plenty of reviews of this and other rigs from this era where the reviewer regrets having sold it - I think this one is a keeper.


The Amplifier

February 2013: I spent the previous two months on-and-off working on a linear. I got fed up with only having 100W on HF - and besides, my licence allows 1kW (as of 2015), which is 10dB or almost two full S-points difference. That doesn't amount to much on a clear band, but at the noise threshold or in the presence of QRM, 10dB is significant. I discovered an invaluable resource in the form of Dutch national treasure Frits Geerligs, PA0FRI, and decided to emulate his Frinear 750, which is a generic linear amplifier suitable for a wide range of tubes, almost as a plug-and-play from one tube to another.


So I asked around locally if anyone had the main parts - I managed to get a TB3-750 triode, a few doorknobs and a 1500-0-1500V transformer that's built like a tank. Sundries like vacuum relays and a Pi-L coil came from a local collector, as did a filament transformer (this tube needs 5V at 14A, which is a little unusual). That left me with the air variable capacitors for the output network. Importing them wasn’t going to be practical, so I decided to dive in and make them – there’s plenty on air variable capacitors on the web, and Bob WB0NNI gives a great overview of tank design at http://wb0nni.dakotamade.com/. Well, I won’t go into the details since again many have done this on the internet, but constructing tube amps from scratch is a real adventure. This took several months of metalwork, soldering, wiring, scrounging around the local industrial areas for small quantities of specialised materials like high-temperature silicone rubber (for the tube chimney), but in the end I had an amp that could pump out several hundred watts on 20m. Upper bands like 10m and 12m are problematic with instability and still a work-in-progress, but 15m-40m are a blast, I'm able to hit the antenna with six to seven hundred watts. I since got hold of a 3-500Z tube, it’s a similar spec to the TB3-750, but operates with zero bias which makes it a lot simpler to use.

A few extras like a forward and reverse power detector from the ARRL Handbook, with a thirty-segment and ten-segment bargraph to display it, and we're in business!

July 2015: Instability problem solved - in a grounded grid configuration, you need to be extremely careful with stray capacitance around the grid circuit that provides feedback from anode to cathode. I was worried that the grid current sensing circuitry in the diagram above was causing an issue, but it was actually that I had the 4n7 grounding capacitor too far from the grid terminals. Putting it inside the tube base compartment (below the ceramic base) solved the problem and now 10m and 12m are alive - a little down on power compared to 20m as expected, but the amp is stable. On 20m I'm now occasionally seeing around 800W PEP, as measured on the station monitor (with 100W continuous as reference). So I call the linear a success.

Another little issue has been that the old ceramic bandswitch that I used had no detent mechanism to lock it in position on-contact. I've now lathe-turned a gear that sits on the switch rotor - this acts as a ratchet for a sprung lever with a little wheel on it that locks into place with a solid click. The mechanism is mounted on the inside of the front panel. I turned a nice large aluminium knob that gives it a really positive feel, as well as smaller knobs for the plate and load capacitors (for safety, the rotor shafts are earthed at the front panel as well as at the base of each capacitor). Next step is crafting an additional bandswitch section to allow for switching of the additional gang of the plate tuning capacitor on lower bands.

August 2015: Now that our licence power has been extended, I was on the lookout for a TL-922 linear amplifier to complement the TS-830S series (see below). The result: an NEC CQ-301 that has an almost identical circuit to the Kenwood amp. Built like the proverbial tank, this amp delivers a kilowatt PEP with not much more than a blush. So I think we're sorted on the QRO front. Next step is a high-power tuner so I can put out a bit of heat on 40m....


Fritz to the rescue again - PA0FRI developed a tuner variant called the S-MatchIt's a really clever design that ensures a balanced output - perfect for my wire antennas with ladderline for the lower bands. I prototyped it in an hour by hot-gluing a variable capacitor, variable inductor and toroidal balun on a sheet of HDPE, and found that it works reliably on my inverted-vee. Easy to tune, too. I happened to have all these parts on hand, luckily. Next step was to gut my damaged MFJ tuner and put the parts in there - still works. Now I'll redeploy the original MFJ SWR meter board in the same box (sawing it into two pieces for fit) and recalibrate it to handle the increased power (may have to beef up the RF sensor toroid). First trial gave me two contacts in Quebec, Canada and one on the US East Coast - not bad for a bunch of spare parts and a load of wire in the sky in Cape Town!


The Whole Shebang

May 2013: I fell upon a rare opportunity in the form of a Kenwood TS-830S – not just the rig, but external VFO, tuner, speaker, station monitor and mic – and it’s the Gold Label version, too. Needed a bit of care in replacing certain old parts like the main relay, but Ken K4EAA has a great website at http://www.k4eaa.com/ that explains all and provides most of what’s needed to get these old rigs humming, as does Ron Baker WB4HFN at http://www.wb4hfn.com. In the end I used http://www.hybridrestore.com/, and got a great delivery service from Jim KE7OAY.

The TS-830S is the pinnacle of 1980’s hybrid design, they simply don’t get better, and this one has style as well as functionality. Not a sexy movie star like the FT-901DM and FT-101ZD, but a demure screen beauty with real class. Somehow Kenwood got the balance exactly right between form and function and produced a lineup that’s both beautiful and well engineered. The 830S lineup is without doubt my favourite rig, and coupled with my 1kW linear it delivers a signal I'm proud of.


A Work of Classic Engineering

April 2014: Then there’s that beauty that appears from out of nowhere that you heard so much about but never met…. the Drake TR-4C. I’ve heard for over thirty years about the engineering in the Drake range but never so much as touched one, so I took the plunge and made an offer on one when it came up on a local swopshop accompanied by an RV-4C external VFO/speaker. The technology is old, but beautifully implemented, I could not fault the opinions I’d heard.


Ron Baker WB4HFN shows how refurbishing is done at http://www.wb4hfn.com/DRAKE/DrakeArticles/DrakeRefurbishing/Refurbishing-01.htm. He has a whole Drake area as well as for Collins, Heathkit and Kenwood legacy kit. This where I learned how to give a transceiver a deep clean. Ron uses a steam cleaner on the entire chassis (only the tubes removed), and I’d seen a writeup somewhere on putting Kenwood rigs through a dishwasher cycle, so I thought I’d take the Drake for a dip in the bath using my daughter’s swimming pool water rifle and plenty of detergent. The colour of the bathwater afterwards was testimony to the years of dirt and grime buildup. A good rinse and shake and a few hours outside in the sun and she was good to go. There were one or two problems, though, the audio transformer was dead and I didn’t have a replacement, so a cellphone charger transformer has been standing in ever since – the audio isn’t as bright as it should be, but I’ve got used to it by now. Then there were little funnies like loss in reception resulting from the front end fuse being too loose in its holder (never saw that one coming!). The real effort was in getting the tuning mechanism sorted out, aligned and new blue filter material behind the dials, but in the end we have a beautiful example of American transceiver engineering on the bench. What a pleasure to operate - and it's true, people do actually compliment "that Drake audio"!


Another Oldie, but a Goodie

November 2015: Again, another classic that I never had a chance to operate came up on a local swop page - an FT-101E in pretty good condition. This now goes really well with the SP-101B Landliner speaker that was originally designed for it. 


I gave this gem a basic service, aligned the Tx/Rx frequencies and clarifier, sprayed and cleaned all the moving parts. I had a YM-34 high impedance mic available and she was good to go. Full power on all bands except 10m (but 75W there is ok for me). The only thing not sorted is the calibration on the relative power meter, but everything else works fine. The noise blanker is quite simply the best I've got on any rig in my shack. Once again, nice audio reports on several QSO's.

December 2016: Picked up another 101E that needed a bit of work, but the power transformer started running hot and smelly, so it needed a rewind. You can read my article on this on eHam.net here. We now also have a Yaesu monitor scope to complement it and a beautiful Astatic D-104 microphone.

A Piece of History

April 2016: And now for a modern classic - the Drake TR7. I've been wanting one of these ever since I got the TR-4C two years ago. I was discussing it on the air last year during a 20m opening to the US, and a day or so later got an email from Stu, K8ST, who had been listening, saying he had a near-mint condition TR7 with accessories looking for a home (not the one here, I don't have a decent picture of my own). Well, we did the deal last month and she's finally here - what a beauty! At serial #4774 it's quite an early build (1979), and it spent its life no more than five miles from the plant where it was made. It's hard to explain the appeal of Drakes but somehow the TR7 takes it to a different level. It really isn't a fancy piece of kit, but it represents an epoch change in the design of amateur equipment. Firstly, it's all semiconductor, one of the first non-tube rigs on the market. And the Sherwood figures really aren't bad for the era, it's up there with the big names of the time in performance. The look of it is almost homebrew, there's no moulded front panel like the Kenwoods used, it's all metal sheet and extrusions, nothing sophisticated. But the performance for the technology is brilliant. Somehow those guys in Ohio really thought this one through and produced a game-changer that has a functional balance that designers have followed for years since.

Based on limited use so far, sensitivity is good, no stability issues, audio is nice and clean both ways. I see 100W+ output as expected. One noticeable feature is the NB7 noise blanker that absolutely kills pulses from neighbours' electric fencing, it's really effective. Then there's the PBT... I rarely use the IF shift on the TS830S, but the Passband Tuning on the Drake just begs to be turned on it's so effective. I run it as a second channel on the Kenwood SP-230. Also have the SP-75 Speech Processor that I'm still setting up. First QSO was Heard Island on 20m.

One minor hitch.... it wasn't switching my linear amplifier (or rather, it was half triggering the amplifier relay in receive, triggering it fully on transmit and then not releasing it) - but a bit of troubleshooting revealed a ceramic decoupling capacitor on the Cinch-Jones connector inside the rig that seems to have partially shorted. A quick replacement, now there's no problem - I guess it's age, this girl was made nearly forty years ago. She drives the NEC tube amp to legal limit with ease, no problems with the match at all.


Some pictures of the operating location:


   Top row: Yaesu FT-101ZD and external VFO;

   Kenwood SM-220 Station Monitor, Drake SP75 speech processor and the left side of a Yaesu FRG-7.


   Middle: Homebrew antenna rotator controller; Drake TR7 and external VFO; Heathkit HM-102 SWR/power meter.


   Bottom: Kenwood lineup - AT-230, VFO-230, SP-230,TS-830S; left side of FT-897D and homebrew CW keyer.

   Foreground: ZS1EL "Vidi" paddle at right; Kenwood MC-50 microphone at centre; Dominion DS-V10 microphone on boom at left.


Below the bench:


  Top row from right: Drake TR-4C and external VFO/speaker (with Astatic D-104 in foreground, covered);

  Yaesu FT-101E and YC-601 external frequency display.


  Bottom from right: NEC CQ301 linear amplifier (twin 3-500Z tubes); Yaesu YO-100 station monitor;

  homebrew linear (PA0FRI "Frinear"). Heathkit Cantenna dummy load on the floor.

  (Paintbrush in pen holder at centre is for gently dusting equipment during overly long QSO's - keeps the kit clean smiley)



Side view:



   Bottom left is my homebrew single-triode linear amplifier based on the PA0FRI "Frinear". I currently use this on 17m, driving it to around 400W with the TB3-750 tube.

   Just above that (with a green LED) is a PTT-controlled antenna switch so that I can transmit on my main 40m phased array and listen on an alternative antenna (e.g. magnetic loop, or even the 20m beam).

   To the right of the Frinear is a pullout desktop for operating Ham Radio Deluxe, PIC programmer, checking out SolarHam, etc.

   What you don't see is the phasing unit for the 40m phased array (pushed back behind the Yaesu frequency display above the Frinear; my Heathkit Cantenna (on the floor below the bench);

   a PSU for the Drake TR7 (on a shelf outside of view at left); 2kVA variac for powering up the NEC linear.













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