by Norm Wilson N6JV – Visit the museum at N6JV.com
152T
In 1940, EIMAC tried using four 75T tubes in parallel and designated it the 304T. The 304T had plates with caps and external grid connections. A cup shield that was concave down was added later (2nd example). I believe the shield is used to protect the glass seals from overheating due to the proximity to the extremely hot anodes and grids. Experiments were made to make the grids connected internally (3rd example).
example 1
example 2
example 3
By 1941 the 304TL (VT-129) with a mu of 12 and the 304TH (VT-254) with a mu of 20 were being produced. They had an external grid ring and the cup shield was now concave up. The late 1942 production of 304TLs was made with their plates open at the top (4th example). In 1943 the caps returned to the covered type and with the external grid ring for the first 3 months. In May of 1943, the grids were all internally connected (5th example). The 304TL was made in great numbers especially in Salt Lake City. In 1941 alone, a total of 544,473 TLs were made. The TLs were used primarily as pulse modulators most commonly in the Army SCR-584 RADAR. With the great demand for these tubes, the type became copied by competitors especially Heinz & Kaufman. The last (6th) example shows a HK-304L which had the same Army VT designation in spite of the fact that was a taller tube and may not fit in all applications. The 304L had no internal shield as there were four separate wire seals that were a distance away from the anode/grid heat sources.
Next meeting: August 30th at Round Table Pizza in Martel (Jackson). Find out more.
In this issue: tubes as always, and… ancient PowerPoints? – new videos! – classifieds – DX – focus contests – State QSO parties! – funny stuff! – and more!
From the Prez
Hello Contesters and DX’ers!
We’re going to talk about CQP at our next meeting so I thought I’d suggest a few items for everyone to peruse.
There are five categories for a California club to enter in:
Yosemite
Joshua Tree
Sequoia
Redwood
Channel Islands
The number of logs submitted determines what category a club is in.
The Yosemite category is for those clubs submitting 31+ logs.
The Joshua Tree Category is for those clubs submitting 21-30 logs.
The Sequoia Category is for those clubs submitting 11-20 logs.
The Redwood Category is for those clubs submitting 6-10 logs
The Channel Islands Category is for those clubs submitting 1-5 logs.
In 2024, the Yosemite category had no entrants. Not one club submitted the required 31 or more logs.
The Joshua Tree Category is where the Southern California Contest Club and MLDXCC ended up, with SCCC submitting 30 logs and MLDXCC submitting 28 logs. SCCC beat us by a lot….775,754 points. In short, we were not even close.
The Redwood Empire DX Association was the only entrant in the Sequoia Category, with 12 logs and, obviously, won the category.
Pizza Lovers 259, with 8 logs submitted, won the Redwood Category beating the West Valley ARA, with 10 logs submitted. This was a fairly close competition.
Last, but not least was the very interesting Channel Islands Category. There were 42 clubs represented in this category. The winner, by around 150,000 points, was the Sierra Foothills ARC. The Orange County ARC came in second.
It is interesting to look at the clubs in MLDXCC territory who submitted logs:
5 logs – Sierra Foothills ARC
2 logs – Calaveras ARS
2 logs – River City ARCS
3 logs – Yuba-Sutter ARC
2 logs – El Dorado County ARC
1 log – Stockton-Delta ARC
1 log – Toulumne County Amateur Radio and Electronics Society
1 log – Fresno ARC
Recruiting from local clubs could be a possibility for us. Something else to dig into are the respectable scores from some of the members of clubs competing in the Channel Islands Category. Let’s take a look at the scores they contributed to their club total (with bonus points).
Sierra Foothills ARC – KD6HOF – 152,768 (Expedition to Butte/Plumas)
Sierra Foothills ARC – N6WYZ – 113,600 (Expedition to Alpine County – new contester)
Sierra Foothills ARC – WU6X – 103,344 (Expedition to Siskiyou County)
Calaveras ARS – KA9MDP – 125,124 (Expedition to Alpine County – new contester)
Calaveras ARS – N6FRG – 61,484 (Expedition to Calaveras County)
River City ARCS – N6PGQ – 105,468 (Placer County)
Yuba-Sutter ARC – W6PNH – 66,750 (new contester, Sutter county)
El Dorado County ARC – KN6UDK – 61,190 (new contester, Madera county)
If you total up all of the above scores, the total is 789,728 points.
You may recall that I mentioned above that SCCC beat us by 775,754 points. Note, however, that if every one of the stations listed above entered logs for MLDXCC, we would be in the Yosemite Category all by ourselves but at least we would have the pleasure of out-scoring SCCC.
So, my question to all of you: Do you know any of the stations mentioned above? These are stations that are ripe for recruiting.
See you on Saturday!
From the Veep
Did you get an opportunity to participate in the NAQP SSB contest? I was pleased to host Skip N6NFB at home during the contest. He ran the contest under his call @ 100 watts and managed to log quite a number of states on 15 meters. Hopefully some of those will turn out to ones he needs for 15 meter WAS.
My HF activity has been someone what limited lately as other jobs tend to take precedence. I’ve yet again allowed myself to be looped into another repeater project. While very time consuming, the results are rewarding.
My six meter quest continues. Band conditions have been on again, off again. I continue to look for Delaware and Rhode Island only to have them fade out. One day last week there were a number of openings, thanks to a sporadic “E” event. This was my first real exposure to that much of an opening. As the name implies, one minute they were there, then gone the next, very frustrating indeed.
I had previously mentioned to a couple of members that I had purchased a receive loop from W6LVP. I’m looking for it to be an asset during the winter season on 40, 80 & 160. I’m still looking for four (4) DX Q’s to confirm on 80 meters.
How’re your DX Marathon numbers looking? Remember even though you’ve worked a DXCC country before, they count as “brand new” again every year for the CQ DX Marathon. Also for those of you using FT8 / FT4, those contacts count in your Marathon totals as well.
I like to urge each one of you to become involved in MLDXCC by attending meetings, submitting your DX contacts to Club Log, participating in the CQ Marathon and by contributing your contest scores. Please list your log submission under the name “Mother Lode DX Contest Club“.
Also invite new people to club meetings. It doesn’t matter if they are new to the hobby, we all started somewhere. MLDXCC is an award winning DX & Contest Club and with your support we can continue to excel.
It’s time to brush up on your code skills for the fall DX and contest season! Two great resources to help are CW Academy and Learn CW Online.
Don’t wait until the last minute to get your RTTY going for the CQ Worldwide next month, visit Don AA5AU’s excellent RTTY Contesting site for help (or ask on the MLDXCC email list.)
A new four-part interview of noted (and perhaps notorious) DXer and DXpeditioner Don Miller W9WNV was posted recently on the NCDXF chat. Here’s the link to it in case you missed it.
For sale:Bob W1RH has a WaveNode WN2 Digital Watt Meter, with four HF sensors. This unit sells new for $385, with a single sensor. I have been using is in an SO2R configuration with a sensor on the input and output of each amplifier.
That way, I can always see my input and output power. Rick, W6SR, who uses my station remotely more than I do, has depended on the software display to know how much power he’s running.
There are several options for the look of the computer display. And there are several other features such as rotator control and antenna switching but I have just used the wattmeter function.
I’m selling this because I have purchased the Flex PGXL amplifier, which has built in and remotable watt meters. It can be yours for $200.
Bob also has for sale an Array Solutions 6-PAK 6 port SO2R antenna switch – $250
“You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.” – Albert Einstein, explaining radio
And a bit of prescience from 1906, stumbled into by your editor:
As of 25 August 2025. You can see complete MLDXCC standings on ClubLog here.
Overall
1
NK7I
232
2
W1SRD
231
3
W6DE
209
4
K6OK
190
5
K6YK
188
CW
1
K6YK
168
2
NO5Z
130
3
K6OK
119
4
NA6O
107
5
N6WM
106
Phone
1
K6YK
118
2
W1SRD
116
3
NO5Z
115
4
N6WM
111
5
K6TQ
101
Data
1
NK7I
223
2
W1SRD
206
3
W6DE
184
4
K7QDX
183
5
K6OK
159
Resources
Check out the Resources menu up there at the top of every web page for useful DX and contest info.
Prepared for the MLDXCC by Editor and Webwookie Jeff WK6I. Please do send me any corrections, omissions, or material for future issues of The Nugget. It is much appreciated!
Meeting was called to order at 12:23 p.m. by Vice President Steve Allred, NC6R. There were 10 attending in person, with four more attending via zoom (sign-in sheet). There was one guest, the meeting speaker: Chris Knox, KI1P introduced by Steve Allred. Steve welcomed everyone. Each member introduced themselves.
Old Business
The June minutes were published in the Newsletter. The motion to accept was made by Norm Wilson N6JV, and seconded by Rick Casey, W6RKC.
The Treasurer’s quarterly report motion to accept was made by Rich Cutler, WC6H, and seconded by Norm Wilson, N6JV. Both motions passed unanimously.
The IDXC 2026 convention is scheduled for Santa Maria on April 10 – 12, 2026.
IDXC 2027 has been announced, it is a go. NCDXC will once again be hosting the event scheduled for March 12 -14 2027 in Visalia.
Steve also encouraged us all to promote the club among our ham radio friends.
Next Meeting
Is Scheduled for August 30, location TBD.
A joint meetings with NCCC is in the works, date and location TBD.
Adjournment: Moved by Jay Harmor, KE6GLA and seconded by Steve Allred, NC6R, passed unanimously at 12:45 PM.
Presentation “QSO Party roving in Style” by Chris Knox KI1P. He outlines his acquisition of first one, and then a second retired news van, each with pneumatic masts and converting them to ham radio rover use. Amazing and inspiring stuff. Much more can be found at his website. Rich Cutler asked if there was any difficulty with wind against a big antenna at the top of the mast. Chris explained that each van weighed more than 10,00 pounds, providing ample ballast (and poor gas mileage).
Our illustrious VP Steve NC6R was rooting around in his desk the other day and chanced upon a couple of thumb drives (remember those?) containing Contest and DX Academy presentations from the 2013 and 2014 International DX Convention (IDXC) in Visalia, CA.
Steve passed these along to your Editor to publish in The Nugget. And so, here they are for you enjoy and reminisce about contesting in the last decade! (And there’s a lot of still-relevant material!)
by Norm Wilson N6JV – Visit the museum at N6JV.com
152T
In 1938, Eimac started experimenting with paralleling 75T tubes in the same envelope. The earliest form of a two-unit tube was the 152Trated at 150 watts. The grids were connected in parallel but the filaments were separated. Eimac advertised that you could run one triode until it failed and then turn the tube 180 degrees and use the second triode. If both sections were to be used, the filaments could be paralleled and run at 5 volts or in series and operated at 10 volts. The plate had a maximum of 3000 volts at 450 ma. The maximum frequency for full power was 40 MHz. When used as a pulse modulator, the maximum voltage was 18 KV. Subsequent tubes made in WWII had a different envelope shape.
The first example (above) is the oldest example I have ever seen. It has an envelope that slopes to the anode connection and a brown ceramic base. Eimac filed a patent numbered 2,355,717 in February 1941 that illustrated the 152T with an envelope that was flat on top as is shown in the second photo. The original design was probably made in 1940 or before. During the war, the grid connection was made internal and an internal shield was added as seen in the third photo. These tubes were used as pulse modulators in the REL MK IIIC gun laying RADAR and other equipment. The later tubes were designated the 152TH with a mu of 20 and the 152TL with a mu of 12.
Next meeting: July 26th in Martel (Jackson). Find out more.
In this issue: tubes, verticals, and… tuning forks? – new videos! – classifieds – DX – contests – State QSO parties! – funny stuff! – and more!
From the Prez
Hello DX’ers and Contesters,
If you missed our last meeting, you missed a good one. Craig, K9CT, gave us a presentation on his contest super-station in Illinois. The good news is that Jeff WK6I will have the video of the presentation up on the website by the time you read this. Look for the Resources tab on the website, click on it and go to Videos (also linked below – J.)
I do have some videos available from our past meetings, but very few were actually recorded. Little by little, I am editing these down and sending them off to Jeff, as YouTube videos, so he can add the links to the website.
The California QSO Party will be here before you know it, so now is the time to start planning whether or not you’re going to operate from home or as a county expedition.
Last year, SCCC’s CQP score was 4,593,487. MLDXCC was well under SCCC, with 3,817,733 points. SCCC also won the Club Competition, in our category, in 2023. MLDXCC beat SCCC in 2022. Let’s go for the WIN in 2025!
County expeditions can be a lot of fun and can be a way to really rack up the points for the Club. A group of us were in Alpine County last year and part of that group has also operated in Tehama County for several years. We had a blast! The more county expeditions MLDXCC members can do, the better, especially if they are in rare counties.
Dean, N6DE, has done an exceptional job with CQP, and that includes compiling an annual list of rare counties. I don’t see any 2025 updates on the website yet, but you can bet that they will be there soon. You’re going to want to look at that rare county list and then claim it. (See below for the latest!)
How many of you have wished you had the ultimate operating location during an HF contest, a VHF contest, or even when trying to work that all-time new one? This could be on the top of a mountain, the side of a mountain, or on an ocean beach. Chris, KI1P, lives in Northfield, Vermont, and with a location like that one would think that he has a pretty darn good QTH. Not the case. An HF beam, pointed at Europe, looks into a granite mountain that is nearly in his back yard. To solve this problem, Chris bought a retired television live truck and turned it into a superb contest station, with top notch equipment. It is essentially an HF and VHF rover. There is a lot more to this story and you can hear all about it at our next meeting, which will be on July 26th, at Round Table Pizza, in Jackson (Martel). I saw Chris’s presentation at the Contest Forum this year in Dayton. Chris has a great sense of humor. You will find it very entertaining and you may just want to find a retired television live truck and build one of these rover contest stations yourself. Hope to see many of you there!
From the Veep
Hello MLDXCC!
Well, Field Day (2025) is now completed, how did you guys do? With a part time effort (due to challenges), there were 392 Q’s in the log. It always gives me pleasure to work the new (younger) operators. Their excitement is refreshing. Make sure you get your score and field day stories to Jeff WK6I so he can put them in the news letter.
Worked any good DX lately? As observed, HF conditions have been a little up and down. Stations in Europe on 20 are now workable in the evening providing some new Marathon contact.
Six meters (50.313 FT8) however has been very active at times. The last several evenings the north (BC, WA & OR) and south (AZ & NM) path has been active. Regarding my WAS search on 6 meters, I’m still waiting for a good east coast opening to Delaware & Rhode Island.
How’s your DX Marathon numbers looking? Remember even though you’ve worked a DXCC country before, they count as “brand new” again every year for the Marathon. WARC band & FT4/FT8 contacts all count for the Marathon as well.
Also listen for the K6C Special Event Station starting July 11th. This is a special call for the California State Fair (Cal Expo). I will be on 20 SSB various evenings, so give me a shout.
Well that’s all for now, time to go work outside before it gets to hot! Remember to stay hydrated!
The California QSO Party (CQP) is October 4th and that day will arrive faster than you think. The CQP web site has just been updated for 2025. You can now go there and register your planned activity, and you can track what others have planned.
The Northern California Contest Club (NCCC) has announced a new special on-air event — the NCCC 55th Anniversary Fiesta, taking place Saturday, August 9, 2025, from 1900Z Saturday-0300Z Sunday (noon to 8pm Pacific Time). This is an “operating event” with no log checking, on CW, SSB, and RTTY. Find out more!
The Southern California DX Club (SCDXC) notes in their July newsletter that due to waning interest, the August 2025 newsletter may be the last one. Readers are encouraged to respond if they desire to see more newsletters after that.
For Sale: New, never used, EHU for BigIR / $250 or best offer – Thank you, Steve / NC6Rk6sca@volcano.net
For Sale: $995 takes all, HF Amp / Tuner / Swr-Power Meter / Dummy Load – see below. Located in Northwest Reno, NV and can deliver to NCCC Truckee BBQ Sun July 27th if desired. Barry K6STk6st@arrl.net
HF Amplifier 160m – 10m Ameritron AL-811H. The Al-811 gives you 600 watts PEP output. 13.75 x 8.65 x 16 inches. Weight: 31 pounds. The Ameritron AL-811H is similar to the AL-811, but with four fully neutralized 811A transmitting tubes for 800 watts of power.
LDG AT-600ProII is a general-purpose automatic tuner intended for use with midsize amplifiers with up to 600 watts output SSB, 500 watts CW, 300W Digital from 1.8 – 54 MHz. Easy to Read Bar Graph – Dual Antenna Switch – Switched-L tuning network.
High Power SWR watt meter. HF, peak reading, 3kW
MFJ-250X VersaLoad KW Wet Dummy Load with oil. Lets you tune up fast!
For sale: Bob W1RH has a WaveNode WN2 Digital Watt Meter, with four HF sensors. This unit sells new for $385, with a single sensor. I have been using is in an SO2R configuration with a sensor on the input and output of each amplifier.
That way, I can always see my input and output power. Rick, W6SR, who uses my station remotely more than I do, has depended on the software display to know how much power he’s running.
There are several options for the look of the computer display. And there are several other features such as rotator control and antenna switching but I have just used the wattmeter function.
I’m selling this because I have purchased the Flex PGXL amplifier, which has built in and remotable watt meters. It can be yours for $200. Contact Bob W1RHw1rh@yahoo.com.
Bob W1RH also has the following items available:
Alpha 91B amplifier. $1200
Brand new, in the box, Svetlana 4CX800A amplifier tube – $250
Array Solutions 6-PAK 6 port SO2R antenna switch – $250
For sale:Eimac 8877 and 3CX800A7 tubes, all tested to factory spec (June 2025) by retired Eimac engineer, includes individual data sheet for each tube. Price $700 each, $1200/pair.
Also for sale Jan 7203/4CX250B NOS in sealed can $100 each and Jan 7609/4CX150D NOS in sealed can $30 each.
As of 17 July 2025. You can see complete MLDXCC standings on ClubLog here.
Overall
1
NK7I
229
2
W1SRD
227
3
W6DE
205
4
K6OK
187
5
K6YK
183
CW
1
K6YK
163
2
NO5Z
122
3
K6OK
120
4
NA6O
106
5
N6WM
104
Phone
1
W1SRD
116
2
K6YK
115
3
NO5Z
115
4
N6WM
111
5
K6TQ
101
Data
1
NK7I
220
2
W1SRD
200
3
W6DE
180
4
K7QDX
173
5
K6OK
157
Resources
Check out the Resources menu up there at the top of every web page for useful DX and contest info.
Prepared for the MLDXCC by Editor and Webwookie Jeff WK6I. Please do send me any corrections, omissions, or material for future issues of The Nugget. It is much appreciated!
Meeting was called to order at 12:27 p.m. by Vice President Steve Allred, NC6R. There were 12 attending in person, with three more attending via zoom. Of these there were three guests.There was one guest: Randy Keen, K6TVT introduced by Steve Allred. Steve welcomed everyone. Each member introduced themselves.
Old Business
The May minutes were published in the Newsletter.
The Treasurer’s reports are now being done on a quarterly basis, so there is no report presented during this meeting.
New Business
None
Member Achievements
Norm Wilson, N6JV, worked his long sought E6 prefix via moonbounce.
Jay Harmor, KE6GLA, activated 3 summits recently.
Skip Chraft, N6NFB, made just under 200 Q’s in 9 hours in the ARRL Digital contest.
The IDXC 2026 convention is scheduled for Santa Maria on April 10 – 12, 2026.
IDXC 2027 has been announced, it is a go. NCDXC will once again be hosting the event scheduled for March 12 -14 2027 in Visalia.
Steve Allred recognized Norm Wilson, N6JV for his tireless effort as the former newsletter editor. He also thanks Jeff Stai, Wk6I, for stepping up, and making a great newsletter and website upgrades.
Steve also encouraged us all to promote the club among our ham radio friends.
Next Meeting
Is Scheduled for July 26, location TBD.
A joint meetings with NCCC is in the works, date and location.
Adjournment: Moved and seconded, passed unanimously at 12:41 PM.
Craig Thompson, K9CT, gave a fascinating virtual tour of his super station. His station defines what a super contesting station should be!
by Norm Wilson N6JV – Visit the museum at N6JV.com
2C40 The Lighthouse
Many of the tubes that were used to make the first experimental RADAR sets were standard types as the frequency was relatively low and would work without modification. Early large ground RADARs were in the 100 – 200 MHz range. Developing higher RADAR frequencies quickly became a race to stay ahead of the competition and their ability to jam your system. The limit that a tube could operate at is determined by its output capacity and the length of any internal inductances. The grid to plate spacing in the 2C40 was only .3 mm.
2C40
The 2C40 was developed to be a low power oscillator or amplifier at a maximum of 3370 MHz to be used in microwave receivers or signal generators. That high frequency was achieved by using a tube with an output capacity of 1.3 pf and coaxial tank elements that were designed to mount directly on the tube. The tunable cavity was designed to use concentric cylinders that were sized to slide over the 2C40 and make contact. When the cavity was assembled, the tube could be plugged into the end and a socket fed with a cable supplied filament power. The filament of the 2C40 was 6.3 volts at .75 amps. In a conventional oscillator or amplifier, the plate voltage would be 450 maximum at 22 ma. If used in a pulse application, 1400 volts could be used.
The 2C40 had a low noise figure for this period so it was used in preamplifiers for RADAR receivers such as the AN/TPS -1D and the AN/FPS-37 and the BP shipboard IFF interrogator.
A holy grail for many hams is an antenna that’s usable on nearly all bands that takes up very little room. This time we’re talking multi-band verticals. While compromised in several ways, they at least get us on the air. For this survey, we’ll only consider the contraptions that are resonant on their supported bands (without adjustment) as opposed to the non-resonant ones that are heavily reliant on an antenna tuner, such as a 43-foot vertical.
What About Radials?
Every vertical antenna has an associated ground radial system, sometimes called a counterpoise. When dealing with multiple bands, an effective solution is ground-based radials which are non-resonant. The drawback is that you have to deploy quite a few long wires in your yard in order to achieve good efficiency (radials provide a low-loss return path instead of the lossy Earth). Another solution could be elevated radials which are resonant, but that would mean that you need separate wires for each band, and that’s quite a cobweb. Yet another solution is an off-center fed vertical dipole (OCFVD) where the radials are a single, fixed length, and need not be very long. We’ll review a couple of designs like that.
Some Models That Use Ground Radials
Reminder: All of these antennas require a robust ground radial system in order to maintain efficiency. See the ARRL Antenna Book for some design recommendations and tradeoffs for ground radials.
DX Commander [Ref. 1] offers several models that use ground-based radials covering everything from 80 through 2m. For the vertical elements, they use an array of parallel 1/4-wavelength wires, making this the vertical equivalent of a fan dipole and nicely resonant on all bands. This is electrically very simple with no traps or elaborate mechanical contraptions though some elements fold back or have small loading inductors. Their kits include plastic guides that keep the wires parallel (Figure 1). Assuming you can put down an adequate radial field, this will be an efficient antenna with good bandwidth on each band. A drawback is that it’s going to be tall, e.g., 33 ft for 40m. They do have a loading kit for 80m to keep it from ending up in the stratosphere. Overall, I really like these antennas because of their straightforward design, efficiency, bandwidth, and power handling.
Figure 1. Detail of the wire guide/guy ring on a DX Commander vertical.
Hustler is an old brand (now owned and sold by DX Engineering) of trapped verticals that require ground-based radials. For instance, the 6BTV covers 10, 15, 20, 30, 40, and 80m and is only 24 ft tall. There are five traps in series which add inductance thus shortening the antenna on the lower bands. They are rated for high power (1 kW CW) and have reasonable SWR bandwidth except on 80m where it’s roughly 80 kHz (2:1), which is typical of any shortened antenna. The only issue I have is loss in the traps and the possibility of trap failure with weather and time.
Butternut is another older company now owned by DX Engineering offering a 6- and a 9-band version. The HF6V covers 10, 15, 20, 30, 40, and 80m and is 26 ft tall. They use several interesting tricks including loading coils, traps, and transmission line matching sections. Their traps are pretty serious, being made of large aluminum tubing and low-loss ceramic capacitors (Figure 2). This minimizes loss and fully supports high power. Once again its reduced height means bandwidth will be limited on 40m (150 kHz, 2:1) and 80m (<80 kHz). Like all complex multi-band verticals, plan on spending some time with an antenna analyzer and your toolkit to adjust the SWR on each band per the instructions. And if you choose the big brother with nine bands, tuning may be even more interesting. Overall, this is another solid though complex antenna design.
Figure 2. Closeup of a Butternut trap. This is very robust and low-loss design.
The OCFVD Vertical
Hy-Gain and Cushcraft made a number of popular models based on off-center fed vertical dipoles such as the R6000, R9 and AV640, but with the demise of MFJ, they are only available on the used market. Today there are a couple of other companies making antennas of this type that we’ll cover. But first, how do these antennas work?
As an antenna hacker, my hat is off to the folks who designed these OCFVD contraptions using an arsenal of tricks. We begin with an off-center feed point. On the short end (nearer to the ground), add a set of radials of modest length, commonly about 6 ft long and made of stainless steel.
Like an OCF dipole, you can experimentally find a place near one end that yields a similar impedance on all the desired bands. It’s similar on all bands, but not 50 ohms, so you add a matching transformer to yield a reasonable SWR.
To improve the match on various bands, add some traps. These effectively cut off the far end of the antenna at their resonant frequency. They also act as an inductor at other frequencies, shortening the antenna. Traps can also be added to the radials.
Next, add some capacitance hats near the top of the antenna. These are a low-loss method of lengthening the antenna. Length of the capacity hat wires is another tuning element. And by placing them between traps, you can tune particular bands. A Christmas tree is born.
Finally, you can add one or more coupled resonator, or open-sleeve elements. These are typically 1/4 wavelength pieces of tubing that may or may not be directly connected to the rest of the antenna. Because they are resonant they literally “suck the power” away from the rest of the antenna structure on a specific band.
Somehow the crafty designer combines some or all of these elements into a reproducible package. A drawback of this complexity is that it can be tricky to tune in the field because some of the elements interact.
I should also mention that, being an off-center fed antenna, the outside of your coax must be isolated via a robust common-mode choke. Most of the commercial antennas include this in their matching box. The matching transformer is also under some stress and between that and the choke, quite often you will find power limitations due to overheating. Running high power, you may see the SWR start to rise. Keep going, and the whole matching unit will eventually melt!
Figure 3. Left to right, antennas from DX Commander, Hustler, Butternut, and Chelegance.
Some OCFVD Models
Chelegance model KC4 [Ref. 2] covers 40, 20, 15, and 10m and is 26 ft long with 9 ft radials. They use three traps in the vertical plus capacitance hats. It has limited power handling, such as 500 W on CW, which indicates that the matching system is under stress and probably dissipates a bit of energy, typical of this kind of antenna. It’s pretty light (16 lbs) and doesn’t take up too much space. Mount it up on a pole as high as you can. This may be the only viable OCFVD antenna on the market at the moment.
Diamond Antenna model CP6AR covers 75, 40, 20, 15, 10, and 6m. It uses three traps plus capacitance hats and, unusually, tuned radials with traps. It’s only 13 ft tall and radials are 6 ft long. Because it’s so short, SWR bandwidth and power handling a highly compromised. For instance on 75m, bandwidth is only about 20 kHz and on 40m about 30 kHz. Also, it’s only rated 70W CW. Clearly there’s an efficiency problem in the matching box, likely qualifying this antenna as an “outdoor dummy load.” The old Cushcraft antennas were taller but way better!
Installation Tips
Install guys: Many verticals require guys and they are most recommended in windy locations. Thankfully the wind loading isn’t too severe so the guy anchors can usually be something simple like a piece of pipe driven in the ground, or a heavy eye bolt attached to the house, fence, or tree. Dacron rope is recommended for long lifetime in the sun.
Use an antenna analyzer: Don’t try tuning up one of theses complex multi-band antennas without an antenna analyzer or it will take forever. You will have to raise and lower the antenna several times.
Elevate the base: If your chosen vertical does not use ground-based radials, it is very desirable to elevate the base of the antenna on some kind of mast or mount it on your roof. This will lower the takeoff angle and increase gain for better DX [Ref. 3]. Ideally the mast would be non-conductive but most of us just use some pipe.
Advantages and Disadvantages
As stated at the opening of this article, the reason for choosing an antenna like this is that you get multiple bands in a fairly compact installation, give or take some ground radials which at least you can hide. Efficiency is your main concern, followed by usable bandwidth, and some of the models we looked at are compromised in either or both aspects, so choose wisely. And like any vertical, we joke that they radiate “equally poorly in all directions,” but seriously, any antenna is better than no antenna.
Terrestrial telegraphy required countless inventions, and one of the more unusual devices from that industry is the subject of this report. I am calling it a Telegraph Tuning Fork (TTF) because I can find no better description at this time. It came to me via a friend who got it from a fellow who collected surplus equipment, in particular from the Navy’s Mare Island facility near Vallejo, CA. Considering the history of the facility beginning in 1854 and the Navy’s extensive use of all forms of communication, this could indeed be the provenance of this item.
Figure 1. My mystery instrument.
Who Made It and When?
There is a partial label on the instrument, seen in Figure 2. It was made for The Western Union Telegraph Co., so indeed it has something to do with telegraphic communications. Its manufacturer turns out to be D. & H. Precision Tool Co. in Newark, NJ. This company was founded no later than 1918 by Mr. DeSaules and Mr. Hall, and still exists today as D & H Cutoff Co. So perhaps it was made in the early 20th century. Someone skilled at identifying early electrical components may have an opinion.
Figure 2. This label gives us a starting point.
Searching online, the closest match to my device was located at the Smithsonian (Figure 3). They identified it as a telegraph tuning fork, and the maker is Western Union Co. It does have some of the basic features and clearly we are on the right track for identification.
Figure 3. Photo from the Smithsonian National Museum of American History, identified as a telegraph tuning fork [Ref. 1].
Overview of the Instrument
Figure 4 is an annotated top view that identifies the major components. The base is of cast bronze and the entire device weighs about 35 pounds. The main structure is literally a long, heavy tuning fork fabricated from steel and anchored at the left end. A series of weights adjust the resonant frequency. A large electromagnet (MAG-1) resides under the fork, with pole pieces just outside of the arms so that when energized the arms are pulled outward. Clearly this is the excitation method. Two sets of SPDT contacts are actuated by movement of the forks. At the far right end is a pair of coils (MAG-2A and B) that apparently are used to sense motion of the forks. Four terminal strips provide connection points.
A clever gear-driven mechanism slides tuning weights along the forks, thus allowing the resonant frequency to be adjusted while the forks are in motion. I located a patent [Ref. 2] “Adjustable-Vibration Tuning Fork” assigned to Western Union Telegraph Co. in 1923 that describes this mechanism. Due to age and corrosion, the mechanism is frozen, and no attempt was made to restore it.
Figure 4. Top view of the TTF, annotated.
Looking at the bottom of the device in Figure 5, a number of electrical components are identified. Three identical capacitors, C1-C3, are all marked 1 uF and in fact tested good despite their age. A stack of three resistors, R1-3, measured 150 Ohms. A pushbutton module is connected in series with MAG-1, so that may be considered the on/off switch for excitation. I didn’t have a suitable instrument for measuring inductance but did measure the resistance of each coil.
Figure 5. Bottom view of the TTF, annotated.
Analysis and Operation
After identifying components and doing some wire tracing, a schematic was produced (Figure 6). Operation is simple. Starting at rest with S2 closed, an applied voltage produces a current in MAG-1, forcing the forks to move outward, which opens S2. Current collapses, allowing the forks to move inward, then the cycle repeats. This is a kind of relaxation oscillator and will preferentially operate at the resonant frequency of the mechanical system. C1 and R1 form a snubber circuit which suppresses arcing when the contacts open.
A second set of contacts, S1, also has snubber on each side and connections are simply routed to a terminal strip TS2. These could be used to synchronize an external device with the vibration of the forks.
Coils MAG-2A and B are connected in series and brought out to TS3. They could be used for monitoring oscillation. TS4 is routed to a pair of wires that are disconnected on this instrument. There are some mounting holes in a black bracket above MAG-2A and B that may have held a now-missing device.
Figure 6. Schematic diagram of the TTF. (Link to PDF)
Even after a hundred years or so, this instrument is still functional! Some cleaning of contacts at S2 and terminals at TS2 was all it required. Connecting a DC power supply and beginning at 40V, I slowly adjusted the contact spacing and the forks sprang to life, with a current draw of just 10 mA. With further adjustment, I found that the TTF would start and run as low as 3 V. Amplitude was roughly proportional to excitation voltage. Sitting on the bench, it made a low purring sound with no vibration felt in the base due to careful dynamic balancing of the forks.
Connecting MAG-2A and B to an oscilloscope, I observed oscillation at exactly 30 Hz. Considering the mass of the tuning forks, this should be a very stable oscillator, drifting only slowly with ambient temperature changes. Assuming the forks are made of ordinary steel, I estimate that the temperature coefficient of frequency is about -24 ppm/degC.
What is it For?
Little information on “telegraph tuning forks” can be located with a web search, but a number of interesting uses are suggested in a patent search. One fundamental application is synchronous telegraphy where the two ends of the connection rely on stable, matched oscillators to encode and decode transmitted data. More importantly, such synchronization allows multiplex telegraphy where several independent data streams may be sent down a single wired connection. In one patent [Ref. 3], a TTF is shown at each end of the link with its auxiliary contacts causing a large rotary switch to advance with each pulse. In effect, the rotary switch dynamically chooses among several sender-receiver pairs in a kind of time-sharing arrangement.
As time went on, manual sending and receiving of Morse code was sometimes replaced with faster automated transmission consisting of punched tape at the sending end and a variety of receiving devices. Synchronous timing is very important and once again the TTF appears. We would now call it a clock oscillator. By the way, these same mechanisms were also used for teletype data. Long terrestrial lines are problematic due to signal loss and distortion. What was needed is an amplifier of some sort, but that did not exist prior to the invention of the vacuum tube. So an electromechanical repeater was devised. The patent in Ref. 4 relies on synchronous telegraphy where the transmission occurs at a fixed frequency, and uses a TTF as a sampling device to pick out the best part of each signal pulse. The auxiliary contacts then produce a nice, clean output for retransmission.
This turns out to be an important and useful invention in the telegraph industry. Being a telegrapher myself (radio, to be exact), these devices are fascinating. If anyone has additional information about the TFF, I’d love to hear about it (email gwj@me.com). Additional high-resolution photos are available.
