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 Larcan VHF Amplifier for 6 Meters

I am working on setting up the repurposed Larcan solid-state TV power amplifier that I purchased from VO1KS (a great guy who provides a ton of helpful advice post sale) for use on 6 Meters. These amps are capable of 20-22 dB gain, which translates to 1 kW out for 6.5-10 Watts in! They require 50 Volt/50 Amp power supplies, which are most readily obtained by using server power supplies that are $50 or less on eBay. I hooked up the PS to the amp, and everything idled nicely (51.2 V/4.7 A = 240 Watts), which indicated the 8 FETs were drawing bias current as designed. It also means that I'm going to have to switch the bias off when not transmitting since my home office/shack is already very warm and doesn't need the constant heat output this time of year.

So, I hooked my Yaesu FTdx5000mp up to the amp input, attached the output to my SteppIR DB36, turned the xcvr down to minimum power and hit the key. The PS immediately faulted and shut off the DC output - bummer! After a myriad of back-and-forth with Warren to see what stupid thing(s) I might have done/not done, it occurred to me that RF might be getting into the PS since both the RF input and output are DC shorts to ground as designed. I added about 6 high-quality snap-on ferrites to the DC power lines and added my 6 dB attenuator inline with the transceiver to see if I could coax everything to work with <1 Watt of output. SUCCESS! The amp immediately pulled 42 Amps at 53 Volts (2.2 kW) and the wattmeter (250 W slug) slammed against the far stop. I switched the 5x attenuator in on the wattmeter and tried again - just about 1 kW output and dead quiet. If I didn't look at the ammeter and wattmeter, I would never know that the amp was working. Very impressive!!

I tried transmitting JT65 for three cycles, just to see if the amp would mind the continuous duty. Of course, it was designed to run video 24/7, so there is nothing taxing about 48 seconds every two minutes at full power, I hope. It worked beautifully into a dead band, although I wonder if any of the local hams that monitor 6 Meters had their rigs start smoking ;-)  I unplugged everything and went to move the amp - OUCH! It was VERY VERY hot. The huge aluminum heat sink was probably approaching 80 °C (175 °F). More than half of the 2200+ Watts going into the amp was dissipated as heat for about 3 minutes, so I shouldn't have been that surprised. I have several 12 V cage fans that I'm planning to use to cool the amp, and this was a lesson that I better hook them up before I do anything else.

Next steps are to add the fans and the T-R switching. I can transmit, but not receive through the amp right now.

Here's the DC input with the amp online - this is 2200 Watts DC during transmit.

I'm really glad to have a home solar power system now.

The wattmeter has a board that includes attenuators, and is set at 5x.

That means that the amp is putting out just under 1 kW here with only a few Watts of drive.

Sharp-eyed viewers will also note that the slug is for 2-30 MHz, and so is likely a bit less sensitive/accurate at 50 MHz.

 

 



Field Day 2016

This year, I ran on emergency power (Class 1E; AGM battery) from the home QTH for the first five or six hours of Field Day, and my daughter, Ashley, made about 10 QSOs. That's why the "cheat sheet" on the unused amplifier. I then headed up to Valley Center, CA for an overnight shift at the Palomar ARC (W6NWG; Class 3A) FD site - I made about 340 QSOs on 20, 40 and 80 Meter CW. Other than almost freezing at 4:30 AM because I only had a light jacket, it was a lot of fun. Next year, I plan to try to run the 1E station for quite a bit longer, and have to think about how to recharge the battery from the home solar system (yes, I have my own solar system, and some say that I also live in my own universe).

The photos show the upgraded SO2R-capable station with Microham u2R interface (very cool once I figured out how to set it up properly), Filter Max 4 bandpass filters (also very cool once I got them working properly), and what seems like a few hundred connecting cables. I am still trying to neaten up the shack, but this is actually as organized as I've had it in a long time. The amount of heat given off by two radios, two amps, several PCs and all the ancillary gear keeps my office around 80 degrees no matter how low I turn the air conditioning in the house. Now that I've gotten the SO2R setup working, my next project is to get the newly-acquired Larcan 1 kW amplifier for 6 Meters on the air. That should also bring the room air temperature up another few degrees!

 

        


I'm very proud of and excited about my first "real" antenna setup - US Tower HDX-555 (55' crankup and tilt-over tower) and SteppIR DB36 with 80M dipole option. I've put up quite a few wire, vertical and directional antennas on push-up masts and roof tripods over the last 39 years, but this is my 1st tower and first time having an antenna more than 35' off the ground. Getting the tower installed (especially getting a two-wheel drive forklift stuck in the dirt a half-dozen times) and then putting this monster of an antenna (200+ lbs with TiltPlate option spread across a 36' boom) on the mast with three trees and a large trellis in the way was a major undertaking. I hope I get a lot of years out of this setup because I don't ever want to do it again! Quite a few of my fellow Poway and San Diego-area ham friends helped, and I absolutely could not have done it without them.


 

 

The DB36 is a VERY big antenna (the driven element loop is 49' across). It's more obvious how big it is when it's near the ground. Even at 25' off the ground, it works very well compared to what I used to use. Doesn't hurt that the ground drops off a few hundred feet over several miles to the north and northeast of my QTH. 

Watching the antenna turn for the first time up on the tower - I felt like a little kid! All that work paid off. One of my twin daughters is in the background, untangling the coax to run 175' to the shack.

Watching the antenna turn for the first time on the tower.

 

SteppIR DB36

DB36 at 60', where it belongs. I've even managed to put my 2M/440 vertical on top, and the coverage is amazing.

The tower was laying down and I hadn't yet put the "trombone" loops on the DB36. Those three trees proved a major impediment when I had to crank up the whole thing. The antenna was so heavy that it bent the 2.5" steel mast at the thrust bearing by about 5 degrees! If you look carefully at some of the other pictures, you can see the mast isn't quite plumb.

It's a LOT easier to crank up the tower with no antenna on it!

This is the hole that was dug for the tower base. 5 feet square and 7-1/2 feet deep. Luckily, the spot that I chose was fill dirt, and not the decomposed granite that makes up most of the local soil. It took a small excavator about four hours (with a professional driver at the wheel). Only one irrigation pipe was killed in the making of this hole (you can see what's left of it at the bottom left of the hole).

Rebar cage and concrete form - right before the pour. 

Does it work?

Here's an excerpt from my log over a 3-day period - you be the judge. I've also been getting a lot of S9 + 20 dB signal reports on 40 meters.

 

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    NC6K_WPX_MIXED_PDF_CERTIFICATE  

 

I was first licensed in January 1977 when I was 13 years old. I lived in Huntington Station, NY and had the call WB2KIH. Interestingly, I got my Advanced class license on July 13, 1977 and failed the Extra exam by one question! Exactly 25 years later, on July 13, 2002, I passed the Extra exam and obtained my current call - NC6K.

I am active on HF and VHF, and am trying to gather enough contacts for 5BDXCC and 10BWAS (I need about 15 states on 6 meters - no easy task from DM13). I enjoy operating almost all modes, although CW is still my favorite. Lately, I've been working JT65 on HF and 6M, and it's pretty neat.

You can find me on the Mt. Woodson repeater (145.180-) when I'm not on HF or 6M. As of 3/27/16, I finally have a "real" antenna and tower (SteppIR DB36 on US Tower HDX-555) - the installation was something (see the photo gallery for pictures).

My current setup is now SO2R-capable, which was a bit of a challenge to get working properly, especially for high power:

XCVRs: Yaesu FTdx5000mp / FlexRadio 6300 (SO2R & SO3V), FT-857D (VHF/UHF FM mostly, and emergency power backup)

AMPs: Alpha 9500 & Ameritron AL-80B. Just picked up a repurposed Larcan 6 Meter Amplifier that was retired from TV service, and am working on getting it OTA.

ANTENNA: SteppIR DB36 at 60' (80 - 6 Meters) & OCF Dipole at 55'. 2 M/440 vertical at 65' for VHF/UHF.

RX ANTENNA: DX Engineering DXE-ARAV3-2P Dual Active Verticals and DXE-NCC-1 Receive Antenna Variable Phasing Controller (oriented SW to NE).

SO2R: Microham u2R 2-Radio Interface with Winkeyer. Filter Max 4 Bandpass Filters, Rigblaster Advantage (for Yaesu voice keying and digital modes), and a lot of cables connecting everything.

I am happy to QSL Direct, Via the Buro, eQSL and especially using LOTW. I still enjoying receiving and collecting paper QSL cards, so don't be surprised if you get a request from me. I promise 100% response to received cards, but be patient as work and family sometimes delay me a few weeks on the replies. If you haven't gotten a card back (for direct requests) in about a month, feel free to email me to remind me. I am a firm believer in the courtesy of returning all cards.

73 and hope to CU on the bands!

Eric NC6K


 

NC6K and Ashley (one of my twins) at Field Day 2013


Operating 20M CW for the Palomar ARC at Field Day 2013
(I've lost 50 lbs since then)

 

7457446 Last modified: 2016-07-22 05:41:31, 19955 bytes

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