Saturday, November 18, 2017

300 watt amp for 630m band - not yet pretty but performs well

Three WSPR transmission just after my sunset (2 watts ERP)
After a week's vacation I arrived home to see that my Mouser order had arrived containing all the parts needed to box up my G0MRF 300W amp kit and finally get it on the air with its companion Ultimate 3S. Unfortunately, the housing that I ordered is too small to accommodate the heat sink so a replacement is now on order.

But the heat sink is installed onto the final FETs (or is it the other way around?). Also, the G0UPL GPS receiver has been moved from the other Ultimate 3S (the one used mainly for HF bands) and I was able to put the combo on the air as it lay spread out on my bench. Power out of the amp is controlled via the supply voltage - 12 to 30 volts DC input produces 30 to 300 watts RF output. With my power supply dialed up to its maximum of 14 volts, I'm getting 40 watts out for an ERP of about 2 watts.

Thursday, November 9, 2017

2018: ARRL's 'International Grid Chase'

UPDATE: After being intially excluded, the new 630- and 2200-meter bands have now been formally added to the list of bands that are available for use in this event.

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Don't sell that KX2 (or the new antenna analyzer) just yet!

Hoping to "build on the success of the highly successful 2016 National Parks on the Air" event the ARRL has announced the International Grid Chase for 2018.

It appears that contacts will be valid on all bands (except 60m) and modes. Collection of grid squares during a QSO or contact are not necessary as long as participants are LoTW users. Their grid squares will be logged and credit given as part of the upload process.

The full dope is here.

As I recall, the NPOTA event started off with a whimper but gradually gained much momentum over the course of the year.

I applaud the ARRL for coming up with this idea as it provides the opportunity to operate portable mobile, RV portable, etc, activating "rare" grids in areas with sparse ham populations.

Now, in which grid square is Bouvet...
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A brief comparison of two antenna analyzers

For the past two weeks I've had access to two very useful antenna analyzers with both models being fairly new on the market: the AA55 Zoom from RigExpert and the FA-VA4, an easy to build kit from FunkAmateur.

My use of each of these analyzers coincides with US amateurs being given new slivers of frequencies on 630 and 2200 meters and it is primarily on 630 meters that I've made use of these analyzers to build a 630m vertical Marconi T antenna from the horizontal section and vertical feedline of my 80m dipole.

The analyzers have made that task much easier than would have been possible without them and they both seem to perform the necessary tasks equally well and with readings that agree with each other quite closely.

Wednesday, November 8, 2017

G0MRF 630m amp built (almost), tested and no smoke



I was a bit apprehensive today as I put the finishing touches on my 300-watt amp kit for the 630m band from David G0MRF. I've built a lot of QRP kits over the years and the first power-on is always a mix of excitement and a dash of "is this going to work?". The fact that QRO power was involved made it a bit more of the latter.

The first iteration of this test was actually a few days ago and amounted to little more than a sputter - 6 watts out. Clearly, something was wrong but going over it in detail found no incorrect components or faulty solder connections. Did I wind the transformer wrong? Nope. All good there.

Tuesday, November 7, 2017

Want to be in demand on the air?

As more and more US stations become active on 630  meters, operating events more typical of the higher bands are beginning to manifest themselves. So far there are no official contests or even psuedo-contests but there are those chasing WAS.

Most stations active on the new-to-the-US band are either rx-only or tx-only but a few are actively making WAS-valid QSOs, mostly on CW and JT9.

A list of them is here (pdf). (EDIT: looks like the page has been deleted)

That's it. Look at all the vacancies.

Thursday, November 2, 2017

Modification to 20W 630m amplifier

John WA3ETD responded to a question I posted regarding options that would allow me to transceive on 630 meters. So far I've only been able to receive or transmit, but not both without changing the cabling to the 630m antenna. This means that I've been limited to WSPR during transmit since WSPR is not a QSO mode.

The solution is as simple as adding 5 small optional parts to the amplifier board that will allow it to act as a solid state relay between the rig and antenna. John was kind enough to offer to send them to me free of charge.

Others wanting to operate on 630 meters may consider this as one of several ways of doing so - and probably the least expensive. There are two caveats however:

  • The feed-through during receive is passive; therefore a certain amount of loss will be induced into the receive path. This could be significant when operating modes where level of the received signal is measured down to the exact dB (WSPR, JT9, FT8). I'll take my soon-to-be modded amp to work in a week or so and measure the loss exactly.

  • The rig used with the amp must be capable of crossband operation since you will be receiving on 472-479 kHz and transmitting on 3274-3279 kHz (the amp transverts the 80m signal down to 630m).

I'm not sure if crossband operation and direct receive of 475 kHz is a feature of most modern transceivers or not. I do know the Flex 6000-series are good to go.

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I've been very much enjoying 630 meters and continue to be surprised at what is possible vs. what I thought was possible. In two nights of transmitting WSPR with one watt ERP, I've been decoded in 26 states, 3 Canadian provinces (MT, AB, ON) and 4 DXCC entities (K, VE, KH6, ZF).
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Tuesday, October 31, 2017

First transmissions on 630 meters at AE5X

The indoor stuff: Ultimate 3S QRPp transmitter, 20-watt 630m amp, power supply

After initial erroneous indications with my antenna analyzer (more about that in a future post including an A/B comparison with a RigExpert AA-55 Zoom) I was able to trial and error my way to resonance on 475 kHz.

Prior to that I laid out a very poor ground system of one radial running 15 feet to my cold water faucet and another radial 100 feet long and then connected to a 30-foot chain link fence. As I said, a poor radial system. With resonance on 475 kHz I had a 2:1 bandwidth of 22 kHz indicating (correctly) an "almost non-existent ground" that would make it "difficult to induce any current into the antenna" according to someone who knows far more about antenna theory than me.

I had low expectations of performance and waited to throw the 'On' switch until two other Texas stations appeared on the WSPR map indicating their status as receiving stations. I had mentally resigned myself that just maybe one of those nearby stations might be able to decode my sub-watt transmissions.