Currently viewing the tag: "The Shack"

A new level of performance reached

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I have finally set up a Harris RF-350 with the associated KW remote controlled amplifer for use with my receive antenna system.

The DX Engineering Receive Antenna Interface for Transceivers is the unit that made this possible.

The only problem was finding a voltage on the Harris radio that would sink to ground under all circumstances of keying.

The solution was found in the Coupler connection on the back of the radio.

I connected a 10k pullup resistor to pin H which carries 13.8VDC and connected the other end of the resistor to pin B (Coupler Key).   This pin goes low on transmit, and could equally well be used to key a small relay if that was desired, but I wanted electronic control of the DX Engineering box.   Pin B in turn went to the Transmit Ground connection on the interface.

In addition, I power the interface itself from pin I, which also carries 13.8V.

Works beautifully.

It was very fitting that the first station I worked with the new setup – operating position C – was JA8NFV.

The Harris radio has filters the size of a amateur transceiver, with performance to match, what an incredible pleasure.

Since both the Harris RF-350K transceiver and the Harris 7224 KW LPA (Linear Power Amplifier) have RF Sample outputs, I set up scope monitoring of the system triggered by the  CW keying.

Update: After using the Harris in battle I am a bit disappointed. The sequencing leaves a bit to be desired, this will be improved with a DX Engineering sequencer already ordered, and there seems to be a bit of filter blow-by on CW. I am hearing CW signals outside the filter passband. I will test another unit to see if this is a common problem, perhaps a bit of contact cleaner will clear this up. On SSB the Harris radios are unsurpassed.

Further analysis indicates that this problem might be caused by  impedance mismatch with the headphones I have been using.  With those headphones, volume is at almost maximum settings so this seems likely.

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Oscilloscope monitoring

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I spent the day designing and building a RF Line Sampler for my new oscilloscope which will be used to monitor transmitted signals.  I built a simple 10:1 resistive divider in a box which is inserted in the feedline.   I used 100k/10k resistors which seem to give good results at these power levels.

The transmitter is putting out a string of dots at approximately 1000W into a 50 ohm Dummy Load.

This is a close up of the oscilloscope screen.

The keying looks a bit hard, the trailing edge in particular, I would appreciate it very much to receive reports on the quality of my CW signals.

I have performed the Key Click modifications on both my Yaesu FT1000MP transceivers, and I believe they are as clean as they can be in this respect.

The scope is triggered  by simply feeding the combined keyer signals to the B input and  selecting the B channel to act as trigger.

The result is that there is no display on the scope until I touch the paddles or generate cw from the logging program – the scope then shows a stationary display of the RF envelope, which enables accurate measurements of delay times and sequencing can now be adjusted to perfection.

The scope is showing the RF envelope of 1KW with a string of dots at 50WPM.

I have now made some measurements and adjustments to the sequencing.   The CW rise time of my Yaesu FT1000MP MK V measures 6mS, the decay time is 4mS.   I adjusted Menu setting 7-4 Bk-in-time = 10ms, Menu setting 7-5 Keyer Delay to 0.10 (10mS).   Sequencer settings are PTT= 10mS, CW=10mS, PreAmp=20mS, LINEAR=10mS…..

PTT delay in Win-Test was set at 10mS.

The radio with the linear amplifier is now incredibly smooth and responsive, I have never experienced anything like it before.

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TX3A – Chesterfield DXpedition

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While tidying up the Shack in preparation for CQ WW next weekend, I recorded TX3A on 160m.

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TF4M operating room

TF4M operating room

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MilSpec communications.

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I am taking the opportunity while the weather is bad to work inside the shack.

New cables have been routed into the equipment room and a 19″ equipment rack installed for the Harris amplifiers.

Two cables were installed for future use with the ends coming out of the ground in strategic places.

Hopefully I will not need to route more cables into the shack.

Operating position “C” is now fully operational – I tested the Harris RT1446/RF-350K with the 1KW amplifier this afternoon and there seem to be no problems.

It only remains to connect and test operating position “D” and then the station will be fully functional.

I would be interested in comments on the quality of my signals.

Champagne

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The heirloom cognac table was used for the first time, the farmers at Krosseyri, Kolla and Sveinbjörn, brought South African Spring Buck for dinner, and afterwards we enjoyed some Champagne in the Communications Center.

19″ equipment racks installed

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I got help from my neighbor – Sveinbjörn from Krosseyri to carry inside three 19″ equipment racks.

Due to the low ceiling height above the operating table, Sveinbjörn had to go inside the rack to be able to lift it on to the table.

I now have plenty of rack space for eventual expansion of the station.

Cognac table

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The new Cognac table in the shack used to be the top part from one of the wooden towers built by the british in WWII at Rjúpnahæð in Reykjavík.

It weighs around 50kg (110lbs)

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