Sunday, May 28, 2023

Long-delayed echo recorded during CQ-WPX-CW?

Jon EA2SN, operating as EE2A during this weekend's CW contest, recorded a segment of his own transmission soon after going back to receive.

Jon was using an Elecraft K3 at 100 watts on 20m with a vertical antenna. The recording was made on 27 May at 0713Z.

The delay was 1.272 seconds.

(UPDATE: As Sverre mentions in the comments, it is meaningless to attribute this degree of accuracy to a transceiver - after all, it is not a piece of test equipment. So let's assume a 1.2 second delay).

This delay is too long to be explained by normal long-path propagation of his own signal back to him - over 10x too long.

Jon shared an MP3 file of one of the examples. I opened the file in Audacity so that it could be seen visually and so that cursors could be placed in order to measure the exact delay:

Sverre LA3ZA explains part of the delay here.

But still - almost 1.3 seconds is a very long delay, even when factoring in sidetone/RF transmission timing differences + receive processing time + LP propagation. The sum total should amount to far less than 150mS.....



Saturday, May 20, 2023

RF output spectrum of FX-4CR

I finally got around to making a series of measurements of the harmonic output of the FX-4CR on all bands. 

I say "series" because I was trying to see if my method, rather than the equipment/radio, was the cause of the reported level on 30 meters.

From the FCC regs:

§97.307   Emission standards.

For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission. For a transmitter of mean power less than 5 W installed on or before January 1, 2003, the attenuation must be at least 30 dB.

No matter how I measured it, the FX-4CR appears to fall 10dB short of compliance on 30 meters, unless the rig is operated at 5W output or less.

But on all other bands, it is fantastic.

Other rigs have had similar issues; the uBitx and the Ultimate 3S come to mind. The (tr)uSDX has unacceptably high levels of IMD. There are similar issues with other radios as well, so the FX-4CR is not alone by any means.

Thursday, May 11, 2023

Elon Musk's upcoming DXpedition to Ducie Island

Don't let the snarky title make you think I'm against it or ridiculing it in any way - I find the implementation of the technology quite interesting.

From 10-24 June, a DXpedition to Ducie Island will be making use of the Starlink satellite system.

I've worked C6AGU a number of times in the past few months. This station was operated remotely, from a nearby ship, via a local 900 MHz link, using Flex equipment on the island. All operators were on the ship, just off-shore.

Commonly referred to as a "RIB" - Radio-in-a-Box - this technique will now implement Starlink for greater range between those operating the island set-up than would be allowed by a local microwave link.

For this DXpedition, the DXpeditioners (can they still be called that?) get to stay at home and work us DXer's - via Ducie Island, operating as VP6A - from the comfort of their homes.

Tuesday, May 9, 2023

Happy Birthday to the best bang-for-the-buck antenna ever

Five years ago, I bought an MFJ product that has turned out to be one of my best ham-related purchases in 45 years.

The MFJ-1979 has surpassed all my expectations. Previously, I had (to some degree) thought of MFJ products either as "unfinished kits" or as disposable, temporary items.

I've owned several MFJ tuners, an antenna analyzer and an AL-80B amp. All of these items informed the above opinion.

And then came the MFJ-1979, which, if you don't know, is a telescoping whip antenna.

At full plumage, it's 17 feet (5.1m) long - a full 1/4-wave on 20 meters. Retracted, it's 27 inches (69cm) short. Partially retracted, it's a full 1/4-wave on any band between 6 and 20 meters.

No inductive loading as with Hamsticks. Add a few - two is enough - radials for a no-compromise DX antenna. Or for a quickly-erected POTA antenna.

Monday, May 1, 2023

Second (replacement) FX-4CR arrives

My new & improved FX-4CR arrived today and, although it has some quirks, it is performing better on CW than the first version I had.

Also, I am able to obtain connectivity to the PC. Without that capability, my first FX-4CR was incapable of operating digital modes and of being updated with new versions of firmware.

Additionally, the radio appears to have been pre-aligned in terms of RF out (and spur suppression too, I'm assuming).

On my original FX-4CR, RF output varied from band to band, going from 20 to 27 watts. Max output on the new radio is 20 watts, regardless of it should be.