Category Archives: equipment

Repairing RJ45 plugs on Icom mike leads

I have had problems with my Icom HM103 mike leads, caused by breaking the locking tab off the RJ45 plug.  This happens usually because the mike and lead are slightly tangled with other gear in my SOTA backpack, even though I use a plastic box to carry the small pieces like headphones, morse paddle, microphone and adaptors.

It also happened once before when I had the microphone of the IC706 stored in the central console of the car.  Pulling it out of where it was carried without due care for the plug  eventually damages it.

And without that little bit of plastic, the mike does not stay in the plug for very long.

Having broken the plugs on my IC703 mike and on the IC706 mike recently I decided to replace the plugs but add the shrouds or covers that protect the crucial locking tab.

The unprotected plug looks like this:

The plug with the protective shroud looks like this:

As a small issue found when re-terminating these plugs, I found that the shield connection was originally made using very small diameter heat-shrink or some other method of making the shield connection look like one of the other wires.  These plugs connect to the wires using connections that cut through the insulation.

I looked for heatshrink tubing that could be used for this purpose, but the smallest I had was labelled 1.5/0.8mm.  A shopping trip to my local computer/electronics parts agent in Yass produced no thinner option.  When compared with the existing wire, the diameter when shrunk was too large to fit into the slot of the connector.  So another method had to be found.

For the first mike I had cut the lead right at the point where the wire enters the plug body.  This created a problem with the shield connection and I had to try to form the shield into a narrow form so that it could slide into the appropriate slot.  After twisting it to create a spiral of multiple strands, it worked but I wished I had found a way to preserve the original insulation.   So when installing the second plug I didn’t cut the wire at the back of the connector, instead I cut the entire connector just behind the crimp point for the conductors.  That way I preserved as much as possible of the original shield wire assembly inside its insulation.

Cutting through the plastic plug body was simple enough but I did that in about 6 sections, ensuring that the wires were not damaged.

Result: a robust plug assembly on both my Icom microphone cables.

I am hoping this surgery will provide longer life for the plugs.

Footnote: I know blue shrouds don’t look right on these black cables and black radios.  But that does not worry me one bit.  And the mike is safe for children.

Preventing the “power spike”

This problem was discussed on the moon-net list in May-June 2016.  I thought it was worth documenting what is going on with many radios that produce a “power spike”.

The problem is that the gain of the amplifier chain (from say, final mixer to output) will vary from rig to rig, also the drive level will vary. Therefore the actual gain required of the amplifier chain varies from rig to rig, purely due to component variations and even due to alignment settings, which are probably done fairly quickly at the factory.

The use of ALC to control the gain of the amplifier chain is a typical and common approach taken by manufacturers. It is a technique that does not work very well for modes other than FM and where external amplifiers are used, where the output power required is less than the maximum rated power of the radio (actually, less than about 1.5 X the rated power).

Other manufacturers also have these problems. They address them in different ways.

In one example, the Yaesu FT8*7 series, there are two controls for each band set (HF, VHF low, VHF high and UHF), being drive gain and output power limit.

Another example is Icom’s IC910 where I understand that the power level control has a dual action, one is to reduce the amplifier gain and the other is to change the output power limit level. So it achieves the same kind of result as the Yaesu 8*7 series, and should result in no power spike when first transmitting.

In any radio, if the driver gain is too high, the output power may momentarily exceed the preset level intended from the radio and set by the power level preset feeding the ALC circuit. The time constant of the ALC circuit determines the attack and delay times but cannot prevent the power level rising above the preset value, momentarily, and that’s all we need to exceed the limits of a solid state amplifier device.

So in the 8*7 series you can set the gain level appropriately so that the radio cannot output any more than your chosen power level, and it is a matter of alignment procedure to adjust output limit and stage gain appropriately to get the result you want. They do (cleverly) offer three power levels and you can set the gain and the output power limit for each power level.

For a radio capable of 100w output it is never going to be enough to set the output limit (driving the ALC) to (say) the 25w level. As already stated, that will still result in a power spike while the ALC sets the output level to what the user requires (via the output power control). It is more obvious and easiest to see in the constant carrier modes like fm and CW.

If the drive level is sufficient to allow the power amp chain to produce 100w, then the initial output (on say CW mode) will be 100w, and if you have set the output limit to 25w, feedback via the ALC circuit will reduce the power to 25w. But the initial spike will always be there. It may only last a few milliseconds, but with solid state circuits it is not a matter of heat or averages, it is whether the input voltage exceeds the correct level at all, for even the first sine wave at 144 MHz, ie. for 1/144 microseconds.

What produces the spike? There is enough drive to the final amplifier for 100w. The output limit setting may be set for a lower power level, if so the ALC line is used to send a gain control voltage back to the gain controlled stage(s).

To make it impossible for a power spike to be produced, the drive level has to be reduced. We need to limit the drive to the power amplifier chain to whatever is needed to produce the nominal power level, whatever it is, 1w, 25 or 75. This could be done in several ways.

The first and typical way to reduce the drive level, when using audio source and ssb mode, as for WSJT and other AFSK type modes, is to reduce the audio level going into the radio.  This would work, but if the reduction in drive required is significant (more than say, 10 db) that decreases the signal level without reducing the level of noise and other inevitable spurious signals, including the suppressed carrier of the ssb signal.  Eg a carrier suppression level of 45 db may be specified by the manufacturer, referenced to its performance at full rated power.  By using the audio drive to reduce total output we are accepting that the suppressed carrier can remain at its current level, and that may be ok for some radios.

The second method of reducing the output is to use a high power attenuator between the radio and the external amplifier.  This attenuator would be in that circuit on receive mode too.  For EME use many operators using the separate receiver antenna input to the receiver, or use another receiver anyway.  But the impact of the attenuator on receive mode is another factor to consider.

Other options include:

  • Modify the radio’s internal gain in the transmitter chain, preferably in the section amplifying at the transmitting frequency.  Depending on the design of the radio, there may be a point where the final mixer output is fed to the amplifier chain, which would be a good place to insert a suitable attenuator.
  • Insert a voltage on the ALC line, setting the gain of the transmitter to the highest it is allowed to be – reducing the output level to the highest it can be to safely drive the external amplifier.
  • Bypass amplifier stages.

Some types of mods would render the radio incapable of higher power output, so would need to be reversed when moving the radio on to another purpose. Whatever method is chosen, it must prevent the drive chain from producing enough power to drive the output stage to full power.

Importantly, it should be done in a way that is absolutely foolproof.  A casual mistake by the operator that destroys the external amplifier is something to prevent entirely.

The metering on the radio would be meaningless if some of these options were taken.  Separate methods of metering the drive level and adjusting for best operation would be required.

This is not a plug and play application. We are using a radio in a way that is outside its designed purpose.

The inability of the TS2000 (or other radio) to be used without modification for lower power purposes is no reflection of its suitability for other purposes. All commercial radios are built for the most common use by the majority of buyers. When we apply these general purpose radios to special uses such as for EME amplifier drivers, we cannot really be surprised that they are not ideal for EME drivers “out of the box”.

FT817 programming

I recently purchased a programming cable for use with the FT817. Plenty are advertised on eBay.

What I received:

  • a cable with plugs for the mini DIN plug for the CAT socket on the radio and a USB plug at the other end
  • A cd containing software

The USB plug is larger than a plain USB plug as usual for one of these USB-serial adaptors, as it contains the electronics to convert from USB to plain serial required by the radio.

The software on the cd included a driver for the USB adaptor and several other programs including a 2012 version of HRDeluxe, a digital modes utility and a few other programs. A specific program for the radio programming was not included.

The cd also included some “readme.txt” files and advice on how to work out which COM port was allocated to the adaptor, as most older software including HRD apparently is designed for COM ports rather than USB.

I installed the driver and it worked ok, revealing that COM9 had been allocated to the USB adaptor.

In HRD the only option appeared to be COM1. Same for a Yaesu programming utility written by a French radio amateur.  (817-mem from F5BUD.free.fr)

I opened the Windows control panel and found the details of the USB adaptor. In the tab revealing the com port allocated I double clicked (or right clicked?) the COM9 and was offered the option of changing it to another unallocated port. I chose COM1.

This still did not allow a connection to the FT817 to work. To see whether the USB hub needed to be restarted to get the new COM port to work, I unplugged and reinserted the USB adaptor cable.

Checking in control panel > device manager showed that the USB adaptor was now indicating COM1.

Launching the 817-mem Yaesu programming tool again, it now found the 817 on COM1 and I could then read the memory contents of the radio, save as csv, modify the csv with notepad++, then reload the csv and send it to the radio.

I set memory freqs for cw and Ssb frequencies on the hf bands and some net frequencies for VHF bands.

Programming the 817 direct using the front panel controls is quite feasible but having the memory channels saved externally is convenient. Also being able to clone and edit in an ordinary text editor is handy. Seeing the frequency and mode settings on a screen is better than having to scroll around them on the 817.

Fake sellers on VK Classifieds

Some recent ads on VKClassifieds.com.au have looked very attractive.  Some Icom and Kenwood high value gear (TS950Sdx and IC756 pro3) being offered at about 1/2 to 2/3 of its typical price in Australia.

An email enquiry to the seller, calling himself Donald [name withheld] of Wilmington Illinois USA and using an email address that looks like a callsign plus the numerals 73, returned some telltale responses.  He asked for payments via Western Union and UPS delivery.  And he used some odd English constructions in his wording.  My brother and I exchanged notes on the seller and agreed there was something fishy about the whole thing.

I posted an item categorised under Events, warning readers about unverifiable sellers and it only lasted an hour on the classifieds site.  I don’t know whether there is an automated system to delete items warning others of scams, or whether the site owner is very vigilant and deletes them himself. But in that time I received several confirming emails from others, one stating that it was a scam and he had already lost $200 to the scammer.

The callsign lookup in QRZ.com does match with the advertiser’s name, but the history of equipment used and the interests of that person do not match well with someone selling a TS950 or an IC756.  However the qrz.com entry does have a prominent comment saying that he had recently obtained the email address used in the advertisement.  This suggests that the email address was chosen to match the QRZ entry, then the QRZ entry was updated (QRZ has no security preventing this) and the comment about the email address was added, to allay any concerns readers of his ads may have about the legitimacy of the email address.  To me it does not match with common practice.  Nobody smart offers their email address in the clear on a website.  No thinking person wants the spam that results from doing that. My conclusion is that the whole thing is a minor example of identity theft, or at least “identity borrowing”.

Don’t send this fellow any money.  As usual, if it looks too good to be true, it is.

 

APRS tx, mini Fox tx, Receivers, GPS receivers

I came across the Byonics website today.

While I cannot understand why anyone would want to advertise the location of their car via a continuous beacon on a 2m fm radio, especially when the car is unattended in a car park, the devices offered by Byonics look interesting and may have other uses for the enterprising electronics or amateur radio experimenter.

The APO3 automatic power-off device is one example.  If your battery voltage drops below a predetermined level, it turns off the power to the radio.

Experimenting with WSPR

Having used some of the WSJT suite during the Norfolk Island VK9NA expedition in January 2011, and following some postings to the VK1 mailing list in recent weeks, I was curious to know how to use WSPR.  The best reference is at the website of its author, Joe Taylor W1JT.

WSPR is part of a suite of software tools that use digital signal processing (DSP) to detect and decode very weak signals, much weaker than can be even detected by the human ear, let alone understood.  Possiblly the best known modes are the FSK441 mode used for meteor scatter contacts on vhf bands, and the JT65 series used for terrestrial dx contacts and Earth-Moon-Earth (EME) contacts on various vhf and uhf bands.  The JT65 modes were used at VK9NA.

Having downloaded and installed the software I then had to see what audio levels were suitable.  I first tried connecting a cable from the speaker/headphone socket of the radio to the mike input on the computer.  Levels were very sensitive and I had to cut everything down, but even then it didn’t work well.  I needed to cut down the audio level output from the radio, an FT817.  It was overdriving the mike input of the sound chip in the laptop.  If there had been a “line in” option I think that would have worked almost without any further change. The microphone input is more sensitive as it is designed for the much lower level of a microphone.  I wired up a potentiometer to enable the sound level going to the computer to be set as a fraction of the output from the radio and that worked very well.  I finished up setting that to about 10% of full scale.

The website http://wsprnet.org/drupal/ is the next resource I found very useful.  It lists the beacon frequencies commonly used world wide, for each band.  I have tried the 7, 10 and 14 MHz bands and found it worked very well.  A good read of the user manual is advisable.  Adjusting the input level on noise to be around 0 db was quite important.  After that it was just a matter of tuning the radio to the correct dial frequency, using USB mode.

Before long I found the screen was gradually building up a list of callsigns received and their signal levels, frequency offsets and the stated power level of their transmitters.  Most seem to be 5w but some are less than 1w and one notable station indicated 1000 watts, but was no stronger than others running 5w, so I think he specified his power incorrectly.

The WSPR screen looked like this at one stage today.

WSPR screen while monitoring 10.140 MHz
WSPR screen, 10.140 MHz

Thanks to Ian VK1HOW for sparking my curiousity about this mode. This must be providing a wealth of data for propagation students.