Tips and Tricks

Simplex/Duplex

After attempting to help a couple of Foundation licence holders with the programming of their FT-991(A)s, I had to point out to them a term that all Radio Amateurs should be aware of:

All MF, HF, VHF, and UHF amateur radio uses simplex, or split-simplex.

The term "split" is often used on HF when a station is transmitting on a different frequency to their receive frequency. This is exactly how VHF and UHF operate when you are working through a repeater. To date, I have not come across a duplex system for Amateur Radio use. Systems that use duplex, such as mobile phones, tend to have a large frequency spacing. See the External link  UMTS Wikipedia page for an example of duplex spacing.


Programming FT-991(A) Memories

The United Kingdom uses a range of repeater shifts for the 70 cm UHF repeaters. The helpful Automatic Repeater Shift function in the FT-991(A) causes a problem when storing UHF repeaters with shifts more than 1.6 MHz, so it is best to switch both ARS options off.

Press the Menu button and using the multi knob, scroll to menu 084 and 085. Set both of them to OFF.

I use the ADMS programming software from External link  RT Systems to set the options and memories. The programming software is handy to restore the radio settings if a firmware update requires a factory-reset. You can also use it to re-arrange the four option buttons at the bottom of the screen. In memory mode, I have the SQL and MCH buttons to hand for easy adjustment and easy memory changes.

I have found it is better to disable the option in the ADMS software that automatically sets the offset splits (yellow circle):

ADMS prefs

... then set the split frequencies manually for the nearby repeaters, as in the example below:

ADMS memories

If you would like to re-use my memory layout (I have the VHF simplex channels matching their respective memory number), you are welcome to download examples from the downloads page to use with ADMS.


LDG AT-200 Pro II :: FT-991(A) Interface cable

I had an LDG AT-200 Pro II aerial matcher (they are not tuners!) to match my doublet dipole (changed mid-2018 for a FC-40 and long-wire) to the FT-991(A), and to switch to my Solarcon Imax2000 vertical (retired August 2017). LDG provide an interface cable to drive the FT-991(A). It is available in the UK for around £ 20. You can make one for around £2.50.

The details of the interface lead is here: External link  http://www.ldgelectronics.com/c/252/products/19/24/1

If you are UK based, you can source the parts needed from Combined Precision Components (or others):

External link  http://cpc.farnell.com/pro-signal/psg08320/3-5mm-jack-plug-3p-red/dp/AV19156

External link  http://cpc.farnell.com/pro-signal/psg03699/3-5mm-3p-jack-to-bare-ends-1m/dp/AV21895

The cable plugs between the LDG AT-200 Pro II's rear 3.5 mm port (black end) and the FT-991(A)'s REM/ALC port (red end). Using the lead means you cannot use the remote control keypad.

Remember: set Menu 143 TUNER SELECT to LAMP

When you wish to match your aerial to a specific frequency, press and hold the TUNE button on the LDG until the red LEDs (of the top bargraph) come together in the centre. The matching cycle will begin by the LDG commanding CW at 5 Watts from the FT-991(A). That will be increased by 10 dB for the mid part of the matching, then another 3 dB for the final match. The next time you use that frequency, the LDG should remember and automatically engage the necessary L and C relays.


FT-991(A) :: FAST

If you are manually scrolling through VHF with a 12.5 kHz step, or UHF with a 25 kHz step, the multi knob will jump 10x if you have the FAST button set.


How not to make a RF connector!

I detest the PL-259 plug and the SO-239 socket. I would be quite happy if they were banned, consigned to history, and replaced with the vastly superior N-type connector. As I am forced to use the SO-239/PL-259*, I make a point of using high-quality connectors that either clamp or crimp the braid. Cheap connectors are usually poor connectors. Avoid anything that has to be screwed on to the coax!

* Unless the equipment is out of warranty, then there is a chance the SO-239 will be replaced with an N-type socket.

July 2019 - I have repaired a Yaesu FT-767GX and an FL-7000 for local Radio Amateur (a G4 callsign). Both units required the replacement of their memory batteries - easy enough. The FT-767GX had a keyer fault (blown input gate on Q60); and the FL-7000 had blown PSU transistors and a blown PA transistor. Having repaired the transceiver and amplifier, I was horrified to see this was the connection to one of the aerials:

Bad PL259
Click on the image to load a larger version (in a new window).

The inner pin rotates and the coax rotates with it! There is no electrical connection to the braid, despite the solder. This was expected to handle 400 Watts! Needless to say I cut it off and replaced it with a crimp PL-259.


Recommended connectors

I have used and recommend the following crimp connectors:

External link  ebay China RF 10x N-type for RG-213/LMR-400

External link  ebay China RF 20x PL-259 for RG-213/LMR-400

You will need the associated crimp tool:

External link  ebay China RF Crimp tool

I have used and recommend the following clamp connectors:

External link  Nevada PL-259 for RG-213/LMR-400

External link  Nevada N-type for RG-213/LMR-400/WF-103

The clamp plugs usually require a 16mm spanner and an 18mm spanner to tighten the compression clamp.


Page updated: 19th July 2019

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