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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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26th Jul 2021, 2:45 pm | #1 |
Diode
Join Date: Jul 2021
Location: Abington Vale, Northampton, Northamptonshire, UK.
Posts: 2
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FT790 Repeater offset modifications
I would like to use the existing crystal osc for repeater offsets to change to the current standard of 7.6Mhz instead of the old 1.6Mhz. Has anyone made this modification, I have a CTCSS tone board to add which is potentially an easier mod. Any Help or suggestions appreciated G4MAB regards Mike
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26th Jul 2021, 5:53 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: FT790 Repeater offset modifications
Surely the way to do this is to store the two separate TX/RX frequencies in a single memory-channel?
That's actually listed as the "way to do odd splits" in the manual. |
26th Jul 2021, 8:12 pm | #3 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: FT790 Repeater offset modifications
I was thinking this might be programmed instead.
I'm blowed if I can find the crystal which does the repeater shift in hardware but the online manuals are not of great quality. They do say 1.6 or 7.6MHz according to market. If it was mine I would want to keep both options with an extra switch somehow. Isn't it another example of how modern changes leave vintage gear behind? Last edited by Jon_G4MDC; 26th Jul 2021 at 8:17 pm. |
26th Jul 2021, 8:26 pm | #4 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: FT790 Repeater offset modifications
The 'old' 1.6MHz shift has by no means gone, I regard the 1.6Mhz shift as 'normal' and the 7.6MHz as the annoying, unnecessary upstart newcomer. I suppose from the point of view of the repeater groups, the greater separation helps to keep the output signal out of the repeater input.
I would go with Jon's idea, try to incorporate both shifts. As soon as you remove one, you will need it. |
26th Jul 2021, 9:20 pm | #5 | |
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
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Re: FT790 Repeater offset modifications
Quote:
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Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW. |
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26th Jul 2021, 9:39 pm | #6 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: FT790 Repeater offset modifications
I can forsee a further bit of awkwardness - I would imagine when in repeater shift mode the display shows the RX frequency in RX mode and the TX frequency in TX mode. If the shift is hard programmed by a crystal on a per market basis then I would assume the indicated frequency shift must also be determined by market specific firmware.
This will mean that no matter what value you change the TX offset crystal to, the radio will still show a +1.6MHz shift on the display in TX mode, when repeater shift is on. |
26th Jul 2021, 10:02 pm | #7 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: FT790 Repeater offset modifications
User manual here:-
http://www.iw2nmx.it/Yaesu/FT-290R/F...e%20Manual.pdf There is an interesting bit on the last part of PDF page 13 / Manual page 23 entitled 'Memory Split Operation'. "The memory split mode is useful for covering unusual repeater splits or other occasions where the receive frequency may be fixed but the transmit frequency is variable. In this mode you receive on a memory channel while transmitting on the VFO frequency. (1) Store the desired receive frequency into a memory channel (2) Dial up the desired transmit frequency on the main dial (3) Now press the yellow F and DIAL/S buttons. You will be receiving on the memory frequency, while transmitting on the VFO frequency. (4) For transmitting purposes, either VFO A or VFO B may be used. Set the VFO selector as needed." This is not as intuitive as it could be - on the -90R2 models I think the shift offset can be programmed, but on the original 290 / 690 / 790, this is a way around your shift offset problem without having to make internal modifications to the radio. |
26th Jul 2021, 11:34 pm | #8 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: FT790 Repeater offset modifications
Belatedly noticed that G6Tanuki spotted much the same thing in a slightly different version of the manual (in #2), although it does not actually store the separate RX and TX frequencies in one memory - that would be too simple and logical. - I have to say it still looks preferable to doing a non-standard mod on what is now quite an antique radio.
As far as CTCSS add ons are concerned, if there is a specific repeater which is driving your interest in doing this work, check to see whether it supports the use of 1750Hz toneburst as well as CTCSS - many do. You may not need to modify the radio at all. |
27th Jul 2021, 12:02 am | #9 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: FT790 Repeater offset modifications
As with all older Yaesu gear, it is pcb jumper modification that will get you where you want to be.
Details here: https://www.mods.dk/view.php?Article...repeater-shift Looks like it is also "one or the other" repeater split, not both at the same time (although you might be able to do that with an added multipole switch). Note: You may need to be registered to see link. |
27th Jul 2021, 12:47 am | #10 |
Tetrode
Join Date: May 2020
Location: Lincoln, Lincolnshire, UK.
Posts: 82
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Re: FT790 Repeater offset modifications
there are also some -7.6 MHz offset repeaters as well ( mainly digital iirc)
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27th Jul 2021, 10:12 am | #11 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: FT790 Repeater offset modifications
So it IS done with links. Now we know.
I would still want it switchable which means either a multipole changeover switch or maybe some trickery with ICs. A 4066 might do it but has only 4 gates when apparently 6 are needed. I think the BS0 to BS3 links are most likely what changes 1.6 to 7.6MHz shift. Suspect the others are changing the direction for TX & RX FWD and REV repeater though more study of the schematic is needed to be sure of that. Last edited by Jon_G4MDC; 27th Jul 2021 at 10:28 am. |
27th Jul 2021, 10:42 am | #12 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: FT790 Repeater offset modifications
There's also the question of whether the firmware only reads the links at start-up - if it did you'd have to be aware of that and always power cycle the unit after changing the position of the 'shift size switch', or with a bit of extra electronics you could have it reset the uP whenever the switch is moved from one position to another.
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27th Jul 2021, 1:33 pm | #13 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: FT790 Repeater offset modifications
You can get some really nice miniature relays around the place, that may be an option (I'm talking thumbnail size and slightly smaller).
A processor reset while these things are running is not usually a good idea as some inputs to the processor will be in a state that is not catered for - not usually serious, just means you have to power down and up again anyway. |