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Author Topic: Icom 718 on 630 meters?  (Read 3434 times)

N0DZQ

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Icom 718 on 630 meters?
« on: October 05, 2018, 10:46:16 AM »

I was wondering if anyone has been successful in modifying an Icom 718 to transmit down on 630M. 

Thanks in advance for any information

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W8JX

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RE: Icom 718 on 630 meters?
« Reply #1 on: October 11, 2018, 11:55:32 AM »

I was wondering if anyone has been successful in modifying an Icom 718 to transmit down on 630M. 

Thanks in advance for any information



Not going to happen, would require a redesign of tank circuit. It is far easier to receive on 630m than transmit.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..

KM1H

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RE: Icom 718 on 630 meters?
« Reply #2 on: October 12, 2018, 12:03:09 PM »

Some rigs make it easy to bring the signal out before it goes into the amp and filtering stages (aka transverter port) and at the ~1-10 milliwatt level. The problem then is to find out what diode has to be cut or some other mod to make it happen on TX. Just about any suitable SS device will work at 630 for the amp stages.

Carl
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AA2UK

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RE: Icom 718 on 630 meters?
« Reply #3 on: October 13, 2018, 11:18:59 AM »

Some of the mods bypass the output filtering providing high power unfiltered output.
As you said Carl most output FET's used in modern transceivers have similar gain and power at 630 meters.
You should use an LPF to keep most of the output on 630.
Bill AA2UK
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KM1H

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RE: Icom 718 on 630 meters?
« Reply #4 on: October 13, 2018, 02:18:36 PM »

Is there a published list of 630 mods by model Bill?

Carl
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AA2UK

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RE: Icom 718 on 630 meters?
« Reply #5 on: October 18, 2018, 10:37:38 AM »

Is there a published list of 630 mods by model Bill?

Carl
Carl try this page although I'm sure there are other conversions. I converted an ICOM IC-735 it produces about 85 watts power measured after the external LPF.
http://www.472khz.org/pages/about-472-khz/getting-started.php

Bill AA2UK
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KM1H

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RE: Icom 718 on 630 meters?
« Reply #6 on: October 18, 2018, 04:31:19 PM »

NUTS!

All those wonderful old Kenwoods just waiting for a hand up ::)

Carl
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AA2UK

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RE: Icom 718 on 630 meters?
« Reply #7 on: October 19, 2018, 08:17:49 AM »

Carl' I'm thinking that with some tweaking if someone could bypass the output filters that they could get the older Kenwood's to produce significant power on 630?
Bill AA2UK
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KM1H

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RE: Icom 718 on 630 meters?
« Reply #8 on: October 19, 2018, 09:55:27 AM »

Bill,
The problem is they are blocked from even going into TX below 1500 kHz. I clipped diodes, long listed on line, to enable full TX from there to 30 MHz. If someone has the time and skills to go thru the diode switching matrix Im sure it can be defeated.
The filtering is the least of my worries as it doesnt come into play until the output board and I'll build a simple Class D or E amp.

Carl
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AA2UK

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RE: Icom 718 on 630 meters?
« Reply #9 on: October 20, 2018, 04:51:36 AM »

Carl, I wanted linear mode operation that's why I converted the IC-735's TX mixers filter and the PA board. I know it's rare to find SSB operations on 630 but we have a small local group building 630 stations and we want the option of being able to use SSB. A class D or E amp won't cut it for SSB..
Bill AA2UK
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KM1H

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RE: Icom 718 on 630 meters?
« Reply #10 on: October 20, 2018, 09:54:41 AM »

Quote
A class D or E amp won't cut it for SSB..

Why not?? Linear SSB will already take up the whole band so might as well do it in "style" :o
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KOP

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RE: Icom 718 on 630 meters?
« Reply #11 on: October 28, 2018, 09:43:43 PM »

A class D or E amp won't cut it for SSB..

To utilize a Class-E power amplifier to amplify SSB signals, a technique of Envelope-Elimination-and-Restoration (EER)
is used. Invented by Leonard Kahn (8), EER is a technique where a switching power amplifier us used
to amplify the instantaneous phase information contained in the SSB signal. A separate audio-
frequency amplifier is used to amplify the envelope waveform, which is then supplied to the RF power
amplifier as a modulated drain voltage supply. The SSB waveform is recreated by the multiplicative
action that takes place in the switching power amplifier. With the technique of EER, it is possible to
amplify a complex, SSB signal at high efficiency, usually exceeding 80%. The SGC Mini-Lini (2)
'linear' amplifier utilized EER in conjunction with a Class-E RF power amplifier
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I considered a microwave oven magnetron and a 4' dish as a drone-killer. The ERP would be on the order of a hundred thousand watts or so. ~anon

November 28, 2018, 09:16:04 AM

KD6VXI

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RE: Icom 718 on 630 meters?
« Reply #12 on: October 31, 2018, 07:30:13 AM »

Bill,
The problem is they are blocked from even going into TX below 1500 kHz. I clipped diodes, long listed on line, to enable full TX from there to 30 MHz. If someone has the time and skills to go thru the diode switching matrix Im sure it can be defeated.
The filtering is the least of my worries as it doesnt come into play until the output board and I'll build a simple Class D or E amp.

Carl

The ts440 and similar radios have a seperate TX inhibit out of the cpu directly.  For those who remember, it's not unlike the 'room locked' CB radio PLL chips.

By studying the service manual I was able to defeat it (iirc it's marked in the schematic) and TX in the am band.  Mine had the rx bc band filter removed as well.  The if filtering was removed so it had to have bandwidth limited in external rack gear(rea, hi fi, essb, etc). It was a proof of concept out of a 'whoa, could it be that simple' moment while troubleshooting something completely different (rig wouldn't produce rf, even though the TX light was lit).

As others have said, a low pass filter might be needed, but I wonder if its necessary.  The antennas are fairly high Q and fed through tuned circuits. At any rate, 3rd harmonic traps in the input and output of the amplifiers should help with efficiency.

Old thread, but thought I'd interject some info.  It is pos sub to get the older Kenwood rigs to go that low, but NOT through a diode matrix 'clip here, add here' method.  It did require board level surgery on the cpu.  This basically made the rig a signal generator, 0 to 100 watts.

--Shane
KD6VXI
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K4TML

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Re: Icom 718 on 630 meters?
« Reply #13 on: March 11, 2022, 03:48:54 PM »

 The great majority of AM broadcsters utilize 1/4 wave vertical radiators, with a pi-network ATU to present a +/- 0j load to the transmission line. This radiator can be a simple steel tower, or in some cases a folded monopole, with 3 or more skirt wires suspended about 1 meter away from the tower, and bonded together at the base and top of the support structure.
 The "Funipole" , fed from the bottom of the skirt, has the advantages of using a grounded tower, making it simple to attach FM, studio-to-transmitter, and communications antennas to the structure without isocouplers presenting detuning  problems, and are inherently broadbanded. Though NRSC and FCC rules have restricted AM audio bandwith, audio quality used to be a major selling point for these antennas.

73 DE,
Ted K4TML
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WA3SKN

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Re: Icom 718 on 630 meters?
« Reply #14 on: March 11, 2022, 03:57:05 PM »

2018 post.
Total rebuild for an ic718.  And with 5 w EIRP, not practical in any way.

-Mike.
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