[600MRG] IC735 mods...an alternative

[John Langridge]

Yes, in fact, as recommended by WA3ETD, the inductor in the LPF (L3) of the
GW3UEP amp is best configured as a trap, where the inductance is decreased
to 13 uH and a precision 2200 pF pulse rated cap is placed in parallel.
That in itself makes a HUGE difference, getting the 2nd harmonic down in
excess of 50 dB compared to something like 38 dB without.. but thats
another discussion entirely...

We can't harp on the need for good LPF's on any modified transceiver enough
because there have been a LOT of questions and a lot of interest in that
approach to getting on the air.

73!

John



On Fri, Jan 26, 2018 at 9:48 AM, Neil Klagge <w0yse at msn.com> wrote:

> I too have taken that drive around The neighborhood to listen to my second
> harmonic on 950 kHz. Adding 1750 pF across one of the inductors in the LPF
> of my GW3UEP amplifier squashed the harmonic down to almost nothing.
>
> Neil, w0yse
>
> Sent from Neil's iPhone
>
> On Jan 26, 2018, at 07:41, John Langridge <kb5njd at gmail.com> wrote:
>
> >Since the target frequency is below 160M, why would harmonics be much of
> an issue with the 160M LPF?
>
>
> Second harmonic of 475 is 950, which is in use in many BC markets...
> 473's third harmonic is right around 1420...
>
> Many of us have taken the drive of shame where we activate our stations on
> WSPR or CW and still hear our signals on 950 kHz many miles away.  Never a
> good thing.  Adding one of the W1VD-designed filters made it where I
> couldn't hear myself sitting in my drive way.
>
> 73,
>
> John
>
>
> On Fri, Jan 26, 2018 at 9:32 AM, J Mcvey via 600MRG <
> 600mrg at mailman.qth.net> wrote:
>
>> Got $9 in the budget?
>> https://www.mouser.com/Passive-Components/Frequency-Control-
>> Timing-Devices/Oscillators/_/N-7jdfi?P=1z0woad
>> just add 3.3 to 5V , a cap and a filter if you like...
>>
>> Those Ic735 mods mostly seem to extend the PA capability downward in
>> frequency.
>> Not sure what shorting the transistor in receive section  was about but
>> those were my initial impressions.
>>
>> The LPF might need some tweaking for 630M. I think going all the way down
>> to 2200 meters is too much of stretch, though.
>> I might try before and after tests with a spectrum analyzer to see what
>> happens when I get time to do it.
>>
>> Since the target frequency is below 160M, why would harmonics be much of
>> an issue with the 160M LPF?
>> Add a 630M section in series with the 160M LPF?
>>
>>
>> On Friday, January 26, 2018 7:53 AM, N1BUG <paul at n1bug.com> wrote:
>>
>>
>> >> Why ruin a perfectly good radio???
>>
>> If I'd had a IC-735 around that wasn't being used on HF, I probably
>> would have 'ruined' it in a heartbeat. That would have been the most
>> cost effective way to get on.
>>
>> With a little help to keep it within budget I build a really cheap
>> transmit converter. But since a good stable 10 MHz oscillator isn't
>> happening here for some time, I'm using a signal generator that I
>> would prefer not to leave running for so many hours. So even now, if
>> I had a 735 that wasn't needed for HF I'd dig into the little
>> bugger... ;-)
>>
>> 73,
>> Paul N1BUG
>>
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