[600MRG] 735 mods

Fri Jan 26 11:59:27 EST 2018

Getting +/- 5x E-12 for less than $50 on e-bay is 
not hard.  I bought a Russian Morian surplus OCXO 
several years ago for my mw transverters.  On 
1296-MHz it holds to 1-Hz with a 
PLL.  1,296,000,000 Hz  so locking 475,000 Hz is easy.

I have no need of a transverter since I have a 
Elecraft K3 which tunes as low as 200 
KHz.  Output is 1mw so an amplifier is needed 
which is supplied by a  modified NDB transmitter 
that I bought for $40.  Modification involved 
pulling the xtal LO card (took less than a 
minute) and wiring a 0.1 uF disc ceramic 
capacitor to a BNC connector.  The slug-tuned 
bandpass filter coil was retuned for max output 
(100w).  I added no LP filter as this is a 
commercial transmitter with FCC acceptance for 250-550 KHz.

But before doing that I made a simple transverter 
using a mixer bought from MiniCircuits and adding 
half dozen capacitors and resistors to make a 
10.5 MHz to 0.5 MHz converter.  Not hard and not 
expensive.  This was done long before Elecraft 
decided to upgrade their synthesizers which 
allowed tuning below 490-KHz.  Those or the K3 
are not cheap, so I can understand modifying and 
old out of date HF radio.  I bought the K3 for 
reasons other than working 600m (that capability was just "gravy").

No need for fancy GPSDO as the cheap surplus OCXO 
is more than adequate.  On 500-KHz my freq 
stability and accuracy is 0.05 Hz (duh).  The 
ExREF ckt in the K3 is not a PLL and only 
improves the accuracy of the internal TCXO-3 to 
0.1 ppm (1 Hz at 10-MHz).  Its good enough at 500-KHz.

Want a cheap high power amp?  Modify a stereo amp 
by removing audio transformers and audio bypasses 
with 0.1 uF.  I'm told the power transistors are able to run at 500-KHz.

I'll crawl back under my rock and continue reading the mail.

73, Ed - KL7UW

At 07:12 AM 1/26/2018, Dave Riley wrote:
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>More 735 mods ++
>
>And you can transvert to/from those frequencies
>>
>>send-receive signals sound at least as good as you would expect the
>>IC735 to sound on 40 meters except use 10mhz. and a mixer for the
>>IF and we can spend another message thread on that choice...
>
>That sounds like an excellent idea! I mean the thread.
>
>Accurate 10 mhz. is so easy to receive now a 
>days... Or even a cheap rubidium osc. on e-bay
>But a diciplined oscillator via GPS is devine 
>and el-cheapo...  Will cite adds later..
>And you can get stable, accurate 10 mhz. too all 
>the way up to Jackman, Paul ;-) So there is half the transverter...
>
>Ken sez;  I had considered a transverter too. I 
>just thought it was very interesting that a "modern"
>transceiver could be effectively modified to cover 630 meters.
>
>Nawww, too much work, I'm retired and lazy now 
>so cheap and easy is the focus...
>Why spend big bux instead of depleting the junk 
>pile?? I am straight lining this one down to 20 years of re-junk...
>That 735 final winding does great from 160-10m 
>but it really hates working @ 630m and hogging a lot of wasted current...
>The spurs and remixed products make me go dizzy, 
>no thanks... Clean is gooder..
>
>
>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.
>OY, easy big fella...Â  The junk pile is the key, Grasshopper, trust me...
>>
>>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,
>Need new thread for this one, Hon Ed. sez my 
>sidekick, Hashtafisti Scratchie!!!
>
>>
>>  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... ;-)
>>
>>
>>Got $9 in the 
>>budget?<https://www.mouser.com/Passive-Components/Frequency-Control-Timing-Devices/Oscillators/_/N-7jdfi?P=1z0woad>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?
>My first dive in to that direction was to use 
>the IC-706 on 10mhz... Removed the B+ RED lead 
>to the final and VOILA!! just the right level to direct feed a DBM...
>But take an old rig like a Johnson Viking 
>Challenger, Heathkit AT-1 or something, then you 
>have 80% of the job done for you already...
>Run the 735 at about 5-10 watts in to the 
>cathode of the original final, put high class 
>GPS 10 mhz on to the grid and you got a 20 watt 
>output 630 or 220, ahh what the hell 4000m 
>also.. With new coil and cap in the final, then 
>just waiting for a LP filter, several examples 
>here, not a problem... Need junk??
>Plug in coils or band switching??? Or hard wired per band??
>
>Then you can take it from SAQ ( 17.2kcs. rx ) 
>all the way up to 4000m, 2200,. 630m and to 
>light, almost... At light frequencies it is even easier...
>The 735 stays happy nice, and the re-employed junk is very proud of you...
>
>More input soon, N1BUG is beating me up with the 
>TA sigs lately...Â  I guess it is time to 
>re-commission the KW1 PA... I'll show em!!!
>
>Doncha just LOVE it??Â Â  73s from TinkerHam Dave @ aa1a
>
>
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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com 
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