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 Post subject: Re: RF Alignment
PostPosted: Jul Wed 07, 2021 4:31 pm 
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Joined: Feb Mon 22, 2021 1:29 am
Posts: 88
Location: Castro Valley CA
Please confirm for the group you have aligned the IF to the crystal frequency, which is probably not exactly 455. Sounds like you are on top of things!

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 Post subject: Re: RF Alignment
PostPosted: Jul Thu 08, 2021 10:31 pm 
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Joined: Mar Mon 17, 2008 5:05 am
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Location: Ashhurst, New Zealand
Here's the final extract from a previous post about my Heathkit "Mohican'" that I had endless problems with.
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I've remembered something that I did which made the alignment come right! It's to do with the minimum capacitance of the bandspread variable capacitor - they tell you to adjust the capacitor to be just fully closed with the pointer on the left hand line of the dial scale then turn the capacitor shaft until it is fully meshed, then tighten the set screw. Then it goes on to set the end stop pin - but here's the problem - with the pointer now set to the "set" mark, the capacitor is not fully open - they say it should be "nearly" fully open but I couldn't get the oscillator on frequency over the band and was running out of inductance at the bottom end. As soon as I adjusted the capacitor to be really fully open (careful - it's a funny shape) and set the trimmer to be on frequency then the coil had sufficient range - then there was a lot of toing-and-froing to get it finally set just right - well as close to "right" as was ever possible!

Someone had already been into the coil pack with the golden screwdriver - so I had to start from scratch - as somebody has already suggested, I used a modern shortwave radio with a digital display to find exactly where the local oscillator was - and to set the frequency of my antiquated (but loyal!) sig gen.

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Cheers - Martin ZL2MC


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 Post subject: Re: RF Alignment
PostPosted: Jul Thu 08, 2021 11:05 pm 
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Joined: May Thu 27, 2021 6:47 pm
Posts: 8
I believe that I have aligned the IF correctly. I also use my IC7300 dig display as my freq check. I used it to check the calibration of my sug.gen. also.

Having said that and knowing that I did not do the RF cal. correctly, I am going to go back tonight/tomorrow and start over.

Again thanks to all. I am so impressed with this group.


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 Post subject: Re: RF Alignment
PostPosted: Jul Wed 21, 2021 3:26 pm 
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Joined: Feb Mon 22, 2021 1:29 am
Posts: 88
Location: Castro Valley CA
Any update for us or did life get in the way?

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 Post subject: Re: RF Alignment
PostPosted: Jul Wed 21, 2021 9:27 pm 
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Joined: May Thu 27, 2021 6:47 pm
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well put. life did get in the way. my wife broke a bone in her foot. surgery tomorrow am. then about 4 weeks in a boot.

meanwhile I had problems looking for a peak voltage to the speaker. I believe my older fluke meter wasn't fast enough and missed it. I was finally able to find a meter with a small range and it should arrive soon.

I will keep you all updated when I get back to finishing this. I do appreciate the help and interest.

paul


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 Post subject: Re: RF Alignment
PostPosted: Jul Thu 22, 2021 1:32 am 
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Joined: Feb Mon 22, 2021 1:29 am
Posts: 88
Location: Castro Valley CA
Very sorry to hear that, best wishes to your wife and yourself. Now put that radio away for a few months so your wife does not give you the boot! Take care and once again best wishes to your wife for a very successful surgery and quick recovery.

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