148 gtl alignment

[kaos513]

During the procedure is it necessary to use a 0.01 uf cap for alignment ?

 

[Handy Andy]

Only to isolate for RF - else some circuits will load down from both DC bias and the RF you're trying to sample.

Is that your question?

Or - what is a Manual telling you to do?

 

[kaos513]

On the 148 gtl alignment asks to use a 0.01uf

 

[Handy Andy]

Hmmm...

I know why you're doing this...
But is it necessary?​

The part with the TR15 and FET gates - its' the quickest way to ruin a stock radios tuning - especially when you have a lot of other noise sources around - injecting both the noise on the probe, the antenna - and the open box you're working on top of. (Radio) That radio makes a mess on it's own rights...

But if it's necessary, then yes, you need it. Else try the "Dummy load on the monitor radio" for your reference thru the stubby antenna "stem" needed just to get enough signal in there - this method is less invasive and can reduce the potential fatality rate - at least for breaking or puncturing the FET's gate from static pokes.

To me the biggest worry is the FET's gates, not an easy part to keep in stock if the tune up goes bad because of the FET getting "Throttled" during the tuneup.

So pay attention to the S-meter and the RF gain control - it's the only way (and Quickest reaction) to offset the AGC clamping. The lag time between the fiddling with the Output on the Generator to reduce it's output to continue the process can take too long and the FET becomes toast.

 

[kaos513]

Thank you sir

 

[Low_Boy]

I never use the cap. and when i tried years ago i noticed no difference. I also just plug in to the antenna jack and go from there. My receive alignments are are mostly down to.1 mv. some are better.

 

[Handy Andy]

The only reason for the cap is for the "down and Dirty" ways of alignment and troubleshooting.

Why it's done? Depends on how severe the radio is in need of service. The step is to verify and align the coils when they are replaced - for the new versus old they don't always line up - the physical use of the 0.01uF cap seems overkill and for those that have the radio in their hands and works, this step isn't really necessary - only if you replace a coil or fix a broken slug to make sure you're bringing the radio into proper alignment is this method used - brute force.

It is strictly for RX image alignment - (note the third step uses the antenna and 27.185 MHz carrier signal) and using the right image - so you separate the 7.8MHz from the 16.xxMHz - why? Because you have those "pairs of coils" past TR20 that give you your SSB and AM - you want the signals going to the right ones and use the correct image from them..

Remember too that the AM LO uses 7.3MHz to use the 7.8MHz to find the 455kHz in there somewhere.

7.8MHz - 7.35MHz = 455kHz - since that last strip uses "pairs" of coils, the alignment step is to make sure the 7.8MHz and 455kHz are separate. and not mixing them together.

 

[Low_Boy]

Thanks Andy the .01 was always a pain. Way too much to clip and hold. LoL.