First meeting - Ramsey 40m receiver build

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First meeting - Ramsey 40m receiver build

Postby Eamon » Sun Apr 22, 2012 9:46 pm

I'll kick this off with a summary of our first Ramsey build meeting which we held April 21st.

We started off with a brief presentation, and then moved to the practical part. Most people had adequate equipment, and a few people lent or borrowed stuff. Everyone is moving at their own pace, but at this rate it looks as if most will be finished by the end of next week.

As of now we have reports of three functional receivers:

- Bram VE2XCS had already build his unit and reported he was hearing a pirate broadcast on it. We adjusted it so it tunes in the ham band.

- Charles VE2RFI started (and finished) building his unit, without even following the instructions! It looks like we got it tuned up as well.

- Tonight on the WIARC net Wayne said he was able to hear something, so it looks as if he managed to get his unit functional, although if it's like the others, it's probably not adjusted to tune in the 7MHz band yet.

The one strange thing about these receivers is that they all seem to tune very low unless you unscrew the VFO inductor slug practically all the way. Another option I've tried is to reduce one of the capacitors in the tuning circuit. Edit: screwing it in so it goes down to the bottom also seems to get most of the receivers to oscillate high enough.

We have gotten pretty good at tuning the VFOs by picking up the frequency using an accurate transceiver (my IC-751A). The others should be easy to tune up.

Another issue we could address in the circuit, is the dependency of the varactor voltage on the battery (which means the tuning could be affected as the battery gets low).

I'll leave it at this and I'll be monitoring this forum for any questions or comments anyone posts.

ramsey.bmp
Here is the schematic so we can talk about it. To grab it, right click > copy, then paste into a Word doc (for example).
ramsey.bmp (5.3 MiB) Viewed 6562 times


- Eamon VE2EGN
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Re: First meeting - Ramsey 40m receiver build

Postby ve2rfi » Fri Apr 27, 2012 5:59 pm

Hello everyone, I have changed things around a bit on my kit. I replaced C12 for a 470uf, C8 for a 100uf capacitor. The idea was to get more coupling between the double mixer, the amp and the speaker. It has given me more sound coming from the speaker. I also replaced C11 and C10 for 220uf capacitors, nearly eliminating the buzz when the rf gain is turned up.
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Re: First meeting - Ramsey 40m receiver build

Postby Eamon » Fri Apr 27, 2012 9:07 pm

Hi Charles,

I'm not surprised that a bigger capacitor (C12) in series with the speaker makes a difference.

I am pretty sure C8 is OK at just 10uF, since the load impedance is high.

It's interesting that additional power supply decoupling lets you set the RF gain higher. This suggests maybe the weirdness we see is a result of some feedback between the audio output section and the RF, through the power supply.

- Eamon
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Re: First meeting - Ramsey 40m receiver build

Postby ve2rfi » Sat Apr 28, 2012 8:15 pm

Hello everyone, I am missing a 6 foot black extention cord. If anyone has it, please keep it for me.

Charles
Last edited by ve2rfi on Sat Apr 28, 2012 11:07 pm, edited 1 time in total.
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Re: First meeting - Ramsey 40m receiver build

Postby ve2rfi » Sat Apr 28, 2012 11:07 pm

Thanks Paul for picking up the extention, you can keep it at the church. I will pick it up at the next solderspot.

Charles
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Power points

Postby Eamon » Sun Apr 29, 2012 9:17 am

Here are the powerpoints for this build.

- Eamon


ramsey-40m-build-session-1.ppt
(468 KiB) Downloaded 697 times


ramsey-40m-build-session-2.ppt
(328.5 KiB) Downloaded 669 times
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