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VFO for BC-610/HT-4B




 
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Author Topic: VFO for BC-610/HT-4B  (Read 3834 times)
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Barrie
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« on: January 20, 2009, 09:23:47 PM »

Hello:

I'd like to add an external VFO to my HT-4B.  I see in the archives that this has been addressed in the past, but without much detail.

Evidently, the tuning unit must be modified in order to plug the VFO into the Xtal socket.  Any further details on that?

Also, What would be a good VFO to use?  160M is a must!  Accurate and stable output would be good.

Any help appreciated!

73, Barrie, W7ALW
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WA1GFZ
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« Reply #1 on: January 20, 2009, 09:37:28 PM »

How about a T195 PTO 1.5 to 3 MHz
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W2PFY
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« Reply #2 on: January 20, 2009, 10:00:04 PM »

Real simple to do if you have a rice box or some other RF source. I did it for years with an IC 746. Just run the output from your RF generator to the banana plug input on the tuning units with the tuning units in the crystal position. Put a 50 ohm non inductive resistor in parallel with it and you done. The keying is done through the 8 in plug on the back of the transmitter. In my case a BC-610.

We can go further if you em me. I'm sure there are others that will have good ideas too but what I did worked. The Icom 746 was set on the CW position and it required the lowest output from the transceiver to drive the 610.
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W3SLK
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« Reply #3 on: January 21, 2009, 09:08:21 AM »

Frank said:
Quote
How about a T195 PTO 1.5 to 3 MHz

I have one of those. What's a good circuit to use it with? I know they were cheap at (un)Fair Radio but I never got around to researching how to best put it to use.
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
Barrie
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« Reply #4 on: January 21, 2009, 08:52:24 PM »

Thanks for all the suggestions.

I think I'll go with the rice-box idea first.

A couple more questions:  What wattage should the non-inductive resistor be?

Since I'd be transfering the power via coax, would there be a polarity issue at the crystal socket?

Also, when reading the archives, I'm pretty sure that K4KYV mentioned that there was a choke that needed to be bypassed when using this proceedure.

On a side note, that I'm sure you all knew, I discovered last evening that these double banana plugs that Radio Shack sells for plugging into the back of speakers exactly fit into the crystal socket in the BC-610 tuning units.

73, Barrie, W7ALW
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W2PFY
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« Reply #5 on: January 21, 2009, 11:02:34 PM »




Quote
would there be a polarity issue at the crystal socket?

There will be no polarity issue with the plug. I used a 50-watt resistor mounted on the side of the BC-610 in a ventilated can. Lots of holes drilled into it or you could use any 50-ohm dummy load with a T RF fitting on it I would often forget to turn my Icom down and whack it with 100 watts and it never caused a problem to the tuning units. I found that if you have too much drive from the RF source, the grid drive to the 250TH would go down. I never needed a choke doing it the way I have described. Hope this helps. I don't know about an HT-4 but all 610's I've seen have a terminal strip on the right rear side on the modulator deck. It has two terminals that supplied 115 volts to open a short across the output that a relay caused when not transmitting. I used this terminal to key my antenna change over relay and the aux contacts on the ant.relay keyed the exciter. The reason the ant was shorted out was due to the fact that many 610's could have been in operation in a very small area and they didn't want to run the risk of getting RF burns from another transmitter transmitting near by. CAUTION. ALWAYS SHORT OUT THE HV BEFORE CHANGING OUT A TANK COIL. LEAVE THE SHORT CONNECTED UNTIL YOU CHANGED THE COIL AND ARE READY FOR OPERATION. IF YOU DON'T, YOU MIGHT MEET GOD OR THE GRIM REAPER   Cry

Terry 
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