Am receiver frequency readout - Page 1
Forum section: electronics / beginners

author: Rascal
author_rank: Contributor
timestamp: June 24, 2013, 12:47:52 pm
content: I have a 1960's un-cased 'home brew' valve radio receiver that covers 60mhz to 186mhz. This is tuned by a mechanical mult-turn pot.I have decided to build the receiver into a case. Unfortunately it doesn't have a frequency readout so I thought it would be an idea include some kind of indicator to do this. I require something that gives me an idea of the frequency it is tuned to - to the nearest 5mhz would be sufficient.Preferably I would like to use an analogue meter to achieve this. I have a connection from the local oscillator (frequency + IF of 21.4mhz) - would it be possible to use this?Any ideas or suggestions would be appreciated.Paul

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: June 24, 2013, 01:39:51 pm
content: How about a mechanical dial and a scale drawn behind it, tune a station, mark the dial The old waySimpleRemember, the Americans spent millions developing a pen that writes upside down in space. the Russians used a pencil

author: digsys
author_rank: Unknown
timestamp: June 24, 2013, 01:50:53 pm
content: Quote from: Mr SmileyIt's a multi-turn pot. You could use a 10Turn 3Digit Potentiometer dial ie Vishay Spectrol 15A31B10Another idea is to have a slave 2nd gang pot that drives a meter. If you have to do it via the circuit, we'd need to see the circuit.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 24, 2013, 02:14:16 pm
content: If it uses a pot,it must adjust the bias on a varicap.Make a high impedance voltmeter & connect it to read the bias voltage.You can try this with your DMM first to see if is workable.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: June 24, 2013, 02:19:35 pm
content: Quote from: Mr Smiley on June 24, 2013, 01:39:51 pmThat is what I would do. it is old school, I keep it that way.Quoterofl!We americans always seem to go around our elbows to get to our A**

author: Rascal
author_rank: Contributor
timestamp: June 24, 2013, 02:54:35 pm
content: Thank you for your replies.I used the word 'pot' out of context - apologies. The receiver is tuned mechanically via a multiturn dial through a slow motion drive- the actual mechanism drives an arm along a coil.Is it possible to use a pre-scaler circuit to divide the local oscillator down to a manageable frequency - then use a LM2907/17 or maybe a ne555 to covert to a voltage?If possible - any ideas on the pre-scaler circuit?Thanks againPaul

author: c4757p
author_rank: Super Contributor
timestamp: June 24, 2013, 02:56:00 pm
content: Pencils make conductive dust that floats in microgravity, you'd be a moron to use that.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 24, 2013, 02:58:41 pm
content: Quote from: Radio Tech on June 24, 2013, 02:19:35 pmMaybe the Americans were worried about pencil sharpener shavings floating around inside the spacecraft!There is no upside down in space,anyway!

author: Radio Tech
author_rank: Frequent Contributor
timestamp: June 24, 2013, 03:39:20 pm
content: Quote from: vk6zgo on June 24, 2013, 02:58:41 pmHmmm, you might just have a "point" there

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: June 24, 2013, 05:45:42 pm
content: We're veering away from the op questionSorry about thatps, they were pressurized ink cartridges, they half filled them with ink, popped in a ball bearing to create a seal between the ink and the top empty chamber and pressurized the empty section above the ball bearing before sealing the end, so the pressure pushed against the ball bearing and that provided a constant supply of ink, you can still buy them today commercially.Was it worth millionsAny way, back to the OP

author: AlfBaz
author_rank: Super Contributor
timestamp: June 24, 2013, 05:49:16 pm
content: Wasn't there a whole Seinfeld episode about it?

author: kfitch42
author_rank: Frequent Contributor
timestamp: June 24, 2013, 06:16:02 pm
content: The space pen is really an amazing story of the power of capitalism, not the epic fail that the one-liner would suggest.http://www.snopes.com/business/genius/spacepen.asp

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: June 24, 2013, 06:31:35 pm
content: I stand correctedNOW BACK TO THE OP

author: edavid
author_rank: Super Contributor
timestamp: June 24, 2013, 07:12:38 pm
content: The most common way to do this is to use a PIC-based frequency counter which subtracts the IF frequency, for example:http://www.morsex.com/aade/counter.htmIf you look around, you can find DIY projects using the same concept. You could adapt one to output PWM to an analog meter instead of using an LCD display. You would have to add a prescaler also (Or is that frequency range a typo? It doesn't seem very useful.)Unless you're really opposed to microcontrollers, it's the easiest and best way to do the job.

author: JackOfVA
author_rank: Unknown
timestamp: June 24, 2013, 09:22:19 pm
content: Sounds like a Mallory Inductatuner, or a knock-off of Mallory's design.If the main tuning knob only has one revolution or less then a mechanical dial is a good solution.If the main tuning knob makes more than one revolution, then the mechanical solution is more complicated. But, perhaps one of the mechanical turns counting dials sold to be used with a multi-turn potentiometer would work. Purchased new they can be a bit pricey but can be found used at a more reasonable price.For a electromechanical solution, I suppose a multi-turn potentiometer ganged with the tuning shaft and read out with an analog meter would preserve the period nature of the receiver.

author: Rascal
author_rank: Contributor
timestamp: June 26, 2013, 12:58:48 pm
content: Quote from: JackOfVA on June 24, 2013, 09:22:19 pmLooks very much like a Mallory InductunerPaul