You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

Looks like a high-school science-fair project.

Might be solid and stable.

Maybe. I would place more trust in one of the chinesium counters on fleabay. Many of them have a temperature-compensated time-base oscillator. I'd be surprised to find that feature in the home-brew counter. Biggest hassle using a frequency counter for alignment is to find a point in the circuit where the crystal you're measuring is isolated from the crystal itself. A so-called "direct" probe will connect the probe tip to the full 100 to 200 pf of capacitance between the shielded wire's center conductor and the shield. Better policy is to use a probe meant for oscilloscopes either a times-ten (X10) that attenuates the input signal by a factor of ten-to-one or one that's switchable. Main benefit is that this reduces the circuit loading when you touch the probe to the circuit being measured. Doesn't eliminate it, just reduces it to a more-manageable level of circuit loading. Just one problem. The counter's input sensitivity must be pretty high, so it can display a steady reading when probing a low-voltage circuit.

Some 'scope probes are switchable, either times one or times ten. A tech is frustrated trying to get a stable reading with the probe in the times ten position. Just not enough signal level to stabilize the display. Switches the probe to times one and gets a steady reading. Just one problem. When the probe is unhooked from the circuit, the frequency will jump up from where it was adjusted with the probe connected to the radio. Removing the capacitor to ground inside the probe and cable made the adjustment irrelevant.

Not all counters are created equal. The sensitivity of the counter's input should be adjustable on the front panel, since driving the counter's input too hard can result in a bogus reading, too.

I'll skip the notion of a preamp on a counter's input for now. Getting a measurement you can trust takes more than just a frequency counter and probe. The setup has to be right, too.

73

<blockquote data-quote="nomadradio" data-source="post: 846990" data-attributes="member: 22">Looks like a high-school science-fair project.Might be solid and stable.Maybe. I would place more trust in one of the chinesium counters on fleabay. Many of them have a temperature-compensated time-base oscillator. I&#039;d be surprised to find that feature in the home-brew counter. Biggest hassle using a frequency counter for alignment is to find a point in the circuit where the crystal you&#039;re measuring is isolated from the crystal itself. A so-called &quot;direct&quot; probe will connect the probe tip to the full 100 to 200 pf of capacitance between the shielded wire&#039;s center conductor and the shield. Better policy is to use a probe meant for oscilloscopes either a times-ten (X10) that attenuates the input signal by a factor of ten-to-one or one that&#039;s switchable. Main benefit is that this reduces the circuit loading when you touch the probe to the circuit being measured. Doesn&#039;t eliminate it, just reduces it to a more-manageable level of circuit loading. Just one problem. The counter&#039;s input sensitivity must be pretty high, so it can display a steady reading when probing a low-voltage circuit.Some &#039;scope probes are switchable, either times one or times ten. A tech is frustrated trying to get a stable reading with the probe in the times ten position. Just not enough signal level to stabilize the display. Switches the probe to times one and gets a steady reading. Just one problem. When the probe is unhooked from the circuit, the frequency will jump up from where it was adjusted with the probe connected to the radio. Removing the capacitor to ground inside the probe and cable made the adjustment irrelevant.Not all counters are created equal. The sensitivity of the counter&#039;s input should be adjustable on the front panel, since driving the counter&#039;s input too hard can result in a bogus reading, too.I&#039;ll skip the notion of a preamp on a counter&#039;s input for now. Getting a measurement you can trust takes more than just a frequency counter and probe. The setup has to be right, too.73</blockquote>

[QUOTE="nomadradio, post: 846990, member: 22"] Looks like a high-school science-fair project. Might be solid and stable. Maybe. I would place more trust in one of the chinesium counters on fleabay. Many of them have a temperature-compensated time-base oscillator. I'd be surprised to find that feature in the home-brew counter. Biggest hassle using a frequency counter for alignment is to find a point in the circuit where the crystal you're measuring is isolated from the crystal itself. A so-called "direct" probe will connect the probe tip to the full 100 to 200 pf of capacitance between the shielded wire's center conductor and the shield. Better policy is to use a probe meant for oscilloscopes either a times-ten (X10) that attenuates the input signal by a factor of ten-to-one or one that's switchable. Main benefit is that this reduces the circuit loading when you touch the probe to the circuit being measured. Doesn't eliminate it, just reduces it to a more-manageable level of circuit loading. Just one problem. The counter's input sensitivity must be pretty high, so it can display a steady reading when probing a low-voltage circuit. Some 'scope probes are switchable, either times one or times ten. A tech is frustrated trying to get a stable reading with the probe in the times ten position. Just not enough signal level to stabilize the display. Switches the probe to times one and gets a steady reading. Just one problem. When the probe is unhooked from the circuit, the frequency will jump up from where it was adjusted with the probe connected to the radio. Removing the capacitor to ground inside the probe and cable made the adjustment irrelevant. Not all counters are created equal. The sensitivity of the counter's input should be adjustable on the front panel, since driving the counter's input too hard can result in a bogus reading, too. I'll skip the notion of a preamp on a counter's input for now. Getting a measurement you can trust takes more than just a frequency counter and probe. The setup has to be right, too. 73 [/QUOTE]

Top Bottom