realignment CB Radio?

[bernie3]

Is it possible to do a realignment with a Volt meter on a SSB CB radio after unlocking the clarifier??? This is new to me and at 66 yrs young, just want to dabble in some of the CB stuff! Any assistance would be appreciated. I have a Red Pitaya Measuring instrument but have never used it and do not know how. Like to get rid of it???

 

[RadioRon]

I wasn't familar with this idea of "unlock the clarifier" so I did some research and from what I understand, the main issue after the mod is done is how to set your frequency precisely. Is that right? In a well equipped lab, one would use a frequency counter, I think. But with only a voltmeter, well that needs a bit of time to consider. Can you confirm that what you have done is mainly to allow the clarifier control to slide both the receive frequency and the transmit frequency a little bit, rather than just the receiver alone?

Without knowledge of your particular radio, I will assume that we need to measure frequency somewhere in the 10 to 30MHz range (perhaps right at 27MHz) and the best way to do that if you don't have an accurate frequency counter is to compare your radio's frequency with a known standard. We used to do that by listening to both on a separate radio, and "zero beating" the two until they were identical, just by listening to the two signals in your speaker. But this idea only works if you have a known good reference signal. Perhaps using another (known accurate) CB radio to act as a signal generator or test receiver would work?

 

[bernie3]

Sorry I wasn't much clearer. Yes, having the clarifier track the receive & transmit. Thanks

 

[RadioRon]

I hadn't heard of the Red Pitaya so had a look at it and still can't determine if it has an accurate frequency reference. I think it relies on host PC timing and this would not be adequate for this problem.

 

[unclejed613]

the Red Pitaya (SDR receiver) can verify your transmit frequency is being changed. you will want to use a dummy load for the radio, and operate the Red Pitaya without an antenna or a very small antenna because SDR radios are easily damaged. you will want to use a 1khz tone into the radio because SSB supresses the carrier. your frequency reading will show 1khz higher (or lower depending on USB/LSB mode) than the actual center frequency because of the audio tone. you would need a frequency counter, an RF generator (preferably with digital input controls like an HP) to do an alignment on the radio. because of the PLL circuitry and the fact that it's an SSB radio AND a transceiver, it's a bit more involved than aligning it like an AM/FM receiver.

 

[poikaa]

Depending on the SSB CB transceiver, you can use a know receiver to align the transmitter. you would have to power down the PA of the CB so you will not damage the receiver of the reference radio or receiver. You can use a short wave receiver as a reference as it can be clocked to signals from WWV. The alignment points vary from CB to CB, it would help to know what SSB CB you have.

poikaa

 

[unclejed613]

I wasn't familar with this idea of "unlock the clarifier" so I did some research and from what I understand, the main issue after the mod is done is how to set your frequency precisely. Is that right?

on most radios, the clarifier only works for the receiver section (we hams call it a BFO control). the clarifier modification makes it work on the transmitter as well, and also provides enough range to slide the radio in between the standard channels (standard channel spacing is 10khz, bandwidth of the SSB signal is 2.5khz), so for instance, with the radio on channel 39 (27.395Mhz), the clarifier gives you a range of 27.390 to 27.400. most of the clarifier mods use a 10 or 20 turn potentiometer, which makes for fine-grained control.

 

[Ylli]

Sounds like something that defeats the 'type acceptance' of the transceiver.

 

[unclejed613]

yes it does, along with other modifications like additional banks of channels, etc... but the FCC walked away from enforcing part 95 a long time ago... occasionally if a modified radio is interfering with "safety of life" services, such as aircraft, emergency services, etc.., the FCC will search for that radio (modification of some parts of the transmitter section can generate harmonics or intermod products which can cause interference in other bands). in making any transmitter adjustments, a spectrum analyzer is a must... a good SDR radio can act as a spectrum analyzer, but with SDRs, you often get what you pay for... if i were trying to use an SDR as a spectrum analyzer for doing transmitter adjustments, i would be using something other than the $5-$25 range of typical SDR radios.

 

[Boxnut]

Working for Pathcom, what I did was alignment with SSB radios. A volt meter is handy but useless.
Half of SSB radios the receiver is hardly more than a converter, then it is the IF stages and filters. The clarifier mod to slider is irrelevant.
You will need a sweep generator, that becomes a network analyzer with a scope. this is so you can 'see' the IF bandpass and ripple. 6Khz wide, and flat.
that has to center on the filters that drop half of this for each sideband. 2.5 Khz each side, then depending the radio, a post filter then downconvert to the product detector that also serves as the modulator in transmit. Usually this is where the BFO 'clarifier' is mixed also. After the transmit mixer you have again, tuneable band pass filters for dropping unwanted overtones and harmonics, then on to the PA gain stages and low pass filter. that section can be swept also inserting the generator after the TX mixer. Don't forget a dummy load with an attenuator tap to the generator input. the balanced mixer is set for minimum carrier.
An ammeter you use adjusting the PA bias with about 1.5 Ma idle PA current for linearity. (class AB1 typical.
That should have your radio aligned acceptably. Another thread on preamps, a post shows such generator/scope setup.

 

[unclejed613]

i used the same sweep gen and scope method for aligning AM/FM receivers (back when there was something to align). somewhere in my toolkit i still have a tool with copper on one and and ferrite on the other end for determining whether to spread or squeeze those air-core coils that were often used. in a lot of CB's there are (and they existed in some FM tuners as well) PLL tuning voltage test points, and alignment procedures often required measuring these.

 

[Boxnut]

i used the same sweep gen and scope method for aligning AM/FM receivers (back when there was something to align). somewhere in my toolkit i still have a tool with copper on one and and ferrite on the other end for determining whether to spread or squeeze those air-core coils that were often used. in a lot of CB's there are (and they existed in some FM tuners as well) PLL tuning voltage test points, and alignment procedures often required measuring these.

Yea, and the beryllium ferrite slug tool doesn't detune the works.