Determining Operating Frequency

Discussion in 'QRP Corner' started by N5XGG, Jul 11, 2017.

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  1. N5XGG

    N5XGG Ham Member QRZ Page

    I've been looking at the MFJ CUB transceiver to get into QRP. How do you know what frequency you are operating on? - Joe
  2. KW4EK

    KW4EK Ham Member QRZ Page

    From the documentation, you do not. All you know for certain is that you will fall somewhere within a 20, 50, or 60 KHz range within the designed band (depending upon model) and where exactly that band edge begins is part of the initial alignment during the build process. You can download all the documentation for these models direct from the MFJ website if you wish to review them before purchase.

    However, you can, while at home, use either a frequency counter or another modern receiver with a digital readout to locate your operating frequency once built. If using a frequency counter you need only attach a length of wire to the input BNC center pin and then transmit within a some feet of that for it to pickup and display your transmit frequency (never connect the transmit antenna output directly to a frequency counter input unless using a sampler to reduce the input power to the counter to safe levels). If using another radio with digital tuner, simply use its regular antenna and transmit with the Cub transceiver's antenna some reasonable distance away (ideally at least a few tens of feet away) and use the other radio's input attenuation if needed to avoid front end overload or simply turn down the RF gain to achieve the same. Whichever way you go you could use either approach to label your Cub's tuning knob either every X KHz or for specific target frequencies so that you have a decent idea where you fall on the band to within a few KHz plus or minus.

    Kit builds can be a lot of fun if you are interested in electronics, so have fun and carefully follow the instructions and you should have a good time while also learning about how your radio works. On the other hand, if one has absolutely zero interest in electronics then kit builds can be a frustrating exercise as they do require patience and attention to detail as well as some basic soldering skills (and desoldering skills if errors are made). If you have never soldered before you may wish to buy a soldering practice kit, or two, online to practice on before tackling a project you really care about if you do not have an Elmer to coach you in person on good soldering technique. Care taken in the initial build process pays big dividends by reducing time and frustration during the debugging process if mistakes are made due to rushing or misidentification (and they often are if Murphy has his way).

    Best wishes and good luck, but most of all, enjoy the build process and your radio.
    VK3YE and KA9JLM like this.
  3. VK3YE

    VK3YE Ham Member QRZ Page

    One little accessory you could take, once you've calibrated it, is a crystal oscillator on a known frequency.

    Eg if it's for 7 or 14 MHz, 7.030 MHz crystals are cheaply available and give you a known 7.030 or 14.060 MHz source.

    A one transistor crystal oscillator (such as at but without the second crystal and series inductor) would be fine as the oscillator.

    It could be built in a small box with a 9 volt battery. Then before you transmit you find the crystal frequency at the right spot on the dial and know your rig hasn't drifted.

    This could be useful for portable operation where the rig may get bumped around.

    Another option is a crystal calibrator. It uses a crystal on say 4 or 10 MHz with IC dividers to give 10, 25 or 50 kHz steps (switchable in better designs). That can help with dial markings.
  4. N8AFT

    N8AFT Subscriber QRZ Page

    Handheld frequency counters are low cost enough new and used with their own antenna or bnc jack.... it's what I use.
  5. KL7KN

    KL7KN Ham Member QRZ Page

    With the Cub, you will only really be able to tell the band edges - maybe. It is an old school analog setup after all. Mostly made in China as well.

    $100 (or $82.95 from a 3rd party vendor) (+ shipping) for a single band kit. 1 or 2 watts. The RX is okay and the VFO is fairly stable. You do get pretty decent documentation for the radio - schematic + alignment details
    An assembled unit lists for $149.95 + shipping.

    Add a digital dial ( $30 + shipping.
    QRPGuys have a digital dial for $15 with a real digital readout. They also have a marker generator with selectable marker intervals for $13. Both fully documented.

    An EK-1C tribander, all digital and assembled is $189 (+ shipping) so, about $50 more but with a solid DDS based VFO, digital readout, full band coverage (x3) and 5+ watts. No technical documentation for what is, in essence, a retreaded HB-1A. The reviews have been positive.
    If you go for the assembled Cub + some kind of digital dial, the real difference here is a few dollars, single band vs triband, full band coverage and a bit more power out....

    The CR kits CS series is a single band CW/SSB rigs, DDS vfo and 5 or 10 watts out. $150 w/shipping from China. CR lits has a rep for using quality parts and has decent technical documentation. (Save $25 if you don't need the mike) No freq display, so you would be in nearly the same boat. SInce it is DDS VFO, the edges would be easy to mark and they would stay put.....

    Good luck.
  6. K8JD

    K8JD Ham Member QRZ Page

    I would not want to need a freq reading device that cost more than the radio !!!
    Wjat I did is use my ACCURATE reading main shack rig to set my freq in the CUB VFO.
    Then took a piece of white heavy paper and glued it on the front of the Cub, Trimmed around the VFO knob shaft.
    Set my main rig to transmit minimum power into a dummy load and sent at a known freq at the low end of the Cub's range, tuned it in and marked the new dial face with the freq and moved up 10 kHz and marked the next freq and so on to the top of the Cub's range, nice little freq dial now.
    WB5YUZ likes this.
  7. KP4SX

    KP4SX XML Subscriber QRZ Page

    I went with a digital DDS VFO to run my Rockmite :) Reads better than my old Icom rig!
  8. N5XGG

    N5XGG Ham Member QRZ Page

    K8JD that sounds like a do-able solution.
  9. KC4FKX

    KC4FKX Subscriber QRZ Page

    You may want to consider this:
    It was off the market for a while but is back now. At $22 it won't break the bank. Mounts inside the rig so no need to modify the case.
  10. K7MEM

    K7MEM Ham Member QRZ Page

    I bought one at a ham fest years ago for $8. The original owner bought it and then decided not to use it. His loss was my gain. I installed it in my HW-8 and it works great. I may have to get a few more.

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