[MRCA] Pondering the conversion of the BC-620 radio for eithet Ham or CB use.

[Tim]

Hi Mark - As others have pointed out, use of a BC-620 on CB in the US is
illegal,  It is not Type Accepted by the FCC and it operates FM which is
not legal on US Part 95 CB transmitters anyway.  (Additionally they could
not receive CB AM transmissions - their receivers are designed to
specifically reject AM signals and noise. )

As to crystals, the required crystal = the desired channel frequency minus
4.3 mc (the IF frequency) all divided by 4.  Crystals in FT-243 holders
might be found that could be ground to the exact freq desired.  With a
proper crystal, tuning a 620 from it's upper limit of 27.9 to say 29.6
might be within its inherent adjustment range or by changing some tuned
circuit parts slightly.  Personally, I'd encourage them to get the simple
Tech ham ticket and be legal - it's a no-brainer by design these days....

If the vehicle guys want something authentic looking (I get it!) and they
want to be legal (I would encourage it) just advise them to put a $ 5.00
flea market CB inside the radio box and wire it up to power and I/O
connectors.  I'm sure others have done that...Vastly easier solution - and
legal as well.

Anyway, my $ 0.02

Tim
N6CC

On Wed, May 30, 2018 at 8:23 AM, WW2RDO via MRCA <mrca at mailman.qth.net>
wrote:

> Some countries outside the US actually do have CB bands that use FM, but
> that doesn't help things here in the US, so........
>
> There are three ways to go with this.  The easiest is to just get a BC-659
> or SCR-608 and work 10 meters between 28.300 and 29.700 MHz FM.  But that
> doesn't satisfy the purists in the vehicle hobby, who say their tank, etc
> didn't use the BC-659 or SCR-608 because they were Artillery radios ( the
> SCR-608 verses the SCR-508 presents the same dilemma for these purists).
> I've seen more than a few who have BC-620's or SCR-508s and use them
> illegally, and they don't care about legalities and will not change until
> they are caught doing so, mostly because they don't think there are other
> options that don't upset their sense of absolute authenticity, and they
> figure they haven't been caught so far, so they'll continue to press their
> luck ( yeah, that's really stupid on their part, I know ).
>
>    The other two options for the BC-620 and SCR-508 are more complicated.
> The first would involve modifying these radios to add the needed operating
> frequency range to get these radios to operate in the phone section of 10
> meters. Now I know this kind of thing has been done with the BC-1000 to
> boost it's operating frequencies into the phone section of the 6 meter
> band.  I'm wondering if anybody has tried to do with the BC-620 or the
> SCR-508 to get them to operate on frequencies in the phone section of 10
> meters.  What would it involve?  Would it be a simple matter of having
> custom crystals cut and installed in the radios, or are other modifications
> needed to be done to the radio to make it work?
>
>     The second option would be to somehow convert these radios to CB band
> operation ( AM ).  In addition to custom crystals, the radios would have to
> have their modulation changed from FM to AM, if that's even possible
> without messing with the outward appearance of these radios. The costs
> would probably scare off most owners.  Figure a vehicle guy would have a
> repair/modification budget of $1000 for their radio ( including repair of
> the power supply).  I don't think any conversion could be done along with
> what would surely be other needed repairs to make that an attractive
> option.  Also, lets face it, especially with the BC-620 being only a two
> trick pony frequency wise, one of the CB channels that would have to be
> installed in these radios would have to be channel 19, and it may not be
> economically or electrically possible to even do that.
>
> Mark D.
> WW2RDO
>
> In a message dated 5/30/2018 9:24:18 AM Eastern Standard Time,
> crp.wd8axb at comcast.net writes:
>
> Mark,
>
> The BC-620 is very wideband FM, something like upwards of + - 15 kHz!
> Citizens Band is 6 kHz AM!
>
> Nothing compatible!
>
> And in the U.S., using FM in the CB band is illegal.
>
> Perhaps a more reasoned approach is the BC-620, paired with the right
> crystals, or a set of these new adjustable crystal-replacement
> mini-circuits, and TEST to see if the 620 will work in the 10 meter FM band.
>
> Find out what multiplication is used for the crystal fundamental
> frequencies for the 620 and 659. (?)
> See if there might be compatibility there. (?)
>
> 73, Charlie WD8AXB
>
>
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