[Heath] Heathkit SB-644A, Remote VFO Cables

[Chris Iwata]

Heathkit back then used phono connectors a lot, probably because they 
were cheap. They are not the best connectors to use for RF. The 
sleeve-fit ground makes for lousy connections.

Since the coax cables are not carrying any appreciable power, just about 
any well-shielded cable will work.  The impedance is not an issue for 
anything less than say 6 feet. The reason for the coax is to keep the RF 
isolated, not to match anything.   Don't use audio coax cable simply 
because the shielding is not very good.

RG-8X is pretty thick and stiff.  It will work but be cumbersome, plus 
you'll have a helluva time trying to solder on the phono plugs.  If 
you're still worried about impedance, use RG-58

One of the major drawbacks of the SB104 is that it lacked RIT (receiver 
incremental tuning) and XIT.  To have a separate VFO just to accomplish 
this simple feature is overkill.   I built RIT/XIT into my much older 
HW-101 (similar solid state VFO) pretty easily with a varactor, a pot, 
and some switching circuitry.

Chris, KL7DM

On 10/8/2021 2:54 PM, Steven Feinsmith wrote:
> I acquired Heathkit Ham radio and worked on my technician and general 
> exams to earn the callsign soon.
>
> I cleaned my SB-644A, Remote VFO, and checked everything to ensure it 
> was in good working order. I have a pair of shielded coaxial cables to 
> link with my Heathkit SB-104A transceiver. Both ends use RCA male 
> phono connectors. I realized they were short, a foot long. They cannot 
> reach the remote VFO unless I have put them on the left instead of the 
> right. I checked the assembly manual, and it showed that #343-3, a 
> large, coaxial cable, came 4 feet long. It has cut to 2 feet long 
> instead of one foot long. I decided to get a new coaxial cable. The 
> original cable labeled as follows:
>
> 300V  80 degree  FR-1  (UL)  AWN  STYLE  1436
>
> I searched for the specification for that cable. Unfortunately, there 
> was almost no information such as 50-ohms? I called three different 
> vendors, and they did not know much about it. I think I can use RG-8x 
> coaxial cable, but I am not sure if this kind of cable can be 
> attached with an RCA male connector? What is your suggestion?
>
> 73,
> Steven
>
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