[Heath] SB-303 / SB-401 LMO, HET and BFO interconnection cables

[Robert Myers]

Hi Wilson,

Thank you for your input.

Don't be offended by my question, please.  The, 'weirdness,' is only that I wasn't sure of the reasoning behind the choices.  Replace 'weirdness' with 'my curiosity and lack of understanding' if it make you feel less hot under the collar :)  I suspected it was a cost (i.e., 'price') saving related measure but I wasn't sure, and several people confirmed that.

I agree that with consumer/commercial equipment out on the market facing competition, saving money is very important.

Congrats on running your '303 / '401 combo with, "everything from RG-58 to scraps of mic cord..."  I will have to try the RCA jumpers that come with video equipment, as you suggested (someone else suggested I try that two).  Quite interesting.  It seems the pair is more robust than their manuals suggest in terms of cabling :)

As for your comment, "Good grief, what's weird about a few feet of RG-62?  Is Collins S line less demanding?"  I don't know, I have never operated their amateur radio equipment.

I think Glen had a great explanation.

Thanks everyone,
--- Rob Myers, VE3JQL

-----Original Message-----
From: Wilson [mailto:infomet at embarqmail.com] 
Sent: August-19-14 11:30 AM
To: Robert Myers; heathkit at yahoogroups.com; heath at puck.nether.net; heathkit at mailman.qth.net
Subject: Re: [Heath] SB-303 / SB-401 LMO, HET and BFO interconnection cables

Good grief, what's weird about a few feet of RG-62?
Is Collins S line less demanding?  Costs 4-5X Heath, of course.
In fact, I've operated the 301/303 with everything from RG-58 to scraps of mic cord with never a problem.
Try the RCA jumpers that come with video equipment.
Of course if using the cable properties saved them a tube/transistor or two that's fine value engineering.
Cable is cheap.  Three cheers for Heath.  I actually prefer the 301/401 to S-line and I have time on both.
My Dad's 401/303 are going strong, since about 1970.
WL

-----Original Message-----
From: Robert Myers
Sent: Monday, August 18, 2014 3:25 PM
To: heathkit at yahoogroups.com ; heath at puck.nether.net ; heathkit at mailman.qth.net
Subject: [Heath] SB-303 / SB-401 LMO, HET and BFO interconnection cables

Question about the SB-303 / SB-401 interconnection cables *required* for the HFO, BFO and LMO.

As I am sure most are aware, the SB-303 and SB-401 manuals call for the following cables to be connected between the various SB-303 oscillator output sockets and the corresponding SB-401 oscillator input sockets:

SB-303 ‘BFO OUT’ -> 24” RG-62/U  -> SB-401 ‘RCVR BFO’
SB-303 ‘HFO OUT’ -> 24” RG-62/U  -> SB-401 ‘HET OSC’
SB-303 ‘LMO OUT’ -> 24” RG-174/U -> SB-401 ‘RCVR LMO’

It seems to me that the designers, for some reason, decided to incorporate the various cable capacitances (that result from their specified lengths) and their characteristic impedances, along with the input impedances of those various oscillator inputs of the SB-401, into what amounts to ‘essential operating circuitry’ of the corresponding oscillators based on the SB-303.  (But why?  To save money?)

Is the requirement for 'cable weirdness' due to the various oscillators’
output circuitry within the ‘303, or is it due to the requirements of various oscillators’ input circuitry within the ‘401?  Or is it a combination of both?

I mean, if the ‘303 requires a particular capacitance ‘hanging off’ the LMO’s output socket (such being provided by exactly 24 inches of RG-174/U) in order to function properly, as well as a 50 Ohm load (inside the 401 during transceiver), would it not have been better to do something like provide all those necessities *within* the ‘303 (right at the LMO
oscillator) and follow that by an isolating buffer/voltage-follower (still inside the ‘303) with a 50 Ohm output impedance?  You could do the same for the HET, and BFO oscillators’ circuitry as well – thus allowing for arbitrary lengths of, say, RG-58/U cables (not different cables) for interconnection of the HET, LMO, and BFO sockets between the two units.

Is there a fix for this cable 'weirdness,' allowing the cables to be the same type (say, 50 Ohm RG-58 since you need that for the antenna connections, for sure), and their lengths to be not critical?

Thanks,
Rob Myers, VE3JQL








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