[HBR] WARC bands?

[Brian Burns]

Hello Walt,

Excellent advice! The stability issue hadn't crossed my mind. Thank you very
much!

Cheers,

Brian

-----Original Message-----
From: HBR [mailto:hbr-bounces at mailman.qth.net] On Behalf Of Walt Hutchens
Sent: Saturday, November 08, 2014 2:08 PM
To: HBR Receiver List
Subject: Re: [HBR] WARC bands?

Brian said:

> So, if you try to extend the range by going to a larger tuning 
> capacitor, you end up in the "general coverage" two dial receiver 
> category, and need the extra complication of a bandspread capacitor and
dial?

You can go that route but in addition to the extra complication you get a
performance hit: Stability and dial accuracy are going to be substantially
hurt.

The larger a tuning capacitor is, the more difficult it is to make it
stable.  The W6TC sets use accurate and stable FIXED capacitors for most of
the capacitance; you can then use a fairly inexpensive tuning cap to do the
small amount that must be variable.

I've had good results using caps designed for the FM receivers of that day.
They're just 'consumer grade' but because the FM sets needed reasonable
stability at 88-108 mcs they're not bad at all for an HBR.
Of course the specified caps are nicer but I think any improvement in
stability will be masked by other factors in the design -- wiring and
chassis movement, changes in tube parameters, the fact that zero temp.
coefficient caps aren't, and so on.

The thing about the W6TC sets is that they were designed to allow a ham of
modest technical skills and wallet produce a receiver that was generally the
equal of the best commercial sets for the ham market and FAR ahead of
anything for similar money. You could -- still can -- work about anything on
any of the bands they cover. Once you add a larger variable capacitor (even
as a band set cap) and the wiring that goes with it, equal stability really
isn't possible. So you can do okay on the lower bands on AM but SSB and the
higher bands probably not.

It is true that the Collins receivers -- particularly the military sets --
did many bands and even general coverage with first-rate performance. It's
also true that they cost ten or more times what a ham set cost and used
techniques that are well beyond hams -- like precision gears and linear
permeability tuning.

As others have said the way to go for WARC bands is to wind coils for them.
Get your receiver built and make at least a couple of coil sets for the
standard bands. Then wind the coils for the additional bands as desired.
You'll end up with a first rate receiver for those bands and any time you
want another, you can wind those coils.

Walt
KJ4KV

______________________________________________________________
HBR mailing list
Home: http://mailman.qth.net/mailman/listinfo/hbr
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:HBR at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html


---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com