[TenTec] PBT and other issues.

Wed Oct 29 11:24:36 EDT 2014

Tony, you bring up an important point which people often neglect.
In the 70s and especially in the 60s when Collins was selling radios with Mechanical filters and IF shift, the band conditions were nothing like they are today.  Today band condx are much worse. 

FACTS ON FILTERS:

Although we speak of filters as being 2.4 kHz or 500 Hz bandwidth, that is only a small part of the story.
The bandwidth we state here is the "6dB bandwidth".  Perhaps more important is the "60dB bandwidth".

Filters are typically spec'd at 6dB and 60dB and the relation of the passband at these two specs is called the "shape factor".   A lower number is better.  I will abbreviate this with "SF"

Here are some typical specs on filters:

--455kHz SSB FILTER-----6dB---------60dB------SF-------TYPE---
-----------------------------------------------------------------
--Collins F455F-21-----2.1kHz------5.3kHZ----2.5:1---Mechanical*
--Collins F455D-25-----2.5kHz------6.5kHZ----2.6:1---Mechanical**
--ICOM FL-44-----------2.4kHz------4.2kHz----1.75:1--Crystal
--ICOM FL-96-----------2.8kHz------5.0kHz----1.8:1---Crystal
--Yaesu FL-110S--------2.6kHz------4.7kHz----1.8:1---Crystal

--455kHz CW FILTER------6dB---------60dB------SF-------TYPE---
---------------------------------------------------------------
--Collins F455F-21-----0.5kHz------2.5kHZ----5.0:1---Mechanical*
--ICOM FL-100----------0.5kHz------1.4kHz----2.8:1---Crystal

--TEN-TEC 9MHz FIL------6dB---------60dB------SF-------TYPE---
---------------------------------------------------------------
--Model 220 SSB -------2.4kHz---- 4.0kHz-----1.7:1---Crystal
--Model 217 CW --------0.5kHz-----0.95kHz----1.9:1---Crystal

*The "F-Series" was used in the Collins S-Line
**The "D-Series", called "Low Cost Series" Mechanical filters, was used by OEMs such as Yaesu.  This is probably what Palstar will use -but I don't know.  Just a hunch.

Keep in mind that "shape factor" is VERY important and a lower number is better.
Though fantastic by 1960s standards, a 2.5:1 shape factor today is considered pathetic.

The really good crystal filters today have a shape factor of 1.4:1.
DSP filters are even better, something like 1.2:1.  Perhaps John Henry can give us the exact specs here.

Having Collins Mechanical filters in modern radios is not bad but clearly nothing to brag about in terms of performance. 

On the other hand, there may be other reasons (i.e. nostalgia) for wanting to own a radio with these filters but let's understand the trade-offs.

If the TR-30A only has IF Shift and no real PBT, then don't expect performance to be anything like that of the Eagle, in terms of close-in BDR3.

There may be many other reasons for wanting to own this radio, but be careful about believing the performance claims.
Everyone makes high performance claims!

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Tony
Sent: Wednesday, October 29, 2014 2:55 PM
To: tentec at contesting.com
Subject: [TenTec] PBT and other issues.

‎Changed the subject away from Ten-Tec repairs.
I always wanted a Collins system but could never afford it. So... I got the poor men's Collins and purchased the Heathkit SB-303‎ and matching TX and was very happy with it. No PBT but in the 70's we didn't need it as much as now.
73, Tony VE3DWI.

Sent from my BlackBerry 10 smartphone on the Bell network.
  Original Message
From: Rick - DJ0IP / NJ0IP
Sent: Wednesday, October 29, 2014 09:41
To: 'Discussion of Ten-Tec Equipment'
Reply To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] repairs

GM Carl,

I didn't know that. I've seen these radios but never used one.
My first Collins encounter was with the S-Line and KWM-2 when I was in the Army.

The "Gold Dust Twins" as it and its matching TX were known by, cost about as much in adjusted dollars back then as two Hilberling PT-8000s cost today.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Carl Moreschi
Sent: Wednesday, October 29, 2014 12:52 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] repairs

The Collins 75A4 did PBT that way. When you moved the PBT knob, it rocked both the BFO control and VFO control for simultaneous movement. 
It was all done mechanically.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 10/29/2014 2:51 AM, Rick - DJ0IP / NJ0IP wrote:
> Hi Sinisa,
>
> Has this technique ever been implemented in a ham radio like this?
>
> With analog technology that would have been a very tough feat to 
> accomplish but with digital technology it ought to be fairly easy to do.
>
> Of course the down side of that method would be, it moves both skirts 
> in the same direction, so while you are moving away from QRM on one 
> side, you may very well be moving into QRM on the other side.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of 
> shristov
> Sent: Wednesday, October 29, 2014 7:34 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] repairs
>
> Rick - DJ0IP / NJ0IP<Rick at DJ0IP.de> wrote:
>
>> Could someone here please explain to me (technically) how PBT can 
>> work with single conversion?
>
>
> PBT (with constant filter bandwidth) is easily done with single 
> conversion and single filter.
> Just vary VFO and BFO frequencies simultaneosly to keep the resulting 
> carrier frequency unchanged.
>
> 73,
>
> Sinisa YT1NT
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