Coax length in-between XCVR and Amplifier

Discussion in 'General Technical Questions and Answers' started by N8FVJ, Nov 9, 2019.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: abrind-2
ad: Subscribe
ad: Left-3
ad: L-MFJ
  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    I read this question long ago & do not remember the answer. Is a 3 foot coax jumper in-between XCVR and amp bad news? Is 6 foot or other length ok?
  2. AG5CK

    AG5CK Ham Member QRZ Page

    That's an old cb myth. If the tuned input on the amp is right it doesn't matter. My ameritron is a little off on 29.000 and using a little longer jumper keeps the transceiver from throwing a high swr warning.
    WA9SVD likes this.
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The Collins amps of yesteryear recommended a critical length to make their circuit work best.

    But in general: NO. I've never measured or cared about this, and everything's always worked fine.
    AG5CK likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Long enough to reach between the rig and the amp with appropriate bends as needed.
    N0TZU and AI3V like this.
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

    With some flex room.... Don't want to strain the coax at the connector. Especially, if you are using RG8 sized cable.

  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    I had one of those. It was the cheap model without a tuned circuit at its input. It made horrible IMD when driven with a solid-state exciter. It was designed to work with a tube exciter with a Pi-Net output, hence that forced a requirement on the length of the cable between the exciter and the amp.
  7. WA9SVD

    WA9SVD Ham Member QRZ Page

    I'd leave an extra foot or two to allow for dusting, etc, behind the rig...
    K7TRF likes this.
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    None of the amplifiers manufactured by the Collins Radio Company for amateur radio use did not have a tuned input. You must be thinking of another brand.

    For best performance, the 30S-1 amplifier was recommended to use an input cable of RG-58/U that was 20.5-feet long. However, the difference between using an input cable 20.5-feet long and 4-feet long was well under 2 dB. The very early, basically prototype, 30L-1 was also recommended to use the 20.5-foot long input cable. However, Art Collins told the design team to "FIX the problem" and the input circuitry was redesigned so that a 4-foot long input cable worked very well.

    The very rare 30S-3 amplifier (3, or 4, depending on which of the design team was asked, were manufactured), was designed to use the 4-foot long input cable.

    Actually, the 4-foot input cable was not critical, any length worked fine. Collins had standardized on 4-foot long RG-58C/U interconnect cables to be used with all of the S-Line equipment.

    Unless someone has been playing around with the input circuitry of any of the Collins amplifiers, solid-state exciters work very well with the units.

    Glen, K9STH
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    HT37? I have had several different amplifiers over the years...
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    The HT-37 was a phasing type SSB transmitter made by Hallicrafters. The HT-31 and HT-33 were linear amplifiers and they did not have tuned inputs. However, those were manufactured by Hallicrafters and not Collins.

    Glen, K9STH

Share This Page