Product Enhancements (PEN)

  • 1
  • Question
  • Updated 2 years ago
  • Answered
  • (Edited)
So have to wonder how big of a deal the "Preamp RMDR" enhancement is?

I should send the thing back and get that done but I am considering  Option # 2 so I don't have to send it back.

I am on my third 6600 series radio since I took delivery of the first one and to be honest I am tired of messing with it. This one is working great. I don't leave the radio on 24x7 but it comes on at 6am and does not get shut off until 9pm. Obviously the first part is a must do fix.

Based on shipping and Flex saying 5-7 days in the service department, this puts me without a radio for 3 weeks.

Appreciate Flex for fixing the issue and covering shipping both ways. Its unfortunate that in my 35 years of amateur radio this has become the most problematic radio I have owned :(


Dear FLEX-6400(M) & FLEX-6600(M) owners,

NOTE: If your radio shipped on or after April 12th, 2018 you can disregard this email.


FlexRadio has a continuous improvement plan in place for the FLEX-6000 Signature Series products. This notification outlines hardware performance improvements that apply to all FLEX-6400/FLEX-6400M/FLEX-6600/FLEX-6600M radios shipped new or from the service department prior to April 12, 2018. All units shipped from FlexRadio Systems on or after April 12, 2018 already incorporate these upgrades.


The A/D converters used in the FLEX-6400/FLEX-6400M/FLEX-6600/FLEX-6600M radios are mounted on plug in PC boards and incorporate a chip top copper heat sink.  The heatsink is affixed to the top of the A/D converter with an adhesive thermal tape supplied by the component manufacturer. Recently it was discovered by our alpha test group members who leave their radios on 24/7 that the heatsinks were coming loose after a few months of continuous operation.  While the A/D chip itself will not be harmed by the lack of a heat sink, the dynamic range performance can degrade or in extreme cases result in a high noise floor. In some cases, the heatsink has become completely detached from the A/D converter and fallen inside the radio.

The solution is to replace the original heatsink with a larger one with a higher rated thermal adhesive that is mounted to the bottom of the A/D converter circuit board.  Since the A/D is on a small plug in circuit board, the new heatsink is relatively easy to field install by anyone with reasonable hand assembly skills. FlexRadio will offer the option to provide the heatsink upgrade kit for field installation or the radio may be returned to FlexRadio to install the upgrade (see instructions later in this notice).

Please note that only FLEX-6400/FLEX-6400M/FLEX-6600/FLEX-6600M model radios shipped new or from service prior to April 12th, 2018 are affected.  If your radio shipped prior to April 12th, we recommend that you power off the radio when not in use until this upgrade is installed.


This upgrade increases reciprocal mixing dynamic range (RMDR) when using the preamplifier on the FLEX-6400/FLEX-6400(M)/FLEX-6600/FLEX-6600(M) radios.  The modification adds two noise reduction capacitors on the LDO voltage regulator powering the preamp to reduce close in amplitude (AM) noise. RMDR with the preamp off (0 dB or -8 dB) is not affected by this modification.  RMDR at 5 kHz with the preamp off has been measured at greater than 115 dB. The modification improves 5 kHz RMDR with the preamp turned on from greater than 105 dB to at least 115 dB.

This is an optional upgrade for radios shipped or serviced prior to April 12, 2018. Unless you frequently operate closer than 10 kHz of a 70 dB over S9 station (e.g. 20m) on the same band, this modification will have no effect.  Typically, this will only improve operation for a multi-1 or multi-2 contest station where you are transmitting and receiving on the same band at very close spacing.


Fill out this survey to determine if you wish to receive the recommended A/D Heatsink Installation Kit by mail or optionally if you prefer to schedule an RMA for our service department to install the upgrades.  

here are three options available for getting the PEN changes applied to your radio.

  • Option 1 -Field install the A/D Heatsink Installation Kit and forego the optional RF Preamp RMDR Enhancement.
  • Option 2- Field install the A/D Heatsink Installation Kit and then send your radio in at a later date for the RF Preamp RMDR Enhancement.
  • Option 3 -Send the radio in for both the A/D Heatsink Installation Kit and the RF Preamp RMDR Enhancement.
If you choose Option 1, the field installed heat sink installation option we will ship the free A/D Heatsink Installation Kit within one week of your request. This is by far the fastest way to complete the recommended upgrade on your radio.

If you prefer to return the radio to our US service department for Option 2, just the RF Preamp RMDR Enhancement or Option 3, both the upgrades, it will be necessary to receive an RMA (return merchandise authorization) and schedule the service time window.

Given a large number of radios shipped and the limited number of service personnel at FlexRadio you will be provided a date when your radio can be shipped in for service.  By waiting until this date to ship your radio for service, it will ensure that you receive your radio back as soon as possible.

FlexRadio will cover UPS ground shipping both directions and will install the upgrades at no cost.  If you desire faster shipping, you may choose to pay the difference in cost to the upgraded shipping method. Please allow 5 to 7 working days in our Service department to complete the upgrades from the time the radio arrives in our office.  The radio must be shipped properly in its original shipping carton and foam packing materials to prevent damage in transit.

A dedicated email address has been set up to assist with technical queries concerning this enhancement notice: The email will allow us to keep all questions and requests about your radio together.


Gerald Youngblood, K5SDR

President and CEO
Photo of Rich McCabe

Rich McCabe

  • 1238 Posts
  • 259 Reply Likes

Posted 2 years ago

  • 1
Photo of Steve G1XOW

Steve G1XOW

  • 324 Posts
  • 135 Reply Likes

The RMDR is probably not that much to worry about. I'd be more concerned about the potential damage caused by the metallic heatsink rattling around and possibly shorting components on the PCBs.

Photo of Gerald - K5SDR

Gerald - K5SDR, Employee

  • 833 Posts
  • 1542 Reply Likes
Official Response
You will 99% certain you not see a difference with the preamp mod.  You would need signals in the range of 0 dBm on 20m for example to get close to the noise floor with no QRM in a rural location. 

You should fill out the survey and let us mail you the heat sink upgrade.  It took me about 10 minutes to install a set including removing the cover.  I know the radio well so double that time and you are safe.
Photo of bahillen


  • 201 Posts
  • 65 Reply Likes
I will be at the Dayton Hamfest this week. Will FRS bring heatsink kits with them? I have run my radio 24/7 since February 1. Flex-6600.

Photo of Gerald - K5SDR

Gerald - K5SDR, Employee

  • 833 Posts
  • 1542 Reply Likes
No, we will not be bringing them to Dayton.  Please answer the survey in the notice sent yesterday to request they be mailed to you.

This conversation is no longer open for comments or replies.