Only one of the five front-end coils for a Range 1 VHF Mitrek (HLD4081, 136-146 MHz) is still available from Motorola Parts. That one is part 2480032A07, the violet coil in L1, for $ 4.15.
The only option may be to tack on some extra wire to the existing coils. Although modifying the tuning screws may work, I suspect the Q will suffer. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Kevin Custer Sent: Friday, December 19, 2008 9:30 PM To: [email protected] Subject: Re: [Repeater-Builder] Holiday Special - MICOR 2 meter receiver conversion from W3KKC Tom, Okay.... I guess I should ask if replacement coils for the Mitrek are still available from Motorola, and if so, at what cost? If they are no longer available, or are cost prohibitive, send me one of your Mitrek receivers and I'll see if I can come up with a new set of coils that properly tune the whole 2M band. I guess at this point we should go to private email. Kevin Hello Kevin Thanks for your reply. Your statement is correct in that all of the receiver coils begin to tune at the bottom of their travel. I have even tuned two or three too far and they dropped out with the resulting work to retrieve the screws. When tuned as best I can for sens the s/n ratio is 1+uv at 12db sinad. The original frequency sens was less than 1uv-usually about .3uv for 12db sinad. Replacing the coils are about the only solution I know of for these high split VHF units. I have in the past replaced two sets of receiver coils with Motorola coils and found I have good sensitivity as before modification. The transmitters all tuned well on this split and gave rated or more power output. The Mitrek coils looked very much like the Micor coils. I have replaced probably a half dozen Micor receiver coils proscured from Motorola in the past 20 or so years. Thanks. 73 de Tom Manning, AF4UG ----- Original Message ----- From: Kevin Custer <mailto:[email protected]> To: [email protected] <mailto:[email protected]> Sent: Thursday, December 18, 2008 10:02 PM Subject: Re: [Repeater-Builder] Holiday Special - MICOR 2 meter receiver conversion from W3KKC Tom, You say you find similar operation on 4 or 5 units. By that do you mean they won't make book specification on any frequency below 146 MHz? If that is the case, I would believe something is wrong. I have seen many Mitrek high-band receivers that were tuned for 144 something and had very good sensitivity. Let me ask you this.... When tuned at 144.89, is the front-end tuning all "one ended", or is there adjustment to spare? In other words, can you tune the front-end without the fear of the tuning screws falling into the casting? If you have room left to go lower in frequency, then the front-end is not the problem, and you'll need to look elsewhere for the lack of sensitivity. Another question - do these 4 or 5 units tune and make book spec sensitivity on their original high-band channel? I guess what I'm saying is I doubt the problem is the front-end helical resonators, but if there is a need for a conversion I'm not opposed to looking into making a modification available, if it is needed. If there are others on the list that have had good luck with the Mitrek on frequencies below 146 MHz, please chime in and let us know what you have and how well it works. Kevin Hello Kevin You are correct on your freqs for xmit and rcv. The Mitrek units I have will only tune receive to 146.00Mhz. This leaves more than one meg to go to meet tolerance on 144.890. I have tried 4 or 5 units and find similar operation of all. This is the reason for my question about the Micor coils working for Mitrek. Thanks. 73 de Tom Manning, AF4UG ----- Original Message ----- From: Kevin Custer <mailto:[email protected]> To: [email protected] <mailto:[email protected]> Sent: Tuesday, December 16, 2008 8:44 PM Subject: Re: [Repeater-Builder] Holiday Special - MICOR 2 meter receiver conversion from W3KKC Tom, Do you mean 144.89 MHz? I would think your repeater would *transmit* on 145.490 MHz.... At any rate, no conversion is necessary for the Mitrek to make book specification sensitivity on 144.890 MHz. Kevin Good afternoon Kevin My need is to convert two or more Mitrek receivers to cover 145.49Mhzz, which is our receive freq for our repeater. Thanks. 73 de Tom Manning, AF4UG ----- Original Message ----- From: Kevin Custer <mailto:[email protected]> To: [email protected] <mailto:[email protected]> Sent: Tuesday, December 16, 2008 12:19 PM Subject: Re: [Repeater-Builder] Holiday Special - MICOR 2 meter receiver conversion from W3KKC Tom Manning wrote: Good morning Kevin I have a question. Will these coils also work in a Mitrek? Thanks. 73 de Tom Manning, AF4UG Hi Tom, To answer your question, the conversion will not work in the Mitrek. Unlike the MICOR, the Mitrek high-band unit that is most common has a lower tuning limit of 146.00 MHz as specified from the factory. This means that the units normally tune anywhere in the 2M ham band without modification. What frequency do you need to listen on? Kevin
