John, That is a good question, and the answer is at the heart of the issue facing the poster.
Using LBI-30057 as the source of information for a high-band VHF Exec II Oscillator-Multiplier, we find that the normal situation uses low-side injection and has an IF frequency of 11.2 MHz. The LO crystal is chosen to operate at a frequency which is the channel frequency minus 11.2 MHz and divided by nine. For example, to receive 150.000 MHz, we first subtract 11.2 MHz and get 138.800 MHz. Then, we divide by 9 and get 15.4222222 MHz, which is the crystal frequency. Most crystal houses express the crystal frequency in kHz, which would be stamped on the crystal can as 15422.222 kHz. Now, if we wanted to use high-side injection, we must add 11.2 MHz instead of subtracting it, and get an injection frequency of 161.200 MHz. Dividing by 9 gives us the crystal frequency of 17.911111 MHz, or 17911.111 kHz. The important point is that the crystal intended for low-side injection is oscillating at a frequency that is about 2.5 MHz lower than a high-side injection crystal, and the oscillator-multiplier must be retuned for it to function. You can usually tell which injection side is currently used in a radio, just by looking at the numbers stamped on the crystal. If the crystal frequency multiplied by nine is a number 11.2 MHz below the stamped channel frequency, it's low-side; if above, it's high-side. So, there is no physical difference in the crystal other than the frequency at which it operates. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of WD7F - John in Tucson Sent: Monday, January 01, 2007 10:13 AM To: [email protected] Subject: Re: [Repeater-Builder] RE: Bomar Crystals Ordered, all the RX not working for GE EXEC II mobiles Curious as to what is different in the crystal when it is cut for low side vs high side. de WD7F John in Tucson ----- Original Message ----- From: "Eric Lemmon" <[EMAIL PROTECTED]> To: <[email protected]> Cc: <[EMAIL PROTECTED]> Sent: Monday, January 01, 2007 10:55 AM Subject: [Repeater-Builder] RE: Bomar Crystals Ordered, all the RX not working for GE EXEC II mobiles Yes, it is a sensitive adjustment. How can an LO crystal not be either high or low side injection? When you order a receive crystal for a Mastr II or Exec II radio, you must state whether it will be used for high or low side injection. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Mathew Quaife Sent: Monday, January 01, 2007 9:31 AM To: [email protected] Subject: RE: [Repeater-Builder] Bomar Crystals Ordered, all the RX not working for GE EXEC II mobiles I ordered just the xtals from them. One the UHF version, the crystals that I had tuned them up are at 434.850, was neither high or low side injection. The xtal that I put in this radio is at 434.875 MHz with a high side injection. Could it be that far off. Mathew Eric Lemmon <[EMAIL PROTECTED]> wrote: Mathew, Did you order just bare crystals to put in some existing channel elements, or did you send the elements to Bomar and have them compensated with the new crystals? That may be part of the problem, but usually the lack of compensation doesn't prevent the crystal from operating- it just might allow them to drift more than the specified tolerance. Since the Exec II radio has tuning adjustments in both the oscillator-multiplier and the RF assembly, the non-operation may be nothing more than a lack of tuning. If the previous frequencies are far removed from the new frequencies, the tuning may be so far off that the oscillator is not even working. What channel frequencies were used previously? It may be that some components may need to be changed to optimize the radios for out-of-band operation. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Mathew Quaife Sent: Monday, January 01, 2007 9:09 AM To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> Subject: Re: [Repeater-Builder] Bowmar Crystals Ordered, all the RX not working for GE EXEC II mobiles Thanks Chuck, found them in the list that was referenced. So these are correct, why do they not work? Anyone with any good ideas? Mathew Chuck Kelsey <[EMAIL PROTECTED] <mailto:kelsey%40madbbs.com> > wrote: For high side, high band -- F+11.2/9 For high side, UHF -- F+11.2/27 Chuck WB2EDV ----- Original Message ----- From: Mathew Quaife <mailto:[EMAIL PROTECTED] <mailto:n9lv%40yahoo.com> > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> > Sent: Monday, January 01, 2007 11:44 AM Subject: Re: [Repeater-Builder] Bowmar Crystals Ordered, all the RX not working for GE EXEC II mobiles Thanks Chuck, that is what they sent me, so your math is just fine. Then there must be something I am missing. I can take one of the old xtals and they work out just fine, so I know the receivers are working. Might I ask what the formula you used was? It's been a long time since I have calculated a crystal freq. so just need the formula configuration. Mathew Chuck Kelsey <[EMAIL PROTECTED] <mailto:kelsey%40madbbs.com> > wrote: If my hasty math is correct: 144.81 low side = 14.845555 144.81 high side = 17.334444 434.875 low side = 16.39537 434.875 high side = 16.521296 Chuck WB2EDV ----- Original Message ----- From: "n9lv" <[EMAIL PROTECTED] <mailto:n9lv%40yahoo.com> <mailto:n9lv%40yahoo.com> > To: <[email protected] <mailto:Repeater-Builder%40yahoogroups.com> <mailto:Repeater-Builder%40yahoogroups.com> > Sent: Monday, January 01, 2007 10:40 AM Subject: [Repeater-Builder] Bowmar Crystals Ordered, all the RX not working for GE EXEC II mobiles > Hope someone can help shed some light here. I ordered xtals from > Bomar (3 week wait) for the GE EXEC II mobile radios, 6 for RX for > 144.810 and one RX of 434.875, all high side injection. None of them > are working at all. At the same time I ordered tx xtals for the same > radio, they all work just fine. What might I be missing here, or did > they just cut them all wrong. > > Mathew __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Yahoo! Groups Links -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.409 / Virus Database: 268.16.2/613 - Release Date: 1/1/2007 Yahoo! Groups Links
