Secret Service VHF radios are set up as follows:

Channel Designation
1 BAKER
2 CHARLIE
3 MIKE
4 TANGO
5 OSCAR
6 PAPA
7 BAKER REPEATER (165.7875/164.4000)
8 CHARLIE REPEATER (165.3750/166.4000)

Frequencies A through Z

Alpha         32.2300    WHCA-Transportation (vans) (possible DC base)
Baker         165.7875  USSS-Field Offices, President/VP/VIP security
Charlie       165.3750   USSS-Field Offices/Protection, command post coordination (Nationwide Primary)
Delta          169.9250  WHCA-Marine Security Detachment, vans
Echo          407.8500  WHCA-SAM Uplink (Air Force 1 phone patch ground uplink)
Foxtrot      415.7000   WHCA-SAM Downlink (Air Force 1 phone patch aircraft downlink)
Golf           166.4000   USSS-Field Offices
                 165.7625    Input to 165.3750 repeaters
Hotel         167.9000   WHCA-V.P. Staff/White House Garage
                 165.6875
                 166.2125   President/VP Security
India          407.9250   USSS-Headquarters (Treasury Security Force)
                 166.2000
Juliet          170.0000   USSS-Paging/Camp David
Kilo           167.8250   Duplex Phone-Pres Res/LBJ, WHCA
Lima          168.7875   Duplex Phone-Pres Res/LBJ, WHCA (voice scramblers)
Lavender   418.1250   WHCA-Transportation
Mike         165.2125   USSS-Dignitary/Former Pres Protection, Counterfeit Division
November 166.7000   WHCA-White House Staff
Oscar        164.8875   USSS-Presidential Protection Division (PPD), WHCA
Papa          164.4000   USSS-Field Offices/Protection, input to 165.2125 repeaters
Quebec      ---
Romeo      166.4000   Input to 165.7875 repeaters
                 164.4000   USSS-Repeater Outputs
Sierra        166.5125   WHCA-White House Staff
Tango       164.6500   USSS-Field Offices/Protection, Presidential/VP Security
Uniform     361.6000  AF-1 Communications
                 165.0875
Victor       164.1000   WHCA, Presidential/VP Protection
Whiskey    167.0250  WHCA-Paging
X-ray        ********  SEE BELOW
Yankee     162.6875  WHCA-Presidential phone uplink or downlink
Zulu          171.2875  WHCA-Presidential phone downlink or uplink

The Treasury Common frequency is 166.4625.

X-ray is the reserve frequency pool and is not Treasury Common. Frequencies here are used whenever a new frequency is needed.

X-ray frequencies

164.7500
164.8000
165.2625
165.3375
165.4125
165.5125
165.6500
165.6875
165.8500
165.9000
166.0500
166.2000
166.5625
166.5875
166.6375
166.8000
167.9000

The most active frequencies used before and during a presidential or vice presidential visit are Baker, Charlie, Mike, and Tango, as well as any channel designated for use by the WHCA. The frequency used most as a nationwide primary repeater channel is Charlie, followed by Baker. Former presidents' security use Mike. Oscar is used for presidential protection nationwide and Papa is used for White House perimeter patrols.

Pres Nighthawk Aircraft Fleet (HMX)

Transport                  46.7500
Transport                  375.0000
VIP Transport Net    34.3500
Command Post         142.7500
Squadron Common   265.8000
USMC helicopters    46.7000, 46.7500, 46.8000, 122.8500, 375.0000

Other Phone Patches

Nationwide-2                407.4750 uplink
Nationwide-2                415.8000 downlink
Limousines (Local/DC)  407.4500 duplex
Limousines (Local/DC)  408.2000 duplex

USSS Uniform Division (All repeaters use PL 103.5 Hz)

Gray      418.3500/407.7500  White House
Orange  418.7750/414.9500  White House
Brown   414.8500/418.8000  Foreign Missions
Red       415.9750/419.7250  Foreign Missions
Silver     415.6500/419.1000  Foreign Missions
Yellow   414.6750/418.1500, 415.9500 WHCA  Foreign Missions Patrol
                ("Boardwalk")                        Primary

Training Division: Beltsville, MD

Green        415.7500/407.8750
Black         415.1000/418.3250
Blue           414.8000
Violet         415.8000
Communications Division:
Gold          415.6750/419.0750
Other:
Lavender   418.1250                     WHCA Transportation
White        407.6750

Technical Security Division (Special Use)

F-1 408.0000
F-2 411.0000
F-3 408.5000
F-4 408.9750

NOTES: Frequencies in 407 Mhz band are used for agents' body radios with "wristwatch" microphones.

WHCA stands for White House Communications Agency.

The PL used by the Secret Service is 103.5 Hz.

The above info was gathered from several sources. Not all sources agreed on the same frequencies.